How does rising atmospheric CO2 affect marine organisms?

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Coral Bleaching and Climate Change
Baker, A.C.  2001.  Reef corals bleach to survive change.  Nature 411: 765-766.

What was done
The author conducted an experiment in which he transplanted corals of different combinations of host and algal symbiont from shallow (2-4 m) to deep (20-23 m) depths and from deep to shallow depths in order to test the hypothesis that the stress of
coral bleaching offers reef corals the opportunity to replace suboptimal algae with those more tolerable of the stressful environmental conditions associated with bleaching.

What was learned
After 8 weeks nearly half of the corals transplanted from the deep to shallow depths had experienced partial or severe bleaching, whereas none of the corals transplanted from shallow to deep depths showed any sign of bleaching.  After 12 months, however, despite "more extensive bleaching, upward transplants showed no mortality," while nearly 20 percent of downward transplants died.  Control transplants showed no sign of bleaching or mortality.  The reason for the bleaching and mortality patterns was explained by symbiont community structure; corals that were transplanted upwards adjusted their algal distributions to more tolerant species, whereas those transplanted downward did not.

What it means
In the words of the author, these findings "support the view that coral bleaching can promote rapid response to environmental change by facilitating compensatory change in algal symbiont communities."  Without bleaching, he continues, "suboptimal host-symbiont combinations persist, leading eventually to significant host mortality."  In light of this information, it appears that coral bleaching may, in the author's words, "ultimately help reef corals to survive" the perceived stress of global warming; and it may help explain why reefs, though depicted by climate alarmists as environmentally fragile, have survived through geologic time.