document_title: List of presidents of the United States by age

question_text: who was the oldest person elected president of the united states

text: Age of U.S. presidents

text: The median age upon accession to the presidency is 55 years and 3 months. This is how old Lyndon B. Johnson was at the time of his inauguration. The youngest person to assume the office was Theodore Roosevelt, who became president at the age of 42 years, 322 days, following William McKinley's assassination; the oldest was Donald Trump, who was 70 years, 220 days old at his inauguration. The youngest person to be elected president was John F. Kennedy, at 43 years, 163 days of age on election day; the oldest was Ronald Reagan, who was 73 years, 274 days old at the time of his election to a second term.

text: Assassinated three years into his term, John F. Kennedy was the youngest at the time of leaving office (46 years, 177 days); the youngest president to leave office at the conclusion of a normal transition was Theodore Roosevelt (50 years, 128 days). The oldest at the time of leaving office was Ronald Reagan (77 years, 349 days).

text: Born on May 29, 1917, John F. Kennedy was younger than four of his successors, the greatest number to date: Lyndon Johnson (8 years, 9 months, and 2 days); Ronald Reagan (6 years, 3 months, and 23 days); Richard Nixon (4 years, 4 months, and 16 days); and Gerald Ford (3 years, 10 months, and 15 days).

text: Born on February 6, 1911, Ronald Reagan was older than four of his predecessors, the greatest number to date: Richard Nixon (1 year, 11 months, and 7 days); Gerald Ford (2 years, 5 months, and 8 days); John F. Kennedy (6 years, 3 months, and 23 days); and Jimmy Carter (13 years, 7 months, and 25 days).

text: Three presidents—Donald Trump, George W. Bush, and Bill Clinton—were born in 1946 (all within the span of 9 weeks). This is the only calendar year in which three presidents have been born. Two presidents—James K. Polk and Warren G. Harding—were born on November 2 (70 years apart). This is the only day of the year having the birthday of multiple presidents.[1]

text: The oldest living U.S. president is George H. W. Bush, born June 12, 1924 (age 93 years, 301 days). On November 25, 2017, he also became the longest-lived president, surpassing the lifespan of Gerald Ford, who died at the age of 93 years, 165 days. The second oldest living president, Jimmy Carter, has the distinction of having the longest post-presidency in U.S. history, currently at 37 years, 79 days. He surpassed the previous record, held by Herbert Hoover (31 years, 230 days) on September 7, 2012. The youngest living president is Barack Obama, born August 4, 1961 (age 56 years, 248 days).

text: The shortest-lived president to have died by natural causes (thereby excluding John F. Kennedy and James A. Garfield, who were both assassinated) was James K. Polk, who died of cholera at the age of 53 years, 225 days; only 103 days after leaving office.

text: Six U.S. presidents have lived into their 90s. They are (in order of birth):

text:
John Adams
(1735–1826)

Herbert Hoover
(1874–1964)

Ronald Reagan
(1911–2004)

Gerald Ford
(1913–2006)

George H. W. Bush
(born 1924)

Jimmy Carter
(born 1924)

text:
#
President
Birth date
Presidency
start date
Age at
start date
Presidency
end date
Age at
end date
Post-presidency
timespan
Death date
Lifespan

1
Washington, GeorgeGeorge Washington
000000001732-02-22-0000Feb 22, 1732[a]
000000001789-04-30-0000Apr 30, 1789
7004208870000000000♠57 years, 67 days
000000001797-03-04-0000Mar 4, 1797
7004237520000000000♠65 years, 10 days
01,0151,015 days
(7003101500000000000♠2 years, 285 days)
000000001799-12-14-0000Dec 14, 1799
7004247670000000000♠67 years, 295 days
(24,767 days)

2
Adams, John A.John Adams
000000001735-10-30-0000Oct 30, 1735[a]
000000001797-03-04-0000Mar 4, 1797
7004224060000000000♠61 years, 125 days
000000001801-03-04-0000Mar 4, 1801
7004238660000000000♠65 years, 125 days
09,2539,253 days
(7003925300000000000♠25 years, 122 days)
000000001826-07-04-0000Jul 4, 1826
7004331190000000000♠90 years, 247 days
(33,119 days)

3
Jefferson, ThomasThomas Jefferson
000000001743-04-13-0000Apr 13, 1743[a]
000000001801-03-04-0000Mar 4, 1801
7004211440000000000♠57 years, 325 days
000000001809-03-04-0000Mar 4, 1809
7004240660000000000♠65 years, 325 days
06,3316,331 days
(7003633100000000000♠17 years, 122 days)
000000001826-07-04-0000Jul 4, 1826
7004303970000000000♠83 years, 82 days
(30,397 days)

4
Madison, JamesJames Madison
000000001751-03-16-0000Mar 16, 1751[a]
000000001809-03-04-0000Mar 4, 1809
7004211720000000000♠57 years, 353 days
000000001817-03-04-0000Mar 4, 1817
7004240940000000000♠65 years, 353 days
07,0567,056 days
(7003705600000000000♠19 years, 116 days)
000000001836-06-28-0000Jun 28, 1836
7004311500000000000♠85 years, 104 days
(31,150 days)

5
Monroe, JamesJames Monroe
000000001758-04-28-0000Apr 28, 1758
000000001817-03-04-0000Mar 4, 1817
7004214940000000000♠58 years, 310 days
000000001825-03-04-0000Mar 4, 1825
7004244160000000000♠66 years, 310 days
02,3132,313 days
(7003231300000000000♠6 years, 122 days)
000000001831-07-04-0000Jul 4, 1831
7004267290000000000♠73 years, 67 days
(26,729 days)

6
Adams, John Q. John Q. Adams
000000001767-07-11-0000Jul 11, 1767
000000001825-03-04-0000Mar 4, 1825
7004210550000000000♠57 years, 236 days
000000001829-03-04-0000Mar 4, 1829
7004225160000000000♠61 years, 236 days
06,9306,930 days
(7003693000000000000♠18 years, 356 days)
000000001848-02-23-0000Feb 23, 1848
7004294460000000000♠80 years, 227 days
(29,446 days)

7
Jackson, AndrewAndrew Jackson
000000001767-03-15-0000Mar 15, 1767
000000001829-03-04-0000Mar 4, 1829
7004226340000000000♠61 years, 354 days
000000001837-03-04-0000Mar 4, 1837
7004255560000000000♠69 years, 354 days
03,0183,018 days
(7003301800000000000♠8 years, 96 days)
000000001845-06-08-0000Jun 8, 1845
7004285740000000000♠78 years, 85 days
(28,574 days)

8
Van Buren, MartinMartin Van Buren
000000001782-12-05-0000Dec 5, 1782
000000001837-03-04-0000Mar 4, 1837
7004198120000000000♠54 years, 89 days
000000001841-03-04-0000Mar 4, 1841
7004212730000000000♠58 years, 89 days
07,8127,812 days
(7003781200000000000♠21 years, 142 days)
000000001862-07-24-0000Jul 24, 1862
7004290850000000000♠79 years, 231 days
(29,085 days)

9
Harrison, William H.William H. Harrison
000000001773-02-09-0000Feb 9, 1773
000000001841-03-04-0000Mar 4, 1841
7004248590000000000♠68 years, 23 days
000000001841-04-04-0000Apr 4, 1841[b]
7004248900000000000♠68 years, 54 days
00,0000 days
000000001841-04-04-0000Apr 4, 1841
7004248900000000000♠68 years, 54 days
(24,890 days)

10
Tyler, JohnJohn Tyler
000000001790-03-29-0000Mar 29, 1790
000000001841-04-04-0000Apr 4, 1841
7004186330000000000♠51 years, 6 days
000000001845-03-04-0000Mar 4, 1845
7004200630000000000♠54 years, 340 days
06,1646,164 days
(7003616400000000000♠16 years, 320 days)
000000001862-01-18-0000Jan 18, 1862
7004262270000000000♠71 years, 295 days
(26,227 days)

11
Polk, James K.James K. Polk
000000001795-11-02-0000Nov 2, 1795
000000001845-03-04-0000Mar 4, 1845
7004180190000000000♠49 years, 122 days
000000001849-03-04-0000Mar 4, 1849
7004194800000000000♠53 years, 122 days
00,103103 days
000000001849-06-15-0000Jun 15, 1849
7004195830000000000♠53 years, 225 days
(19,583 days)

12
Taylor, ZacharyZachary Taylor
000000001784-11-24-0000Nov 24, 1784
000000001849-03-04-0000Mar 4, 1849
7004234750000000000♠64 years, 100 days
000000001850-07-09-0000Jul 9, 1850[b]
7004239670000000000♠65 years, 227 days
00,0000 days
000000001850-07-09-0000Jul 9, 1850
7004239670000000000♠65 years, 227 days
(23,967 days)

13
Fillmore, MillardMillard Fillmore
000000001800-01-07-0000Jan 7, 1800
000000001850-07-09-0000Jul 9, 1850
7004184450000000000♠50 years, 183 days
000000001853-03-04-0000Mar 4, 1853
7004194140000000000♠53 years, 56 days
07,6747,674 days
(7003767400000000000♠21 years, 4 days)
000000001874-03-08-0000Mar 8, 1874
7004270880000000000♠74 years, 60 days
(27,088 days)

14
Pierce, FranklinFranklin Pierce
000000001804-11-23-0000Nov 23, 1804
000000001853-03-04-0000Mar 4, 1853
7004176330000000000♠48 years, 101 days
000000001857-03-04-0000Mar 4, 1857
7004190940000000000♠52 years, 101 days
04,6014,601 days
(7003460100000000000♠12 years, 218 days)
000000001869-10-08-0000Oct 8, 1869
7004236950000000000♠64 years, 319 days
(23,695 days)

