Diel variation in decapod crustacean and fish assemblages in New Jersey polyhaline marsh creeks

Diel variation in fish and decapod crustacean abundance and species assemblages were examined in two studies to determine patterns of subtidal and intertidal marsh creek habitat use in a southern New Jersey estuary. In the first study, two subtidal marsh creeks were sampled with weirs from April-November 1988 (n = 42) and seines from July-November 1988 (n = 33), while in the second study two intertidal creeks were sampled with weirs from July-October 1989 (n = 28). Fish and decapod species assemblages captured in subtidal weir, subtidal seine and intertidal weir, as measured by both relative abundance and canonical discrimination analyses, were all highly affected by diel period. Total abundance and abundances of 15 species of fish and decapods exhibited significant diel differences, some of which were strongly influenced by season and life history stage (i.e. size cohorts). A detailed examination of the most abundant species, Menidia menidia, reveals that adults were more abundant during the day in early summer, suggesting diurnal reproductive movements into the creeks. In contrast, young-of-the-year cohorts were significantly more abundant at night during the late summer and fall, suggesting nocturnal movement into shallow marsh creek habitats. Our observations of strong diel differences in species assemblages point out the need for both day and night sampling in marsh habitats, if the importance of these habitats to fishes and decapods are to be fully understood.