Distribution of Epifaunal Biomass on a Sublittoral Rock-Reef 
Willis E. Pequegnat 1 
Previously the author reported on the quanti- 
tative distribution of epifaunal species and indi- 
viduals and their donation on a siltstone reef 
located in the open ocean near Corona del Mar, 
California (Pequegnat, 1964). A marked top- 
to-bottom reduction in numbers of species and 
individuals was observed to exist on this reef, 
and these changes were related to a reduction of 
wave-induced water movements from the reef’s 
upper to lower levels. Three observations 
pointed to the desirability of determining the 
distribution of biomass over the rock-reef: 
(1) the populations of some species were 
greatest on the reefs lower levels, (2) several 
of the largest species with relatively small 
numbers of individuals occurred here, and (3) 
there appeared to be a shift from a prepon- 
derance of suspension-feeders at the top toward 
increasing importance of deposit-feeders and 
scavengers at the base. 
Accordingly, the objectives of the present 
study were: (1) to determine the quantitative 
distribution of biomass over the reef’s surface, 
and (2) to relate the observed pattern to (a) 
position on the reef, (b) feeding types, (c) the 
frequency of occurrence of species on quadrats, 
and (d) the number of individuals per species. 
The present study was supported by the 
Office of Naval Research and the Texas A&M 
Research Foundation. I also thank Dr. Claude 
E. ZoBell and Dr. Francis T. Haxo for labora- 
tory space at the Scripps Institution of Ocean- 
ography. 
STUDY SITE AND METHODS 
Because descriptions of the study site and 
sampling methods used have been published 
elsewhere (Pequegnat, 1964), only a brief out- 
line of them is given here. The rock-reef is 
1 Department of Oceanography, Texas A&M 
University, College Station, Texas. Manuscript re- 
ceived January 25, 1967. 
located about 500 m offshore (referred to here- 
inafter as Reef 500) where, at mean sea level, 
its depth ranges from 9.5 m at the top to 18.5 m 
on the seaward bottom. Because the epifauna 
exhibits marked changes in composition down 
the reef, it has been subdivided into four zones. 
These zones, together with their general depth 
limits along the transect where the present 
sampling was done, are: Reef-top Zone, 9.5- 
12.5 m, where the important epifaunal feature 
is an incrustation formed by the rock oyster 
Chama pellucida; the Mid-reef Zone, 12.5- 
14.5 m, which supports a thick growth of 
calcareous ectoprocts ; the Reef-base Zone, 14.5- 
16.5 m, where large sea urchins and deposit- 
feeding sea cucumbers predominate; and the 
Mixed-bottom Zone, 16.5+ m , which is 
located on the adjacent sea bottom of sediments 
and rock slabs and which supports a mixture 
of infaunal and epifaunal species. In the follow- 
ing sections the term reef-proper will embrace 
the first three zones, while the term reef- 
complex will include the mixed-bottom as well. 
All samples were taken under water through 
use of conventional Scuba techniques. Small 
species were sampled on the reef -proper from 
0.1 m 2 quadrats, and from 0.25 m 2 quadrats on 
the mixed-bottom. Quadrats encompassing 1 m 2 
were used to sample large species (gorgonians, 
sea urchins, and the like) on the reef -complex. 
The animals taken in samples were sorted into 
species, counted, and weighed dry. These gen- 
eral procedures were followed prior to drying: 
(1) mollusks were removed from their shells, 
(2) all tubiculous species were processed with- 
out tubes, (3) echinoderms, large decapods, 
and the like were decalcified, and (4) sponge 
and ascidian mats were picked free of motile 
species and rinsed free of sediments in filtered 
sea water. 
Samples were taken during parts of 1958, 
1959, and 1963. Unless specifically stated other- 
wise, all tabular data are based upon samples 
taken during all three years. 
37 