15
Buchanan, JamesJames Buchanan
000000001791-04-23-0000Apr 23, 1791
000000001857-03-04-0000Mar 4, 1857
7004240560000000000♠65 years, 315 days
000000001861-03-04-0000Mar 4, 1861
7004255170000000000♠69 years, 315 days
02,6462,646 days
(7003264600000000000♠7 years, 89 days)
000000001868-06-01-0000Jun 1, 1868
7004281630000000000♠77 years, 39 days
(28,163 days)

16
Lincoln, AbrahamAbraham Lincoln
000000001809-02-12-0000Feb 12, 1809
000000001861-03-04-0000Mar 4, 1861
7004190130000000000♠52 years, 20 days
000000001865-04-15-0000Apr 15, 1865[b]
7004205160000000000♠56 years, 62 days
00,0000 days
000000001865-04-15-0000Apr 15, 1865
7004205160000000000♠56 years, 62 days
(20,516 days)

17
Johnson, AndrewAndrew Johnson
000000001808-12-29-0000Dec 29, 1808
000000001865-04-15-0000Apr 15, 1865
7004205610000000000♠56 years, 107 days
000000001869-03-04-0000Mar 4, 1869
7004219800000000000♠60 years, 65 days
02,3402,340 days
(7003234000000000000♠6 years, 149 days)
000000001875-07-31-0000Jul 31, 1875
7004243200000000000♠66 years, 214 days
(24,320 days)

18
Grant, Ulysses S.Ulysses S. Grant
000000001822-04-27-0000Apr 27, 1822
000000001869-03-04-0000Mar 4, 1869
7004171130000000000♠46 years, 311 days
000000001877-03-04-0000Mar 4, 1877
7004200350000000000♠54 years, 311 days
03,0633,063 days
(7003306300000000000♠8 years, 141 days)
000000001885-07-23-0000Jul 23, 1885
7004230980000000000♠63 years, 87 days
(23,098 days)

19
Hayes, Rutherford B.Rutherford B. Hayes
000000001822-10-04-0000Oct 4, 1822
000000001877-03-04-0000Mar 4, 1877
7004198750000000000♠54 years, 151 days
000000001881-03-04-0000Mar 4, 1881
7004213360000000000♠58 years, 151 days
04,3374,337 days
(7003433700000000000♠11 years, 319 days)
000000001893-01-17-0000Jan 17, 1893
7004256730000000000♠70 years, 105 days
(25,673 days)

20
Garfield, James A.James A. Garfield
000000001831-11-19-0000Nov 19, 1831
000000001881-03-04-0000Mar 4, 1881
7004180030000000000♠49 years, 105 days
000000001881-09-19-0000Sep 19, 1881[b]
7004182020000000000♠49 years, 304 days
00,0000 days
000000001881-09-19-0000Sep 19, 1881
7004182020000000000♠49 years, 304 days
(18,202 days)

21
Arthur, Chester A.Chester A. Arthur
000000001829-10-05-0000Oct 5, 1829
000000001881-09-19-0000Sep 19, 1881
7004189770000000000♠51 years, 349 days
000000001885-03-04-0000Mar 4, 1885
7004202390000000000♠55 years, 150 days
00,624624 days
(7002624000000000000♠1 year, 259 days)
000000001886-11-18-0000Nov 18, 1886
7004208630000000000♠57 years, 44 days
(20,863 days)

22
Cleveland, GroverGrover Cleveland
000000001837-03-18-0000Mar 18, 1837
000000001885-03-04-0000Mar 4, 1885
7004175180000000000♠47 years, 351 days
000000001889-03-04-0000Mar 4, 1889
7004189790000000000♠51 years, 351 days
05,5905,590 days[c]
(15 years, 112 days)
000000001908-06-24-0000Jun 24, 1908
7004260300000000000♠71 years, 98 days
(26,030 days)

23
Harrison, BenjaminBenjamin Harrison
000000001833-08-20-0000Aug 20, 1833
000000001889-03-04-0000Mar 4, 1889
7004202850000000000♠55 years, 196 days
000000001893-03-04-0000Mar 4, 1893
7004217460000000000♠59 years, 196 days
02,9302,930 days
(7003293000000000000♠8 years, 9 days)
000000001901-03-13-0000Mar 13, 1901
7004246760000000000♠67 years, 205 days
(24,676 days)

24
Cleveland, GroverGrover Cleveland
000000001837-03-18-0000Mar 18, 1837
000000001893-03-04-0000Mar 4, 1893
7004204400000000000♠55 years, 351 days
000000001897-03-04-0000Mar 4, 1897
7004219010000000000♠59 years, 351 days
05,5905,590 days[c]
(15 years, 112 days)
000000001908-06-24-0000Jun 24, 1908
7004260300000000000♠71 years, 98 days
(26,030 days)

25
McKinley, WilliamWilliam McKinley
000000001843-01-29-0000Jan 29, 1843
000000001897-03-04-0000Mar 4, 1897
7004197580000000000♠54 years, 34 days
000000001901-09-14-0000Sep 14, 1901[b]
7004214120000000000♠58 years, 228 days
00,0000 days
000000001901-09-14-0000Sep 14, 1901
7004214120000000000♠58 years, 228 days
(21,412 days)

26
Roosevelt, TheodoreTheodore Roosevelt
000000001858-10-27-0000Oct 27, 1858
000000001901-09-14-0000Sep 14, 1901
7004156620000000000♠42 years, 322 days
000000001909-03-04-0000Mar 4, 1909
7004183900000000000♠50 years, 128 days
03,5953,595 days
(7003359500000000000♠9 years, 308 days)
000000001919-01-06-0000Jan 6, 1919
7004219850000000000♠60 years, 71 days
(21,985 days)

27
Taft, William H.William H. Taft
000000001857-09-15-0000Sep 15, 1857
000000001909-03-04-0000Mar 4, 1909
7004187970000000000♠51 years, 170 days
000000001913-03-04-0000Mar 4, 1913
7004202580000000000♠55 years, 170 days
06,2136,213 days
(7003621300000000000♠17 years, 4 days)
000000001930-03-08-0000Mar 8, 1930
7004264710000000000♠72 years, 174 days
(26,471 days)

28
Wilson, WoodrowWoodrow Wilson
000000001856-12-28-0000Dec 28, 1856
000000001913-03-04-0000Mar 4, 1913
7004205190000000000♠56 years, 66 days
000000001921-03-04-0000Mar 4, 1921
7004234410000000000♠64 years, 66 days
01,0661,066 days
(7003106600000000000♠2 years, 336 days)
000000001924-02-03-0000Feb 3, 1924
7004245070000000000♠67 years, 37 days
(24,507 days)

29
Harding, Warren G.Warren G. Harding
000000001865-11-02-0000Nov 2, 1865
000000001921-03-04-0000Mar 4, 1921
7004202100000000000♠55 years, 122 days
000000001923-08-02-0000Aug 2, 1923[b]
7004210910000000000♠57 years, 273 days
00,0000 days
000000001923-08-02-0000Aug 2, 1923
7004210910000000000♠57 years, 273 days
(21,091 days)

30
Coolidge, CalvinCalvin Coolidge
000000001872-07-04-0000Jul 4, 1872
000000001923-08-02-0000Aug 2, 1923
7004186550000000000♠51 years, 29 days
000000001929-03-04-0000Mar 4, 1929
7004206960000000000♠56 years, 243 days
01,4031,403 days
(7003140300000000000♠3 years, 307 days)
000000001933-01-05-0000Jan 5, 1933
7004220990000000000♠60 years, 185 days
(22,099 days)

31
Hoover, HerbertHerbert Hoover
000000001874-08-10-0000Aug 10, 1874
000000001929-03-04-0000Mar 4, 1929
7004199290000000000♠54 years, 206 days
000000001933-03-04-0000Mar 4, 1933
7004213900000000000♠58 years, 206 days
11,55311,553 days
(7004115530000000000♠31 years, 230 days)
000000001964-10-20-0000Oct 20, 1964
7004329430000000000♠90 years, 71 days
(32,943 days)

32
Roosevelt, Franklin D.Franklin D. Roosevelt
000000001882-01-30-0000Jan 30, 1882
000000001933-03-04-0000Mar 4, 1933
7004186600000000000♠51 years, 33 days
000000001945-04-12-0000Apr 12, 1945[b]
7004230820000000000♠63 years, 72 days
00,0000 days
000000001945-04-12-0000Apr 12, 1945
7004230820000000000♠63 years, 72 days
(23,082 days)

33
Truman, Harry S.Harry S. Truman
000000001884-05-08-0000May 8, 1884
000000001945-04-12-0000Apr 12, 1945
7004222530000000000♠60 years, 339 days
000000001953-01-20-0000Jan 20, 1953
7004250930000000000♠68 years, 257 days
07,2807,280 days
(7003728000000000000♠19 years, 341 days)
000000001972-12-26-0000Dec 26, 1972
7004323730000000000♠88 years, 232 days
(32,373 days)

34
Eisenhower, Dwight D.Dwight D. Eisenhower
000000001890-10-14-0000Oct 14, 1890
000000001953-01-20-0000Jan 20, 1953
7004227430000000000♠62 years, 98 days
000000001961-01-20-0000Jan 20, 1961
7004256650000000000♠70 years, 98 days
02,9892,989 days
(7003298900000000000♠8 years, 67 days)
000000001969-03-28-0000Mar 28, 1969
7004286540000000000♠78 years, 165 days
(28,654 days)

35
Kennedy, John F.John F. Kennedy
000000001917-05-29-0000May 29, 1917
000000001961-01-20-0000Jan 20, 1961
7004159420000000000♠43 years, 236 days
000000001963-11-22-0000Nov 22, 1963[b]
7004169780000000000♠46 years, 177 days
00,0000 days
000000001963-11-22-0000Nov 22, 1963
7004169780000000000♠46 years, 177 days
(16,978 days)

