The Gulf is classified as a moderate eutrophic area (Flander-Putrle and Malej, 2003) with primary production ranging from 0.2 to 15.9 mmol C dm23 day21 (Malej et al., 1995; Cantoni et al., 2003) and mean mesozooplankton dry weight and ash-free biomass 18.5 and 13.6 mg m23, respectively (Benovic´et al., 1984; Fonda Umani et al., 1992).