Control of plankton dynamics and fish recruitment by climate variation : example of Corsica, a Mediterranean island

In coastal areas of temperate and tropical small islands, most exploited fish species have undergone large reductions in stock size over the last decades. This impact is believed to be due, in large measure, to overfishing. However, in some cases, the poor recruitment of young fish or crustaceans of commercial interest is related to climate change.
Here we present results acquired from three decades in Corsica, a small Mediterranean island where water quality is unbiased by terrestrial inputs and local activities. We show how plankton dynamics and fish recruitment are controlled by climate variation.
Long-term changes of surface plankton dynamics are studied from 1979 at a permanent station in the oligotrophic Bay of Calvi (Corsica, Mediterranean Sea). As a distinctive feature of the area, the plankton bloom is characterized by a very large interannual variability reaching one order of magnitude from one year to another. Studies conducted to understand mechanisms controlling plankton variability emphasize a close relationship between climate variation (mainly winter wind stress intensity), water temperature and phytoplankton biomass. Shifts in phytoplankton community structure contribute to control the dynamics of zooplankton that rely on phytoplankton as food and influence the temporal succession of zooplankton assemblages. Changes in the timing, the biomass and the composition of the zooplankton communities result in a mismatch with the presence of the main food source of the small fish and alter recruitment success.
The Corsican example could help to be aware of the potential consequences that changes in plankton dynamics controlled by climate variation will pose to coastal fishermen of small islands.