Algal Cup Reefs
The highest portion of the cup reef is a protruding overhanging lip which extends into either the high subtidal zone of the intertidal zone. It is the most actively growing zone and builds both laterally and vertically. This peripheral lip may extend completely around the central depression or may only be found on one side. If restricted to the one side, it is usually the seaward one. The lip varies from a well defined rim 15-100 cm in width on the nearshore reefs to an indefinite ledge on the offshore reefs. The latter type of lip slopes downward and inward to merge with the central depression. The actively growing lip is composed of vermetid gastropods, red coralline algae, hydrozoan and foraminifera. It is often bored and drilled by echinoderms and bivalves. The actions of these burrowing and boring organisms, together with hydraulic mining, often causes areas of the lip to weaken and blocks to collapse and drop to the bottom. This leaves gaps or irregularities in the lips of many "boilers".
Here we can see a view of the South Shore "Boilers" These cup reefs occur close to the shore at Warwick Long Beach, they occur from a few meters from shore to a thousand meters from shore, but can be easily be reached by swimming from the beach.