Deep-Water Biological Assemblages of a Hard-Bottom Bank-Ridge Complex of the Southern California Continental Borderland
Lissner, Andrew L.
Dorsey, John H.
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A manned submersible survey of Tanner and Cortes Banks and Santa Rosa-Cortes Ridge, offshore of southern California, U.S.A., was conducted to characterize the hard-bottom, biological assemblages from 14 m to approximately 150 m depth. Four major assemblages were observed; their dominant taxa were: 1) Eisenia arborea/erect coralline algae from at least 14 to 40 m; 2) Agarum fimbriatum/Laminaria farlowii from 40 to 60 m; 3) encrusting coralline algae from 60 to 90 m; and 4) Florometra serratissima/ ophiuroid from 90 to at least 150 m depth. Subdominate organisms in the shallow assemblage consisted of understory algae (reds and browns) and brittle stars; coralline algae, brown algae, gorgonians and seastars at mid-depth; and seastars, gorgonians and sponges at greater depths. The species and assemblages observed on the banks and ridge are very similar with those occurring in other hard-bottom areas adjacent to the southern California mainland and Channel Islands. However, the depth ranges for these assemblages and several of their species are much greater than observed elsewhere. An exception to this observation is the Florometra/ ophiuroid assemblage, which is quite common in some deeper- water (100 m to at least 300 m) areas of the Southern California Bight and the Santa Maria Basin. The increased depth ranges and high abundance of the bank assemblages appear to be influenced by water clarity, probably related to their isolation from coastal influences including runoff, the potential for a deep mixed layer caused by strong wave and surge activity, and the greater survey area compared with other studies.