http://www.vifishandwildlife.com/Education/NaturalHistoryGuide/PDF/MarineEcosystems.pdf
"SAND HALO:
At the edge of most coral reefs in the Caribbean, there is a narrow band of coarse-grained carbonate sand, conspicuous in its absence of algae and sea grasses, which occur immediately adjacent to it. Scientists have attributed its presence to several phenomenon including the grazing activities of parrot fishes and the sea urchin, Diadema antillarum, and of refraction of wave energy during the times of high swells. This band is generally sparsely covered, although its coverage by the bluegreen algae, Schizothrix sp., during prolonged periods of calm weather has been observed. The spermatophyte Halophila baillonis frequently serves as a transitional species on the seaward borders of the halo and the offshore algal plain or grass flats. Scattered algae (Halimeda, Caulerpa) are occasionally present. The ichthyofauna is generally limited to several blennies and gobies, jawfishes, and the sand tilefish Malacanthus plumieri. Invertebrates are present as infauna and are generally limited to tube worms and burrowing molluscs."
