Impacts of artificial reef addition on the nekton community of Louisiana marsh ponds: a before-after-control-impact analysis

Abstract

Louisiana’s coastal estuaries are dynamic, highly variable environments that provide nursery areas for numerous recreationally and commercially important species. Louisiana’s coastline is constantly changing due to natural and anthropogenic processes, and it is important to know how nektonic species are impacted by such changes. This study sought to assess the effects of introducing a hard substrate artificial reef on the nekton community of a Louisiana estuary. A before-after-control-impact (BACI) design was used to assess the impacts of artificial reef addition on nektonic fishes and crustaceans in four shallow marsh ponds near Empire, Louisiana. Marsh ponds were sampled by purse seine and fyke nets every other month from May 2009 to November 2010. Five sites within each pond, four consisting of soft-bottom habitat and one of marsh edge habitat, were sampled. Midway through the study period (March 2010), 110 tons of limestone cobble were distributed across two soft-bottom sites in two of the ponds to mimic oyster reefs. Over 113,000 individuals comprising 57 species were collected. A combination of statistical analyses, including ANOVA, PERMANOVA, and ANOSIM, were used on a variety of nekton community parameters, including species richness, diversity, nekton density, and community structure, to determine the impacts of artificial reef addition on the nekton community. Individual species shown to contribute to changes at impacted areas were also examined. Overall, the addition of artificial reefs had no significant effect on the nekton community as a whole. Select life-stages of estuarine nekton may be positively or negatively affected by reef presence depending on ontogenetic shifts in prey and habitat selection of each species. Once colonized and evolved into functioning oyster reefs, I believe in the absence of natural oyster reefs that the artificial reefs constructed in this study can act as quality nekton habitat. Longer study periods as well as further information on the movement behavior and habitat utilization of individual estuarine species may help elucidate the relationship between estuarine nekton and the habitats they occupy.