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| Organisms living in habitats characterized by a
marked seasonal temperature variation often have a greater
thermal tolerance than those living in more stable habitats.
To determine the extent to which this hypothesis applies to
reef corals, we compared thermal tolerance of the early life
stages of five scleractinian species from three locations
spanning 17" of latitude along the east coast of Australia.
Embryos were exposed to an 8 "C temperature range
around the local ambient temperature at the time of
spawning. Upper thermal thresholds, defined as the temperature
treatment at which the proportion of abnormal
embryos or median life span was significantly different to
ambient controls, varied predictably among locations. At
Lizard Island, the northern-most site with the least annual
variation in temperature, the proportion of abnormal
embryos increased and life span decreased 2 "C above
ambient in the two species tested. At two southern sites,
One Tree Island and Lord Howe Island, where annual
temperature variation was greater, upper temperature
thresholds were generally 4 "C or greater above ambient
for both variables in the four species tested. The absolute
upper thermal threshold temperature also varied among
locations: 30 "C at Lizard Island; 28 "C at One Tree Island;
26 "C at Lord Howe Island. These results support previous
work on adult corals demonstrating predictable differences
in upper thermal thresholds with latitude. With projected
ocean warming, these temperature thresholds will be
exceeded in northern locations in the near future, adding to
a growing body of evidence indicating that climate change
is likely to be more detrimental to low latitude than high
latitude corals. | |
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