Weinstein et al. 2019

scientific chapter |


Weinstein DK, Maher RL, Correa AMS


The study of bioerosion, a widespread process greatly impacting reef biodiversity, structural complexity, and sediment production, has largely focused on shallow-water reefs with no review of this process in deeper environments. In this first synthesis of bioerosion literature for mesophotic reefs (subtropical and tropical ecosystems in low-light conditions at depths of ~30 to 150 m), we show that the distribution of key bioeroder taxa, their abundances, and overall bioerosion rates are considerably different on mesophotic reefs compared to their shallow-water counterparts. In particular, carbonate grazing and phototrophic microboring rates decline with depth from shallow to mesophotic reefs. In the absence of significant erosive action by grazers, sponges are hypothesized as the primary long-term bioeroders on lower mesophotic reefs (60–150 m) and possibly on some upper mesophotic reefs (30–60 m). Given these factors, we postulate that mesophotic reef substrates experience slower bioerosion rates and lose less carbonate than shallower reefs over the same timeframe. This likely stems from differences in photo-synthetically active radiation and other factors such as temperature, sedimentation, bioeroder food abundance and quality, substrate characteristics, and exposure time for bioerosion. There is a critical need to document mesophotic bioeroders via taxonomic inventories, as well as quantify their bioerosion rates across mesophotic depths in terms of specific bioeroder guilds using experimental substrates. These data will aid management efforts to maintain positive net carbonate budgets on mesophotic reefs, ensuring that sufficient three-dimensional structure is available to support biodiversity at mesophotic depths.