Fish Assemblage Structure of the Shallow Ocean Surf-Zone on the Eastern Shore of Virginia Barrier Islands

Abstract

This study provides an in-depth description of the fishes in the shallow surf-zone (<0·4m), a little-studied micro-habitat of the ocean surf. Fish assemblages were examined with respect to three temporal cycles (seasonal, diel and tidal) and at both large and small spatial scales. Sampling was conducted at the Virginia barrier islands using an 8m bag seine dragged parallel to the beach in water with an average depth of 0·2m. The fish assemblage was relatively species poor, in fact, there were only two year-round residents, Membras martinica (rough silverside) and Mugil curema (white mullet). Three species, M. martinica, Trachinotus carolinus (Florida pompano) and Menticirrhus littoralis (gulf kingfish), comprised 94% of all species captured. Both fish species richness and total abundance peaked in the late summer and were lowest in the winter. Multidimensional scaling analysis failed to identify a distinct nighttime fish assemblage. However, univariate analyses found there was a significant increase in species richness at night, due to an influx of predatory adult fishes. Further, significantly more species were collected at high than low tide. Higher species richness and total fish abundance occurred in the shallow water (<0·4m) of runnels, low wave energy habitats on the backside of small sand bars. The increased richness and abundance suggests a small-scale movement of fishes parallel to the beach face as fishes seek sheltered runnel habitats. This study quantifies the observation that many fishes do utilize the shallow surf-zone, perhaps to minimize predator encounters and/or take advantage of an under-utilized intertidal food source.