Ocean Acidification and Warming Affect Survival and Growth of Atlantic Cod (Gadus morhua) Larvae

This study investigated the effect of ocean acidification (OA) and warming on the survival of Western Baltic cod (Gadus morhua) larvae reared in the laboratory in 90 L tanks at ambient CO₂ concentrations (400 ppm) and CO₂ concentrations as predicted for the end of the century (1000 ppm). Temperature (7°C and 9°C) as an additional stressor was studied in a full-factorial design with CO₂. Larvae were fed natural plankton at a low food density and mortality was measured daily by removing dead larvae from the tanks. Growth measurements including standard length, myotome height as well as otolith measurements were analysed. The results clearly show that an increased CO₂ concentration had a significant negative effect on the survival of the larvae mostly during critical phases in larval development. An increase in temperature, however, did not further increase mortality. Growth and otolith measurements strongly suggest an increase in growth rate and size-selective mortality with selection for larger larvae occurring under increased CO₂ conditions. The results will be compared and discussed in relation to other experimental results with respect to OA and cod larvae. The larval response to OA seems to be dependent on the developmental stage and their nutritional condition.