Ocean freshening and acidification differentially influence mortality and behaviorof the Antarctic amphipod Gondogeneia antarctica

Abstract

Increase in anthropogenic CO2 to the atmosphere causes rapid glacial retreat by regional warming and high CO2 dissolution to the Southern Ocean, resulting in declining trends of mean salinity and pH in seawater of the Antarctica. The Marian Cove, King George Island in the Western Antarctic Peninsula (WAP) is one of the regions that undergoes one of the highest rates of glacier retreat. Ocean freshening and acidification caused by meltwater intrusion near the glacier are inevitable, so the changes in the marine ecosystem are expected. One of the abundant gammarid amphipod species, Gondogeneia antarctica, occupies essential ecological niche in the WAP. To test the effects of the low salinity and low pH on the population, we exposed G. antarctica to 4 different treatments combining two salinity (34 and 27 psu) and two pH (pH 8.0 and 7.6) levels for 27 days. Mortality except cannibalized individuals significantly decreased under low salinity, while increased under low pH. Accordingly, low salinity increased cannibalism rates, while low pH reduced the food detection significantly. Shelter-using during the daytime decreased by low salinity and pH respectively, which indicates two stressors act as behavioral disruptors for the amphipods. Under low salinity conditions, swimming behavior during the daytime increased, whereas swimming during the nighttime decreased significantly. Although the interactions between low salinity and low pH were not observed during the experiments, the results suggest that each stressor due to glacier melting causes amphipods' abnormal behavior and eventually may threat population persistence in the cove.