36
Johnson, Lyndon B.Lyndon B. Johnson
000000001908-08-27-0000Aug 27, 1908
000000001963-11-22-0000Nov 22, 1963
7004201750000000000♠55 years, 87 days
000000001969-01-20-0000Jan 20, 1969
7004220610000000000♠60 years, 146 days
01,4631,463 days
(7003146300000000000♠4 years, 2 days)
000000001973-01-22-0000Jan 22, 1973
7004235240000000000♠64 years, 148 days
(23,524 days)

37
Nixon, RichardRichard Nixon
000000001913-01-09-0000Jan 9, 1913
000000001969-01-20-0000Jan 20, 1969
7004204650000000000♠56 years, 11 days
000000001974-08-09-0000Aug 9, 1974[d]
7004224920000000000♠61 years, 212 days
07,1967,196 days
(7003719600000000000♠19 years, 256 days)
000000001994-04-22-0000Apr 22, 1994
7004296880000000000♠81 years, 103 days
(29,688 days)

38
Ford, GeraldGerald Ford
000000001913-07-14-0000Jul 14, 1913
000000001974-08-09-0000Aug 9, 1974
7004223060000000000♠61 years, 26 days
000000001977-01-20-0000Jan 20, 1977
7004232010000000000♠63 years, 190 days
10,93210,932 days
(7004109320000000000♠29 years, 340 days)
000000002006-12-26-0000Dec 26, 2006
7004341330000000000♠93 years, 165 days
(34,133 days)

39
Carter, JimmyJimmy Carter
000000001924-10-01-0000Oct 1, 1924
000000001977-01-20-0000Jan 20, 1977
7004191040000000000♠52 years, 111 days
000000001981-01-20-0000Jan 20, 1981
7004205650000000000♠56 years, 111 days
13,59313,593 days[e]
(7004135930000000000♠37 years, 79 days)
2018-04-9
7004341580000000000♠93 years, 190 days(34,158 days)

40
Reagan, RonaldRonald Reagan
000000001911-02-06-0000Feb 6, 1911
000000001981-01-20-0000Jan 20, 1981
7004255510000000000♠69 years, 349 days
000000001989-01-20-0000Jan 20, 1989
7004284730000000000♠77 years, 349 days
05,6155,615 days
(7003561500000000000♠15 years, 137 days)
000000002004-06-05-0000Jun 5, 2004
7004340880000000000♠93 years, 120 days
(34,088 days)

41
Bush, George H. W.George H. W. Bush
000000001924-06-12-0000Jun 12, 1924
000000001989-01-20-0000Jan 20, 1989
7004235980000000000♠64 years, 222 days
000000001993-01-20-0000Jan 20, 1993
7004250590000000000♠68 years, 222 days
09,2109,210 days[e]
(7003921000000000000♠25 years, 79 days)
2018-04-9
7004342690000000000♠93 years, 301 days(34,269 days)

42
Clinton, BillBill Clinton
000000001946-08-19-0000Aug 19, 1946
000000001993-01-20-0000Jan 20, 1993
7004169560000000000♠46 years, 154 days
000000002001-01-20-0000Jan 20, 2001
7004198780000000000♠54 years, 154 days
06,2886,288 days[e]
(7003628800000000000♠17 years, 79 days)
2018-04-9
7004261660000000000♠71 years, 233 days(26,166 days)

43
Bush, George W.George W. Bush
000000001946-07-06-0000Jul 6, 1946
000000002001-01-20-0000Jan 20, 2001
7004199220000000000♠54 years, 198 days
000000002009-01-20-0000Jan 20, 2009
7004228440000000000♠62 years, 198 days
03,3663,366 days[e]
(7003336600000000000♠9 years, 79 days)
2018-04-9
7004262100000000000♠71 years, 277 days(26,210 days)

44
Obama, BarackBarack Obama
000000001961-08-04-0000Aug 4, 1961
000000002009-01-20-0000Jan 20, 2009
7004173360000000000♠47 years, 169 days
000000002017-01-20-0000Jan 20, 2017
7004202580000000000♠55 years, 169 days
00,134444444 days[e]
(7002444000000000000♠1 year, 79 days)
2018-04-9
7004207020000000000♠56 years, 248 days(20,702 days)

45
Trump, DonaldDonald Trump
000000001946-06-14-0000Jun 14, 1946
000000002017-01-20-0000Jan 20, 2017
7004257880000000000♠70 years, 220 days
2018-04-9
7004288540000000000♠78 years, 364 days
24,935
2018-04-9
7004262320000000000♠71 years, 299 days(26,232 days)

#
President
Birth date
Presidency
start date
Age at
start date
Presidency
end date
Age at
end date
Post-presidency
timespan
Death date
Lifespan

text: Notes

text:
^ Jump up to: a b c d Birthdate as changed to New Style.
^ Jump up to: a b c d e f g h Died in office.
^ Jump up to: a b Cleveland was retired for 1,461 days between his two terms (1889–1893), and then another 4,129 days from the end of his 2nd term (1897) until his death (1908).
Jump up ^ Resigned from office.
^ Jump up to: a b c d e As of April 9, 2018.

tag: ol

text: Oldest living U.S. presidents

text: Of the 44 persons who have served as president, 24 have become the oldest such individual of their time. Herbert Hoover held this distinction for the longest period of any, from the death of Calvin Coolidge in January 1933 until his own death 31 years later. Lyndon B. Johnson held it for the shortest, from the death of Harry S. Truman in December 1972 until his own death only 27 days later.

text: On three occasions the oldest living president lost this distinction not by his death, but by the inauguration of a president who was older. Theodore Roosevelt (born 1858) lost this distinction when William Taft (born 1857) was inaugurated, then four years later Taft lost it when Woodrow Wilson (born 1856) was inaugurated. More recently, Richard Nixon (born 1913) ceased being the oldest living president when Ronald Reagan (born 1911) was inaugurated. Furthermore, although Theodore Roosevelt was the youngest ever to become both the oldest living president (at age 49) and a former president (at age 50), he was the only living president or former president by the end of his term. Consequently, Taft was the oldest living president twice: first during his presidency (having succeeded the younger Roosevelt), and a second time after Wilson (his successor as president but an older man) died. Gerald Ford was the oldest individual to acquire this distinction, at the age of 90.

text: On seven occasions, the oldest living president has acquired this distinction during his term in office. In the cases of John Adams, Ulysses S. Grant, Theodore Roosevelt, Herbert Hoover and Richard Nixon, this happened at the same time as their becoming the only living president; in the cases of Andrew Jackson and Benjamin Harrison, the only other living president at the time was a younger predecessor (John Quincy Adams and Grover Cleveland respectively).

text:
President
Dates
Age at
start date
Age at
end date
Length

Washington, GeorgeGeorge Washington
000000001789-04-30-0000April 30, 1789 – December 14, 1799
7004208870000000000♠57 years, 67 days
7004247670000000000♠67 years, 295 days
7003388000000000000♠10 years, 228 days

Adams, JohnJohn Adams
000000001799-12-14-0000December 14, 1799 – July 4, 1826
7004234210000000000♠64 years, 45 days
7004331190000000000♠90 years, 247 days
7003969800000000000♠26 years, 202 days

Madison, JamesJames Madison
000000001826-07-04-0000July 4, 1826 – June 28, 1836
7004275030000000000♠75 years, 110 days
7004311500000000000♠85 years, 104 days
7003364700000000000♠9 years, 360 days

Jackson, AndrewAndrew Jackson
000000001836-06-28-0000June 28, 1836 – June 8, 1845
7004253070000000000♠69 years, 105 days
7004285740000000000♠78 years, 85 days
7003326700000000000♠8 years, 345 days

Adams, John QuincyJohn Quincy Adams
000000001845-06-08-0000June 8, 1845 – February 23, 1848
7004284560000000000♠77 years, 332 days
7004294460000000000♠80 years, 227 days
7002990000000000000♠2 years, 260 days

Van Buren, MartinMartin Van Buren
000000001848-02-23-0000February 23, 1848 – July 24, 1862
7004238200000000000♠65 years, 80 days
7004290850000000000♠79 years, 231 days
7003526500000000000♠14 years, 151 days

Buchanan, JamesJames Buchanan
000000001862-07-24-0000July 24, 1862 – June 1, 1868
7004260240000000000♠71 years, 92 days
7004281630000000000♠77 years, 39 days
7003213900000000000♠5 years, 313 days

Fillmore, MillardMillard Fillmore
000000001868-06-01-0000June 1, 1868 – March 8, 1874
7004249820000000000♠68 years, 146 days
7004270880000000000♠74 years, 60 days
7003210600000000000♠5 years, 280 days

Johnson, AndrewAndrew Johnson
000000001874-03-08-0000March 8, 1874 – July 31, 1875
7004238100000000000♠65 years, 69 days
7004243200000000000♠66 years, 214 days
7002510000000000000♠1 year, 145 days

Grant, Ulysses S.Ulysses S. Grant
000000001875-07-31-0000July 31, 1875 – July 23, 1885
7004194530000000000♠53 years, 95 days
7004230980000000000♠63 years, 87 days
7003364500000000000♠9 years, 357 days

Hayes, Rutherford B.Rutherford B. Hayes
000000001885-07-23-0000July 23, 1885 – January 17, 1893
7004229380000000000♠62 years, 292 days
7004256730000000000♠70 years, 105 days
7003273500000000000♠7 years, 178 days

Harrison, BenjaminBenjamin Harrison
000000001893-01-17-0000January 17, 1893 – March 13, 1901
7004217000000000000♠59 years, 150 days
7004246760000000000♠67 years, 205 days
7003297600000000000♠8 years, 55 days

