The groove and spur structures of Chagos Atolls and their coral zonation
- The groove and spur formations of two atolls of the Chagos Archipelago, Indian Ocean are described and the coral zonations on and immediately to seaward of them outlined. A gradation of spur and algal ridge structures are traced, from very rudimentary calcareous spurs in one lagoon through to full development of 75 m long spurs integral with a broad, high ridge on some seaward reefs. Spurs may exist without a ridge in areas of low wave energy, while a ridge never existed without spurs. Unusual structures existed in a lagoon pass where two superimposed sets of grooves and spurs intersect at right angles, and on seaward shores that lack a reef flat. The corals from low water to _ 5 m are zoned in relation to depth and distance from the algal ridge. On seaward reefs two categories of coral community exist; one dominated by encrusting Acropora palifera and one that almost entirely lacks this species. The former are the most common, and have a coral cover of 50% or more. A. palifera-absent communities occur on the longest and most exposed spurs only and have a coral cover of 5_10%. Other species occur in approximately the same order in both cases, though in different proportions, and at least five species are characteristic of this turbulent area.
- Sheppard Charles .
- marine algae, spurs, calcareous sediments, algae, coral atolls, zonation, coral reefs