Fish Census of Selected Artificial Reefs in Broward County
Principal Investigator: Richard Spieler, Ph.D.
Derelict ships are commonly deployed as artificial reefs in the United States, mainly for recreational fishers and divers. Over 500 vessel-reefs lie in Florida waters alone. Despite their popularity, few studies have rigorously examined fish assemblages on these artificial reefs and compared them to natural reef.
Project and Findings
Six vessel-reefs off the coast of southeast Florida were censused quarterly (two ships per month) to characterize the associated fish assemblages. SCUBA divers used a non-destructive point-count method to visually assess the fish assemblages over 13- and 12-month intervals (March 2000 to March 2001 and March 2002 to February 2003). During the same intervals, fish assemblages at neighboring natural reefs were also censused. A total of 114,448 fishes of 193 species was counted on natural and vessel-reefs combined. Fish abundance and species richness were significantly higher on vessel-reefs in comparison to natural reef. Haemulidae (grunts), the most abundant family on vessel-reefs, represented 46% of total abundance.
On natural reefs, wrasses were the most abundant family, accounting for 24% of total abundance. The number of species also differed among vessel-reefs, with the most recently deployed having fewer species than the earliest deployed. Fish assemblage structure on natural versus artificial reefs exhibited a low similarity (27%). Interestingly, the juvenile phase of two deep-water, economically important species was repeatedly recorded on vessel-reefs, but has never been observed on natural reef in our study area. This may be an indication that vessel-reefs are supplying ancillary nursery/juvenile habitat for these animals that may be unavailable or limited on surrounding natural reef. Further, a comparison of natural reef sites immediately adjacent to the vessels with those more distant, does not support a simple aggregation hypothesis.
Implications for Management
Artificial Reefs remain important tools for resource managers. This study clearly shows that the effects of deploying vessel-reefs on the natural environment are complex and not a simple aggregation from neighboring habitat.
Additional research is currently ongoing examining the fish assemblages on deeper vessel-reefs (>50 m) and neighboring hardbottom using a remotely operated vehicle (ROV).
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