Theses and Dissertations

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Defense Date

7-2005

Document Type

Dissertation - NSU Access Only

Degree Name

Ph.D. Oceanography/Marine Biology

Department

Oceanographic Center

First Advisor

Richard E. Spieler

Second Advisor

Robin L. Sherman

Third Advisor

Mahmood S. Shivji

Fourth Advisor

Andrew Rogerson

Abstract

Derelict vessels are commonly deployed as artificial reefs in theUnited States, mainly for recreational fishers and divers.Broward County,Floridaalone has more than 70 vessel-reefs located in its coastal waters. Despite their popularity, few studies have rigorously examined fish assemblages on these structures and compared them to natural reefs. Resource managers need information about fish assemblages on vessel-reefs and natural reefs to better understand the dynamics of local fish populations, understanding which can then effect more informed management decisions.

The nearshore environment ofBroward County,Floridaconsists of three reef terraces, each separated by sand substrate, running parallel to the coastline in sequentially deeper water. All vessel-reefs in this study were located in 19 to 21 m of water, on the sand flat, which separates the middle and offshore reef terraces. SCUBA diving was used to perform a non-destructive point-count method to visually assess the fish assemblages at both artificial and natural reef sites.

A total of 279 point-counts were performed to characterize the fish assemblages on six vessel-reefs and neighboring natural reefs offshore of Broward County, Florida over 25 months in two intervals (March 2000 to March 2001 and March 2002 to February 2003). This study tested the hypotheses of no difference in fish assemblages between vessel- and natural reefs and also of no difference in fish assemblages between individual vessel-reefs.

In a second study, initial fish colonization on a newly deployed vessel-reef, the Ebinizer II, a 25.5m merchant marine vessel, was studied from May 2002 – February 2004. The ship was scuttled in May 2002 off Broward County, Florida and was censused 13 times during the study period. Adjacent natural reefs and the McAllister, a nearby, 30m vessel-reef deployed in June 1998, were also censused during the same period. This study tested the hypothesis that vessel-reefs simply attract fish from surrounding areas rather than increase fish production. If this was the case, initial fish colonization of the vessel-reef would be primarily composed of adult fishes.

In general, vessel-reefs had significantly greater mean abundance, species richness, and biomass than nearby natural reefs (p < 0.05, Mixed model ANOVA). Vessel-reef fish assemblages were found to be unique when compared to the nearby natural reefs (SIMPER, MDS, ANOSIM) and the trophic structure differed strikingly between the two reef types. Planktivores dominated on vessel-reefs where these fishes may be utilizing food resources and habitat characteristics not accessible from or found at natural reefs. These results support recent research which suggests artificial reefs that provide unique habitat characteristics not found at local natural reefs may develop a distinct fish assemblage. Additionally, observations of recruitment and growth of particular species (e.g., Lutjanus buccanella, Haemulon aurolineatum, Chromis scotti), which was not observed at nearby natural reefs provides evidence for species-specific production at vessel-reef sites.

The initial colonization of the Ebinizer II did reveal attraction of transient piscivores from the family Carangidae, as well as attraction of adult herbivores. However, juvenile fishes dominated (63% of total fish abundance) during the first two sample periods and data from subsequent censuses provided some evidence for continued growth and survival of these recruits. The results also reveal some economically important fish species (i.e. lutjanids and carangids) seem to prefer vessel-reefs, as there was a greater abundance of these species on vessel-reefs than surrounding natural reef areas. Vessel-reef locations are public knowledge and many of these sites are popular fishing spots. The concentration of these valuable species on vessel-reefs should concern local resource managers as these fishes may be exposed to considerable amounts of fishing pressure.

Fish assemblages at natural reef sites within artificial reef permit areas were compared to those found in areas with no artificial reefs nearby (> 1.9 km) to further elucidate the potential effects of attraction. Mean fish abundance, mean fish biomass and mean species richness were greater at natural reefs neighboring vessel-reefs (< 1.9 km away), but were not significantly different from natural reefs with no artificial structures nearby. This suggests vessel-reefs are not simply attracting fish away from neighboring natural reefs. As a whole, the results of my studies demonstrate the importance of species-specific analyses when trying to determine the extent to which attraction and/or production may be occurring at a specific artificial reef.

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