Composition and temporal stability of turf sediments on inner-shelf coral reefs

• EAM sediment loads were sampled from algal turfs on inner-shelf coral reefs.
• Sampling was repeated over a 6-month period including a wet season and a cyclone.
• Sediment loads varied among reef zones but were consistent between bays.
• Sediment loads were consistent for 6-months, even with flooding and a cyclone.
• Benthic sediments change slowly, but changes may have long-term impacts.

Elevated sediment loads within the epilithic algal matrix (EAM) of coral reefs can increase coral mortality and inhibit herbivory. Yet the composition, distribution and temporal variability of EAM sediment loads are poorly known, especially on inshore reefs. This study quantified EAM sediment loads (including organic particulates) and algal length across the reef profile of two bays at Orpheus Island (inner-shelf Great Barrier Reef) over a six month period. We examined the total sediment mass, organic load, carbonate and silicate content, and the particle sizes of EAM sediments. Throughout the study period, all EAM sediment variables exhibited marked variation among reef zones. However, EAM sediment loads and algal length were consistent between bays and over time, despite major seasonal variation in climate including a severe tropical cyclone. This study provides a comprehensive description of EAM sediments on inshore reefs and highlights the exceptional temporal stability of EAM sediments on coral reefs.