VI. SUMMARY AND CONCLUSIONS 



Rincon Island's rock revetments offer a diversity of habitat 

 features for a great variety of marine species which do not occur in 

 adjacent natural bottom areas. This study added 160 taxa of macro- 

 biota to the master species list for the island, bringing the total 

 to 458. 



Extensive beds of mollusk shells lie at the bases of the three 

 sides of the island most exposed to wave action. The bed on the west 

 [seaward-facing) side is the most extensive; it is composed primarily 

 of shells of the California mussel, Mytilus calif ornianus . The 

 volume of shell on the north and south sides combined are an order of 

 magnitude less than on the west-side bed. Species other than mussels 

 characterize these beds. Shell accumulations are lacking along the 

 flanks of the east (landward) side. 



Densities of 53 common taxa occurring in permanent transects on 

 each of the four sides of the island were analyzed for seasonal 

 variability. About three-fourths of these showed statistically 

 significant variation. This was the case for most of the algae 

 tested and generally for ectoprocts, sea urchins, and certain worms, 

 coelenterates, and sponges. 



Thirteen major species associations were provisionally iden- 

 tified on the basis of dominant biotic components. Detailed charts 

 of the boundaries of these associations, referenced to permanent 

 features on the island, were prepared from field measurements of 

 depths and distances. Sharpness of the boundaries generally de- 

 creases with depth. In general, the associations are continuous 

 horizontally around the island and grade into one another vertically. 



Statistical analysis of species abundance and biomass data from 

 each of the 13 preliminary major species associations provided a 

 basis for final characterization of associations. Five of the pre- 

 liminary 13 associations could not be differentiated statistically. 

 Combination of these and addition of one association resulted in a 

 total of nine distinctly different major species associations. An 

 association dominated by acorn barnacle and limpet biomass encircles 

 the island in the uppermost part of the intertidal. Below this on 

 the west side lies a mussel-gooseneck barnacle association, which ex- 

 ceeds all other associations in biomass per unit area. Small pockets 

 of an intertidal anemone association are found on the southeast wing. 

 Starting at about the MLLW line and extending a few meters down the 

 revetments, a macrophytic algae association is found on all but the 

 east sides. Below this is a broad zone characterized by encrusting 

 and filamentous algae and a species of polychaete worm. The deeper 

 parts of the revetments are characterized by an association dominated 

 by ectoprocts, colonial anemones, corals, and gorgonians. Talus beds 



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