Cleveland, GroverGrover Cleveland
000000001901-03-13-0000March 13, 1901 – June 24, 1908
7004233700000000000♠63 years, 360 days
7004260300000000000♠71 years, 98 days
7003266000000000000♠7 years, 103 days

Roosevelt, TheodoreTheodore Roosevelt
000000001908-06-24-0000June 24, 1908 – March 4, 1909
7004181370000000000♠49 years, 241 days
7004183900000000000♠50 years, 128 days
7002253000000000000♠253 days

Taft, William HowardWilliam Howard Taft
000000001909-03-04-0000March 4, 1909 – March 4, 1913
7004187970000000000♠51 years, 170 days
7004202580000000000♠55 years, 170 days
7003146100000000000♠4 years, 0 days

Wilson, WoodrowWoodrow Wilson
000000001913-03-04-0000March 4, 1913 – February 3, 1924
7004205190000000000♠56 years, 66 days
7004245070000000000♠67 years, 37 days
7003398800000000000♠10 years, 336 days

Taft, William HowardWilliam Howard Taft
000000001924-02-03-0000February 3, 1924 – March 8, 1930
7004242460000000000♠66 years, 141 days
7004264710000000000♠72 years, 174 days
7003222500000000000♠6 years, 33 days

Coolidge, CalvinCalvin Coolidge
000000001930-03-08-0000March 8, 1930 – January 5, 1933
7004210650000000000♠57 years, 247 days
7004220990000000000♠60 years, 185 days
7003103400000000000♠2 years, 303 days

Hoover, HerbertHerbert Hoover
000000001933-01-05-0000January 5, 1933 – October 20, 1964
7004213320000000000♠58 years, 148 days
7004329430000000000♠90 years, 71 days
7004116110000000000♠31 years, 289 days

Truman, Harry S.Harry S. Truman
000000001964-10-20-0000October 20, 1964 – December 26, 1972
7004293840000000000♠80 years, 165 days
7004323730000000000♠88 years, 232 days
7003298900000000000♠8 years, 67 days

Johnson, Lyndon B.Lyndon B. Johnson
000000001972-12-26-0000December 26, 1972 – January 22, 1973
7004234970000000000♠64 years, 121 days
7004235240000000000♠64 years, 148 days
7001270000000000000♠27 days

Nixon, RichardRichard Nixon
000000001973-01-22-0000January 22, 1973 – January 20, 1981
7004219280000000000♠60 years, 13 days
7004248480000000000♠68 years, 11 days
7003292000000000000♠7 years, 364 days

Reagan, RonaldRonald Reagan
000000001981-01-20-0000January 20, 1981 – June 5, 2004
7004255510000000000♠69 years, 349 days
7004340880000000000♠93 years, 120 days
7003853700000000000♠23 years, 137 days

Ford, GeraldGerald Ford
000000002004-06-05-0000June 5, 2004 – December 26, 2006
7004331990000000000♠90 years, 327 days
7004341330000000000♠93 years, 165 days
7002934000000000000♠2 years, 204 days

Bush, George H. W.George H. W. Bush
000000002006-12-26-0000December 26, 2006 – present
7004301470000000000♠82 years, 197 days
Current
7003412200000000000♠11 years, 104 days

President
Dates
Age at
start date
Age at
end date
Length


document_title: Coral reef

question_text: the optimum temperature for coral formation occurs where the average annual temperatures are between

question_tokens: the optimum temperature for coral formation occurs where the average annual temperatures are between

root

text: Coral reef

text: Formation[edit]

text: Most of the coral reefs we can see today were formed after the last glacial period when melting ice caused the sea level to rise and flood the continental shelves. This means that most modern coral reefs are less than 10,000 years old. As communities established themselves on the shelves, the reefs grew upwards, pacing rising sea levels. Reefs that rose too slowly could become drowned reefs. They are covered by so much water that there was insufficient light.[12] Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and as atolls. The vast majority of these islands are volcanic in origin. The few exceptions have tectonic origins where plate movements have lifted the deep ocean floor on the surface.

tag: p

text: In 1842 in his first monograph, The Structure and Distribution of Coral Reefs,[13] Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle. He theorized uplift and subsidence of the Earth's crust under the oceans formed the atolls.[14] Darwin’s theory sets out a sequence of three stages in atoll formation. It starts with a fringing reef forming around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef, and ultimately an atoll reef.

text:
Darwin’s theory starts with a volcanic island which becomes extinct

As the island and ocean floor subside, coral growth builds a fringing reef, often including a shallow lagoon between the land and the main reef.

As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper lagoon inside.

Ultimately, the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon.

tag: ul

text: Darwin predicted that underneath each lagoon would be a bed rock base, the remains of the original volcano. Subsequent drilling proved this correct. Darwin's theory followed from his understanding that coral polyps thrive in the clean seas of the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form what he called fringing reefs, and can eventually grow out from the shore to become a barrier reef.

text: Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies and becomes white limestone. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles, but are broken in places by storms. Like sea level rise, a rapidly subsiding bottom can overwhelm coral growth, killing the coral polyps and the reef, due to what is called coral drowning.[16] Corals that rely on zooxanthellae can drown when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure.[17]

text: The two main variables determining the geomorphology, or shape, of coral reefs are the nature of the underlying substrate on which they rest, and the history of the change in sea level relative to that substrate.

text: The approximately 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was then 120 m (390 ft) lower than in the 21st century.[18][19] As sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain. By 13,000 years ago, sea level had risen to 60 m (200 ft)  lower than at present, and many hills of the coastal plains had become continental islands. As the sea level rise continued, water topped most of the continental islands. The corals could then overgrow the hills, forming the present cays and reefs. Sea level on the Great Barrier Reef has not changed significantly in the last 6,000 years,[19] and the age of the modern living reef structure is estimated to be between 6,000 and 8,000 years.[20] Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, since Australia is not about to submerge. It formed the world's largest barrier reef, 300–1,000 m (980–3,280 ft) from shore, stretching for 2,000 km (1,200 mi).[21]

text: Healthy tropical coral reefs grow horizontally from 1 to 3 cm (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only at depths shallower than 150 m (490 ft) because of their need for sunlight, and cannot grow above sea level.[22]

text: Materials[edit]

text: As the name implies, the bulk of coral reefs is made up of coral skeletons from mostly intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However, shell fragments and the remains of calcareous algae such as the green-segmented genus Halimeda can add to the reef's ability to withstand damage from storms and other threats. Such mixtures are visible in structures such as Eniwetok Atoll.[23]

text: Types[edit]

text: Since Darwin's identification of the three classical reef formations – the fringing reef around a volcanic island becoming a barrier reef and then an atoll[24] – scientists have identified further reef types. While some sources still maintain that there are only three,[25][26] Thomas and Goudie list four "principal large-scale coral reef types" – the fringing reef, barrier reef, atoll and table reef[27] – while Spalding et al. list five "main types" – the fringing reef, barrier reef, atoll, "bank or platform reef" and patch reef.[28]

text: Fringing reef[edit]

text: A fringing reef, also called a shore reef,[29] is directly attached to a shore,[30] or borders it with an intervening narrow, shallow channel or lagoon.[31] It is the most common reef type.[31]  Fringing reefs follow coastlines and can be many kilometres long.[32] They are usually less than 100 metres wide, but some are up to several hundred metres wide.[33] Fringing reefs are initially formed immediately on the shore at the low water level and expand increasingly  seawards as they grow in size. The final width depends on where the sea bed begins to drop steeply. The surface of the fringe reef always remains at the same height: just below the waterline. In older fringed reefs, whose outer regions have pushed themselves far out into the sea, the inner part is deepened by erosion and will eventually form a lagoon.[34] Fringing reef lagoons can become over 100 metres wide and several metres deep. Like the fringing reef itself, they run parallel to the coast. The fringing reefs of the Red Sea are "some of the best developed in the world" and occur along all its shores except off sandy bays.[35]

text: Barrier reef[edit]

text: Barrier reefs are separated from a mainland or island shore by a deep channel or lagoon.[31] They resemble the later stages of a fringing reef with its lagoon, but differ from the latter mainly in size and origin. Their lagoons can be several kilometres wide and 30 to 70 metres deep. Above all, the offshore outer reef edge is not a reef that used to be by the shore and, as it grew, expanded further and further into the open sea, but is a reef that has been there from the very beginning. Like an atoll, it is thought that these reefs are formed either by the lowering of the seabed or by an increase in sea level. Since a geological process is thus needed for their formation and the formation itself takes considerably longer than that of fringing reef, barrier reefs are much rarer. The best-known and largest example of a barrier reef is the Australian Great Barrier Reef.[31][36] Other major examples are the Belize Barrier Reef and the New Caledonian Barrier Reef.[36] Barrier reefs are also found on the coasts of Providencia,[36] Mayotte, the Gambier Islands, on the southeast coast coast of Kalimantan, on parts of the coast of Sulawesi, southeastern New Guinea and the south coast of the Louisiade Archipelago.

text: Platform reef[edit]

text: While the aforementioned reef types always originate along the coasts of islands or continents, platform reefs, variously called bank or table reefs, can form on the continental shelf, as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals.[37] There are several platform reefs in the southern Great Barrier Reef, the Swain[38] and Capricorn Group[39] on the continental shelf, about 100–200 km from the coast. Some platform reefs of the northern Mascarenes are even several thousand kilometres from the mainland. Unlike fringing and barrier reefs which only extend seawards, platform reefs grown in all directions.[37] They are very variable in size, ranging from a few hundred metres to many kilometres across. Their usual shape is oval to strongly elongated. Parts of these reefs can reach the surface and form sandbanks and small islands around which may form their own fringing reefs. In the middle of a platform reef, there may be a lagoon. Platform reefs can also be found within atolls. Here they are called patch reefs which are only a few dozen metres in diameter. Where platform reefs form on an elongated structure, e. g. an old, eroded barrier reef, they can form a linear arrangement. This is the case, for example, on the east coast of the Red Sea near Jeddah. In very old platform reefs, the inner part can be so heavily eroded that they form a pseudo-atoll.[37] These can only be distinguished from real atolls by detailed investigation and possibly drilling holes. Some platform reefs of the Laccadives are U-shaped, due to wind and water flow.

