Theses and Dissertations

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Defense Date

8-2006

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Richard Spieler

Second Advisor

David S. Gilliam

Third Advisor

R. Grant Gilmore, Jr.

Abstract

The southeastern United States continental shelf supports a diverse community of recreationally and commercially important reef fish. However, little is known about the reef fish community associated with the shelf edge between the depths of 50 and 120m. Offshore of Broward County, Florida, the continental shelf is narrow and appears to provide limited natural fish habitat. Numerous artificial vessel-reefs have been deployed throughout this region to enhance local recreational fisheries. The reef fish assemblage has not been adequately described at these vessel-reefs and interactions between fish assemblages on vessel-reefs and those on neighboring natural habitat are unclear. Remotely operated vehicle (ROV) surveys, were conducted at three separate vessel-reefs along with several regions of neighboring natural substrate to determine the reef fish assemblage, species richness, and abundances. During two years of study, 785 minutes of video were recorded from vessel-reefs along with 488 minutes from natural substrate.

ROV surveys along the continental shelf between 50 and 120m depths revealed no regions of exposed hardbottom with vertical relief greater than one meter. Twenty-seven different species were observed on natural substrate transects with an average of 32.0 (+/- 39.2 SD) fish per survey hour. Manmade artifacts, such as tires, were commonly observed during surveys and harbored a large percentage of the fish recorded along the continental shelf. Bank sea bass, Centropristis ocyurus, and tattler bass, Serranus phoebe, were common among tires along with occasional juvenile snowy groupers, Epinephelus niveatus. At a depth of 110m, grey tilefish, Caulolatilus microps, and tilefish burrows were observed. A majority (66%) of species observed has been recorded at depths less than 30m in Broward County, however trophic structure differs between depths. Planktivores, benthic carnivores, and piscivores numerically dominate deep regions, while herbivores and omnivores were absent.

Fifty-three different fish species were observed on three vessel-reefs, Bill Boyd, Caicos Express, and Papa’s Reef, at depths between 50 and 120m. Vessel-reefs had a significantly higher species richness (21.4 +/- 4.1 SD) and abundance (255.1 +/-250.0 SD minus anthiine fishes) of fish observed per hour of video compared to natural substrate surveys (p < 0.01 and p = 0.01 respectively, T-test). Anthiine fishes, numerically dominated vessel-reefs, with several thousand (2277.8 +/-1735.9, during 2005/06) observed on each survey. Seventy percent of total species recorded are typically found as adults in less than 30m depth in Broward County. Most of these fishes were predators that were not found on the natural substrate between 50 and 120m depths during this study.

Several deeper reef fish (ie. fishes that spend a majority of their adult life at depths greater than 50m) were recorded on vessel-reefs. Spotfin hogfish Bodianus pulchellus, replaced its shallow water congener spanish hogfish, B. rufus. Bank butterflyfish, Prognathodes aya were more common than reef butterflyfish, Chaetodon sedentarius. Juvenile deep reef serranids, speckled hind, Epinephelus drummondhayi and snowy grouper, Epinephelus niveatus were observed. Two deep reef lutjanids were also recorded, blackfin snapper, Lutjanus buccanella and vermilion snapper, Rhomboplites aurorubens.

A Bray Curtis MDS plot of similarity indices suggested some differences in assemblage structure between the vessel-reefs (2D stress = 0.18). These differences were due to a few species. The Caicos Express, located in the shallowest depth (74m), had a large school (300+ fish) of tomtates, Haemulon aurolineatum, associated with it, while the Bill Boyd, located in 82m depth, typically had a large mixed school of amberjack, Seriola dumerili and almaco jack, Seriola rivoliana around its more extensive superstructure. Papa’s Reef had two Sciaenids, black bat drum, Pareques iwamotoi and cubbyu, Pareques umbrosus that were uncommon on other vessel-reefs. Vessel-reefs were sampled throughout the year and there was no significant change in species richness or abundance with the change of seasons ( p = 0.922 and p = 0.419 respectively, ANOVA). The deep reef fish community on small artificial structures as well as vessel-reefs was more similar to communities reported from equivocal habitats at the same depth hundreds of kilometers away than with the nearby outer reef tract in 30m depth.

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