Impact of ocean warming and food restriction on the fecundity of the sea star Asterias rubens

Sea stars are major predators in marine ecosystems that impact shellfish aquaculture because of their predation on cultured bivalves. As ectotherms, their reproductive success is expected to be impacted by rising ocean temperatures and change in prey availability induced by climate change. As reproduction is a key process in the reduction, maintenance, and proliferation of populations, the impacts of ocean warming and food ration on the fecundity of the sea star Asterias rubens were investigated. Males and females were exposed for 6 months either to monthly temperatures from the 1995-2014 periods or to temperatures projected at the end of the century by the "business as usual" scenario of greenhouse gases emission. Sea stars were also fed with a normal (3 mussels twice a week) or restricted (1 mussel twice a week) food ration. Biometric parameters (body weight, arm length, pyloric caeca weight, gonad weight, pyloric index, gonadosomatic index), gamete concentration (number of oocytes or sperm per gram of gonad) and fecundity (number of oocytes or sperm per individual) were assessed at the end of the experimental period. Sea stars exposed to elevated temperatures or to food restriction had reduced fecundity because of their reduced gonads weight. However, fecundity of food-restricted males was not reduced compared to well-fed ones despite their lower gonads weight, thanks to higher sperm concentration in their gonads. Overall, these results indicate that future environmental conditions induced by climate change could reduce the reproductive success of A. rubens.