DIEL VARIATION IN IMMIGRATION OF FISHES AND DECAPOD CRUSTACEANS TO ARTIFICIAL SEAGRASS HABITAT

Fish and decapod entry into small (1.5 m2) artificial seagrass habitat s positioned on an open sand area in a New Jersey estuary was examined to determine if immigration varied between day and night. To encounte r the structured habitats, colonizers had to cross an expanse of bare sand, with its presumably higher predation risk. Contrasts in abundanc e in the artificial seagrass plots between dawn and dusk indicated hig her nighttime immigration for four species, including the fishes Fundu lus heteroclitus and Myoxocephalus anaeus, and the caridean shrimps Pa laemonetes vulgaris and Hippolyte pleuracanthus. Size-frequency distri butions of colonizers varied between day and night for two fish specie s, Menidia menidia and Syngnathus fuscus, with a greater proportion of smaller individuals immigrating to the artificial seagrass at night. Callinectes saphidus also displayed a diel contrast in size distributi on but, for this species, proportionately more small individuals colon ized the plots during the day. We suggest that diel variability in pre dation risk and/or diel patterns in motor activity may be responsible for these patterns in immigration.