Castle Harbour Nearshore

In the southwest corner of Castle Harbour, at Wallers Bay, is a typical nearshore environment. In water over a meter deep, the sediments are relatively clean skeletal sands with numerous shrubs of Halimeda, Penicillus, and Udotea. Much of the sediment is burrowed by Calianassa and large areas are covered with Thalassia grass. Inshore, below the rock cliffs, the sand is more open and not grass covered.

Growing on the rocks and often rolling loose in the sediments at certain times of year are brown algal sea biscuits. These small laminatd algal hemispheres are formed primarily by the alga Phormidium hendersonii.