The majority of recent studies investigating the habitat value of intertidal oyster reefs have compared the nektonic assemblages on natural oyster reefs, salt marshes, mud bottom, and subtidal oyster shell habitats using methods that involve some degree of habitat disturbance. The current study used a novel, non-destructive sampling approach involving the deployment of a drop net around study plots to compare the nektonic assemblages associated with intertidal oyster reefs (natural and enhanced) with those of neighboring soft sediment habitats at 3 sites in South Carolina. At each site, the nektonic organisms collected on a reef plot were compared with those collected on an adjacent control plot lacking a structurally complex habitat. Nekton abundance was significantly higher on the reef plot compared with the control plot at all 3 sites. Nekton abundance also varied among seasons, with the greatest numbers occurring during summer compared with spring and fall. Notably, grass shrimp (Palaemonetes spp.) were especially dominant on reef plots. A total of 60 taxa were identified, 57 of which were identified to species level. Reef plots exhibited significantly greater taxon richness than control plots. The number of taxa present also accumulated over time at a higher rate on the reef plots than on the control plots at 2 of the 3 sites. Among the 60 taxa collected, 36 were found on both the reef and control plots, whereas 14 taxa were unique to the reef plots. For data pooled across all sites and seasons, 33 taxa were more numerous on reef plots than control plots, 3 taxa occurred in equal numbers, and 24 taxa were more numerous on control plots. For taxa collected on more than 1 occasion, paired t-tests performed with Bonferroni-adjusted significance thresholds revealed that Alpheus heterochaelis and Palaemonetes spp. were significantly more abundant on the reef plots than on the control plots, whereas unadjusted analyses revealed the same pattern for Gobiosoma bosc, Menidia menidia, and Fundulus heteroclitus. In contrast, no taxa were significantly more abundant on the control plots at either significance threshold. Although nekton abundance was generally higher on the reef plots, measures of diversity were significantly higher on the control plots, regardless of season, site, or date. Greater abundance of a limited number of species on the reef plots accounted for lower evenness and therefore lower diversity measures for this treatment. Overall, community structure was driven more by site than by treatment, whereas the seasonal occurrences of certain species on the reef plots highlighted the importance of oyster reefs as essential fish habitat for the critical life stages of finfish species with complex life histories.
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Vol. 31 • No. 4