ECOLOGICAL EFFECTS OF AN ARTIFICIAL ISLAND 

 Rincon Island, Punta Gorda, California 



by 

 G.F. Johnson and L.A. deWit 



I . INTRODUCTION 



Several studies on the ecological effects of the addition of 

 artificial substrate in a nearshore coastal marine environment have 

 been conducted in the past. The California Department of Fish and 

 Game, for example, has made detailed studies at oil platforms and in 

 areas where artificial reefs composed of streetcars, old car bodies, 

 concrete cubicles, and riprap have been established (Carlisle, Turner , 

 and Ebert; 1964; Turner, Ebert, and Given, 1969). 



In g-eneral, these studies conclude that the habitat features 

 created by the addition of solid substrate are beneficial to the 

 local ecosystem, especially in areas where such substrate is limited. 

 In time, communities of organisms develop which usually support more 

 species than the sedimentary habitat that existed before the addition 

 of hard, high-relief substrate. The biomass of the encrusting flora 

 and fauna is an important food source for species of recreational, 

 commercial, or aesthetic value which would otherwise not populate the 

 area. In addition, physical characteristics of the solid substratum, 

 such as crevices and vertical relief in an otherwise featureless 

 bottom, attract a variety of fishes. 



The armor rock revetments of Rincon Island represent a signifi- 

 cant addition of solid substratum to the local nearshore marine envi- 

 ronment which has contributed to an enhancement in the richness of 

 local marine communities (Carlisle, Turner, and Ebert, 1964; Brisby's 

 Biota Appendix in Keith and Skjei, 1974). Although observations on 

 Rincon Island's marine life have been made since these studies, no 

 comprehensive delineation of major habitats nor detailed character- 

 ization of communities extant at any one time or on a seasonal basis 

 has been done. This study was undertaken with the recognition that 

 this information would be valuable in understanding the ecological 

 consequences of artificial island construction. The objectives of 

 the study were to: 



(a) Delineate, map, and quantitatively characterize major 

 species associations around Rincon Island, and compare 

 these with the biota of the natural bottom between the 

 island and shore; 



(b) document the morphology and volume of the beds of shell 

 debris lying along the flanks of each of the four cardinal 

 sides of the island; 



