Sediment resuspension and transport patterns on a fringing reef flat, Molokai, Hawaii

Abstract

Corals are known to flourish in various turbid environments around the world. The quantitative distinction between clear and turbid water in coral habitats is not well defined nor are the amount of sediment in suspension and rates of sedimentation used to evaluate the condition of reef environments well established. This study of sediment resuspension, transport, and resulting deposition on a fringing reef flat off Molokai, Hawaii, uses a year of time-series data from a small, instrumented tripod. It shows the importance of trade winds and ocean wave heights in controlling the movement of sediment. Sediment is typically resuspended daily and the dominant controls on the magnitude of events (10–25 mg/l) are the trade-wind-generated waves and currents and tidal elevation on the reef flat. The net flux of sediment on this reef is primarily along the reef flat in the direction of the prevailing trade winds (to the west), with a secondary direction of slightly offshore, towards a zone of low coral abundance.