Tropical intertidal seagrass beds as fish habitat: Similarities between fish assemblages of intertidal and subtidal seagrass beds in the Philippines

Abstract

Tropical intertidal seagrass beds have recently been identified as foraging grounds for multiple fish species, although the possible drivers of fish migration to such beds remain unknown. Investigations of fishes occurring in intertidal and subtidal seagrass beds, and comparison of food resources of the dominant trophic groups in the intertidal and subtidal beds, and surrounding bare-sand areas, were conducted at two sites in northern Mindanao, Philippines. Fish species collected in the intertidal and subtidal seagrass beds overlapped by 65%, with species richness and abundance of both residents and visitors between the two habitats not differing substantially (although significantly higher than in intertidal and subtidal bare-sand areas), as many site-attached residents appeared to remain in the intertidal beds during low tide. Benthic-invertebrate feeders, including juveniles of commercially important species, dominated intertidal seagrass beds, comprising >70% of species richness and abundance. Four of them (Halichoeres argus, H. papilionaceous, Lethrinus harak, and Parupeneus barberinus) fed primarily on small crustaceans, such as harpacticoid copepods and amphipods, the densities of such food resources being significantly higher in the intertidal and subtidal seagrass beds than in the surrounding bare-sand areas. The results demonstrated that intertidal seagrass beds function as foraging grounds for many visiting fishes, in addition to providing a permanent habitat for resident species. Recognition of the importance of tropical intertidal seagrass beds as fish habitat has significant implications for the management and protection of coastal fish biodiversity and fishery resources.