with high densities of tube worms and tube anemones separate the deep 

 associations from natural bottom on all sides except the east side. 

 Two associations are unique to the east side. The shallower of the 

 two is composed almost entirely of large barnacles and encrusting 

 algae. The deeper association has high densities of certain species 

 of red algae. 



Twenty-three species of fishes were captured in gill nets placed 

 on all four sides of the island. Rockfish, surfperch, toadfish, and 

 swell sharks dominated the catch. Nets on the west (most exposed) 

 side yielded the highest catch (numbers and species) during day- 

 time sets. The east-side nets had the highest catches in the com- 

 bined day-night sets. 



The biota along a transect over natural bottom from near the 

 island to shore were considerably lower in abundance or density and 

 in number of species relative to biota at corresponding depths on the 

 island's revetments. This was especially the case for sedimentary 

 bottom in deeper water where the island is situated. Samples of 

 natural sediments were dominated by polychaete worms (35 percent of 

 biomass and 50 percent of species), small crustaceans, clams, ribbon 

 worms, and brittle stars. 



The construction of Rincon Island has had a major beneficial 

 effect on local ecological conditions. The quarry rock and tetrapod 

 construction materials offer habitat features which are not found in 

 a natural sedimentary bottom area. The solid substratum is colonized 

 by a high diversity of encrusting and attached biota. Many of these 

 are habitat-forming species in the sense that they provide shelter 

 and food for additional species. High vertical relief and vast 

 amounts of interstitial space attract many species of fishes which 

 are seldom or never encountered over sedimentary bottom areas. 



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