Most of the ocean acidification research conducted to date has focused solely on the biological impacts of declining seawater pH. Few studies have investigated the interactive effects of ocean acidification and temperature. This summary examines what has been learned in several such studies of various marine organisms that challenge the alarming and negative projections of the IPCC on the matter.
Starting with some of the smallest of marine animals, calanoid copepods are a type of zooplankton that feeds on phytoplankton and are themselves the food of higher trophic levels. In a study of the long-term effects of both high CO2 levels and temperatures on Arctic calanoid copepods, Hildebrandt et al. (2014)1 "incubated late copepodites and females of two dominant Arctic species, Calanus glacialis and Calanus hyperboreus, at 0°C and at 390 and 3000 µatm pCO2 for several months in fall/winter 2010," while in an attempt "to detect synergistic effects," they say that in 2011 "C. hyperboreus females were kept at different pCO2 and temperatures (0,5, 10°C)." The three German researchers indicate that their experiments, which were conducted over several months with repeated measurements, including several aspects of the animals' ecology and physiology, demonstrated that the sub-adult and adult life stages of the Arctic Calanus species they studied "were robust to pCO2 even above future levels of ocean acidification," with the "only synergistic effects of pCO2 and temperature on body mass of C. hyperboreus females found at 5°C." And in light of what they observed in the laboratory, Hildebrandt et al. conclude that Arctic calanoid copepods "can tolerate pCO2predicted for a future ocean." But they caution that in combination with increasing temperatures they could possibly experience some form of negative repercussion, but one that would not be fatal.
Thiyagarajan and Ko (2012)2 conducted a number of laboratory studies designed to see how the larval growth stage of the Portuguese oyster responds to various "climate change stressors," as they describe them, by investigating the effects of low pH (7.9, 7.6, 7.4) at ambient salinity (34 ppt) and low salinity (27 ppt), while "the combined effect of pH (8.1, 7.6), salinity (24 and 34 ppt) and temperature (24°C and 30°C) was examined using factorial experimental design." In describing their findings, the two researchers say, "surprisingly, the early growth phase from hatching to 5-day-old veliger stage showed high tolerance to pH 7.9 and pH 7.6 at both 34 ppt and 27 ppt," while they report "larval shell area was significantly smaller at pH 7.4 only in lowsalinity." Then, in the 3-factor experiment, they observed "shell area was affected by salinity and the interaction between salinity and temperature but not by other combinations." And they discovered "larvae produced the largest shell at the elevated temperature in low-salinity, regardless of pH." In light of these several positive findings, Thiyagarajan and Ko conclude "the growth of the Portuguese oyster larvae appears to be robust to near-future pH level (>7.6) when combined with projected elevated temperature and low-salinity in the coastal aquaculture zones of [the] South China Sea."