Theses and Dissertations

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Defense Date

2008

Document Type

Thesis - NSU Access Only

Department

Oceanographic Center

First Advisor

Mahmood Shivji

Second Advisor

Charles Messing

Third Advisor

Bernhard Riegl

Abstract

Chapter 1

The only coral reef ecosystem in the continental USA occurs off southeastern Florida and is under considerable strain due to intense urbanization and coastal development in this region. Coherent management and conservation efforts for this rapidly degrading ecosystem will benefit from knowledge about the patterns of genetic connectivity along the entire Florida reef tract. Because of their substantial biomass and extensive species diversity, the Porifera are an important model for investigating connectivity among coral reefs in Florida. We determined the genetic population structure of a common brooding species, the branching vase sponge, Callyspongia vaginalis, along 465 km of the Florida reef system from Palm Beach to the Dry Tortugas based on sequence data from the mitochondrial cytochrome oxidase subunit 1 (COI) gene. Populations of C. vaginalis were highly structured (overall ΦST=0.33), in some cases over distances as small as tens of kilometers. However, nonsignificant pairwise ΦST values were also found between a few relatively distant sampling sites suggesting that some long distance dispersal, perhaps by means of larval transport via sponge fragments, may occur along continuous, shallow coastlines. Indeed, sufficient gene flow appears to occur along the Florida reef tract to obscure a signal of isolation by distance, but not to homogenize COI haplotype frequencies. There was strong genetic differentiation among most of the sampling locations highlighting the fact that recruitment in this species is largely locally source-driven and that management needs to occur on a local scale. The C. vaginalis population at the northern end of the Florida reef tract (Palm Beach) had the lowest genetic diversity observed. This portion of the reef tract generally receives much less management attention than the southern reefs of the Florida Keys National Marine Sanctuary, and may require targeted conservation efforts for biodiversity preservation.

Chapter 2

The Porifera constitute a substantial part of the biomass on coral reefs, frequently have higher species diversity than corals and algae, and promote species richness through the fauna they support, making this phylum an important model for investigating connectivity among coral reefs. However, sponges have been neglected in population level genetic studies, particularly in the Caribbean. We determined genetic connectivity among populations of the branching vase sponge (Callyspongia vaginalis) by analyzing DNA sequence variation in 511bp of the mitochondrial cytochrome oxidase (COI) gene from 401 sponges sampled at 14 locations in Florida and the Caribbean. A significant signal of isolation by distance (P < 0.0001) was detected and an analysis of molecular variance (AMOVA) showed a pattern of high genetic structure among populations (ΦST = 0.57, P < 0.0001) with 82 of 91 pairwise comparisons being significant. Statistical parsimony analysis revealed two highly divergent haplotypes, suggestive of cryptic speciation. Inferences from a nested clade analysis suggested a northward movement out of the hypothesized ancestral population in Central America and into the Gulf of Mexico and Florida. The strong genetic structure observed Caribbean-wide indicates that there is little gene flow among populations and that recruitment of C. vaginalis is driven largely from local sources. As a result, recovery of this species on degraded reefs by seeding from distant, healthier reefs is unlikely. These results underscore the need for reef management and conservation efforts on small spatial scales.

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