Degree of Fragmentation Affects Fish Assemblage Structure in Andros Island (Bahamas) Estuaries

—We used underwater visual census (UVC) to characterize fish assemblages among estuaries with different degrees of fragmentation on Andros Island, Bahamas. Estuaries were classified a priori into four fragmentation categories: totally fragmented (no surface water connectivity to the ocean), partially fragmented, minimally fragmented, and unfragmented (unimpeded surface water connectivity through the estuary to the ocean). Visual surveys (n = 159) were conducted in thirty estuarine systems using snorkeling gear in four habitat types: flat, mangrove, rock, and seagrass. Fish species density differed significantly among habitat types and among estuaries with different degrees of fragmentation. Highest species density occurred in rock habitats in unfragmented or minimally fragmented estuaries; lowest species density was in totally fragmented estuaries. Assemblages in unfragmented and minimally fragmented estuaries were characterized by presence of reef-associated (e.g., damselfish and parrotfish) and transient marine (e.g., jacks) taxa. In completely fragmented sites, assemblages were dominated by species tolerant of temperature and salinity extremes (e.g., sheepshead minnow). Multi-dimensional scaling suggested fish assemblages in mangrove and rock habitats experienced the greatest impact of estuary fragmentation (i.e., the most differentiation among surveys in estuaries with different fragmentation status). Fish assemblages were especially variable among partially fragmented estuaries (i.e., estuaries where hydrologic connectivity was maintained by a culvert), suggesting hydrologic connectivity through culverts may not be sufficient to maintain habitat quality, recruitment dynamics, or upstream movements by vagile organisms. These data reveal effects fragmentation has on faunal assemblages, and demonstrates that faunal presence/absence may guide initiatives to conserve and restore sub-tropical estuaries.