Changes in coral reef community structure along a sediment gradient in Fouha Bay, Guam

Abstract

High sedimentation rates have well-documented, deleterious impacts on coral reefs. However, few previous studies have attempted to quantitatively describe a coral reef community across a large continuous sediment gradient. In this study distinct benthic assemblages in Fouha Bay, Guam, were identified using a Moving Window Analysis conducted along a two-order of magnitude sediment gradient, with transition boundaries that were generally consistent with sediment thresholds identified in the literature. Coral richness dropped exponentially with increasing sedimentation rate. Richness was nearly three times greater in assemblages with sedimentation rates <10 mg cm−2 d−1 compared to assemblages experiencing rates between 10 and 50 mg cm−2 d−1, and nearly 30 times greater than assemblages experiencing rates between 50 and 100 mg cm−2 d−1. No corals were found in assemblages with sedimentation rates >110 mg cm−2 d−1. Reducing sedimentation in this area could result in a shift of more diverse and abundant coral assemblages toward the head of the bay.