text: Atoll[edit]

text: Atolls or atoll reefs are more or less circular or continuous barrier reef extends all the way around a lagoon without a central island.[40] They are usually formed from fringing reefs around volcanic islands.[31] Over the course of time, the island is eroded away and sinks below the level of the sea.[31]  Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which enclose a lagoon.  Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the Caroline Islands, the Cook Islands, French Polynesia, the Marshall Islands and Micronesia.[36] Many atolls are also found in the Indian Ocean, for example, in the Maldives, the Chagos Islands, the Seychelles and around Cocos Island.[36] The Maldives consist of 26  atolls.[41]

text: Other reef types or variants[edit]

text:
Apron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore. The initial stage of a fringing reef.[29]
Bank reef - isolated, flat-topped reef larger than a patch reef and usually on mid-shelf regions and linear or semi-circular in shape; a type of platform reef.[36]
Patch reef – common, isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or seagrass. Type of platform reef.[36]
Ribbon reef – long, narrow, possibly winding reef, usually associated with an atoll lagoon. Also called a shelf-edge reef or sill reef.[29]
Habili – reef specific to the Red Sea; does not reach the surface near enough to cause visible surf; may be a hazard to ships (from the Arabic for "unborn")
Microatoll – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using radioactive carbon dating and have been used to reconstruct Holocene sea levels[42]
Cays – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, forming an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land
Seamount or guyot – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded and guyots are flat; flat tops of guyots, or tablemounts, are due to erosion by waves, winds, and atmospheric processes

text: Zones[edit]

text: Coral reef ecosystems contain distinct zones that represent different kinds of habitats. Usually, three major zones are recognized: the fore reef, reef crest, and the back reef (frequently referred to as the reef lagoon).

text: All three zones are physically and ecologically interconnected. Reef life and oceanic processes create opportunities for exchange of seawater, sediments, nutrients, and marine life among one another.

text: Thus, they are integrated components of the coral reef ecosystem, each playing a role in the support of the reefs' abundant and diverse fish assemblages.

text: Most coral reefs exist in shallow waters less than 50 m deep. Some inhabit tropical continental shelves where cool, nutrient rich upwelling does not occur, such as Great Barrier Reef. Others are found in the deep ocean surrounding islands or as atolls, such as in the Maldives. The reefs surrounding islands form when islands subside into the ocean, and atolls form when an island subsides below the surface of the sea.

text: Alternatively, Moyle and Cech distinguish six zones, though most reefs possess only some of the zones.[43]

text: The reef surface is the shallowest part of the reef. It is subject to the surge and the rise and fall of tides. When waves pass over shallow areas, they shoal, as shown in the diagram at the right. This means the water is often agitated. These are the precise condition under which corals flourish. Shallowness means there is plenty of light for photosynthesis by the symbiotic zooxanthellae, and agitated water promotes the ability of coral to feed on plankton. However, other organisms must be able to withstand the robust conditions to flourish in this zone.

text: The off-reef floor is the shallow sea floor surrounding a reef. This zone occurs by reefs on continental shelves. Reefs around tropical islands and atolls drop abruptly to great depths, and do not have a floor. Usually sandy, the floor often supports seagrass meadows which are important foraging areas for reef fish.

text: The reef drop-off is, for its first 50 m, habitat for many reef fish who find shelter on the cliff face and plankton in the water nearby. The drop-off zone applies mainly to the reefs surrounding oceanic islands and atolls.

text: The reef face is the zone above the reef floor or the reef drop-off. This zone is often the most diverse area of the reef. Coral and calcareous algae growths provide complex habitats and areas which offer protection, such as cracks and crevices. Invertebrates and epiphytic algae provide much of the food for other organisms.[43] A common feature on this forereef zone is spur and groove formations which serve to transport sediment downslope.

text: The reef flat is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as a protective area, or it may lie between the reef and the shore, and in this case is a flat, rocky area. Fishes tend to prefer living in that flat, rocky area, compared to any other zone, when it is present.[43]

text: The reef lagoon is an entirely enclosed region, which creates an area less affected by wave action that often contains small reef patches.[43]

text: However, the "topography of coral reefs is constantly changing. Each reef is made up of irregular patches of algae, sessile invertebrates, and bare rock and sand. The size, shape and relative abundance of these patches changes from year to year in response to the various factors that favor one type of patch over another. Growing coral, for example, produces constant change in the fine structure of reefs. On a larger scale, tropical storms may knock out large sections of reef and cause boulders on sandy areas to move."[44]

text: Locations[edit]

text: Coral reefs are estimated to cover 284,300 km2 (109,800 sq mi),[45] just under 0.1% of the oceans' surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%.[2]

text: Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from approximately 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26–27 °C (79–81 °F), and few reefs exist in waters below 18 °C (64 °F).[46] However, reefs in the Persian Gulf have adapted to temperatures of 13 °C (55 °F) in winter and 38 °C (100 °F) in summer.[47] There are 37 species of scleractinian corals identified in such harsh environment around Larak Island.[48]

text: Deep-water coral can exist at greater depths and colder temperatures at much higher latitudes, as far north as Norway.[49] Although deep water corals can form reefs, very little is known about them.

text: Coral reefs are rare along the west coasts of the Americas and Africa, due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (respectively the Peru, Benguela and Canary streams).[50] Corals are seldom found along the coastline of South Asia—from the eastern tip of India (Chennai) to the Bangladesh and Myanmar borders[2]—as well as along the coasts of northeastern South America and Bangladesh, due to the freshwater release from the Amazon and Ganges Rivers respectively.

text:
The Great Barrier Reef—largest, comprising over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers (1,600 mi) off Queensland, Australia
The Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers (620 mi) from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras
The New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers (930 mi)
The Andros, Bahamas Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau
The Red Sea—includes 6000-year-old fringing reefs located around a 2,000 km (1,240 mi) coastline
The Florida Reef Tract—largest continental US reef and the third largest coral barrier reef system in the world, extends from Soldier Key, located in Biscayne Bay, to the Dry Tortugas in the Gulf of Mexico[51]
Pulley Ridge—deepest photosynthetic coral reef, Florida
Numerous reefs scattered over the Maldives
The Philippines coral reef area, the second largest in Southeast Asia, is estimated at 26,000 square kilometers and holds an extraordinary diversity of species. Scientists have identified 915 reef fish species and more than 400 scleractinian coral species, 12 of which are endemic.
The Raja Ampat Islands in Indonesia's West Papua province offer the highest known marine diversity.[52]
Bermuda is known for its northernmost coral reef system, located at 32.4° N and 64.8° W. The presence of coral reefs at this high latitude is due to the proximity of the Gulf Stream. Bermuda has a fairly consistent diversity of coral species, representing a subset of those found in the greater Caribbean.[53]
The world's northernmost individual coral reef so far discovered is located within a bay of Japan's Tsushima Island in the Korea Strait.[54]
The world's southernmost coral reef is at Lord Howe Island, in the Pacific Ocean off the east coast of Australia.

text: Biology[edit]

text: When alive, corals are colonies of small animals embedded in calcium carbonate shells. It is a mistake to think of coral as plants or rocks. Coral heads consist of accumulations of individual animals called polyps, arranged in diverse shapes.[55] Polyps are usually tiny, but they can range in size from a pinhead to 12 inches (30 cm) across.

text: Reef-building or hermatypic corals live only in the photic zone (above 50 m), the depth to which sufficient sunlight penetrates the water, allowing photosynthesis to occur. Coral polyps do not photosynthesize, but have a symbiotic relationship with microscopic algae of the genus Symbiodinium, commonly referred to as zooxanthellae. These organisms live within the tissues of polyps and provide organic nutrients that nourish the polyp. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Without their symbionts, coral growth would be too slow to form significant reef structures. Corals get up to 90% of their nutrients from their symbionts.[56]

text: Reefs grow as polyps and other organisms deposit calcium carbonate,[57][58] the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards.[59] Waves, grazing fish (such as parrotfish), sea urchins, sponges, and other forces and organisms act as bioeroders, breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons.

text: Typical shapes for coral species are named by their resemblance to  wrinkled brains, cabbages, table tops, antlers, wire strands and pillars. These shapes can depend on the life history of the coral, like light exposure and wave action,[60] and events such as breakages.[61]

text: Corals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesenteries, membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few species change sex as they grow.

text: Internally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny larva, known as a planula. Externally fertilized eggs develop during synchronized spawning. Polyps simultaneously release eggs and sperm into the water en-masse. Eggs disperse over a large area. The timing of spawning depends on time of year, water temperature, and tidal and lunar cycles. Spawning is most successful when there is little variation between high and low tide. The less water movement, the better the chance for fertilization. Ideal timing occurs in the spring. Release of eggs or planula usually occurs at night, and is sometimes in phase with the lunar cycle (three to six days after a full moon). The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks. They are vulnerable to predation and environmental conditions. The lucky few planulae which successfully attach to substrate next confront competition for food and space.[citation needed]

text: There are eight clades of Symbiodinium phylotypes. Most research has been completed on the Symbiodinium clades A–D. Each one of the eight contributes their own benefits as well as less compatible attributes to the survival of their coral hosts. Each photosynthetic organism has a specific level of sensitivity to photodamage of compounds needed for survival, such as proteins. Rates of regeneration and replication determine the organism's ability to survive. Phylotype A is found more in the shallow regions of marine waters. It is able to produce mycosporine-like amino acids that are UV resistant, using a derivative of glycerin to absorb the UV radiation and allowing them to become more receptive to warmer water temperatures. In the event of UV or thermal damage, if and when repair occurs, it will increase the likelihood of survival of the host and symbiont. This leads to the idea that, evolutionarily, clade A is more UV resistant and thermally resistant than the other clades.[62]

text: Clades B and C are found more frequently in the deeper water regions, which may explain the higher susceptibility to increased temperatures. Terrestrial plants that receive less sunlight because they are found in the undergrowth can be analogized to clades B, C, and D. Since clades B through D are found at deeper depths, they require an elevated light absorption rate to be able to synthesize as much energy. With elevated absorption rates at UV wavelengths, the deeper occurring phylotypes are more prone to coral bleaching versus the more shallow clades.

