CONTRIBUTION OF ZOOPLANKTON LIPIDS TO THE FLUX OF ORGANIC-MATTER IN THE NORTHERN ADRIATIC SEA

Analyses of particulate material collected by sediment traps moored at a location in the northern Adriatic Sea in 1991 revealed the presence of zooplankton fatty acids, even though zooplankton and other 'swimmers' killed by the trap's preservative were carefully removed. Laboratory experiments were conducted to (1) prove the existence of zooplankton lipids within fecal pellets, (2) exclude the possibility of incomplete separation of swimmers and other material as eventual contamination with polyunsaturated fatty acids in fecal pellets, (3) evaluate the importance of zooplankton lipids to mass flux and (4) reveal the mechanisms which lead to excretion of undigested organic matter, in this case polyunsaturated fatty acids. Our results show that the main source of fatty acids found in mass flux were zooplankton lipid droplets inside fecal pellets. The predominant fatty acids of zooplankton fecal pellets were saturated acid 16:0, monounsaturated acid 18:1 and polyunsaturated acid 22:6. Lipid composition of fecal pellets was compared with those of zooplankton and phytoplankton. Aliquots of collected fecal pellets were stained with Nile Red in order to visualize lipid droplets within fecal pellets.