Zooplankton communities fluctuations from 1995 to 2005 in the Bay of Villefranche-sur-Mer (Northern Ligurian Sea, France)

Abstract

An integrated analysis of the pelagic ecosystems of the Ligurian Sea is performed combining time series of different zooplankton groups (small and large copepods, chaetognaths, appendicularians, pteropods, thaliaceans, decapods larvae, other crustaceans, other gelatinous and other zooplankton), chlorophyll-<i>a</i> and nutrients, seawater salinity, temperature and density and local weather at the Point B coastal station (Northern Ligurian Sea). From January 1995 to December 2005, a shift in most variables occurred ca. 2000. From 1995 to 2000 winters were wet and mild resulting in lower winter sea surface density. These years showed lower than average nutrients and zooplankton concentrations while phytoplankton biomass was higher. After 2000, winters were colder and dryer resulting in higher sea surface density. Nutrients and zooplankton showed higher concentrations while phytoplankton was lower than average. The ca. 2000 shift was observed for most zooplankton groups with a one year delay for certain groups. The observed patterns suggest that the pelagic ecosystem trophic state is mostly set by the winter forcing on the convection that upwells nutrients to the surface sustaining the spring bloom. However, low phytoplankton concentrations in higher nitrate and zooplankton conditions during the well mixed years suggest that phytoplankton is controlled by grazers. The proposed mechanisms of convection regimes hold for most of the time series, but specific years with contradicting patterns needed to be explained by other factors. The limitation of phytoplankton growth by the light availability in spring/summer was then proposed as a secondary driving force that can moderate or even reverse the winter forcing. Finally, the eleven years of observation did not reveal a clear link with the North Atlantic Oscillation, suggesting a more complex dynamics linking large scale climate to Ligurian Sea ecosystems or that the length of the plankton monitoring is not yet sufficient to detect those links

Synchronous marine pelagic regime shifts in the Northern Hemisphere

“…On the other hand, our findings for this site are consistent with the observations of decadal oscillations in zooplankton found by García-Comas et al [80] and Vandromme et al [81]. They proposed that the long-term warming of seawaters in the northwest supplementary material, table B).…”

Temporal and inter-specific variations in forage fish feeding conditions in the NW Mediterranean: lipid content and fatty acid compositional changes

“…The Mediterranean Sea has been recognised as a 'hotspot' for climate change (Giorgi & Lionello 2008), with predictions that temperatures will rise and plankton productivity will decline (Lionello et al 2006, Durrieu de Madron et al 2011). In the NW Mediterranean Sea, long-term shifts in plankton productivity and temperature have already been recorded (Marty & Chiaverini 2002, Vandromme et al 2010. Directly relevant to foraging fish stocks, recent reports present evidence that the GoL has shown signs of disequilibrium since 2008, with important changes in the stock structure of sardine and anchovy and an unusually high abundance of sprat (FAO 2011).…”

Testing the usefulness of optical data for zooplankton long‐term monitoring: Taxonomic composition, abundance, biomass, and size spectra from ZooScan image analysis

“…The image parameters associated with each individual image include variables for shape and size (Gorsky et al 2010; Vandromme et al 2012). Among others, they describe the primary (“major”) and the secondary (“minor”) axis of the best fitting ellipse of the objects.…”