During the summer of 1980, the mussel Brachidontes exustus covered 
more than 50% of the subtidal rock space at station SPO, whereas the 
bryozoan Bugula neritina and the red algae Lomentaria batleyana were 
more prevalent at station SPI (Appendix C). These differences probably 
reflect the different duration of rock submergence at these sites as 
noted for the north jetty stations. Other fauna commonly found in the 
subtidal zone during this season included the polychaetes Sabellarta 
vulgarts and Hydrotdes sp. (mostly H. dtanthus), the ascidians Molgula 
manhattensts and Perophora virtdis, the barnacles Balanus spp., and the 
encrusting bryozoans Schtzoporella errata and Membrantpora tenuts 
(Tables 6 and 7). 
Mussels continued to dominate the subtidal rocks at SPO for the 
remainder of the study, generally covering more than 70% of the rocks. 
At SPI, on the other hand, ascidians, serpulid polychaetes, and hydroids 
formed the dominant biota cover (Appendices C and D). With few exceptions, 
the subtidal community composition at both south jetty stations was not 
very similar to equivalent areas on the north jetty during the same 
sampling periods, or after equivalent periods of rock submergence. This 
was particularly evident for the algal component, which dominanted biota 
cover on the north jetty rocks during 1981 and 1982, but not on the south 
jetty where algae were rarely observed. 
Cluster analysis of south jetty data confirms that some seasonal and 
yearly changes occurred in the jetty community composition (Fig. 12), but 
the differences are not as clear as those noted on the north jetty. 
Stations sampled during the first season (Group 1) had relatively dissimilar 
faunal and floral composition to all other station collections. As noted 
previously, biota cover on the rocks at this time was relatively 
depauperate, thus accounting for this separation of collections, Station 
groupings from most later collections did not indicate any distinct 
seasonal separation (Groups 2-4), but it is interesting to note that 
within those groups, collections from the protected side often grouped 
separately from collections on the exposed side. This is most probably due 
to the presence of subtidal fauna and flora at the protected sites as 
compared with the exposed side where waters were too shallow to sample 
subtidally. 
(3). Vertical Zonation Patterns 
Obvious gradients were observed in the vertical 
distribution of most species found on the north and south jetties (Figs. 
13 and 14). These distribution patterns were generally similar over the 
entire study period, with only minor differences noted between sides 
(Appendices A-D). 
Rocks at 2.5 m above MLW were usually devoid of any biota since this 
level was well above the mean high water mark. Only occasional small 
patches of blue-green algae were noted. These patches were probably 
established during periods of heavy wave swell (e.g. storms), but they 
appeared to be short lived based on observations during subsequent 
sampling periods. 
38 
