Grainsize, composition and bedform patterns in a fringing reef system

Predicting future changes to coastlines fringed by coral reefs requires quantifying sediment budgets in these environments. To do this we must understand the physical parameters and biological composition of sediment deposits; the ecology of the calcifying (production) community; and the dominant sediment transport mechanisms. This study collected sedimentological, biological and hydrodynamic measurements at a section of a major fringing reef system along Australia's northwest coast, Ningaloo Reef. Sediment in the system is predominantly medium, moderately sorted, coarse skewed sand. Coral fragments are the dominant sediment constituent, however, live coral accounts for less than 5% of the calcifying community. Wave-driven shear stresses are ~5 N/m2 and oriented perpendicular to lagoonal sand ripples; current-driven shear stresses are ~0.5 N/m2 and oriented parallel to ripple crests. It is suggested here that wavedriven transport is the principle mechanism for supplying sediment to the system and driving ripple migration shoreward through the lagoon.