SUBSTRATUM SELECTION BY JUVENILE PLAICE (PLEURONECTES-PLATESSA L) - IMPACT OF BENTHIC MICROALGAE AND FILAMENTOUS MACROALGAE

Preference by juvenile plaice for vegetated or unvegetated substratum was investigated in laboratory experiments to study the impact of rece nt changes in vegetation structure in shallow nursery areas on the rec ruitment of plaice. The experiments were done in circular tanks with f iltered flow-through seawater. The tanks were divided into two parts, one with bare sediment and the other with mat-forming benthic microalg ae or patches of filamentous macroalgae (Enteromorpha intestinalis and Rhizoclonium spp.) attached to small cobbles. Substratum preferences were tested for different size-classes of juvenile plaice, ranging in size from 11 to 50 mm. Recently metamorphosed (11-15 mm) and post-sett lement (16-26 mm) juveniles showed a significant preference for bare s ediment compared with areas containing patches of filamentous algae. P ost-settlement juveniles (16-26 mm) also exhibited a significant prefe rence for bare sediment compared with sediment covered with mat-formin g benthic microalgae. The differences in substratum selection disappea red 6 to 8 weeks after settlement in individuals that were 35 to 50 mm in total length. Field sampling verified that density of plaice (17-3 4 mm) was significantly lower in vegetation patches than in areas of b are sediment