Seasonal and diel variation in the standing crop of fishes and macroinvertebrates from a Gulf of Mexico surf zone

Abstract

To determine the relative importance of surf zones as habitats for fishes and macroinvertebrates, compared to other inshore marine environments, seasonal and diel abundance patterns were studied for one year. Both study sites were located on the south shore of Horn Island, a barrier in the northern Gulf of Mexico. At each site a 300 m 2 area was sampled, using a 50-m seine set around steel poles. Capture efficiency of the seine, determined from escapement tests, averaged 82%. While 59 species were captured during the study, only six species, Harengula jaguana, Anchoa hepsetus, A. mitchilli, Callinectes sapidus, A. lyolepis and Menticirrhus littoralis, comprised 90% of the total catch by number. Summer macrofaunal standing crop (mean = 9·8 gm −2, wet weight) was significantly greater than other seasons. The lowest values for both density and standing crop were those obtained in the winter. Both standing crop and average weight of the fishes increased significantly in night samples; a similar pattern did not occur for blue carbs. This primarily reflects the movement of larger, but generally rarer, fish species into the shallow surf zone after dark. Principal components analysis indicated that the standing crop of fishes was lowest during periods of reduced water volume and wave activity. However, seasonal factors appear, overall, to be more important in influencing fish abundance. Compared to a wide range of inshore marine habitats, surf zones appear intermediate in standing crop. Thus, at least during the summer, such habitats are important contributors to inshore standing crops of fishes.