Long-term fluctuations (1974-1999) of the salps Thalia democratica and Salpa fusiformis in the northwestern Mediterranean Sea: Relationships with hydroclimatic variability

We investigated the long-term variability of the salps Thalia democratica and Salpa fusiformis during the period 1974-1999 at a coastal site in the Bay of Villefranche-sur-mer. During this period T. democratica varied both interannually and seasonally, whereas S. fusiformis showed only seasonal fluctuations. Weeks in which T. democratica and S. fusiformis populations were developing in situ (i.e., near the sampling station without advection) are defined as the informative periods. Different species-specific optima of temperature, salinity, and chlorophyll a concentration, as well as stability conditions of the water column, were related to informative periods for the two Thalia and Salpa species. Long-term temperature oscillations were significantly related to the interannual maxima of T. democratica. The link between positive anomalies of temperature and outbreaks of T. democratica stress the importance of primary consumers as indicators of changes occurring in the marine system.