Title page for ETD etd-11142005-101616


Type of Document Master's Thesis
Author Caudill, Melanie Christine
Author's Email Address mcaudi1@lsu.edu
URN etd-11142005-101616
Title Nekton Utilization of Black Mangrove (Avicennia germinans) and Smooth Cordgrass (Spartina alterniflora) Sites in Southwestern Caminada Bay, Louisiana
Degree Master of Science (M.S.)
Department Oceanography & Coastal Sciences
Advisory Committee
Advisor Name Title
Richard F. Shaw Committee Chair
Donald M. Baltz Committee Member
Irving A. Mendelssohn Committee Member
Lawrence P. Rozas Committee Member
Keywords
  • salt marsh
  • decapod crustaceans
  • fish
  • mangrove
  • habitat use
Date of Defense 2005-07-06
Availability unrestricted
Abstract
This is the first study to compare nekton use and habitat value among Spartina alterniflora (Spartina), Avicennia germinans (black mangrove), and transition (S. alterniflora and A. germinans) sites within Louisiana's salt marsh-mangrove ecotone. Fishes and crustaceans were collected in Caminada Bay during fall 2003 and spring 2004 using 4 m2, bottomless lift nets. Although analyses were unable to demonstrate significant differences in fish (p=0.0753) and crustacean (p=0.1457) densities and species composition (p=0.8801) across sites, habitat-specific trends in nekton use were evident. Fishes, including gulf killifish and sheepshead minnows, showed affinities for the Spartina site, while crustaceans, especially white shrimp, were more associated with the mangrove site. Total fish biomass (p=0.0396) and gulf killifish biomass (p=0.0223) and densities (p=0.0543) were significantly greater at Spartina than mangrove sites. White shrimp biomass was significantly greater at mangrove than Spartina (p=0.0062) and transition sites (p=0.0143) and gulf stone crab densities were also higher at mangrove than transition sites (p=0.0061). Habitat type, areal stem cover (ASC), turbidity, and temperature explained 52% of the variability in nekton densities. Greater structural complexity (ASC, p<0.0001) at the mangrove site may increase refuge value for crustaceans given that (1) most were juveniles, including white shrimp, brown shrimp, blue crabs, and gulf stone crabs, and (2) white shrimp and brown shrimp were positively associated with ASC. Lower ASC and greater flooding depths (p=0.0318) and durations (p=0.0065) at Spartina than at the higher elevation mangrove site may benefit larger nekton by increasing access to the flooded marsh. The transition site had similar vegetation characteristics as the Spartina site, but flooding depths and durations resembled the mangrove site. Nekton densities were positively related to flooding duration at mangrove (fish, p=0.0031; crustacean, p=0.0040) and transition sites (fish, p=0.0018). Low fish use at mangrove and transition sites during spring 2004 suggests that (1) reduced hydroperiod negatively affects fishes, and (2) Spartina marshes may become especially important when meteorological events reduce access to mangrove and transition habitat types. More research is necessary to determine if these findings are representative of Louisiana's salt marsh-mangrove ecotone statewide, and to understand the fisheries implications of continued mangrove expansions.
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