together (Group 1) and were relatively dissimilar to those obtained in 
later years. For the most part, 1980 samples were also relatively similar 
to one another (Group 2) and relatively dissimilar to the other groups. 
Collections from 1981 and 1982 formed Group 3, indicating higher 
similarity of faunal composition during these later years as compared 
with earlier years. This suggests that the initial changes in the 
motile community were more significant than those in later years. 
Differences in faunal similarity on wave-exposed versus protected sides 
were not pronounced. 
(b). South Jetty 
Four species of amphipods were the only abundant 
motile fauna on the south jetty during the spring of 1980, shortly 
after construction was completed. These amphipods were generally 
restricted to MLW and below (Fig. 20), and their densities were greater 
than those for other species during any sampling period, with the excep- 
tion of Paradella quadripunetata (Fig. 19). Dense mats of the hydroid 
Tubularia crocea occurred during this season (Appendices C and D), 
supporting very high densities of the caprellids C. penantis and C. 
equtlibra, and the tubicolous gammarids Jassa falcata and Corophium sp. 
Bynum (1978) also noted an association between this hydroid and C. 
penantis in North Carolina waters. Other species found during the spring 
were very low in abundance (Fig. 19). 
By the following summer, all of the initially dominant species had 
declined considerably, in number, and only C. penantits remained at 
moderate densities. Most of the other species collected during this season 
were rare, and only 10 of the 23 dominant species were present. Much of 
this decline may be attributed to decreased coverage by 7. crocea, which 
was present only when water temperatures were low. Differences in the 
relative abundance of motile species were also noted between the north 
and south jetties during this season (Figs. 18 and 19). 
Dominance continued to change during the fall and winter seasons, with 
P. quadrtpunetata being most abundant during the fall and J. falcata 
dominating during winter. Astyris lunata was also relatively common during 
both seasons, as were a number of amphipod species. Many of these seasonal 
changes are attributable to the reproductive periodicities of the motile 
species, and to changes in dominance of sessile taxa (Figs. 9 and 11). 
During the last two years, the high intertidal isopod P. quadrtpunctata 
was the most abundant species (Figs. 19 and 20), and it was frequently 
observed in the empty tests of the barnacle C. fragilis. Shoaling had 
occurred around the south jetty by this time, resulting in the loss of 
most lower sampling levels. As a consequence, the decreased abundance of 
the other dominants (generally most common subtidally) was probably not 
strictly a function of temporal change, but largely reflected this 
intertidal sampling bias. 
The poor representation of subtidal levels on the south jetty also 
obscured the interpretation of cluster analysis of the suction data from 
55 
