Interaction between climate forcing and plankton communities in a pristine NW Mediterranean site, the Bay of Calvi (Corsica) : a long term study

In the Mediterranean coastal areas, most of the long-term studies of plankton dynamics concern highly urbanized areas, where long-term variability reflects the combined effects of climate and anthropogenic forcing. Here we use a unique long-term time series (1979-) performed in a NW Mediterranean coastal area unbiased by local anthropogenic pressure (Bay of Calvi, Corsica) to understand how climate variation drives changes in plankton communities.
From high-frequency field data, we describe a mechanism that links winter physics, nutrient replenishment of the surface layer and plankton biomass and composition under the different combinations of meteorological conditions that occurred during the 4 decades of observations. Focusing on phytoplankton, we point out how climate variation affected (i) the timing, duration and magnitude of the winter-spring phytoplankton blooms, (ii) the mean yearly biomasses, (iii) the abundance of phytoplankton functional groups. We identify threshold values of physical variables below and above which they strongly impact nutrient availability, phytoplankton bloom characteristics and seasonal succession of functional groups. We show that food webs are resource controlled.
Striking similarities between our observations and events elsewhere in the NW Mediterranean Sea are presented. We explore ecological consequences of changes occurring at the base of the food webs on services provided by plankton in the Mediterranean coastal waters.