text: Clade D has been observed to be high temperature-tolerant, and as a result it has a higher rate of survival than clades B and C during modern bleaching events.[62]

text: Other reef builders[edit]

text: Corals are the most prodigious reef-builders. However many other organisms living in the reef community also contribute skeletal calcium carbonate in the same manner as corals. These include coralline algae and some sponges.[63] Reefs are always built by the combined efforts of these different phyla, with different organisms having been the predominant reef-builders in different geological periods.[citation needed]

text: Coralline algae[edit]

text: Coralline algae are important contributors to reef structure. Although their mineral deposition-rates are much slower than corals, they are more tolerant of rough wave-action, and so help to create a protective crust over those parts of the reef subjected to the greatest forces by waves, such as the reef front facing the open ocean. They also strengthen the reef structure by depositing limestone in sheets over the reef surface.[citation needed]

text: Sponges[edit]

text: “Sclerosponge” is the descriptive name for all Porifera (sponges) that build reefs. In the early Cambrian period, Archaeocyatha sponges were the world's first reef-building organisms, and sponges were the only reef-builders until the Ordovician. Sclerosponges still assist corals building modern reefs, but like coralline algae are much slower-growing than corals and their contribution is (usually) minor.[citation needed]

text: In the northern Pacific Ocean cloud sponges still create deep-water mineral-structures without corals, although the structures are not recognizable from the surface like tropical reefs. They are the only extant organisms known to build reef-like structures in cold water.[citation needed]

text: Gallery of reef-building corals and their reef-building assistants[edit]

text:
Brain coral

Staghorn coral

Spiral wire coral

Pillar coral

Mushroom coral

Maze coral

Black coral

Fluorescent coral[64]

Corraline algae Mesophyllum sp.

Encrusting corraline algae

coralline algae Corallina officinalis

text: Darwin's paradox[edit]

text:
Darwin's paradox"Coral... seems to proliferate when ocean waters are warm, poor, clear and agitated, a fact which Darwin had already noted when he passed through Tahiti in 1842. This constitutes a fundamental paradox, shown quantitatively by the apparent impossibility of balancing input and output of the nutritive elements which control the coral polyp metabolism.
Recent oceanographic research has brought to light the reality of this paradox by confirming that the oligotrophy of the ocean euphotic zone persists right up to the swell-battered reef crest. When you approach the reef edges and atolls from the quasidesert of the open sea, the near absence of living matter suddenly becomes a plethora of life, without transition. So why is there something rather than nothing, and more precisely, where do the necessary nutrients for the functioning of this extraordinary coral reef machine come from?"

— Francis Rougerie[65]

tag: div

text: In The Structure and Distribution of Coral Reefs, published in 1842, Darwin described how coral reefs were found in some areas of the tropical seas but not others, with no obvious cause. The largest and strongest corals grew in parts of the reef exposed to the most violent surf and corals were weakened or absent where loose sediment accumulated.[66]

text: Tropical waters contain few nutrients[67] yet a coral reef can flourish like an "oasis in the desert".[68] This has given rise to the ecosystem conundrum, sometimes called "Darwin's paradox": "How can such high production flourish in such nutrient poor conditions?"[69][70][71]

text: Coral reefs cover less than 0.1% of the surface of the world’s ocean, about half the land area of France, yet they support over one-quarter of all marine species. This diversity results in complex food webs, with large predator fish eating smaller forage fish that eat yet smaller zooplankton and so on. However, all food webs eventually depend on plants, which are the primary producers. Coral reefs' primary productivity is very high, typically producing 5–10 grams of carbon per square meter per day (gC·m−2·day−1) biomass.[72][73]

text: One reason for the unusual clarity of tropical waters is they are deficient in nutrients and drifting plankton. Further, the sun shines year-round in the tropics, warming the surface layer, making it less dense than subsurface layers. The warmer water is separated from deeper, cooler water by a stable thermocline, where the temperature makes a rapid change. This keeps the warm surface waters floating above the cooler deeper waters. In most parts of the ocean, there is little exchange between these layers. Organisms that die in aquatic environments generally sink to the bottom, where they decompose, which releases nutrients in the form of nitrogen (N), phosphorus (P) and potassium (K). These nutrients are necessary for plant growth, but in the tropics, they do not directly return to the surface.[citation needed]

text: Plants form the base of the food chain and need sunlight and nutrients to grow. In the ocean, these plants are mainly microscopic phytoplankton which drift in the water column. They need sunlight for photosynthesis, which powers carbon fixation, so they are found only relatively near the surface, but they also need nutrients. Phytoplankton rapidly use nutrients in the surface waters, and in the tropics, these nutrients are not usually replaced because of the thermocline.[citation needed]

text: Explanations[edit]

text: Around coral reefs, lagoons fill in with material eroded from the reef and the island. They become havens for marine life, providing protection from waves and storms.

text: Most importantly, reefs recycle nutrients, which happens much less in the open ocean. In coral reefs and lagoons, producers include phytoplankton, as well as seaweed and coralline algae, especially small types called turf algae, which pass nutrients to corals.[74] The phytoplankton are eaten by fish and crustaceans, who also pass nutrients along the food web. Recycling ensures fewer nutrients are needed overall to support the community.

text: Coral reefs support many symbiotic relationships. One of particular importance is the relationship many corals have with a type of photosynthetic algae called zooxanthellae.  These single-celled dinoflagellates live in the tissues of many types of cnidarians, including corals, and help provide energy to their host in the form of glucose, glycerol, and amino acids. [75] Zooxanthellae can provide up to 90% of a coral’s energy requirements.[56] In return, as an example of mutualism, the corals shelter the zooxanthellae, averaging one million for every cubic centimeter of coral, and provide a constant supply of the carbon dioxide they need for photosynthesis.

text: Corals also absorb nutrients, including inorganic nitrogen and phosphorus, directly from water. Many corals extend their tentacles at night to catch zooplankton that brush them when the water is agitated. Zooplankton provide the polyp with nitrogen, and the polyp shares some of the nitrogen with the zooxanthellae, which also require this element.[74] The varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance, and give brown corals their colors. Other pigments such as reds, blues, greens, etc. come from colored proteins made by the coral animals. Coral which loses a large fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are richly pigmented with their own colorful proteins) and is said to be bleached, a condition which, unless corrected, can kill the coral.

text: Sponges are another key: they live in crevices in the coral reefs. They are efficient filter feeders, and in the Red Sea they consume about 60% of the phytoplankton that drifts by. The sponges eventually excrete nutrients in a form the corals can use.[76]

text: The roughness of coral surfaces is the key to coral survival in agitated waters. Normally, a boundary layer of still water surrounds a submerged object, which acts as a barrier. Waves breaking on the extremely rough edges of corals disrupt the boundary layer, allowing the corals access to passing nutrients. Turbulent water thereby promotes reef growth and branching. Without the nutritional gains brought by rough coral surfaces, even the most effective recycling would leave corals wanting in nutrients.[77]

text: Studies have shown that deep nutrient-rich water entering coral reefs through isolated events may have significant effects on temperature and nutrient systems.[78][79]  This water movement disrupts the relatively stable thermocline that usually exists between warm shallow water to deeper colder water. Leichter et al. (2006)[80]  found that temperature regimes on coral reefs in the Bahamas and Florida were highly variable with temporal scales of minutes to seasons and spatial scales across depths.

text: Water can be moved through coral reefs in various ways, including current rings, surface waves, internal waves and tidal changes.[78][81][82][83]  Movement is generally created by tides and wind. As tides interact with varying bathymetry and wind mixes with surface water, internal waves are created. An internal wave is a gravity wave that moves along density stratification within the ocean. When a water parcel encounters a different density it will oscillate and create internal waves.[84] While internal waves generally have a lower frequency than surface waves, they often form as a single wave that breaks into multiple waves as it hits a slope and moves upward.[85] This vertical break up of internal waves causes significant diapycnal mixing and turbulence.[86][87] Internal waves can act as nutrient pumps, bringing plankton and cool nutrient-rich water up to the surface.[78][83][88][89][90][91][92][93][94][95][96]

text: The irregular structure characteristic of coral reef bathymetry may enhance mixing and produce pockets of cooler water and variable nutrient content.[97] Arrival of cool, nutrient-rich water from depths due to internal waves and tidal bores has been linked to growth rates of suspension feeders and benthic algae[83][96][98]  as well as plankton and larval organisms.[83][99] Leichter et al.[96]  proposed that the seaweed Codium isthmocladum reacts to deep water nutrient sources due to their tissues having different concentrations of nutrients dependent upon depth. Wolanski and Hamner[90] noted aggregations of eggs, larval organisms and plankton on reefs in response to deep water intrusions. Similarly, as internal waves and bores move vertically, surface-dwelling larval organisms are carried toward the shore.[99] This has significant biological importance to cascading effects of food chains in coral reef ecosystems and may provide yet another key to unlocking "Darwin's Paradox".

