Global change and climate-driven invasion of the Pacific oyster (Crassostrea gigas) along European coasts: a bioenergetics modelling approach

Aim The spread of non-indigenous species in marine ecosystems world-wide is one of today's most serious environmental concerns. Using mechanistic modelling, we investigated how global change relates to the invasion of European coasts by a non-native marine invertebrate, the Pacific oyster Crassostrea gigas. Location Bourgneuf Bay on the French Atlantic coast was considered as the northern boundary of C. gigas expansion at the time of its introduction to Europe in the 1970s. From this latitudinal reference, variations in the spatial distribution of the C. gigas reproductive niche were analysed along the north-western European coast from Gibraltar to Norway. Methods The effects of environmental variations on C. gigas physiology and phenology were studied using a bioenergetics model based on Dynamic Energy Budget theory. The model was forced with environmental time series including in situ phytoplankton data, and satellite data of sea surface temperature and suspended particulate matter concentration. Results Simulation outputs were successfully validated against in situ oyster growth data. In Bourgneuf Bay, the rise in seawater temperature and phytoplankton concentration has increased C. gigas reproductive effort and led to precocious spawning periods since the 1960s. At the European scale, seawater temperature increase caused a drastic northward shift (1400 km within 30 years) in the C. gigas reproductive niche and optimal thermal conditions for early life stage development. Main conclusions We demonstrated that the poleward expansion of the invasive species C. gigas is related to global warming and increase in phytoplankton abundance. The combination of mechanistic bioenergetics modelling with in situ and satellite environmental data is a valuable framework for ecosystem studies. It offers a generic approach to analyse historical geographical shifts and to predict the biogeographical changes expected to occur in a climate-changing world.

Indicator species of intertidal boulder fields on the French Basque coast

The rocky Basque coast presents an interest both in terms of biogeography and its patrimonial situation, alongside its habitats, fauna and flora. The aim of the BIGORNO project (Intertidal Biodiversity of the south of the Bay of Biscay and Observation for New research and Monitoring for decision support), financed by the Agency of Marine Protected Areas (AAMP) and the Departmental Council (CD 64), is to respond to significant deficiencies on biocenosis in the southern marine subregion “Bay of Biscay”. Investigations carried out in the WFD, since 2008, constitute an important basis of work for integration of fauna. Field studies undertaken since 2015 consisting of a sampling design suited to the substrates heterogeneity and the presence of microhabitats were established on an intertidal area specifically on a "Boulder fields" habitat. Assessment was undertaken by sampling quadrats of 0.1 m² drawn randomly from a spatially stratified sampling plan. Our study aims for a better understanding of stratification of this habitat and allowed us to highligh tindicator taxa of the "Boulder fields" habitat. Functions included in the package indicspecies (CRAN) were used to conduct indicator species analysis and to assess the significance of the relationship between taxa or taxa combinations and the habitat. It is therefore possible to describe some species or species groups which are specific to boulder fields through the assessment of their functional traits and local biodiversity. These various analyses allow for a sustainable way of monitoring the Basque intertidal rocky shore.