Nekton use of Ruppia maritima and non-vegetated bottom habitat types within brackish marsh ponds

Abstract

Nekton (fishes and decapod crustaceans) use of brackish submerged aquatic vegetation (SAV) habitat has been largely overlooked in comparison to fresh and marine SAV habitats. This study was designed to examine nekton use of brackish marsh SAV habitat and non-vegetated bottom. Specifically, we examined the effects of habitat location (defined by SAV distance from marsh edge) and complexity (defined by SAV biomass) on nekton community density, biomass, and diversity in shallow water brackish marsh ponds, which contained monospecific beds of Ruppia maritima L. Three habitat types were investigated: (1) inner-pond SAV (SAV habitat > 1 m from marsh edge), (2) near marsh-edge SAV (SAV habitat < 1 m from marsh edge), and (3) non-vegetated bottom. We tested the null hypotheses that nekton density, biomass, and diversity were unrelated to habitat type or habitat characteristics. Ninety-six quantitative samples were taken with a 1 m 2 throw trap between September 2001 and July 2002. Using multivariate analysis of variance (MANOVA), a significant habitat type by season interaction was found (Wilks' λ = 0.32, F24, 259 = 4.21, p < 0.0001) for nekton density, biomass, and diversity. Simple linear regression showed a positive relationship between SAV and nekton biomass (p < 0.0001); however, distance of the vegetated habitat from the marsh edge did not significantly influence SAV or nekton biomass. SAV biomass, but not location, appears to be a dominant factor that influences nekton use within these small brackish marsh ponds. This study highlights some of the intricacies associated with the identification and use of broad scale habitat classification for management purposes. Although brackish marsh SAV habitat types support higher densities of nekton compared to non-vegetated habitat, variation within this gross classifica- tion indicates a wide range of habitat 'value' that needs to be considered for management purposes.