Influence of Habitat Structure on the Fish Assemblages Associated with Two Cooling-Water Intake Structures in Southern California

The offshore intake structures of coastal electric power generating stations in southern California consist of high relief conduits surrounded by structurally complex rock rip-rap. In order to determine what component of an intake's fish assemblage was associated directly with the rip-rap, fish communities at two intake structures and four other artificial reefs lacking either high relief or complex habitat substrata were compared. Results indicated that all reefs were nearly comparable in species number and number of individuals for water-column oriented species regardless of habitat type. The ubiquity of a majority of water-column species at all reefs suggests that the provision of a visual landmark or hard surfaces supporting algal and invertebrate populations is essential for concentrating these species. In contrast, the presence of most benthic species was directly related to habitat cover as a reef with no habitat refuge and a reef with complex habitat but large interstitial spaces both had depauperate benthic species assemblages. Vertical diversity rather than substrate rugosity proved to be a better indicator for relating fish community structure to habitat structure.