Beach Cusps and Burrowing Activity of Crabs on a Fine-Grained Sandy Beach, Southeastern Nigeria
The significance of morphological features have usually been under-emphasized in ecological studies of sandy beaches. One consequence of the latter is the widely-held view that organisms inhabiting beach ecosystems depict an unpredictable longshore distribution pattern. The above is refuted in this present study of burrow density of crab species (Ocypoda africana and Ocypoda cursor) encountered on cusps along a fine-grained, mesotidal, sandy beach fringing the southeastern coast of Nigeria. Generally, higher burrow densities were observed on transects along cusp horns compared with those of the adjacent bays. In contrast with the cusped foreshore segments, burrow densities on adjacent non-cusped segments were devoid of any predictable pattern. Averages of the mean values of burrow diameter and depth were relatively higher on cusp horn compared with cusp bay. Elevated values of depth-diameter ratio were also evident on the former. The lower burrow depth on bay is related to the moisture needs of the organisms and is a function of the water table. Cusp topography dictates that the latter would be closer to the surface on bays than on horns. The above results elucidate the essence for in-depth evaluation of morphologic characteristics in the course of ecologic studies of beaches.