How does rising atmospheric CO2 affect marine organisms?

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The Thermal Tolerance of a Large Tropical Freshwater Shrimp
Ern, R., Huong, D.T.T., Phuong, N.T., Wang, T. and Bayley, M. 2014. Oxygen delivery does not limit thermal tolerance in a tropical eurythermal crustacean. The Journal of Experimental Biology 217: 809-814.

Ern et al. write that "in aquatic environments, rising water temperatures reduce water oxygen content while increasing oxygen demand, leading several authors to propose cardiorespiratory oxygen transport capacity as the main determinant of aquatic animal fitness." They also say it has been argued that "tropical species, compared with temperate species, live very close to their upper thermal limit and, hence, are vulnerable to even small elevations in temperature." So do these two potential "weaknesses" leave such creatures susceptible to near-certain death in the face of the CO2-induced warming that is typically predicted to occur by the world's climate alarmists?

What was done
In a study relevant to this question, the team of scientists from Denmark and Vietnam measured "the effect of a 6°C increase in temperature from 27 to 33°C on growth capacity over a 3-month period in the giant freshwater shrimp (Macrobrachium rosenbergii de Man 1879)," which they describe as "a crustacean of global importance to tropical aquaculture with annual production exceeding 400,000,000 kg per year." In addition, they examined whether increased temperature causes collapse of the oxygen supply capacity by the creatures' cardiorespiratory systems by measuring the oxygen uptake of resting and exercising shrimp at various temperatures, as well as their heart rates, ventilation rates and hemolymph lactate levels during acute rises in temperature.

What was learned
First of all, the five researchers report that the giant shrimp "maintains normal growth when challenged by a temperature rise of 6°C above the present-day average (from 27°C to 33°C)." Secondly, they state that "by measuring heart rate, gill ventilation rate, resting and maximum oxygen uptake, and hemolymph lactate, we show that oxygen transport capacity is maintained up to the critical maximum temperature around 41°C." And last of all, they say that the shrimp's "heart rate and gill ventilation rate increase exponentially until immediately below critical temperatures, and at 38°C the animals still retained more than 76% of aerobic scope measured at 30°C, and there was no indication of anaerobic metabolism at the high temperatures."

What it means
In concluding the report of their study, Ern et al. write that (1) "in the giant freshwater shrimp the current worst-case scenario predicting a 3°C increase in tropical water temperature by the end of this century does not cause a negative effect on its growth performance," that (2) "oxygen transport capacity of the cardiorespiratory system does not seem to be universally coupled to animal fitness in aquatic organisms as previously proposed," and that (3) "too heavy a reliance on the relatively easily measured aerobic performance characters such as heart rate, gill ventilation rate, aerobic scope and anaerobic metabolites will therefore yield inaccurate predictions on the impact of climate change in these species."

Reviewed 21 May 2014