Geo‐ecological functions provided by coral reef fishes vary among regions and impact reef carbonate cycling regimes

Abstract

AbstractCoral reef fishes perform essential and well‐documented ecological functions on reefs, but also contribute important geo‐ecological functions, which influence reef carbonate cycling regimes. These functions include reef framework modification (through bioerosion and breakage), and the production, reworking, and transport of reefal sediments. To explore how these functions vary across reefs and regions, we compiled a dataset of available taxa‐specific function rates and applied these to fish census data from sites in the Pacific Ocean (PO), Indian Ocean (IO), and Greater Caribbean (GC), each region displaying a gradient in fish biomass. The highest overall function rates occur at the highest fish biomass sites in the PO (Kingman Reef) and IO (Chagos Archipelago), where bioerosion dominates framework modification and sediment generation (up to 7 kg m−2 year−1). At the lowest biomass PO and IO sites, framework modification and sediment generation are driven mainly by breakage and occur at lower rates (~2 kg m−2 year−1). Sediment reworking rates are high across all PO and IO sites (~1–5 kg m−2 year−1) and higher than other function rates at low biomass sites. Geo‐ecological function rates are generally low across the GC sites, despite total fish biomass being comparable to, or even exceeding, some PO and IO sites, with sediment reworking (up to ~1 kg m−2 year−1) being the dominant function. These site‐level differences partly reflect total fish biomass, but fish assemblage size structure and species identity are critical, with a few fish families (and species) underpinning the highest function rates and regulating the “health” of the fish‐driven carbonate cycling regime. Reefs with high fish‐driven framework modification, sediment production and reworking rates define one end of this spectrum, while at lower biomass sites little new sediment is produced and sediment reworking dominates. While additional species‐level rate data are urgently needed to better constrain function rates, these transitions align with ideas about the progressive shutdown of carbonate production regimes on ecologically perturbed reefs, with important implications for reef‐building, shoreline sediment supply, and sediment carbon and nutrient cycling.