text: Cyanobacteria provide soluble nitrates for the reef via nitrogen fixation.[100]

text: Coral reefs also often depend on surrounding habitats, such as seagrass meadows and mangrove forests, for nutrients. Seagrass and mangroves supply dead plants and animals which are rich in nitrogen and also serve to feed fish and animals from the reef by supplying wood and vegetation. Reefs, in turn, protect mangroves and seagrass from waves and produce sediment in which the mangroves and seagrass can root.[47]

text: Biodiversity[edit]

text: Coral reefs form some of the world's most productive ecosystems, providing complex and varied marine habitats that support a wide range of other organisms.[101][102]Fringing reefs just below low tide level have a mutually beneficial relationship with mangrove forests at high tide level and sea grass meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or erode the sediments in which they are rooted, while the mangroves and sea grass protect the coral from large influxes of silt, fresh water and pollutants. This level of variety in the environment benefits many coral reef animals, which, for example, may feed in the sea grass and use the reefs for protection or breeding.[103]

text: Reefs are home to a large variety of animals, including fish, seabirds, sponges, cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, cleaner shrimp, spiny lobsters and crabs), mollusks (including cephalopods), echinoderms (including starfish, sea urchins and sea cucumbers), sea squirts, sea turtles and sea snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins being the main exception. A few of these varied species feed directly on corals, while others graze on algae on the reef.[2][74] Reef biomass is positively related to species diversity.[104]

text: The same hideouts in a reef may be regularly inhabited by different species at different times of day. Nighttime predators such as cardinalfish and squirrelfish hide during the day, while damselfish, surgeonfish, triggerfish, wrasses and parrotfish hide from eels and sharks.[23]:49

text: Algae[edit]

text: Reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral.[105][106] Increased nutrient levels can be a result of sewage or chemical fertilizer runoff from nearby coastal developments. Runoff can carry nitrogen and phosphorus which promote excess algae growth. Algae can sometimes out-compete the coral for space. The algae can then smother the coral by decreasing the oxygen supply available to the reef.[107] Decreased oxygen levels can slow down coral's calcification rates weakening the coral and leaving it more susceptible to disease and degradation.[108] In surveys done around largely uninhabited US Pacific islands, algae inhabit a large percentage of surveyed coral locations.[109] The algal population consists of turf algae, coralline algae, and macro algae. Some sea urchins (such as Diadema antillarum, ...) eat these algae and could thus decrease the risk of algal encroachment.

text: Sponges[edit]

text: Sponges are essential for the functioning of the coral reef's ecosystem. Algae and corals in coral reefs produce organic material. This is filtered through sponges which convert this organic material into small particles which in turn are absorbed by algae and corals.[110]

text: Fish[edit]

text: Over 4,000 species of fish inhabit coral reefs.[2] The reasons for this diversity remain unclear. Hypotheses include the "lottery", in which the first (lucky winner) recruit to a territory is typically able to defend it against latecomers, "competition", in which adults compete for territory, and less-competitive species must be able to survive in poorer habitat, and "predation", in which population size is a function of postsettlement piscivore mortality.[111] Healthy reefs can produce up to 35 tons of fish per square kilometer each year, but damaged reefs produce much less.[112]

text: Invertebrates[edit]

text: Sea urchins, Dotidae and sea slugs eat seaweed. Some species of sea urchins, such as Diadema antillarum, can play a pivotal part in preventing algae from overrunning reefs.[113] In Hawaii, researchers are even investigating the use of native collector urchins, Tripneustes gratilla, for their potential as biocontrol agents to mitigate the spread of invasive algae species on coral reefs.[114][115] Nudibranchia and sea anemones eat sponges.

text: A number of invertebrates, collectively called "cryptofauna," inhabit the coral skeletal substrate itself, either boring into the skeletons (through the process of bioerosion) or living in pre-existing voids and crevices. Those animals boring into the rock include sponges, bivalve mollusks, and sipunculans. Those settling on the reef include many other species, particularly crustaceans and polychaete worms.[50]

text: Seabirds[edit]

text: Coral reef systems provide important habitats for seabird species, some endangered. For example, Midway Atoll in Hawaii supports nearly three million seabirds, including two-thirds (1.5 million) of the global population of Laysan albatross, and one-third of the global population of black-footed albatross.[116] Each seabird species has specific sites on the atoll where they nest. Altogether, 17 species of seabirds live on Midway. The short-tailed albatross is the rarest, with fewer than 2,200 surviving after excessive feather hunting in the late 19th century.[117]

text: Other[edit]

text: Sea snakes feed exclusively on fish and their eggs.[118][119][120] Marine birds, such as herons, gannets, pelicans and boobies, feed on reef fish. Some land-based reptiles intermittently associate with reefs, such as monitor lizards, the marine crocodile and semiaquatic snakes, such as Laticauda colubrina. Sea turtles, particularly hawksbill sea turtles, feed on sponges.[121][122][123]

text:
Schooling reef fish

Caribbean reef squid

Banded coral shrimp

Whitetip reef shark

Green turtle

Giant clam

Soft coral, cup coral, sponges and ascidians

Banded sea krait

The shell of Latiaxis wormaldi, a coral snail

text: Importance[edit]

text: Coral reefs deliver ecosystem services to tourism, fisheries and coastline protection. The global economic value of coral reefs has been estimated to be between US $29.8 billion[6] and $375 billion per year.[7] Coral reefs protect shorelines by absorbing wave energy, and many small islands would not exist without their reefs to protect them. According to the environmental group World Wide Fund for Nature, the economic cost over a 25-year period of destroying one  kilometer of coral reef is somewhere between $137,000 and $1,200,000.[124] About six million tons of fish are taken each year from coral reefs. Well-managed coral reefs have an annual yield of 15 tons of seafood on average per square kilometer. Southeast Asia's coral reef fisheries alone yield about $2.4 billion annually from seafood.[124]

text: To improve the management of coastal coral reefs, another environmental group, the World Resources Institute (WRI) developed and published tools for calculating the value of coral reef-related tourism, shoreline protection and fisheries, partnering with five Caribbean countries. As of April 2011, published working papers covered St. Lucia, Tobago, Belize, and the Dominican Republic, with a paper for Jamaica in preparation. The WRI was also "making sure that the study results support improved coastal policies and management planning".[125] The Belize study estimated the value of reef and mangrove services at $395–559 million annually.[126]

text: Bermuda's coral reefs provide economic benefits to the Island worth on average $722 million per year, based on six key ecosystem services, according to Sarkis et al (2010).[127]

text: Threats[edit]

text: Coral reefs are dying around the world.[128] In particular, coral mining, agricultural and urban runoff, pollution (organic and inorganic), overfishing, blast fishing, disease, and the digging of canals and access into islands and bays are localized threats to coral ecosystems. Broader threats are sea temperature rise, sea level rise and pH changes from ocean acidification, all associated with greenhouse gas emissions. A 2014 study lists factors such as population explosion along the coast lines, overfishing, the pollution of coastal areas, global warming and invasive species among the main reasons that have put reefs in danger of extinction.[129]

text: A study released in April 2013 has shown that air pollution can also stunt the growth of coral reefs; researchers from Australia, Panama and the UK used coral records (between 1880 and 2000) from the western Caribbean to show the threat of factors such as coal-burning and volcanic eruptions.[130] Pollutants, such as Tributyltin, a biocide released into water from in anti-fouling paint can be toxic to corals.

text: In 2011, researchers suggested that "extant marine invertebrates face the same synergistic effects of multiple stressors" that occurred during the end-Permian extinction, and that genera "with poorly buffered respiratory physiology and calcareous shells", such as corals, were particularly vulnerable.[131][132][133]

text: Rock coral on seamounts across the ocean are under fire from bottom trawling. Reportedly up to 50% of the catch is rock coral, and the practice transforms coral structures to rubble. With it taking years to regrow, these coral communities are disappearing faster than they can sustain themselves.[134]

text: Another cause for the death of coral reefs is bioerosion. Various fishes graze corals, dead or alive and change the morphology of coral reefs making them more susceptible to other physical and chemical threats. It has been generally observed that only the algae growing on dead corals is eaten and the live ones are not. However, this act still destroys the top layer of coral substrate and makes it harder for the reefs to sustain.[135]

text: In El Niño-year 2010, preliminary reports show global coral bleaching reached its worst level since another El Niño year, 1998, when 16% of the world's reefs died as a result of increased water temperature. In Indonesia's Aceh province, surveys showed some 80% of bleached corals died. Scientists do not yet understand the long-term impacts of coral bleaching, but they do know that bleaching leaves corals vulnerable to disease, stunts their growth, and affects their reproduction, while severe bleaching kills them.[136] In July, Malaysia closed several dive sites where virtually all the corals were damaged by bleaching.[137][138]

text: To find answers for these problems, researchers study the various factors that impact reefs. The list includes the ocean's role as a carbon dioxide sink, atmospheric changes, ultraviolet light, ocean acidification, viruses, impacts of dust storms carrying agents to far-flung reefs, pollutants, algal blooms and others. Reefs are threatened well beyond coastal areas.[citation needed] Coral reefs with one type of zooxanthellae are more prone to bleaching than are reefs with another, more hardy, species.[139]

text: General estimates show approximately 10% of the world's coral reefs are dead.[140][141] About 60% of the world's reefs are at risk due to destructive, human-related activities. The threat to the health of reefs is particularly high in Southeast Asia, where 95% of reefs are at risk from local threats.[142] By the 2030s, 90% of reefs are expected to be at risk from both human activities and climate change; by 2050, all coral reefs will be in danger.[143]

text: Current research is showing that ecotourism in the Great Barrier Reef is contributing to coral disease,[144] and that chemicals in sunscreens may contribute to the impact of viruses on zooxanthellae.[8]

