Influence of marsh island size on nekton communities: intermediate optima rather than Single-Large-or-Several-Small (SLOSS)

Abstract

Habitat extent and configuration are critical drivers of faunal abundance, diversity, and ecosystem functioning. Evidence from terrestrial systems often suggests that large contiguous tracts of habitat generally support more species and individuals than several small patches of equal summed area. However, studies from shallow-water marine systems often suggest the opposite trend or that there are more complex interactions. Since tidal wetlands (e.g. salt marshes and mangrove forests) are at the interface between terrestrial and marine ecosystems and provide essential nursery habitat for a variety of estuarine taxa, it is important to elucidate how the size, configuration, and surrounding matrix of these wetlands influence their role in supporting faunal communities. We sampled 12 isolated marsh islands ranging in size from 300 to 55000 m2 within North Carolina, USA, to better understand the influence of marsh size and configuration on overall biodiversity and faunal abundance of estuarine nekton. Field observations indicated that nekton catch rates were directly correlated with marsh area and perimeter; however, species richness did not change with marsh size or configuration. Further analysis indicated that small and medium marsh islands support higher species turnover among islands than large marsh islands. Quantitative simulations using the ‘Single-Large-Or-Several-Small’ framework and idealized, circular islands showed that intermediate-sized islands support the highest relative abundance of nekton after standardizing for total marsh area. Our findings suggest that focused conservation or restoration efforts for marsh islands ranging in size from 1000 to 10000 m2 may help maintain and enhance estuarine nekton communities.