Population Dynamics— Pequegn AT 
425 
Fig. 1. Location of the two sublittoral rock-reefs 
under study, in relation to the city of Corona Del Mar 
and the entrance to Newport Harbor, Orange County, 
California. 
appearance of certain predominant species ap- 
parently triggered increases and decreases in 
associated species. And these changes proved to 
be very extensive, involving some species that 
would not have been expected to react to changes 
in Mytilus populations. 
STUDY SITE 
The rock mass under study is composed of 
siltstone that has been subjected to complex 
folding. Gorsline (1962) advises that these 
promontories may properly be called submarine 
hogbacks. The dip of the strata ranges from a 
few degrees to 90°, but the larger part exhibits 
the latter dip. Because it is located approximately 
200 m offshore, I shall refer to it hereinafter 
as Reef 200. 
Situated about 2.5 km southeast of the en- 
trance to Newport Harbor, Reef 200 ( Fig. 1 ) 
rises from a sand bottom at a greatest depth of 
11.2 m to a shallow point of 2 m at standard 
mean sea level. It has a minimum surface area 
of 1,200 m 2 distributed over a length of 58 m 
and an average width of 27 m (ranges from 8 
to 44 m). Because its long axis parallels the 
shore, the hogback lies athwart the direction 
of surface wave propagation. This results in in- 
terference with wave transmission and a high 
degree of turbulence at shallow points. The 
magnitude of turbulence is inversely related to 
depth; hence it falls off rapidly down the walls 
and is barely perceptible at the reef base on 
days of average swell. 
Most of the Mytilus population was confined 
to the reef’s flat top, between depths of 2 and 
4 m. The same was true of such brown algae as 
Eisenia arborea , Egregia australis , and Laminaria 
farlowi. 
STUDY METHODS 
Samples of the Mytilus populations of Reef 
200 were obtained under water by using SCUBA. 
Quadrats were established by placing metal rings 
encompassing 0.1 m 2 against the biota and re- 
moving all components by hand. Where re- 
quired, hammers, chisels, and. forceps were also 
utilized. All specimens were placed in canvas 
bags, which were sealed prior to ascent and re- 
turned to the laboratory. Subsequently species 
were identified, and individuals of numerable 
species (noncolonial) were counted and meas- 
ured. 
Prior to the Mytilus decline, study sites were 
selected by dropping metal rings onto the reef 
from a moving boat. Samples were removed 
from the sites where the rings came to rest. 
During and after the decline, conscious attempts 
were made to remove samples within a few 
meters of predecline quadrats. This was possible 
since chisel marks were still evident on the 
rocks. The first samples were taken on October 
29, 1958, and the last on February 22, I960. 
The longest period without samples extended 
from February 15 to August 19, 1959, when 
the author was in Europe. For most purposes I 
have divided the dates of sampling into three 
periods of time: Predecline (October, 1958, to 
January 15, 1959), Decline (January 16 to 
October 15, 1959), Postdecline (October 16, 
1959, to February, I960). Although Mytilus had 
not disappeared completely from the reef at the 
end of the study, its average population per 0.1 
m 2 quadrat was then only 0.5% of its original 
value. Twelve 0.1 m 2 quadrats were studied 
during the above periods. 
Large species, such as Pisaster giganteus, 
Strongylocentrotns purpuratus, and Parasticho- 
pus parvimensis, were sampled with metal rings 
encompassing 1 m 2 . Specimens of these species 
were not removed from the reef. Samples were 
