The Epifauna of a California Siltstone Reef

Abstract

Between 300 and 400 described species of macroscopic animals (including 22 fishes) were encountered on 1,385 m 2 of a silt—stone, submarine hogback and adjacent mixed bottom located in the shallow sublittoral (9.5 to 18 m depth) about 500 m off the coast of Corona del Mar, California. The components of the epifauna are not distributed uniformly over the reef. Both the numbers of species and individuals per unit area of reef surface vary inversely with depth. Although more species achieve maximum population densities at the top of the reef than elsewhere, some species are most abundant on the reef's mid—section, on the base, or on the rock—sediment bottom. Delineations among these major groups are sufficiently marked to warrant recognition of 3 vertical epifaunal zones on the reef itself and a 4th on the surrounding bottom within a meter of the reef base. Although changing conditions associated with the highly irregular rocky surface create a high degree of patchiness in the epifauna, within any of the zones some aggregations of species are sufficiently uniform and widespread to permit recognition of communities. In general the predominant species in the upper 2 zones are sessile suspension feeders, which form thick incrustations that form biotopes for large numbers of small sessile and motile species. In the lower zones, on the other hand, the predominant species tend to be motile scavengers and deposit feedes, and the incrustations that are present are thin and formed by single species. The degree of water movement on the reef, which results primarily from the propagation of surface waves, also varies inversely with depth. It is suggested that this pattern of water movement determines the distribution of the major units of the epifauna through its effects upon the availability of food of different types at particular points on the reef. Suspended organic matter is not only more abundant on the upper levels of the reef, but its rate of delivery to crustforming organisms is enhanced by turbulence. Deposition of organic materials removed from the upper part of the reef is facilitated by the sharp reduction in degree of water movement along the lower sides and bottom of the reef.

Vertical distributions of the epifauna on manganese nodules: Implications for settlement and feeding

“…Suspension feeders are often found in areas of high particulate flux (Ebling et al 1948;Pequegnat 1964;Riedl 197 1;Hughes 1975;Genin et al 1986). Taxa with this feeding habit were expected to dominate in zones of relatively higher current over manganese nodules.…”

Spatial distribution and the effects of competition on some temperate Scleractinia and Corallimorpharia

“…on temperate subtidal rocks, a phenomenon well known for corals on tropical reef slopes (Sheppard 1979, Benayahu & Loya 1981. The zonation pattern is consistent among sites in Central and Southern California, at different depths and vertical scales (Pequegnat 1964, Chadwick 1988bFigs. 1 & 2).…”

“…I quantified patterns of vertical distribution and abundance of the above anthozoans on 3 large rocks that extended 2.5 to 4.5 m in height above a sand plain at 11 to 12 m water depth. The abundance of anthozoans was determined from photographs taken by height above the sandy bottom (the anthozoans appeared to be distributed with reference to height rather than depth, Pequegnat 1964). Six 12 X 18 cm framed photographs were taken of randomly-selected areas at a n interval of 0.5 m up the vertical sides and along the horizontal top of each rock.…”

“…On large subtidal rocks, the inverse pattern may hold; lower limits may b e determined by extreme physical conditions near the sand-rock interface, such as low water flow (Pequegnat 1964), sedimentation, and/or sand scour (N. Chadwick pers. obs.…”

“…In temperate marine habitats, anthozoans such a s actinian sea anemones, corallimorpharians, and ahermatypic scleractinian corals may dominate benthic communities on hard substrata (Pequegnat 1964, Turner et al 1969, Castric-Fey et al 1978, Schmieder 1985, Lissner & Dorsey 1986, and the extent to which their competitive interactions influence community structure is of interest. An assemblage of 4 interacting anthozoans on subtidal rocks on the California coast is particularly amenable to experimental analysis, in contrast with tropical reef assemblages which contain u p to 54 species of interacting corals (Sheppard 1979).…”