Influence of tidal and diurnal rhythms on fish assemblages in the surf zone of sandy beaches

The surf zones are significantly affected by tides, however, several gaps still in knowledge of fish assemblages in surf zones response to spring-neap and daily tidal cycles. We investigated fish assemblages in a surf zone of Gaolong Bay in China. The dynamics of fish assemblages were examined during the neap tide and the spring tide to test the hypotheses that (1) fish assemblages reflect a combination of species from around coastal habitats, and (2) dynamics of the fish assemblages were determined by both the spring-neap cycles and diel rhythms of fish species. We collected 46 fish species comprising 16 coral reef-seagrass species, 24 mangrove-estuarine species, and 6 common coastal species. Fish abundance and richness were significantly higher during the neap tide than during the spring tide. Furthermore, during the neap tide, fish assemblages were mostly carnivorous coral reef-seagrass species at night and were mostly omnivorous and planktivorous species during the daytime. However, no clear diel patterns were observed during the spring tide. We suggested that dynamics of the fish assemblages were mainly shaped by the diurnal rhythms of fish during the neap tide and by the tidal cycle during the spring tide. Our results support the notion that surveys of fish assemblages during the neap tide could collect more abundance and rich species of multiple ecotypes of fish to evaluate fish resource status in the around coastal habitats. Consequently, management approaches around surf zones with heterogeneous seascapes can lead to positive outcomes for inshore fish resources and ecosystem conservation.