Sediment trap height affects mass, particle size, and biogeochemical composition of material collected in an equatorial coral reef.

Abstract

Anthropogenic sedimentation is a major contributor to the worldwide decline in coral cover. Resuspension of benthic material can exacerbate the threat to corals, but evidence of vertical sediment gradients is limited. Here, we installed sediment traps at 10, 20, 30, 40, and 50cm above the substrate at three equatorial reef sites for three months and determined the dry mass, particle size, and biogeochemical composition of the material collected. As the trap mouth height increased from 10 to 50cm, dry mass decreased as sediments became finer, poorer in carbonate, and richer in silicate. Despite among-site differences in collected sediment, this vertical gradient was present in all trap arrays, likely driven by resuspension mechanisms on seabed sediments. These results have implications for coral vertical ecology and underline the importance of standardising sediment collection protocols.