The fore-reef buttress zone is composed of broad, terrace-like outgrowths at depths between 12 and 28 m. Coral-dominated buttresses--20 m wide, 50 m long, and less than 10 m vertical relief--are transected by regularly dispersed carbonate-sand channels cut subperpendicular to the strike of the reef slope. The width of the channels ranges from 12 to 20 m.

The construction buttresses are the result of vigorous outgrowth and lateral accretion, and can be divided into two major zones based on the contribution of the corals to the reef framework. In zone 1, water depths range from 12 to 17 m. Acropora cervicornis is dominant, and intergrown colonies exhibit polyp fusion creating a thicket that is an effective stabilizer. An abundance of broken, dead A. cervicornis rubble infills voids between primary hermatypic corals such as Agaricia. Species of A. agaricites are found commonly filling voids in the Acropora cervicornis meshwork. Agaricites colonies range in size from 4 to 30 cm, growing in close nonrandom distribution. This growth pattern reflects a defense mechanism for more aggressive corals, substrate preference (commonly dead Acropora cervicornis), and preference for a shaded environment. Along the steepsided flanks of the buttress A. cervicornis is of limited abundance and Agaricia agaricites is dominant. Interspecific aggression was not observed and it appears that growth of many Agaricites colonies is subsequent to the meshwork of Acropora cervicornis. Water depths in zone 2 range from 18 to 28 m. The predominance of A. cervicornis diminishes with depth and A. cervicornis occurs as loosely aggregated rubble piles and smaller living meshworks adjacent to the buttress. Agaricia lamarki replaces A. agaricites as a dominant primary hermatype. Rapid growth and fusion generally occur on vertical overhangs of the buttress and the change in species reflects diminishing illumination. The ability of broken Acropora cervicorn s to regenerate, and its high growth rate, contribute to lateral outgrowth. Subsequent growth of Agaricia sp. in newly created preferential niches strengthens the buttress.

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