Blue-green algae cover increased considerably at the next two lower 
levels, becoming the dominant biota cover at 2.0 m above MLW (Figs. 13 
and 14). As noted previously, the common blue-green algal species 
observed on the rocks throughout the study were Microcoleus lyngbyaceous, 
Calothrix crustacea, and Anacystis aeruginosa. The combined cover of these 
species was usually dense enough to form a thick "black-colored" band on 
the rocks. The only macroinvertebrates noted at 2.0 m above MLW were the 
barnacles Chthamalus fragilts, but average coverage of this species was 
quite low at this level. 
Chthamalus fragilis density was much greater at 1.5 m above MLW and 
this species was often the only fauna present on the rocks at this level. 
The barnacles were usually coated with blue-green algae which often ob- 
scured them when observed from a distance. Other algae occasionally observed 
at the 1.5-m level were Porphyra sp. and Enteromorpha sp. 
Maximum densities of C. fragilts were observed at 1.0 m above MLW. 
At this level, other species which had been either rare or absent at 
higher levels were also present on the rocks. These included the mussel 
Brachidontes exustus, the oyster Crassostrea virgintca, and the algae 
Ulva sp., Enteromorpha sp., Polystphonta sp., Porphyra sp. and 
Cladophora sp. Only Porphyra sp. reached its maximum cover at this level. 
All other species were more common at lower intertidal levels. Although 
blue-green algae were still present at 1.0-m above MLW, their percent 
cover was considerably reduced as compared with their coverage at higher 
levels. 
Major changes occurred in the sessile community between the 1.0-m 
and 0.5-m levels, primarily due to a change from barnacle to mussel 
dominance. During the earlier stages of jetty community development, 
the 0.5-m rocks were covered by dense mats of B. exustus and numbers of 
C. fragilis were greatly reduced. Although mussel density decreased 
during later years, mussels were still abundant at this level and at MLW. 
Chthamalus fragilts was rare or absent at the 0.5-m level during the first 
sampling period on both jetties, but more numerous later on the bare rock 
space that was opened when mussel density declined. Another barnacle, 
Balanus eburneus, was also present on the rocks at 0.5 m and the oyster 
C. virginica was most common at this level (Figs. 13 and 14). 
The number of sessile species attached to the rocks increased 
substantially at the MLW level (Appendices A-D), although mussels still 
heavily dominated the rocks. When mussel density declined with time, 
algal growth on the rocks increased and generally filled the bare rock 
spaces. Species which reached peak abundance at this level included the 
green algae Ulva sp. and Enteromorpha sp., and the red algae Hypnea 
musctformis, Polysiphonta sp., and Gracilaria folitfera. 
Blue-green algae were least abundant at this level and were rarely 
observed below MLW. Oysters and barnacles were also common at MLW but 
C. fragilis was replaced by Balanus spp., primarily B. eburneus. 
Gradients in the vertical distribution of most species found sub- 
tidally were less pronounced, mostly because there were fewer differences 
in the physical environment between levels of that zone. However, it is 
42 
