HCNSO Student Theses and Dissertations

Defense Date

6-30-2010

Document Type

Thesis

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Amy Hirons

Second Advisor

Jonathan Shenker

Third Advisor

Alexander Soloviev

Abstract

Knowledge of the temporal and spatial distribution and density of the larvae of Florida‘s commercially important crab species, the blue crab, Callinectes sapidus, the golden crab, Chaceon fenneri, and the stone crab, Menippe mercenaria in the nearshore and offshore waters of Florida‘s southeast coast is minimal. Such data, however, can be crucial to our understanding of the population dynamics of these vital fishery species. To obtain baseline data of the occurrence and distribution of these species‘ larvae in the Florida Current, densities were obtained from zooplankton tows from an E-W transect northeast of Port Everglades, Ft. Lauderdale, Florida along the inshore edge of the Florida Current during the months of February, March, April, May, July, September, and November of 2007. Results showed that densities of C. sapidus and C. fenneri were much lower than expected over the course of the sampling period though peak density patterns were seen for all species. Statistical analysis was not possible for C. fenneri and M. mercenaria due to their extremely low densities from the samples. However, peaks in larval density from all three species were seen to coincide with known peak spawning periods. Minimal occurrence for M. mercenaria was not unexpected as this species has not been observed to use the major ocean currents as a dispersal mechanism. Low densities of C. fenneri, however, were unexpected as adult females of this species ascend the slope to shallower depths to release eggs. This migration to shallower depths would position them directly within the flow of the Florida Current making it highly likely that their larvae would be collected in the water column from this area. However, this was not observed from this study‘s samples. C. sapidus was observed to have the highest densities of all three species although only the megalopa stage and no zoeal stage individuals were identified. C. sapidus megalops occurred during all months except April with a peak density in May. Results confirmed a year-round spawning of C. sapidus in southeast Florida with peak spawning in the spring and a smaller peak in late summer. It is concluded that none of the species observed utilize the Florida Current as a means of long distance dispersal. Regarding C. sapidus especially, it is presumed that local recruitment plays an important role in population enhancement. For the larvae of M. mercenaria, however, it is thought that those individuals caught in the strong currents are likely occurring accidentally and lost from parent populations. Expanding sampling and study area and of the physical processes of the nearshore and offshore waters of southeast Florida will help shed light on the dispersal and recruitment patterns for these species. It is with this information that managers have the necessary tools for maintaining sustainable fisheries.

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