greenbean36191
Premium Member
Yes. 91.4 was the lowest temperature over 89.6 that was tested and the first temperature at which there was a decrease. At temperatures up to and including 89.6, respiration was increasing.
Actually it was 3 hours. That is consistent with the duration of hot water exposure events on the reef as measured by Craig, Birkeland, and Belliveau 2001. Although temperature got above 32 C for 35 days, it only stayed there for 2.4 hours a day on average. Also, these short exposure times are the nature of the beast when working with controlled respirometry. It's not practical to run longer experiments and as a result you will very rarely see a respirometry experiment run longer than a few hours.
Yes, they were looking for the threshold of acute stress. However, it does not follow that the threshold of chronic stress is significantly lower when you're using respiration as the stress indicator.
As for this just being a single coral, and not Acropora, I was only using this paper to illustrate that A) the temperature stress threshold is a product of acclimatization and B) that 84 isn't the magic temperature at which respiration shuts down. There have actually been very few papers looking at respiration vs. temp in corals, and none using Acropora exposed to high temps AFAIK. However, the only case I'm aware of where ANY coral has shown a decline in respiration at 84 is one from about a year and a half ago that used new recruits of 4 different species of Caribbean coral. Porites showed a decrease at 84, while the other 3 were still increasing at 84. That's a 3 deg F increase above ambient temp though, which the rule of thumb tells us should be stressful.
It's about a temperate, ahermatypic coral in a temperate environment. They've bleached every year for more than 15 yrs once the temperature gets to 82, which is the average temp for tropical reefs. IOW, it's not very relevant to the question of how hot is too hot for tropical reef corals. Furthermore, it's since been shown that Vibrio is virtually non-existent among the same corals in the wild during bleaching events, so the idea that Vibrio goes from harmless to virulent as temperature increases doesn't hold much water. See:
http://www.nature.com/ismej/journal/v2/n1/pdf/ismej200788a.pdf
