Biological Processes and Ecological Development on an Artificial Reef in Puget Sound, Washington

Research at the Gedney Island artificial reef complex examined sustained aggregation and production of recreationally important fishes, and the rate of biota development toward a natural temperate reef situation. Algal and invertebrate species diversity increased following starfish and nudibranch predation of the space dominating barnacles. Algae colonization was a major contributor to the physical structure of the reef, and increased colonization by small crustaceans. Fishes colonizing the reef structures were most likely itinerant in the surrounding environment, and initially aggregated for orientation and protective habitat. Fish community structure evolved to include both reef foragers and aggregators, as food items developed on the reef structures. Fish densities considerably greater than on expansive rocky reefs, resulted from the artificial reef “oasis” or “home base” effect in the otherwise featureless sand habitat.

Simulated fishery removals of adult rockfish determined that a density of 0.104 fish/m² is sufficient to withstand actual and potential fishery removals. Monitoring for this rockfish threshold density appears to provide a workable technique for managing artificial reef fisheries in Puget Sound. Anglers fishing over the artificial reef retained 2.4 times more fish per hour than anglers fishing over nearby natural areas. The reef fishery appears to approximate an adult rockfish removal rate of 31%.

Diet analysis indicated that increases in adult copper rockfish may be correlated to successional biota development on the reef structures, which provided alternative prey items when normal forage fish species were in cyclic low abundance. Quillback rockfish increases appear correlated with increased abundance of structure-oriented prey items following the proliferation of algal growth.