Patterns of coral reef development on Tarawa Atoll (Kiribati)
Abstract:Tarawa Atoll lies in the equatorial upwelling region, has the largest human population of any Pacific atoll, and has an unusual, asymmetrical form: the triangular lagoon is largely enclosed along the east and south, but communicates with the ocean through a submerged barrier reef along its entire western border. How do these unusual characteristics affect reefs? After characterizing lagoonal reefs, the interactions and influence of various physical and biotic factors are examined. Coral cover and diversity increase from northwest to southeast as a consequence of polarized exchange with the surrounding ocean. Macroalgae are abundant in the central lagoon, probably as a result of high productivity and low levels of herbivory, the latter a likely consequence of overfishing. Coral communities of these central reefs are dominated by clonal, fragmenting species of encrusting Montipora and branching Acropora. A substantial loss of coral cover and diversity occurred in the southeastern lagoon apparently a few hundred years ago. As a consequence of this mortality, much of the reef habitat and associated communities of the southeastern lagoon were lost, and patch reefs in the area developed into sand-dominated shoals by intense bioerosion and burial. The high productivity of the region has also resulted in high rates of mobile sediment production through bioerosion and the accumulation of skeletal remains of a rich suspension and deposit feeding lagoonal biota. The productivity and sediment production in turn had major geomorphological consequences, creating an atoll with an unusually wide, sand-dominated rim and shallow, sedimentchoked lagoon, and may have been partly responsible for the submergent nature of the western barrier reef through the impact of inimical lagoonal backwaters.
Document Type: Research Article
Publication date: November 1, 2001
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