Effects of low pH and raised temperature on egg production, hatching and metabolic rates of a Mediterranean copepod species (Acartia clausi) under oligotrophic conditions

This study includes the first information on the combined effect of low pH and raised temperature on egg production rate (EP), hatching success (HS), excretion and respiration of the Mediterranean copepod Acartia clausi. Adult individuals of A. clausi and fresh surface seawater were collected at a coastal station in Saronikos Gulf during April 2012. Four different conditions were applied: two different pH levels (present: 8.09 and future: 7.83) and two temperature values (present: 16 degrees C and present+ 4 degrees C= 20 degrees C). EP and HS decreased significantly over the duration of exposure at future pH under both temperature conditions. However, the analysis of the combined effect of pH, T, chlorophyll alpha and the duration of the EP and HS experiments revealed that ocean acidification had no discernible effect, whereas warming, food and the duration of exposure were more significant for the reproductive output of A. clausi. Temperature appeared to have a positive effect on respiration and excretion. Acidification had no clear effect on respiration, but a negative effect on excretion was observed. Acidification and warming resulted in an increase of the excretion rate and the increase was higher than that observed by warming only. Our findings show that acidification does not have an obvious direct effect on the vital rates of the copepod, with the exception of excretion possibly. Therefore, the combination of acidification, ambient oligotrophic conditions and warming could affect the ability of the species to allocate resources for coping with multiple stressors.