Marine & Environmental Sciences Faculty Reports

Document Type

Report

Publication Date

2003

Abstract

A study has been undertaken to monitor Broward County, Florida (southeast Florida) coral communities, reef fish assemblages and sedimentation rates in relation to possible effects from a proposed extensive beach renourishment (restoration) project. Coral communities and reef fish assemblages will be monitored at a total of 23 stations distributed offshore Broward County. This monitoring effort will characterize and quantify populations of scleractinian (stony) corals, octocorallian (gorgonian) corals, sponges, and reef fishes. In addition, sediment traps located at each station will be sampled and analyzed.

This document reports the data collected during the third year of this project. Coral communities and fish assemblages were monitored at each of the 23 sites between September and October 2002. In addition, sedimentation analysis for the November 2001, January 200-, March 2002, May 2002, July 2002 and September 2002 collections are reported.

For September/October 2002 (=Year 3), mean (± 1 S.D.) stony coral density for the 23 sites was 2.84 + 1.30 colonies/m2. Mean stony coral coverage was 2.16 ± 3.53%. Mean octocoral density was 8.93 ± 10.17 colonies/m2 and mean sponge density was 13.47 ± 5.90 colonies/m2. Although no significant difference was found between the three reef tracts for stony coral cover, stony coral density, and octocoral density, First Reef sites had greater mean stony coral coverage but lower octocoral density than Second and Third Reef sites. First Reef coral cover was much lower than the Third Reef when the First Reet site, FTL4, was removed from the analysis. FTL4 had much greater stony coral cover than the mean cover for the remaining First Reef sites (17.40% compared to 1.65%). Sponge density was significantly greater on the Third Reef sites than the First or Second Reef sites, which did not significantly differ. Shannon-Weaver Diversity Indices performed on the overall transect data resulted in values of 1.49 ± 0.48 and 1.71 ± 0.46 for cover and number of species respectively. Overall evenness was 0.67 ± 0.20 for number of species and 0.76 ± 0.14 for cover.

Examining the 23 total sites, mean stony coral density has not significantly changed from the Year 1 (January/February 2001) Year 2 (September/October 2001) and Year 3 (September/October 2002) monitoring events. Mean stony coral cover at these 23 sites was found to be significantly greater in Year 2 than in Year 1 or 3, which did not significantly differ. At these 23 sites, mean octocoral density did not significantly differ between Years while mean sponge density was found to be significantly greater in Year 1 than in Year 2 or 3, which did not significantly differ.

Stony coral density, stony coral coverage, octocoral density and sponge density data collected from the 18 monitoring sites established in 1997 and visited yearly from 1997 to 2002 were analyzed. There has been no significant difference in stony coral density from 1998 to 2002. The density of stony corals in 1997 was found to be significantly less than what was found in 1998 and 2002. Mean stony coral cover increased from 1997 to 2001 but decreased slightly in 2002. Statistically, stony coral cover did not differ from 1998 to 2002, but 1997 was found to have significantly less cover than in 2000 and 2001. The mean density of octocorals did not differ statistically between 1998 and 2002. Mean sponge density was found to be greatest in 1998 and has decrease each year with a low in density found in 2002. Statistically 1998 and 1999 had the greatest sponge density compared to 2001 and 2002, which had the lowest sponge density.

The results of a multivariate statistical procedure indicate that the stony coral assemblages off Broward County have changed little from 1997 to 2002. This procedure has also shown that the stony coral assemblages on the Third and Second Reef sites have gieater similarity and that either have with most of the First Reef sites.

Trends in fish density were similar to those trends identified within the coral community transects. The greatest density of fishes occurs on the Third Reef followed by the Second and First. A difference in richness was seen amongst the three Reefs with the First Reef having the lowest number of species. The differences noted in abundance, density, and richness between the data collected in January/February 2001 and in September/October 2001 and September/October 2002 confirm previous reports of temporal differences in the fish assemblage offshore Broward County (Spieler 1998).

The First Reef had a statistically higher rate of sedimentation than both the Second and Third Reefs for the period from November 2001 to September 2002. The November 2001 samples had the greatest sedimentation rates. Sedimentation analysis indicates that the average grain size was significantly highest on First Reef sites, with Second and Third Reel sites lacking significant difference from one another. Average sediment rates for the three reefs since August 1997 indicate that the First Reef typically has the highest rate of sedimentation followed by the Second, then Third Reefs. Both sedimentation rate and average grain size from November 2001 to September 2002 appear to be consistent with data collected from previous years during these same sampling intervals. A comparison of sedimentation rate and wind speed revealed a similar pattern: when wind speed is low, sedimentation rates are low, and vise versa. This relationship is logical considering winddriven waves may cause sediment resuspension.

Data collected and analyses completed during this monitoring project will be used to help evaluate effects from the proposed beach renourishment project.

Report Number

Technical Report DPEP 03-01

Comments

Prepared for the Broward County Board of County Commissioners - Department of Planning and Environmental Protection - Biological Resources Division

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