Artificial reef observations from a manned submersible off southeast Florida

Abstract

Examination of 16 artificial reef structures with a two-person submersible in depths ranging from 30 to 120 m (100–400 ft) indicated that the highest numbers of fish are found around reefs in water shallower than 46 m (150 ft). Fewer fish, especially those with tropical coral reef affinities, below 46 m was probably caused by a thermocline, observed on all dives deeper than 43 m (140 ft). During 4 days in September 1987, temperatures from the surface down to approximately 43 m were 30° to 31°C (86°–88°F), whereas below 43 m the temperature dropped as low as 10.6°C (51°F) at 120 m (390 ft). Algae and reef community encrusters (gorgonians, bryozoans, branching sponges, and corals), abundant on shallower structures, were absent below 46 m. Structures that penetrated above the thermocline, such as two upright oil "rigs" and a hopper barge, were also effective reefs. The open structure and high profile of the rigs enhance their use as artificial reefs by providing a range of well-aerated habitats. Any effect of substrate or post-deployment age on fish abundance could not be documented. Wood appeared to be a more effective fish-concentrating material but has a shorter useful life than does steel. The greatest diversity and numbers of fish were observedat the Miami sewer outfall.