Incorporating benthic community changes into hydrochemical-based projections of coral reef calcium carbonate production under ocean acidification

Abstract

The existence of coral reefs is dependent on the production and maintenance of calcium carbonate (CaCO3) framework that is produced through calcification. The net production of CaCO3 will likely decline in the future, from both declining net calcification rates (decreasing calcification and increasing dissolution) and shifts in benthic community composition from calcifying organisms to non-calcifying organisms. Here, we present a framework for hydrochemical studies that allows both declining net calcification rates and changes in benthic community composition to be incorporated into projections of coral reef CaCO3 production. The framework involves upscaling net calcification rates for each benthic community type using mapped proportional cover of the benthic communities. This upscaling process was applied to the reef flats at One Tree and Lady Elliot reefs (Great Barrier Reef) and Shiraho Reef (Okinawa), and compared to existing data. Future CaCO3 budgets were projected for Lady Elliot Reef, predicting a decline of 53 % from the present value by end-century (800 ppm CO2) without any changes to benthic community composition. A further 5.7 % decline in net CaCO3 production is expected for each 10 % decline in calcifier cover, and net dissolution is predicted by end-century if calcifier cover drops below 18 % of the present extent. These results show the combined negative effect of both declining net calcification rates and changing benthic community composition on reefs and the importance of considering both processes for determining future reef CaCO3 production. AbstractThe existence of coral reefs is dependent on the production and maintenance of calcium carbonate (CaCO 3 ) framework that is produced through biogenic calcification. The net production of CaCO 3 is likely to decline in the future, both due to declining net calcification rates (decreasing calcification and increasing dissolution rates) and shifts in benthic community composition from calcifying organisms (e.g. corals) to non-calcifying organisms (e.g. fleshy algae). Here we present a framework for hydrochemical studies that allows both declining net calcification rates and changes in benthic community composition to be incorporated into projections of coral reef CaCO 3 production. The framework involves upscaling net calcification rates for each benthic community type by using mapped proportional cover of the benthic communities. This upscaling process was applied to One Tree and Lady Elliot Reefs (Great Barrier Reef) and Shiraho Reef (Okinawa) and compared to existing data. Future CaCO 3 budgets were projected for Lady Elliot reef, predicting a decline to 47% of the present value by end-century (800 ppm CO 2 ) without any changes to benthic community composition. Under a 50% reduction in the benthic cover of calcifying organisms at Lady Elliot reef, CaCO 3 production was projected to decline to 18% of the present value. These results show the combined negative effect of both declining net calcification rates and changing benthic communi...

Caribbean massive corals not recovering from repeated thermal stress events during 2005–2013

“…Silverstein et al. () demonstrated this concept in the laboratory over a time frame of approximately 1 year, and it is compelling to find this effect also seemingly demonstrated 5 years after the initial exposure. This acclimative effect on previously bleached corals has been described as a possible “nugget of hope” for coral reefs in times of climate change, and our results do provide possible in situ support for the concept that previous bleaching can confer a possible benefit to the short‐term survival of individual colonies of some scleractinian species, and thus to the long‐term survival of coral reefs as growing, structural ecosystems (Berkelmans & van Oppen, ).…”

“…In particular, ocean acidification (OA) may manifest with such slow but persistent impacts (Shaw, Phinn, Tilbrook, & Steven, 2015). Furthermore, the effect of altered growth or persistence on specific members of the reef community may affect overall net reef deposition (Shaw, Hamylton, & Phinn, 2016); one indication of this is that areas of the northern Florida Reef Tract may already be in a condition of negative net community calcification (Muehllehner et al, 2016). The species-specific differences in postdisturbance recovery documented here increase capacity for improved modeling of growth and calcification dynamics for reef systems.…”

“…Our research investigates the different long‐term responses of individual coral colonies stemming from thermal stress exposure alone vs. those following expressions of acute visible bleaching, and differs from Silverstein et al. () in that it extends that time frame for response observation to 89 months, and importantly provides validation of this phenomenon in a field setting following a natural bleaching event (Figure ). These three species are all are massive, hermatypic, relatively slow‐growing corals, and all have similar physiological energetics (i.e., zooxanthellate) and are broadcast reproduction (Szmant, ), leading to relatively high genetic connectivity across the Caribbean basin (Nunes, Norris, & Knowlton, ).…”

Net Community Metabolism and Seawater Carbonate Chemistry Scale Non-intuitively with Coral Cover

“…Combined with refinement and application of existing ecological theory, this approach provides an initial foundation to integrate metabolic rates across functional, spatial and temporal scales (Andersson et al, 2015;Edmunds et al, 2016;Shaw et al, 2016). Being able to integrate metabolic rates across scales will be critical to predict how coral reefs as a whole will respond to environmental perturbations, such as climate change and OA.…”

Reef Habitat Type and Spatial Extent as Interacting Controls on Platform-Scale Carbonate Budgets

“…This has encompassed assessments of both reef framework carbonate production (Perry et al, 2014a;Pratchett et al, 2015) and bioerosion rates (Perry et al, 2014a;Weinstein et al, 2014), and considerations of how rates of both may respond to future climate change drivers (e.g., Fang et al, 2013;Barkley et al, 2015;DeCarlo et al, 2015;Januchowski-Hartley et al, 2017;Schönberg et al, 2017). In addition, there has been considerable effort aimed at improving the understanding of how net reef carbonate budget states vary between reefs and how they may respond to ecological change, these being based on either census (e.g., Stearn et al, 1977;Scoffin et al, 1980;Hubbard et al, 1990;Eakin, 1996;Mallela and Perry, 2007;Perry et al, 2012Perry et al, , 2013b or hydrochemical (e.g., Smith and Kinsey, 1976;Gattuso et al, 1996;Andersson and Gledhill, 2013;Shaw et al, 2016) in-situ measurements. In some cases a combination of both methods have been applied (e.g., Courtney et al, 2016) and up-scaling, based on remotely sensed imagery, applied to derive reef-wide production rates (e.g., Andréfouët and Payri, 2001;Moses et al, 2009;Hamylton et al, 2013b).…”