Feeding of anchovy Engraulis encrasicolus larvae in the northwestern Adriatic Sea in response to changing hydrobiological conditions

Results from depth integrated and vertically stratified plankton sampling i n the northwestern Adriatic Sea were used for comparison of gut contents of larvae of European anchovy Engraulis encrasicolus with composition and con centration of potential prey in the plankton. Sampling was carried out over a grid of stations both before and after a period of increased wind mixing to investigate changes in food availability and larval feeding success. AU larvae had empty guts soon after dusk, indicating daytime feeding and rapi d gut clearance. With increasing larval length there was a greater percenta ge of specimens with empty guts, despite suitable food being available in t he plankton for these larger larvae; this suggests differential gut evacuat ion during sampling-possibly related to the degree of gut development. Larv al diet was principally the various developmental stages of copepods, espec ially calanoid and cyclopoid nauplii, which were preferentially selected by larvae, whereas selection was against harpacticoid nauplii. Lamellibranch larvae and Peridinium spp. were generally abundant in the plankton, but wer e only present in the gut contents in any number when the preferred dietary organisms were present in the plankton at low concentrations. The number o f food organisms in the gut contents increased with concentration of the pr eferred food organisms in the plankton up to a Limit of similar to 50 organ isms l(-1). Within the upper 18 m of the water column, there was a reductio n in the proportion of larvae with food in their guts with increasing depth , irrespective of the vertical profile of food concentration. Following a p eriod of wind mixing the composition of the plankton changed. This was refl ected in the diet of anchovy larvae, which altered in parallel. There was a lso an overall 41% decrease in concentration of the preferred food particle s of larvae in the plankton following the period of wind mixing, but larvae were still able to maintain their food intake. These results show that anc hovy larvae can successfully adapt their diet to a changing prey field and suggest that in the conditions observed in the northern Adriatic, quite rad ical changes in the feeding environment were probably insufficient to affec t overall larval mortality.