A Half-Moonlight Feast: Trophic Function of Postlarval Amphidromous Goby Recruitment in Caribbean Freshwater-Marine Ecotones

Amphidromous fishes are ubiquitous, ecologically important, and culturally significant components of tropical stream communities. These species face multiple threats related to a life history that requires river-ocean connectivity during early stages. In amphidromy, eggs are spawned in freshwater streams, and larvae drift to the ocean. After an oceanic pelagic larval phase, they transition to postlarvae, and migrate back into freshwater and ascend rivers where they grow to adults and spawn. Postlarval recruitment (i.e., river ingress) is essential to amphidromous fish population dynamics, and artisanal fisheries that target the postlarval stage make this process culturally significant to local peoples. Moreover, recruitment constitutes the transfer of biomass from the ocean to freshwaters, which could be an important subsidy for the ecology of freshwater-marine ecotones. Despite the importance of post-larval recruitment for people, fisheries, and ecosystems, there have been few studies of Caribbean amphidromous fish recruitment. We resolved the recruitment phenology of Caribbean amphidromous gobies by quantifying seasonal and lunar periodicity of recruit abundances at multiple river mouths in Puerto Rico. We also determined the trophic role of amphidromous postlarval ingress with diet analysis of estuarine and riverine predatory fishes. Our results and conclusions are useful for Caribbean ecosystem and fisheries managers.