(1977) contention that a stable "climax" community of sessile invertebrates 
is not likely to occur. 
b. Motile Epifauna 
Ranked abundance estimates for all motile macroinvertebrates are 
provided in Appendix F for the four north-jetty sites and in Appendix G 
for the four south-jetty sites. 
(1). Total Abundance and Number of Taxa 
Slurp gun sampling at intertidal and subtidal levels of both 
jetties resulted in the collection of 131 species over the four-year period. 
Amphipods, polychaetes and molluscs represented over 70% of all species 
found on the north-jetty rocks (Table 8). Amphipods alone dominated the 
motile epifauna on the south jetty, representing approximately 40% of all 
such species collected. On both jetties, motile biota rapidly colonized 
the rocks, with densities generally as high in the first sampling period 
as in subsequent sampling periods (Appendix H). Amphipods and isopods 
were the two most numerically abundant taxa on both jetties even though 
only a few isopod species were represented. Over all levels, 11 major 
taxonomic groups were found on the north jetty and 10 on the south jetty 
(Table 8). 
Both the number of species and the abundance of motile fauna were 
inversely correlated with tidal elevation at north- and south-jetty stations 
(Figs. 15 and 16). The increase in species richness and abundance at 
the lower levels is related to the increased structural complexity of the 
sessile community at those levels. Dean (1981) found a similar relation- 
ship between structural complexity and the number of motile species on a 
fouling community in North Carolina. Increased environmental stresses 
probably also played an important role in limiting the motile epifauna 
at the upper levels (Connell, 1972). 
Estimates of species diversity (Appendix H) for the epifaunal 
assemblages on both jetties paralleled the patterns noted for species 
number and abundance. However, no discernible trends were observed in 
these parameters that could be attributed to the effects of differing 
degrees of exposure (protected versus exposed) or duration of submergence 
(inner versus outer) of the jetty rocks (Figs. 15 and 16). 
(2). Community Composition and Vertical Distribution 
Twenty-three species accounted for approximately 90% of 
the 7,209 animals collected in suction samples. The remaining 10% (806 
animals) were distributed among 108 other species. Thirteen of the 23 
numerically dominant species were amphipods, four were isopods, three 
were molluscs, and three represented other taxa (Fig. 17). With few 
exceptions, mean densities of these species were greater on the north 
versus south jetty. This is most likely due to the greater representation 
of subtidal levels at north-jetty stations, where most of these species 
were more prevalent. Temporal variations were also observed in the abun- 
dance of these species on both the north and south jetties (Figs. 18 and 19). 
45 
