For the 21 years of the study, an examination of trends in chlorophyll concentration revealed a general decline throughout the Gulf over the production period. These trends, extracted from dynamic linear model, also allowed this decline to be quantified. Expressed as a percentage, a large part of the area below the 50 m bathymetric line showed a decrease of at least 10% over the period, corresponding to a value of at least 0.1 µg.l-1. However, the spatial distribution reveals some more local phenomena. In southern Brittany, from Quimper to Vannes, a particular feature appears, with an upward trend over several kilometres along the coast, followed by a pronounced gradient along the coast. This gradient includes a zone where a continuous monotonic increasing trend is observed, then a zone where the trend becomes not significant and finally, about 15 km from the coast, a new zone where a significant continuous monotonic decreasing trend is observed. The increase in chlorophyll a concentration in the very coastal part is greater than 0.1 µg.l-1 over the period. Another peculiarity concerns the central part, located at the edge of the plateau at Cap Ferrat and Pente Aquitaine, where an increase in chlorophyll a was observed, but the variations remained small, being less than 0.1 µg.l-1. About a hundred kilometres south-west of Saint Nazaire, an area of about 40 by 50 km shows a decrease in chlorophyll a of more than 20%, quantified as more than 0.1 µg.l-1 over the period.

The use of an ecological niche model has made it possible to characterize on the one hand the effects of climate change on the native species of the Gulf of Lio, such as displacements of favorable habitats or the reduction of the surface of the habitat. favor of native species. On the other hand, the potential displacement of the favorable habitat of some subtropical species in the Gulf of Lion could be expected. They would then become non-indigenous species (NIS)

The use of an ecological niche model has made it possible to characterize, on the one hand, the effects of climate change on the native species of the Bay of Biscay, such as displacements of favorable habitats towards higher latitudes, or, in a to a lesser extent, a decrease in the area of ​​favorable habitat for native species. On the other hand, the potential displacement of the favorable habitat of some subtropical species (currently present along the Moroccan coast) in the Bay of Biscay could be expected. They would then become non-indigenous species (NIS)