Ocean acidification effects on the nutritional quality of phytoplankton for copepod reproduction

Four species of phytoplankton (Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans, Isochrysis galbana) were grown under present-day low (400ppm pCOi, pH~8.1) and predicted-future high (lOOOppm pCOi, pH~7.8) ocean acidification conditions using nitrate-limited semi-continuous batch cultures. For four days, female Acartia tonsa copepods were fed a phytoplankton mixture from either the low or high pCC>2 treatment cultures. Phytoplankton fatty acid profiles were analyzed to assess changes in cellular essential fatty acid (EFA) content. Copepod egg production (EP), hatching success (HS), and egg viability (EV) were analyzed to assess differences in copepod reproductive success. Phytoplankton cultured under high pCC>2 contained less EFAs compared to phytoplankton cultured under low pCC>2. Female copepods fed high pCC>2 phytoplankton had lower EP, HS, and EV compared to females fed low pCC>2 phytoplankton. This laboratory study demonstrates that ocean acidification changes the nutritional quality of primary producers, which affects the potential reproductive success of fundamental primary consumers.