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

Abstract

Coral 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 À2 year À1 ). 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 À2 year À1 ). Sediment reworking rates are high across all PO and IO sites (~1-5 kg m À2 year À1 ) 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 À2 year À1 ) 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

Consumer feces impact coral health in guild-specific ways

“…with corals, some grazer/detritivores (including C. striatus) graze on early successional turf algae and may thereby promote postdisturbance recovery of reefs (Marshell and Mumby, 2012;Tebbett et al, 2017a;Nalley et al, 2022). Additionally, some grazer/detritivores remove sediments from dense late successional algal turf assemblages (Goatley and Bellwood, 2010;Perry et al, 2022). This process may be vital to reef health because sediments in the algal matrix can inhibit coral recruitment (Birrell et al, 2005;Fabricius, 2005).…”

Quantifying reef-derived sediment generation: Introducing the SedBudget methodology to support tropical coastline and island vulnerability studies

“…Species of both pufferfishes and triggerfishes can generate coarse sand to pebble grade sedimentary material through physical breakage of reef framework (Guzman and Lopez, 1991;Glynn and Manzello, 2015), either whilst feeding on coral (some pufferfishes) or whilst foraging for invertebrates in coral skeletons (some triggerfishes) (Perry et al, 2022).…”

“…Direct contributions derive post-mortem from skeletal fauna such as molluscs and foraminifera (Bosence, 1989), and from the disaggregation of the calcified segments of calcareous green and red algae (Neumann and Land, 1975). The grazing activities of some species of parrotfish and sea urchins, which excrete carbonate particles after ingestion Bellwood, 1996), also represent a major sediment source, and species of triggerfish and pufferfish can produce coral rubble as they break coral colonies whilst foraging (Perry et al, 2022). All bony marine fish (teleosts) additionally excrete silt and clay grade carbonate generated through intestinal secretions (Perry et al, 2011;Salter et al, 2012).…”

Herbivory through the lens of ecological processes across Pacific coral reefs

“…Efforts to leverage existing observations through data compilation and synthesis can reduce (or eliminate) the additional field effort needed to assess local herbivore communities, thereby broadening the utility of reef-monitoring data to inform management. For example, foraging observations that have been compiled and summarized allow users to calculate parrotfish bioerosion as an input of reef erosion in carbonate budgets (Perry et al, 2012(Perry et al, , 2018(Perry et al, , 2022.…”

“…Total herbivore biomass has often been used to infer the provision of ecological processes from local fish assemblages on coral reefs; however, this metric does not incorporate variation in the functional role of individual fish both within and among species. To account for this variation, recent studies have developed methods that integrate species-and size-specific data on fish abundance, feeding behavior, and resource intake to estimate rates of herbivory on coral reefs (Kelly et al, 2017;Lange et al, 2020;Perry et al, 2012Perry et al, , 2022Robinson et al, 2019;Ruttenberg et al, 2019). These methods, however, hinge on in situ foraging observations that are both time-intensive and costly.…”