Most of the mangrove marshes along the Indian River Lagoon were impounded to control mosquito production. The impoundments were initially kept permanently flooded and isolated from the lagoon. Earlier studies showed that installation of culverts to allow the exchange of water with the
lagoon resulted in re-establishment of marsh vegetation and increase in the abundance and diversity of fish and decapods. Today, 52% of the mosquito control impoundments are closed to maintain high water levels during the peak mosquito breeding season in the summer, and left open to allow
exchange of water (through culverts) for rest of the year (the Rotational Impoundment Management—RIM). Twenty one percent of the mosquito control impoundments are left open the entire year (“unmanaged”). A 1-year study was conducted to compare the effects of these two major
management regimes (RIM and “unmanaged”) on the abundance and community structure of fish and decapods utilizing the perimeter canal. Monthly samples were taken at duplicate sites at each of the two RIM and two “unmanaged” impoundments at St. Lucie County, Florida using
a seine net (mesh size 3 mm). A total of 38 taxa were collected, most of which were transient species that spend their larval and/or juvenile stage(s) in the marshes. However, two resident species [mosquito fish (Gambusia affinis) and sailfin molly (Poecilia latipinna)] accounted
for almost 90% of the total number captured. Proportions of mosquito fish are much higher in the RIM than in the “unmanaged” impoundments throughout the year. In general, fewer species and numbers were caught in the summer, followed by a large increase in the fall and a decrease
between fall and spring. The summer closure of the RIM impoundments resulted in even lower abundance and fewer species captured compared with “unmanaged” impoundments. Fortunately, transient species, which are most greatly affected by marsh management practices, use the mangrove
marsh primarily during the spring and fall.
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