text: Some scientists, including those associated with the National Oceanic and Atmospheric Administration, posit that US coral reefs are likely to disappear within a few decades as a result of global warming.[145]

text: Protection[edit]

text: Marine protected areas (MPAs) have become increasingly prominent for reef management. MPAs promote responsible fishery management and habitat protection. Much like national parks and wildlife refuges, and to varying degrees, MPAs restrict potentially damaging activities. MPAs encompass both social and biological objectives, including reef restoration, aesthetics, biodiversity, and economic benefits. However, there are very few MPAs that have actually made a substantial difference. Research in Indonesia, Philippines and Papua New Guinea shows that there is no significant difference between an MPA site and an unprotected site.[146][147] Conflicts surrounding MPAs involve lack of participation, clashing views of the government and fisheries, effectiveness of the area, and funding.[148] In some situations, as in the Phoenix Islands Protected Area, MPAs can also provide revenue, potentially equal to the income they would have generated without controls, as Kiribati did for its Phoenix Islands.[149]

text: According to the Caribbean Coral Reefs - Status Report 1970-2012 made by the IUCN. States that; stopping overfishing especially key fishes to coral reef like parrotfish, coastal zone management which reduce human pressure on reef, (for example restricting the coastal settlement, development and tourism in coastal reef) and controlling pollution specially sewage wastage, may not only reduce coral declining but also reverse it and may let to coral reef more adaptable to changes relates to climate and acidification. The report shows that healthier reef in the Caribbean are those with large population of parrotfish in countries which protect these key fishes and sea urchins, banning fish trap and Spearfishing creating "resilient reefs".[150]

text: To help combat ocean acidification, some laws are in place to reduce greenhouse gases such as carbon dioxide. The Clean Water Act puts pressure on state government agencies to monitor and limit runoff of pollutants that can cause ocean acidification. Stormwater surge preventions are also in place, as well as coastal buffers between agricultural land and the coastline. This act also ensures that delicate watershed ecosystems are intact, such as wetlands. The Clean Water Act is funded by the federal government, and is monitored by various watershed groups. Many land use laws aim to reduce CO2 emissions by limiting deforestation. Deforestation causes erosion, which releases a large amount of carbon stored in the soil, which then flows into the ocean, contributing to ocean acidification. Incentives are used to reduce miles traveled by vehicles, which reduces the carbon emissions into the atmosphere, thereby reducing the amount of dissolved CO2 in the ocean. State and federal governments also control coastal erosion, which releases stored carbon in the soil into the ocean, increasing ocean acidification.[151] High-end satellite technology is increasingly being employed to monitor coral reef conditions.[152]

text: Biosphere reserve, marine park, national monument and world heritage status can protect reefs. For example, Belize's barrier reef, Sian Ka'an, the Galapagos islands, Great Barrier Reef, Henderson Island, Palau and Papahānaumokuākea Marine National Monument are world heritage sites.[153]

text: In Australia, the Great Barrier Reef is protected by the Great Barrier Reef Marine Park Authority, and is the subject of much legislation, including a biodiversity action plan.[154] They have compiled a Coral Reef Resilience Action Plan. This detailed action plan consists of numerous adaptive management strategies, including reducing our carbon footprint, which would ultimately reduce the amount of ocean acidification in the oceans surrounding the Great Barrier Reef. An extensive public awareness plan is also in place to provide education on the “rainforests of the sea” and how people can reduce carbon emissions, thereby reducing ocean acidification.[155]

text: Inhabitants of Ahus Island, Manus Province, Papua New Guinea, have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. Their cultural traditions allow line fishing, but no net or spear fishing. The result is both the biomass and individual fish sizes are significantly larger than in places where fishing is unrestricted.[156][157]

text: Restoration[edit]

text: Coral farming[edit]

text: Coral aquaculture, also known as coral farming or coral gardening, is showing promise as a potentially effective tool for restoring coral reefs, which have been declining around the world.[158][159][160]

text: The “gardening” process bypasses the early growth stages of corals when they are most at risk of dying. Coral seeds are grown in nurseries, then replanted on the reef.[161] Coral is farmed by coral farmers who live locally to the reefs and farm for reef conservation or for income.

text: Creating new substrate[edit]

text: Efforts to expand the size and number of coral reefs generally involve supplying substrate to allow more corals to find a home. Substrate materials include discarded vehicle tires, scuttled ships, subway cars, and formed concrete, such as reef balls. Reefs also grow unaided on marine structures such as oil rigs.[162] In large restoration projects, propagated hermatypic coral on substrate can be secured with metal pins, superglue or milliput.[163] Needle and thread can also attach A-hermatype coral to substrate.[164]

text: A substrate for growing corals referred to as Biorock is produced by running low voltage electrical currents through seawater to crystallize dissolved minerals onto steel structures. The resultant white carbonate (aragonite) is the same mineral that makes up natural coral reefs. Corals rapidly colonize and grow at accelerated rates on these coated structures. The electrical currents also accelerate formation and growth of both chemical limestone rock and the skeletons of corals and other shell-bearing organisms. The vicinity of the anode and cathode provides a high-pH environment which inhibits the growth of competitive filamentous and fleshy algae. The increased growth rates fully depend on the accretion activity.[165]

text: During accretion, the settled corals display an increased growth rate, size and density, but after the process is complete, growth rate and density return to levels comparable to natural growth, and are about the same size or slightly smaller.[165]

text: Relocation[edit]

text: One case study with coral reef restoration was conducted on the island of Oahu in Hawaii. The University of Hawaii has come up with a Coral Reef Assessment and Monitoring Program to help relocate and restore coral reefs in Hawaii. A boat channel on the island of Oahu to the Hawaii Institute of Marine Biology was overcrowded with coral reefs. Also, many areas of coral reef patches in the channel had been damaged from past dredging in the channel.

text: Dredging covers the existing corals with sand, and their larvae cannot build and thrive on sand; they can only build on to existing reefs. Because of this, the University of Hawaii decided to relocate some of the coral reef to a different transplant site. They transplanted them with the help of the United States Army divers, to a relocation site relatively close to the channel. They observed very little, if any, damage occurred to any of the colonies while they were being transported, and no mortality of coral reefs has been observed on the new transplant site, but they will be continuing to monitor the new transplant site to see how potential environmental impacts (i.e. ocean acidification) will harm the overall reef mortality rate. While trying to attach the coral to the new transplant site, they found the coral placed on hard rock is growing considerably well, and coral was even growing on the wires that attached the transplant corals to the transplant site.

text: This gives new hope to future research on coral reef transplant sites. As a result of this coral restoration project, no environmental effects were seen from the transplantation process, no recreational activities were decreased, and no scenic areas were affected by the project. This is a great example that coral transplantation and restoration can work and thrive under the right conditions, which means there may be hope for other damaged coral reefs.[166]

text: Heat-tolerant symbionts[edit]

text: Another possibility for coral restoration is gene therapy: Through inoculating coral with genetically modified bacteria, or naturally-occurring heat-tolerant varieties of coral symbiotes, it may be possible to grow corals that are more resistant to climate change and other threats.[167]

text: Clearing out invasive algae[edit]

text: Hawaiian coral reefs smothered by the spread of invasive algae were managed with a two prong approach: First, divers manually removed invasive algae, with the support of super-sucker barges. Second, grazing pressure on the algae needed to be increased to prevent the regrowth of the invasive algae, once the majority of the algae had been cleaned off the coral.

text: Researchers found that native collector urchins were reasonable candidate grazers for algae biocontrol, to extirpate the remaining invasive algae from the reef.[114]

text: Reefs in the past[edit]

text: Throughout Earth's history, from a few thousand years after hard skeletons were developed by marine organisms, there were almost always reefs. The times of maximum development were in the Middle Cambrian (513–501 Ma), Devonian (416–359 Ma) and Carboniferous (359–299 Ma), owing to order Rugosa extinct corals, and Late Cretaceous (100–66 Ma) and all Neogene (23 Ma–present), owing to order Scleractinia corals.

text: Not all reefs in the past were formed by corals: those in the Early Cambrian (542–513 Ma) resulted from calcareous algae and archaeocyathids (small animals with conical shape, probably related to sponges) and in the Late Cretaceous (100–66 Ma), when there also existed reefs formed by a group of bivalves called rudists; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.

text: Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral reefs, such as Porites, can indicate changes in the sea surface temperature and sea surface salinity conditions of the ocean during the growth of the coral. This technique is often used by climate scientists to infer the paleoclimate of a region.[168]


document_title: Time in Oregon

question_text: why is part of oregon in mountain time

question_tokens: why is part of oregon in mountain time

text: Time in Oregon

text: Time in Oregon is divided into two zones. The vast majority of the state is contained in the Pacific Time Zone. Most of sparsely populated Malheur County, including its largest city, Ontario, and its county seat, Vale, are in the Mountain Time Zone due to their proximity to Boise, Idaho. The time zone division occurs at the southwest corner of township 35 S, range 37 E (approximately 42.45 degrees north latitude), continuing east to the state line, then south along the Oregon-Idaho border to the Nevada state line.[1]

text: Drewsey in Harney County is officially in the Pacific Time Zone, but some residents unofficially observe Mountain Time due to proximity to Malheur County. Local businesses and the Oregon Department of Transportation strictly enforce the practice of Pacific Time, however.

text: IANA time zone database[edit]

text: In the IANA time zone database, Oregon is contained in two zones:

text:
c.c.*
coordinates*
TZ*
comments*
UTC offset
UTC offset DST
Note

US
+340308-1181434
America/Los_Angeles
Pacific Time
−08:00
UTC−07
All except northern 3/4 of Malheur County

US
+433649-1161209
America/Boise
Mountain Time - south Idaho & east Oregon
−07:00
UTC−06
Northern 3/4 of Malheur County only

tag: table