An examination of the Shannon-Weaver Diversity (Fig. 28) and Pielou's 
Equitability (Fig. 29) Indexes for both beaches indicated that the most diverse 
community present was that of the Fort Macon beach before nourishment. When 
the maximum possible diversity or species richness (Fig. 30) is considered, it 
can be seen that the reason for this was the high species number associated 
with the Fort Macon beach. The dominance criterion (Fig. 31) is less affected 
by species number and indicates that the before nourishment beach at Fort 
Macon closely resembled the Emerald Isle beach. 
The effects of nourishment are evident in all the community measures. 
There was a decrease in diversity to near zero when nourishment began, and 
this situation continued throughout the study. At one point in March no orga- 
nisms were found, and all measures of community structure were therefore 
undefined. On two separate occasions (in June and July), only F. talpotda 
were found on the beach; thus diversity was 0.00 and dominance was complete 
(1.00). The species richness value dwindled because the total number of 
species decreased to one or two at the Fort Macon beach during nourishment. 
b. Community Functional Relationships. Community organization has two 
components: structural and functional. Structural properties are easily seen 
and measured, whereas functional properties cannot be as easily discerned. The 
mathematical relationships of diversity, equitability, etc. generally describe 
the structural aspects of a community. Examples of the functional relation- 
ships of a community can often be represented qualitatively in trophic level 
or energy flow diagrams (see App., Figs. A-l, A-2, and A-3); however, the 
quantification of such models is time consuming, costly, and often unmanageable. 
For this reason most environmental assessments contain the purely structural 
measurements of a community. 
Deevy (1969) suggested that species diversity (a measure of the structure 
of a community) is related in an unclear, complex way to the functional rela- 
tionships within a community. Peterson (1977) suggested that in order to 
explore the relationship between structure and function, the behavior of the 
species diversity function in "neutral communities" should first be examined. 
Caswell (1976) defined a "neutral community" as a community in which there are 
no species interactions and, thus, structural representations of the community 
very closely reflect functional relationships. 
c. Competition. The intertidal sandy beach macrobenthic community is 
probably a good example of a neutral community. There is no predation from 
within, and there does not appear to be resource or space competition. Thus, 
according to Peterson's (1977) model for predicting the possible effect of a 
perturbation, if the probability of each species being affected is equal (which 
it was for beach nourishment) and the proportion of reduction due to the stress 
for each species is the same (which it was, because all species were removed 
from the nourished zone), species diversity will decrease due to the pertur-— 
bation without any one species having an advantage. Because the high-energy 
psammolittoral community represented a basically "neutral community," species 
diversity did decrease and no single species garnered an advantage. 
The rapid recovery of £. talpotda populations was due to the chance finish 
of nourishment activities just as the main cohort of £. talpotda larvae began 
to arrive. The Donax spp. were probably no more disadvantaged by nourishment 
than the &. talpotda, but because their larvae arrived while nourishment was 
still underway and turbidity high, they were unable to become established. 
23 
