Title: “Study of the climatic and environmental determinants involved in the variability of the reproduction and recruitment of three bivalves exploited in Brittany”
Summary: Current trends in global warming could lead to severe ecological consequences for marine species and communities in coastal areas. Using three marine bivalve species as models (C. gigas, O. edulis, and P. maximus), the objective of this thesis was to improve our knowledge of the potential effect of climate variability on coastal benthic organisms, particularly with respect to their reproduction and recruitment. Using a numerical modelling tool (DEB model) coupled with IPCC climate scenarios, we have highlighted new perspectives on the reproductive responses of C. gigas and P. maximus to global warming. With regard to C. gigas, we have shown that the increase in water temperature has allowed a greater number of spawnings in the Brest harbour since 1995.
In P. maximus, the model made it possible to explain the different reproduction strategies between two Breton ecosystems: the water temperature modulates the onset of egg laying in Saint-Brieuc Bay, whereas it is the phytoplankton concentration in the Brest harbour. In addition, we carried out a retrospective analysis of the breeding cycle and recruitment of O. edulis in another ecosystem in Brittany, Quiberon Bay. The use of a generalized linear model allowed us to show that NAO+ winter weather regimes explain part of the variability in flat oyster reproduction: the higher the occurrence of NAO+ days in winter, the earlier the appearance of milky and slate oysters in the year.