Demographics of the Ribbed Mussel Geukensia demissa (Dillwyn, 1817) and the Effects of Its Simulated Manual Harvest on Salt Marsh Health in South Carolina, Usa

Abstract

The ribbed mussel Geukensia demissa is a mytilid bivalve that inhabits salt marshes along the east coast of North America. It is an important ecosystem engineer, contributing to salt marsh species diversity and landscape-scale ecosystem processes. Furthermore, local interest in the human consumption of G. demissa in South Carolina has created demand for this species from both restaurant and retail outlets. In response, commercial harvest of G. demissa increased markedly between 2014 and 2016. There are, however, currently no species-specific commercial or recreational harvesting regulations for G. demissa in this state, either in terms of minimum size or maximum quantity, raising concerns about the sustainability of commercial harvest, especially considering that harvesting practices can be destructive to the salt marsh ecosystem. The goal of the current study was to characterize the demographics of G. demissa at a harvested site and at two unharvested reference sites over the course of 1 y. Furthermore, the current study investigated the effects of simulated harvest on parameters of salt marsh health. Quarterly and monthly demographic sampling at commercially harvested and unharvested sites in South Carolina revealed that patches of G. demissa primarily consist of large individuals with low rates of recruitment. A similar relationship between size and age was observed at each of the sites. A year-long manipulation experiment revealed that selective harvesting practices mitigated the effect of harvest on metrics of smooth cordgrass, Spartina alterniflora health, but not on recruitment of G. demissa. The current study offers important demographic information on G. demissa in South Carolina that can be used to support future management decisions associated with its commercial and recreational fisheries.