Some shallow (<7 m, water depth) nearshore hardbottom areas of southeast Florida have been reported to function as important juvenile fish habitat. Much of this area has been impacted by one or more local beach renourishments (sand fill to offset erosion). In order to evaluate the impact of a planned beach renourishment project, we obtained baseline data on hardbottom coral-reef fish assemblages adjacent to the beach.
Project and Findings
In 2001, we characterized the nearshore fish communities along a 30-km stretch of coastline, primarily in Broward County, using three visual census methods. Two hundred transect-counts, 100 point-counts, and 98 rover-diver counts were completed during June-August. Because beach renourishment did not proceed as scheduled, we recounted the fish, at the same locations, in 2003 at 89 transect, 45 point-count, and 45 rover-diver count sites. In total, 164 species and over 72,000 fish were recorded in 2001 and a total of 7,555 fish consisting of at least 130 species in 2003. The highest number of species was recorded with the rover-diver counts and the highest fish density with transect-counts.
Fish exhibited a 62.8% decrease in abundance between the 2001 and 2003 surveys. Juvenile grunts (Haemulon spp.) (<5 cm total length, TL) alone decreased 72.8% in abundance. The second most abundant species, slippery dicks, also primarily juveniles, also showed a significant decrease between the 2001 and 2003 surveys. Even after removal of the two most abundant taxa, total abundance remained significantly lower the second survey year, suggesting the possibility of a community-wide decrease in abundance. However, the decrease between years was mainly due to a decrease in juveniles. When fish less than 5 cm TL were removed from the dataset, no significant difference in abundance between years was detected. Species richness also declined significantly with slightly fewer species noted in 2003 and eight fewer total species between years.
Implications for Management
Our results provide critical baseline data for determining the effects of beach renourishment on nearshore fishes in Broward County. In addition, the large variation in fish abundance and species richness noted between years has widespread implications for determining potential anthropogenic change in fish assemblages (e.g., caused by beach renourishment). For example, had beach renourishment proceeded as originally scheduled, the natural variation between years might have, wrongly, been attributed to the renourishment. Clearly, temporal as well as spatial variation must be considered in establishing a baseline database.
Broward County Department of Environmental Protection
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