The results of this study indicate that there is no effective competition 
between E. talpotda and Donax spp. There is no competition among other 
organisms of the beach macrofauna because all are filling different resource 
niches, except the amphipods who fill different spatial niches. Leber (1977) 
theorized that the large populations of #. talpotda competitively excluded the 
Donax spp. from the swash zone by their large numbers and superior swimming 
ability. He concluded that as £. talpotda populations grew in late summer, 
D. vartabtlis compensated by remaining stranded at the higher tidal levels by 
the receding tide, while D. parvula compensated by leaving the intertidal zone 
until the following spring. This migration pattern was not noted by Matta 
(1977) or in the present study. Thus, it would appear that interspecific 
competition is not the controlling factor in mediating the coexistence of 
these three species. 
This leaves two possible mediators to explain why one of these three species 
has not completely overridden the other two. The extreme physical variation 
in the intertidal zone makes the high-energy sandy beach a perfect example of 
Sanders' (1968) physically controlled community. Such a community is typified 
by low species diversity. Physical stress is likely to be a factor in species 
coexistence when severe weather conditions or major perturbations such as beach 
nourishment deplete the breeding stock to the extent that not enough young of 
the year are produced to fill the spatial or resource niche. Physically medi- 
ated coexistence is unlikely to be of major significance on the beaches studied 
here because of the low frequency of major perturbations. 
d. Predation. A much more likely explanation for coexistence among the 
macrofaunal species is predator mediation; i.e., predators utilizing this 
community are responsible for structuring it. The predators in this case were 
migrating consumers from supralittoral and sublittoral sources. This type of 
mediation was first theorized by Darwin (1859) and has been postulated for 
many systems since then. Wolcott (1978) postulated that ghost crabs are 
responsible for cropping most of the secondary production of #. talpotda and 
Donax spp. Thus, he believes that ghost crabs are the primary structuring 
force in the intertidal community. 
Wolcott (1978) arrived at his conclusion largely by calculation rather than 
by measurement. He failed to consider predation by subtidal consumers. Leber 
(1977) found subtidal portunid crab densities to be of the same order of magni- 
tude as Ocypode at Emerald Isle, Anderson, et al. (1977) reported that one 
subtidal crab A. ertbrartus, also Leber's most important species, was the 
second most important species by weight in the surf zone of Folly Beach, South 
Carolina. Night surveys of the surf zone during this study always turned up 
large numbers of fish feeding on FE, talpotda and Donax spp. Another factor 
Wolcott failed to consider was that while ghost crabs can only feed on £. 
talpotda and Donax spp. during summer when they are on the beach, subtidal 
fishes and crabs feed on them during the summer, by migrating to the surf and 
swash zones, and also feed on them in the winter while they are located 
offshore. 
Several models for predator-mediated coexistence have been postulated; 
however, most fall short of their goal of explaining natural systems by 
assuming them to be closed (cells) or by solving for the equilibrium state, 
which has a low probability of occurring (Caswell, 1978). Gurney and Nisbet 
(1978) proposed a model for predator-prey fluctuations in patchy environments. 
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