Epifaunal Biomass on a Rock-Reef — Pequegnat 
39 
feeders, on the other hand, exhibit a marked 
increase of biomass toward the bottom. 
These patterns of biomass distribution on the 
reef and among the feeding types coincide well 
with expectations for those on a sublittoral 
rock-reef so situated as to have significantly 
higher values of water movement and suspended 
matter at the top than at the base (resulting 
from surface-wave propagation ) . I have already 
demonstrated that such a pattern of water move- 
ment exists on Reef 500 (Pequegnat, 1964). 
Suspension-feeders are favored by active water 
movement, whereas scavengers and deposit- 
feeders are benefited by calm waters at the 
reef-base that permit deposition of debris and 
detritus. Nevertheless, it is apparent that all 
feeding types are represented at every level on 
the reef. This permits the development of true 
communities that make effective use of the 
products of the primary producers. Some insight 
into the efficiency of this utilization of organic 
matter is revealed by the fact that the standing 
crop of deposit-feeders on the reef is little more 
than 1 % that of the suspension-feeders. 
FREQUENCY OF OCCURRENCE ON QUADRATS 
AND INDIVIDUALS PER SPECIES 
The sublittoral epifauna displays a high de- 
gree of heterogeneity, i.e., a large percentage of 
species occur on a small per cent of quadrats, 
reflecting a poor fit of the Poisson distribution. 
This has a certain relationship to the production 
of biomass (Fig. 1). Of the 265 species of 
macroinvertebrates detected on the reef -proper, 
only 15 (6%) were found on 80-100% of 
quadrats (Group V), whereas 159 (60%) 
were found on only 0-19% of quadrats. But 
the latter group, even though 10 times as 
numerous as Group V, contribute only a tenth 
as much to the total biomass as do the 15 
high-frequency species. Thus, the majority of 
species contribute very little to the standing 
crop biomass. Typical examples of each fre- 
quency group are: (I) the small gastropod Seila 
montereyensis, (II) the terebellid polychaete 
Thelepus crispus, (III) the holothuroid Cu- 
cumaria lubrica, (IV) the starfish Pisaster 
giganteus, and (V) Chama pellucida. The 
largest contributors to the biomass are suspen- 
I 1 XL m BE 3 E 
0 - 19 % 20 - 39 % 40 - 59 % 60 - 79 % 80 - 100 % 
% OCCURENCE ON QUADRATS 
Fig. 1 . The inverse relationship between per cent 
of species total and per cent frequency of species 
among quadrats, and the concentration of biomass in 
high-frequency species. Examples of species in the 
frequency groups I to V are given in the text. 
sion-feeders that are of intermediate size, have a 
tendency to aggregate, are broadly adapted to 
the changing physicochemical factors on the 
reef’s vertical axis, and are either colonial or 
represented by large numbers of individuals. 
Taking the species of the four most important 
noncolonial phyla on the reef-proper (viz., 
Mollusca, Arthropoda, Echinodermata, and An- 
nelida), the mean number of individuals per 
square meter of those species occurring on 
80-100% of quadrats is 283, while for the 
0-19% group the mean drops to only 3. Ap- 
parently the multiplicity of microhabitats present 
on a rock-reef such as this favor highly adapted 
species whose small populations reflect the 
small area of each such habitat. 
These findings may appear to support Tur- 
paeva’s (1957) conclusion that the basic nature 
of marine benthic biocoenoses can be ascertained 
from the dominant species alone. Perhaps this 
conclusion is valid for level bottom communi- 
ties, but lack of critical information precludes 
its immediate application to complex epifaunal 
assemblages. We need to know that species 
