Unusual changes of zooplankton fatty acid composition in the northern Adriatic during the 1991 mucilage event

Abstract

Fatty acids and pristane/heptadecane (Pr/C17) ratlo were analysed in zooplankton samples collected with a sediment trap in the northeastern Adriatic Sea from April 1991 to June 1992 in 2 to 6 wk intervals. Saturated (SAT; 22 to 68% of total fatty acid mass fraction), monounsaturated (MONO; 20 to 39'0), and polyunsaturated (PUFA; 6 to 49%) fatty acid proportions, total fatty acid mass fraction (2.3 to 46.5 mg g-I dry wt), and Pr/CII ratio (0.5 to 27) varied significantly during the investigated period. Unusually low fatty acid mass fractions (2.3 to 5.1 mg g.' dry wt), PUFA proportions (6%) , and Pr/C17 ratio [< l ) measured In summer 1991 were ascribed to a drastic zooplankton starvation due to a mucilage event, a phenomenon that can occur periodically (every 10 to 50 yr) in the region. Low PUFA proportions (12%) were also measured in winter/early spring 1992, but the C14:O and C16:l proportions, and Pr/C,, ratio (9 to 21) exhibited their highest values of the investigated period. This indicated more favourable feeding conditions and significant phytoplankton contributions in the zooplankton diets than in summer 1991. The highest total mass fraction (12.2 to 46.5 mg g-' dry wt) and PUFA proportions (30 to 49 %) were observed during spring and autumn, when the food supply was probably sufficient and diverse. The olelc acid (C18:lng) proportions (12 to 22%) in the northeastern Adriatic were higher than in other marine regions.