Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab Hyas araneus

Abstract

Future scenarios for the oceans project combined developments of CO 2 accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO2 concentrations on thermal tolerance of the cold-eurythermal spider crab Hyas araneus from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO 2), CO2 levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO2 (PeO 2) were measured during progressive short term cooling from 10 to 0deg;C and during warming from 10 to 25deg;C. An increase of PeO 2 occurred during cooling, the highest values being reached at 0deg;C under all three CO2 levels. Heart rate increased during warming until a critical temperature (Tc) was reached. The putative T c under normocapnia was presumably gt;25deg;C, from where it fell to 23.5deg;C under 710 ppm and then 21.1deg;C under 3000 ppm. At the same time, thermal sensitivity, as seen in the Q10 values of heart rate, rose with increasing CO2 concentration in the warmth. Our results suggest a narrowing of the thermal window of Hyas araneus under moderate increases in CO2 levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance.