Quantifying reef-derived sediment generation: Introducing the SedBudget methodology to support tropical coastline and island vulnerability studies

Abstract

Standardised methodologies for assessing reef-derived sediment generation rates do not presently exist. This represents a major knowledge gap relevant to better predicting reef-derived shoreline sediment supply. The census-based SedBudget method introduced here generates estimates of sediment composition and grain-size production as a function of the abundance and productivity of the major sediment-generating taxa at a reef site. Initial application of the method to several reefs in the northern Chagos Archipelago, Indian Ocean, generated total sediment generation estimates ranging from (mean ± SE) 0.7 ± 0.1 to 4.3 ± 1.3 kg CaCO3 m-2 yr-1. Sediment production was dominated by parrotfishes (>90% at most sites), with site-variable secondary contributions from sea urchins (up to 20%), endolithic sponges (~1-7%) and benthic foraminifera (~0.5-3.5%). These taxa-level contributions are predicted to generate sediments that at all sites are coral- (83-94%) and crustose coralline algae-dominated (range ~ 5-12%). Comparisons between these estimates and sedimentary data from proximal reef and island beach samples generally show a high degree of consistency, suggesting promise in the SedBudget approach. We conclude by outlining areas where additional datasets and revised methodologies are most needed to improve rate estimates and hope that the methodology will stimulate research on questions around sediment production, transport and shoreline maintenance.