Ecotone Effects on Seagrass and Saltmarsh Habitat Use by Juvenile Nekton in a Temperate Estuary

While considering important juvenile fish habitats individually, both seagrass and saltmarsh are often highly connected with other subtidal and intertidal habitats. As a result, juvenile fishes and crustaceans may utilize multiple habitats across tidal, diel, or seasonal cycles in a manner that makes interhabitat proximity an important driver of fish distribution and community composition. In this context, we examined the importance of seagrass (Zostera marina and Halodule wrightii) and saltmarsh (Spartina alterniflora) habitat characteristics in driving fish and crustacean catch rates and community composition in a temperate, polyhaline-euhaline, estuary. We found that habitats with highly connected seagrass and saltmarsh vegetation exhibited higher average catch rates of many recreationally and commercially valuable fish and crustacean species, as well as overall nekton catch rates and Shannon diversity (H), than habitats composed of either seagrass or saltmarsh habitat alone. Nekton-habitat associations varied temporally, showing strong seasonal trends which were potentially indicative of temporal shifts in relative habitat value. Catch rates of numerous recreationally and commercially targeted species were correlated with patch-scale variables, particularly seagrass canopy height, water temperature, and depth; however, regression analysis indicated that habitat type was more powerful in predicting overall nekton catch rates and Shannon diversity (H). We conclude that emergent properties (i.e., those operating at 10-100s m) are important drivers of nekton distributions among and within habitats. Considering the spatial and temporal scales at which humans are encroaching on estuarine ecosystems, our findings highlight the need for investigating organism-habitat associations at expanded spatial scales, as well as the need to adopt fishery and coastal management plans that consider habitat characteristics at multiple spatial scales to account for interhabitat connectivity.