Algal Cup Reefs

The Base

Scoured: Cup reefs exhibiting this characteristic have a slightly flared base. This flared base may be readily apparent or may be hidden beneath a thin sediment cover. With the exception of a smooth coralline algal veneer, it is devoid of encrustation. The sand size around this scoured base ranges from 0.5 to 2.0 millimeters and may even exhibit coarser bioclastic components. The walls and bases of cup reefs farther from shore do not overhang to the same extent as those closer to shore. This may be a response to either active undercutting or the ability of more mobile nearshore sand to nullify construction by coralline algae.

Coral Encrusted: This second type of base is associated with the offshore boiler rows where coral reef flats have developed. Coral encroaches upon the base and walls of the cup reefs. The algal-vermetid association is established in the high energy zones along the shore. Hence, it has the initial growth advantage over coral which must wait for a suitable low energy environment for them to compete with the already established cup reefs. The coral buildup of the base is aided in another way. Blocks broken from the upper part of the cup reef provide fresh surfaces for coral planulae and other organisms to colonize. This type of base is most commonly found on the larger offshore cup reefs.