important to note that many of the taxa observed at subtidal levels, such 
as hydroids, bryozoans and ascidians, were present in only that zone. This 
is due, in part, to their inability to tolerate desiccation and other 
stresses present in the intertidal zone. In the first year, B. exustus 
was extremely abundant on the subtidal rocks, particularly at the outer 
stations which had been submerged for the least period of time. As noted 
previously, when mussel density declined, algae, ascidians, bryozoans 
and hydroids became more prominent on the rocks at both levels. Generally, 
green algae were more prevalent at the shallower depths where better light 
penetration occurred (Fig. 13). Red algae species were also common at 
that level and at the -2-m level where green algae were rarely observed. 
Most hydroid, bryozoan, and ascidian species were also slightly more common 
at the -2-m level where algae cover on the rocks was not as dense. Some 
exceptions to this trend were the hydroids Obelta gentculata and 0. 
dichotoma, which were most often observed growing on the red algae 
G. folttfera and R. pseudopalmata. On the channel side of the rocks, light 
penetration was generally lower and algae were not as abundant. As a result, 
hydroids, bryozoans, and ascidians were more common at shallower depths 
on that side than the wave-exposed side (Appendices A-D). 
(4). General Discussion 
Community composition and patterns of vertical zonation 
resembled those described from the jetties at Charleston, South Carolina, 
by Stephenson and Stephenson (1952, 1972). They reported finding the 
barnacle Chthamalus fragilts in the black band of blue-green algae and 
lichens marking the splash zone (supralittoral fringe). Peak abundances 
of this barnacle were found high in the intertidal zone. Mussels 
(Brachidontes exustus), reported in "colossal quantities," oysters 
(Crassostrea virgintea), and balanid barnacles (Balanus eburneus, B. 
improvisus) were the dominant invertebrates in the middle and lower 
intertidal zones. Although mussels and balanid barnacles were also 
abundant near MLW on the Murrells Inlet jetties, oysters were not always 
common. Other invertebrates reported near MLW on the Charleston jetties 
included the gastropod Urosalpinx cinerea, the scleractinian coral 
Oculina arbuscula, the ascidian Molgula manhattensis, the asteroid 
Asterias forbesti, the echinoid Arbacia punctulata, the hydroid Tubularia 
crocea, the bryozoans Angutnella palmata, Electra monostachys, and 
Membrantpora tenuis, the actiniarian Bunodosoma cavernata, and a red sponge 
believed to be Hymentactdon heltophtla. 
Many factors, both biotic and abiotic, influence epifaunal community 
structure and development on rocky shores. Although biotic factors have 
not been ignored, most descriptive investigations have attributed 
distributional patterns largely to abiotic factors such as wave exposure, 
tides, desiccation, climate, temperature, light intensity, width of the 
rocky tract, proximity of sand, and rock composition, texture, and 
configuration (see Stephenson and Stephenson, 1972; Lewis, 1972; Newell, 
1979). Experimental research, beginning with Connell (1961a,b; 1970) 
and including studies such as those of Paine (1966, 1969, 1974), Dayton 
(1971, 1975), Menge (1976), Lubchenco and Menge (1978), and others, has 
emphasized biological interactions such as predation and inter- and 
intra-specific competition in community development and species distribution. 
43 
