The vertical distribution of decapod larvae off the northwest Portuguese coast was analysed in relation to associated environmental conditions from sampling during a 69 h period around a current meter mooring located on the shelf, approximately 21 km off the coast. Plankton samples were collected every 2 h at the surface with a neuston net and through the water column with a Longhurst Hardy Plankton Recorder (Pro-LHPR), allowing a very detailed resolution of larval vertical distribution. Environmental data (temperature, salinity, and chlorophyll a) were obtained every hour. To investigate the horizontal distribution of decapod larvae in relation to the coast, a plankton-sampling grid was carried out before the 69 h fixed station. Larvae of shelf decapod species were widely distributed over the shelf, while those of inshore species were found much closer to the coast. Decapod larvae (zoeae and megalopae) showed clear diel vertical migrations, only appearing in the upper 20 m at night, a migration that did not appear to be affected by physical conditions in the water column. Larval densities were highly variable, 0.01 to 215 ind. m -3 for zoeae and 0 to 93 ind. m -3 for megalopae, the zoeae being generally more abundant. The results indicated that during the day larvae accumulate very close to the bottom. The diel vertical migration behaviour is discussed as one of the contributing mechanisms for larval retention over the shelf, even with offshore transport conditions promoted by coastal upwelling, and is hence of major relevance for the recruitment success of decapod species that inhabit inshore and shelf zones of coastal upwelling systems.

Results from depth integrated and vertically stratified plankton sampling in the northwestern Adriatic Sea were used for comparison of gut contents of larvae of European anchovy Engraulis encrasicolus with composition and concentration 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. All larvae had empty guts soon after dusk, indicating daytime feeding and rapld gut clearance. With increasing larval length there was a greater percentage of specimens with empty guts, despite suitable food being ava~lable in the plankton for these larger larvae; this suggests differential gut evacuation during sampling-possibly related to the degree of gut development. Larval diet was principally the various developmental stages of copepods, especially calanoid and cyclopoid nauplii, which were preferentially selected by larvae, whereas selection was against harpacticoid nauplii. Lamellibranch larvae and Peridiniurn spp. were generally abundant in the plankton, but were only present in the gut contents in any number when the preferred dietary organisms were present in the plankton at low concentrations. The number of food organisms in the gut contents increased with concentration of the preferred food organisms in the plankton .up to a limit of -50 organisms 1-'. Within the upper 18 m of the water column, there was a reduct~on in the proportion of larvae with food in their guts with increasing depth, irrespective of the vertical profile of food concentration. Following a period of wind mixing the compos~tion of the plankton changed. This was reflected in the diet of anchovy larvae, which altered in parallel. There was also an overall 4 1 R:, decrease in concentration of the preferred food particles 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 anchovy larvae can successfully adapt their diet to a changing prey field and suggest that in the conditions observed in the northern Adriatic, quite radical changes in the feeding environment were probably insufficient to affect overall larval mortality.

Fish eggs and larvae were analysed from 63 vertically stratified plankton hauls in the Irish Sea and southern North Sea. The dominant species were sprat (Sprattus sprattus), dragonet (Callionymus spp.), dab (Limanda limanda) and to a lesser extent rockling species, sandeel (Ammodytes spp.), whiting (Merlangius merlangus) and flounder (Platichthys flesus). There was little difference between species in the vertical distribution of either eggs or larvae. Most were concentrated in the upper 50 m of the water column, eggs in progressively increasing numbers towards the surface and larvae with a sub-surface peak at a depth of 10-15 m. The vertical distribution of eggs extended deeper in the water column than larvae, possibly due to some combination of eggs being spawned deeper and their passive susceptibility to turbulent mixing. There were no significant differences between day and night distributions and under mixed or isothermal conditions. 1997 International Council for the Exploration of the Sea

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