Reef to island sediment connections within an inshore turbid reef island system of the eastern Indian Ocean

Abstract

Reef islands are low-lying sedimentary landforms formed from the accumulation of unconsolidated skeletal material generated by carbonate-producing reef organisms. The coupling between ecological (extant community assemblage) and sedimentary processes (sediment composition and supply) that maintain these reef-fronted landforms make them increasingly sensitive to the impacts of future environmental change. To understand this interconnection we examine the benthic reef community assemblage and sediment characteristics (composition and texture) at Eva Island, an inshore turbid reef island system located in the Pilbara region of Western Australia. Benthic surveys and sediment composition identified molluscs as a unique primary sand-sized sediment constituent (34% of reef and sediments, respectively), alongside coral, despite low mollusc abundance in the reef ecology (n = 94 extant individuals). This result, alongside homogeneity within reef and island biosedimentary facies, suggest a coupling between source (reef) and sink (island) environments may exist, with the sediment reservoir providing suitable sand-grade material for island nourishment. In light of these findings, assuming island building can keep up with rising sea levels, Eva may be resilient to the immediate impacts of climate change. However, dependency on a few primary sediment constituents (molluscs and coral that are sensitive to environmental perturbations) may compromise long-term resilience (over decades), particularly the direct effect on sediment producing habitats and sensitive calcifying organisms under future changing climatic conditions.