HCNSO Student Theses and Dissertations

Defense Date

2006

Document Type

Thesis

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Richard E. Spieler

Second Advisor

David S. Gilliam

Third Advisor

Stephen M. Blair

Abstract

Beach erosion is an ongoing problem in South Florida. Beach replenishment has been the primary means of maintaining these economically important beaches, and dredging offshore sand deposits, adjacent to reef tracts, has been the pervasive method since the 1970's. Over the past ten years, greater attention has been paid to potential impacts dredging can have on adjacent reef communities, which has led to increased monitoring efforts. With the increase in monitoring efforts, scope has expanded from a strict focus on the benthic community to include the fish communities. This study evaluates the effects of dredging on reef fish communities associated with two separate beach replenishment projects, offshore of Miami-Dade County, Florida, U.S.A. Monitoring programs were developed and conducted by the Miami-Dade, Department of Environmental Resources Management (DERM). Monitoring took place between March 1997 and September 2000, with one project in northern portion of the county, off offshore of Golden Beach, and the other in the southern portion offshore of Key Biscayne. Both monitoring programs employed a Before After Control Impact design, with established test and control reef stations. Eight reef fish visual point count censuses (Bohnsack and Bannerot, 1986) were performed at each station prior to dredging, immediately following dredging, and three periods at bi-quarterly intervals after that.

In general evaluations of both project,s showed no indications that dredging activities had major impacts on the fish communities of adjacent reefs. For the Golden Beach project, there was one aspect of the analysis, which may be indicative of dredging related impacts; was species richness at one test station declined significantly following dredging activities (ANOVA p=0.047). However, in terms of abundance, diversity and Multidimensional scaling (MDS) plots of the Bray-Curtis dissimilarity index did not indicate that dredging activities impacted the test station. During the monitoring period of the Key Biscayne project, the south Florida region was impacted by two tropical storm events, which obscures the isolation of impacts associated with dredging. Changes in the reef fish communities, consistent with the impact and recovery of the tropical storms are evident in species richness, abundance, and MDS plots of the Bray-Curtis dissimilarity index, at both the test and control stations.

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