430 
PACIFIC SCIENCE, VoL XVII, October 1963 
that while the number of numerable (non- 
colonial) species per quadrat dropped about 
25% during the decline, the total of individuals 
persisted unchanged for many months. But, as 
can be seen, by the beginning of the postdecline 
the total number of individuals in the numerable 
species fell markedly, in spite of the marked 
increase in numbers of species per quadrat. We 
find part of the explanation of this in the fact 
that when Mytilus was at its peak there was an 
average of 31 individuals per numerable species 
(aside from Mytilus) on each quadrat; that 
during the decline this jumped to 41, and then 
dropped to 12 in the early postdecline. These 
phenomena are based upon the following oc- 
currences: (1) the rapid population increases 
of a few such species as Nereis grubei, Balanus 
tintinnabulum, and Ophiactis simplex; while 
(2) other species were leaving the sites; (3) 
formerly absent species, principally motile ones 
(Table 2), invaded the sites, resulting in an 
increase of 30% over the original number of 
species; (4) those species that underwent rapid 
population increases overshot the mark and 
dropped back; and (5) all of the invading 
species, at least during the period of this study, 
were represented by a small number of indi- 
viduals. It is of interest that no single animal 
species equalled the former population density 
of Mytilus . Balanus came closest, but it is only 
a fraction the size of the mussel. This indicates 
that the animal contribution to the total biomass 
in the Hyperbenthal Zone (Pequegnat, 1961) 
was markedly reduced; the emigrations of the 
echinoderms mentioned above also account for 
a considerable loss. Reciprocally, the plant com- 
ponent must have risen through the Corallina 
increase. 
For several reasons the appearance of the 
Corallina mat and associated species appears to 
comprise an unstable complex. Judging from the 
population changes discussed above and from 
observations made elsewhere in the subtidal and 
intertidal, one gains the impression that ex- 
tremely dense growths of Corallina are asso- 
ciated with disturbed conditions. Though one 
might expect this predominance of the corallines 
to be temporary, Dawson (1959) points to the 
distinct possibility that the corallines encroach 
upon and later dominate areas subject to pol- 
lution from human wastes. Hence interest is 
heightened in obtaining additional samples in 
the future. 
REFERENCES 
Dawson, E, Yale. 1959. A Primary Report 
on the Benthic Marine Flora of Southern 
California. Oceanogr. Survey of the Continen- 
tal Shelf Area of S. Calif. Publ. No. 20. State 
Water Pollution Control Board. Sacramento, 
California. 
Gorsline, Donn S. 1962. Personal communi- 
cation. 
HARTMAN, 0. 1944. Polychaetous annelids. Rep. 
Allan Hancock Pacif. Exped. 3:1-33. 
1950. Goniadidae, Glyceridae, Nephyti- 
dae. Rep. Allan Hancock Pacif. Exped. 15: 
1-181. 
— 1951. The littoral marine annelids of 
the Gulf of Mexico. Publ. Inst. Mar. Sci., 
Univ. Texas 2:7-124. 
Pequegnat, Willis E. 1961. New world for 
marine biologists. Nat. Hist. 70(4). 
