Ocean acidification has direct physiological effects on organisms by, for example, dissolving the calcium carbonate structures of calcifying species. However, non-calcifiers may also be affected by changes in seawater chemistry. To disentangle the direct and indirect effects of ocean acidification on zooplankton growth, we carried out a study with two model organisms. We investigated the individual effect of short term exposure to (1) high and low seawater pCO2 and (2) different phytoplankton qualities as a result of different CO2 incubations on the growth of a heterotrophic dinoflagellate and a copepod species. It has been previously observed that higher CO2 concentrations can decrease phytoplankton food quality in terms of carbon:nutrient ratios. We therefore expected both seawater pCO2 (pH) and phytoplankton quality to result in a decrease of zooplankton growth. Although we expected lowest growth rates for all zooplankters under high seawater pCO2 and low algal quality, we found that direct pH effects on consumers seem to be of lesser importance than the associated decrease in algal quality. The decrease of primary producersâ quality under high pCO2 conditions negatively affected zooplankton growth, which may lead to lower availability of food for the next trophic level and thus potentially affect the recruitment of higher trophic levels.
Meunier C., Alguera-MuÃiz M., Horn H., Lange J. & Boersma M., in press. Direct and indirect impact of near-future pCO2 levels on zooplankton dynamics. Marine & Freshwater research. Article.
