Applicability of the source–sink population concept to marine intertidal macro-invertebrates with planktonic larval stages

Abstract

Local populations of marine benthic macro-invertebrates with planktonic larvae are believed to be in source–sink relationships via larval dispersal in a regional population complex. Practically, such a region is definable only after connectivity of constituent local populations is explored. Numerical simulations abound for hydrodynamic connectivity by larvae between local/regional populations. Empirical studies have scarcely integrated inter-local connectivity and intra-local population dynamics into demographic connectivity analysis. I review the current research and indicate fundamental and technical problems to demonstrate that some source–sink systems in intertidal shores, which are most accessible among benthic habitats, are a good model. The challenge in benthic source–sink research comes from that existent local populations may not be self-sustaining because of low larval self-seeding rates and/or low benthos' survival rates and yet can persist as latent sinks. They may receive larvae leaking from sources at good-quality habitat patches with stationary larval retention areas for self-recruitment. On an intertidal sandflat in an estuary–coastal ocean region, Kyushu, Japan during 1979–2019, the population of a trochid gastropod with 3- to 9-day larval duration became extinct and recovered. The extinction was caused by sediment destabilization by a callianassid shrimp population which increased in the early 1980s. The gastropod recovery was owing to the shrimp decline by stingray predation and the transport of larvae from some self-sustainable populations with lower shrimp densities 30 km away. It was estimated that the gastropod population before the shrimp proliferation on that sandflat might be a latent sink requiring allochthonous larval subsidy due to epi-benthic predation on juveniles.