Nekton use and growth in three brackish marsh pond microhabitats

Abstract

With continued marsh break-up and loss in Louisiana, small interior ponds are created, increasing areas of shallow water habitats. These shallow water habitats are potential sites for submerged aquatic vegetation (SAV) establishment. It is important to characterize nekton community composition, density, biomass, and growth within brackish marsh pond microhabitats because SAV is often cited as essential fish habitat (EFH). Three microhabitat types were investigated: (1) inner-pond SAV (> 1 m from edge); (2) near marsh-edge SAV (< 1 m from edge) and (3) nonvegetated bottom. We tested the null hypotheses that nekton community composition, density, and biomass were not related to microhabitat type and characteristics. Ninety-six quantitative samples were taken with a 1-m2 throw trap between September 2001 and July 2002. The two vegetated microhabitats were characterized by monotypic stands of widgeon grass Ruppia maritima and contained similar biomass. Nekton community composition, density, and biomass did not differ between vegetated microhabitats, but differed significantly from the nonvegetated microhabitat (p < 0.0001). Therefore, SAV appears to be a dominant factor influencing nekton distribution within ponds. Submerged aquatic vegetation beds may also provide nekton with better growth environments by providing better quality or quantities of food for nekton than nonvegetated habitats. We also tested the null hypothesis that nekton growth was similar between vegetated and nonvegetated habitat types to determine if SAV provided a greater food resource than nonvegetated bottom. An in situ field experiment was conducted that compared growth rates of Atlantic croaker Micropogonias undulatus between vegetated and nonvegetated habitats to investigate the role of SAV in supporting nekton growth. We detected no statistically significant difference in nekton growth between vegetated and nonvegetated habitats (p = 0.125).