Coral reef erosion: In situ measurement on different dead coral substrates on a Caribbean reef

Abstract

AbstractWidespread mortality of reef‐building coral substantially reduces the capacity for reef growth and makes available extensive bare substrate areas that in the absence of coral recovery will be eroded by a variety of external and internal bioeroders. Here, we analyze rates of external erosion on six different types of carbonate substrates under in situ conditions over a 2‐yr period. We measure vertical changes in the surface elevation of four species of recently dead corals afflicted by the stony coral tissue loss disease outbreak, and other two common types of calcareous substrates, long‐dead Acropora palmata fronds and bare calcareous hardground, as a reference for “bare” carbonate substrates that occur widely in Caribbean reefs. The surface of the recently dead colonies experienced significant erosion after 2 yr of exposure, but at different rates depending on the species. Dead skeletons of Orbicella faveolata experienced the greatest rates of erosion after 2 yr at −9.9 mm (±3.2 mm); Dendrogyra cylindrus eroded −3.6 mm (±2.8 mm), Pseudodiploria strigosa −3.3 mm (±3.7 mm), and Siderastrea siderea −1.2 mm (±0.9 mm), while long‐dead substrates remained unchanged. There was significant erosion in the presence of parrotfish grazing scars and of short algal turf mats, while crustose coralline algae cover and sand‐and‐high turf mats were not associated with significant changes in elevation, arguably indicating a protective effect. This study provides new insights into how and at what rates external carbonate erosion is shaping contemporary reefs at fine spatial and temporal scales.