Theses and Dissertations


Title: THE EFFECTS OF HABITAT COMPLEXITY AND PREDATOR EXCLUSION ON THE ABUNDANCE OF JUVENILE RED SNAPPER, Lutjanus campechanus,IN THE NORTHERN GULF OF MEXICO

Name: Piko, Amy Ann

Degree: MS

Chair: Stephen T. Szedlmayer

Resides:

University: Auburn University

Location: Auburn, Alabama

Date: 2003

Pages: 75

Keywords: habitat complexity,predator exclusion,red snapper

Abstract:

Factors affecting juvenile red snapper abundance were examined through placement of experimental artificial habitats in situ and in laboratory experiments. From July 2001 to August 2001, artificial habitats were built southeast of Dauphin Island, Alabama in the northern Gulf of Mexico. Twenty oyster shell habitats and twenty oyster shell-concrete block habitats were built at two sites, 20 km (Site 1) and 23 km (Site 2) offshore. At each site, predator exclusion cages were placed over 10 shell habitats and 10 block habitats. Ten cages were also placed over open sand substrate as controls. A 1 m PVC stake was set into the ground near each reef to indicate shrimp trawl activity, i.e. if the stakes were displaced, shrimp trawls may have caused high mortality at that site. SCUBA divers visually surveyed the reefs to count juvenile red snapper abundance during five time periods from August 16, 2001 to November 19, 2001.Juvenile red snapper were first most abundant at Site 1 and, as the season progressed, became more abundant at Site 2. There was a significant correlation between red snapper abundance and temperature. Habitats with predator exclusion cages showed significantly more age-0 red snapper, but no effect was detected for age-1 red snapper. The increased habitat complexity of the block reefs was significantly correlated with greater abundance of all red snapper.Predation effects on juvenile red snapper habitat selection were tested with shell and block habitats in the laboratory with Gulf flounder, Paralichlhyes albigutta, as the predator. Groups of 3 age-0 red snapper were observed for habitat selection between shell and block, both with and without the presence of a predator. The laboratory tests confirmed age-0 red snapper (~160 mm SL) prefer complex to simple habitats in the absence of predators and predation pressure significantly increases the time red snapper spend on the complex habitat.This study showed that habitat complexity and predation are significant factors that affect the abundance of juvenile red snapper in nursery areas in the Gulf of Mexico. Predation may affect juvenile red snapper abundance directly through mortality and indirectly by influencing habitat selection. In addition, by forcing juveniles to actively seek appropriate shelter, predation may also increase competition for habitat.

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