Habitat Use by Nekton in a Saltmarsh Estuary along a Stream-Order Gradient in Northeastern Barataria Bay, Louisiana

• Main Author: Granados-Dieseldorff, Pablo
• Other Authors: R. Eugene Turner
• Format: Others
• Language: en
• Published: LSU 2006
• Subjects: Oceanography & Coastal Sciences
• Online Access: http://etd.lsu.edu/docs/available/etd-11022006-162629/

Mesohaline estuarine regions in Louisiana play an important role in coastal ecosystems. To begin to understand how nektonic species and communities respond to environmental variables before habitat modification, I examined patterns of habitat use by fishes and decapod crustaceans in a seemingly pristine mesohaline system that drains into Bay Batiste, southeastern Louisiana. The study area was focused on a relatively unaltered core saltmarsh complex drained by intertidal and subtidal streams and it was representative of a larger surrounding system in terms of nekton community structure and associated environmental variables. Stratified monthly sampling (February November 2004) along a stream-order gradient examined changes in nekton abundance, species richness, and community structure within the study area. Analyses were based on a microhabitat approach used to characterize nekton responses to seasonal and spatial gradients of water depth, temperature, dissolved oxygen concentration, salinity, turbidity, bottom slope, stream width and distance to mouth. In 81 seine samples, 3757 individuals from 30 taxa were collected. Daggerblade grass shrimp was the numerically dominant species (72.7 %), followed by penaeid shrimp (13.4 %), bay anchovy (1.7 %) and inland silverside (1.7 %). Univariate ANOVAs detected the significant effects of stream order and season on nekton abundance and associated environmental variables. Greater numbers of nekton were mainly distributed in streams of low order. Kendalls W tests of ranked abundances indicated that nekton community structure was concordant among stream orders but not among seasons. Seasonal and spatial differences of environmental variables across stream orders and among seasons were attributed to the geomorphological and hydrological characteristics of the study area. A factor analysis resolved eight environmental variables into four orthogonal axes that explained 80 % of environmental variation. Factor one was interpreted as a stream-order axis, Factor two as a morphological axis, Factor three as a seasonal axis, and Factor four as a salinity axis. Differences in use of the four-dimensional factor space by dominant species reflected habitat selection, species residency status and seasonality of recruitment.