The first appearance of the three portunid crabs appeared to be linked to 
water temperatures rising above 16° Celsius; however, the numbers varied 
widely throughout the year (Fig. 17). The cause of this variation was not 
clear. Certainly some variation was related to difficult collecting conditions 
(in turbid waters the crabs are difficult to see), but steepness of the beach 
slope, grain size, food availability, predation, and current velocity are also 
possible controlling factors. 
—Ocypode 
—-——Ovalipes 
----Arenaeus 
sss) Nourishment 
Period 
Number Per km 
JF MA M JJ AS ON DJS FMAM JS JA 
OOSNGOOORONOOOUONOOOOORNNOGOOENOOOO0NNOOCRNOD 
Month 
Figure 17. Densities of A. ertbrartus, 0. ocellatus, and 0. quadrata in 
the surf zone at Fort Macon, January 1977 to August 1978. 
The slashed line below the X-axis represents the actual 
duration of the nourishment. 
Regardless of what factors normally control the densities of these three 
species of surf zone consumers (0. ocellatus, A. ertbrarius, and C. saptdus), 
the nourishment at Fort Macon severely reduced their abundance. Collections 
during nourishment were more difficult due to increased turbidity and greater 
beach slope and could have prevented detection of some crabs. However, poor 
collecting conditions are not believed to fully explain the low numbers observed 
because, even after nourishment had ceased and collecting conditions had 
improved, the number of crabs present remained markedly lower compared to den- 
sities recorded before nourishment. Several explanations for the reduced 
numbers of crabs in the surf zone are possible: 
3| 
