Sediment fluxes on turbid coral reefs are modulated by monsoon variability in equatorial Southeast Asia

Turbid coral reefs experience high sedimentation and rapid light attenuation. However, local environmental conditions vary considerably across time and space influencing benthic reef communities and their depth distributions. Sediment fluxes and the hydrodynamic drivers of turbidity on reefs remain poorly quantified despite their control on coral ecology. Field measurements are required to assess long-term water quality change and the environmental thresholds of turbid coral communities. Here, we present a one-year time series of sediment flux and hydrodynamic conditions on turbid reefs in Singapore. Our results show strong seasonality in turbidity related to synoptic forcing, with peaks occuring during the Southwest Monsoon, and gross sedimentation rates ranging from 9.8 to 39.6 mg cm^-2 d^-1. Elevated turbidity was associated with increased siliciclastic silt inputs, which decreased during the subsequent inter-monsoon period. This transition was accompanied by reduced current velocities and the deposition of finer silt particles on reefs. Heterogeneity in sediment stress was observed to have a strong influence on coral cover across reefs. Our findings show the dynamic nature of equatorial turbid reefs over scales of hours to weeks, where corals must tolerate substantial fluctuations in turbidity and sedimentation. Field measurements demonstrate the complexities of defining quantitative thresholds for nearshore environments and highlight the need for expanded geographic datasets to improve our understanding of reef habitats under terrestrial influence.