Similar habitats, different communities: Fish and large invertebrate assemblages in eastern Gulf of Mexico polyhaline seagrasses relate more to estuary morphology than latitude

Seagrass habitats are a dominant component of coastal waters along the eastern Gulf of Mexico coast and are recognized as essential habitats for many species. Although various ecologically and economically important species depend on seagrass habitats at some life stages, these habitats are vulnerable to anthropogenic influences. As coastal human populations continue to grow, and nearshore habitats are affected, understanding the structure and function of assemblages associated with nearshore habitats is important for management and mitigation efforts. Therefore, we sampled estuarine and nearshore polyhaline seagrass beds monthly (May November) from 2008 through 2015 using a 6.1-m otter trawl in seven estuaries in the eastern Gulf of Mexico. Despite latitudinal variability, assemblage structure of fishes and selected larger invertebrates was predominantly driven by estuary morphology-semi-enclosed estuaries had significantly higher catch-per-unit effort (CPUE) of estuarine obligates and incidental marine taxa, whereas open estuaries had higher CPUE of small forage and cryptic species. Furthermore, abundances of several important fishery species differed markedly between semi-enclosed and open systems. Our results highlight (1) the relative importance of different scales of environmental factors' influence on communities, (2) the need for understanding how seemingly similar habitats in estuaries of differing morphologies can support different fishery species, and (3) the importance of regional scale monitoring data and its value in tracking ecological changes.