Nekton use of submerged aquatic vegetation, marsh, and shallow unvegetatedbottom in the Atchafalaya River Delta, a Louisiana tidal freshwater ecosystem

We sampled nekton (fishes and decapod crustaceans) in submerged aquatic veg etation (SAV) (Potamogeton nodosus, Najas guadalupensis), in emergent marsh vegetation (Sagittaria spp. and Scirpus americanus), and over unvegetated bottom associated with three islands in the Atchafalaya River Delta, Louisi ana. The purpose of our study was to quantify nekton densities in these maj or aquatic habitat types and to document the relative importance of these a reas to numerically dominant aquatic organisms. We collected a total of 33 species of fishes and 7 species of crustaceans in 298 1-m(2) throw trap sam ples taken over three seasons: summer (July and August 1994), fall (Septemb er and October 1994), and spring (May and June 1995). Fishes numerically ac counted for > 65% of the total organisms collected. Vegetated areas general ly supported much higher nekton densities than unvegetated sites, although bay anchovies Anchoa mitchilli were more abundant over unvegetated bottom t han in most vegetated habitat types. Among vegetation types, most species s howed no apparent preference between SAV and marsh. However, inland silvers ides Menidia beryllina and freshwater gobies Gobionellus shufeldti were mos t abundant in Scirpus marsh in summer, and blue crabs Callinectes sapidus w ere most abundant in SAV (Potamogeton) in spring. Several species (sheepshe ad minnow Cyprinodon variegatus, rainwater killifish Lucania parva, and blu e crab) apparently selected the vegetated backmarsh of islands (opposite of riverside) over streamside Scirpus marsh. Freshwater gobies, in contrast, were most abundant in streamside Scirpus marsh. Densities of juvenile blue crabs were high (up to 17 m(-2)) in vegetated delta habitat types and compa rable to values reported from more saline regions of Gulf Coast estuaries. Shallow vegetated habitat types of the Atchafalaya River Delta and other ti dal freshwater systems of the Gulf Coast may be: important nursery areas fo r blue crabs and other estuarine species.