Bernstein, W. N., Hughen, K. A., Langdon, C., McCorkle, D. C., & Lentz, S. J. (2016). Environmental controls on daytime net community calcification on a Red Sea reef flat. Coral Reefs, 35(2), 697–711.
Abstract: Coral growth and carbonate accumulation form the foundation of the coral reef ecosystem. Changes in environmental conditions due to coastal development, climate change, and ocean acidification may pose a threat to net carbonate production in the near future. Controlled laboratory studies demonstrate that calcification by corals and coralline algae is sensitive to changes in aragonite saturation state (a"broken vertical bar(a)), as well as temperature, light, and nutrition. Studies also show that the dissolution rate of carbonate substrates is impacted by changes in carbonate chemistry. The sensitivity of coral reefs to these parameters must be confirmed and quantified in the natural environment in order to predict how coral reefs will respond to local and global changes, particularly ocean acidification. We estimated the daytime hourly net community metabolic rates, both net community calcification (NCC) and net community productivity (NCP), at Sheltered Reef, an offshore platform reef in the central Red Sea. Average NCC was 8 +/- A 3 mmol m(-2) h(-1) in December 2010 and 11 +/- A 1 mmol m(-2) h(-1) in May 2011, and NCP was 21 +/- A 7 mmol m(-2) h(-1) in December 2010 and 44 +/- A 4 mmol m(-2) h(-1) in May 2011. We also monitored a suite of physical and chemical properties to help relate the rates at Sheltered Reef to published rates from other sites. While previous research shows that short-term field studies investigating the NCC-a"broken vertical bar(a) relationship have differing results due to confounding factors, it is important to continue estimating NCC in different places, seasons, and years, in order to monitor changes in NCC versus a"broken vertical bar in space and time, and to ultimately resolve a broader understanding of this relationship.
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Enochs, I. C., Manzello, D. P., Kolodziej, G., Noonan, S. H. C., Valentino, L., & Fabricius, K. E. (2016). Enhanced macroboring and depressed calcification drive net dissolution at high-CO[sub:2]coral reefs. Proc. R. Soc. B, 283(1842), 20161742.
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Enochs, I. C., Manzello, D. P., Wirshing, H. H., Carlton, R., & Serafy, J. (2016). Micro-CT analysis of the Caribbean octocoral Eunicea flexuosa subjected to elevated pCO(2). ICES J. Mar. Sci., 73(3), 910–919.
Abstract: Rising anthropogenic carbon dioxide has resulted in a drop in ocean pH, a phenomenon known as ocean acidification (OA). These acidified waters have many ramifications for diverse marine biota, especially those species which precipitate calcium carbonate skeletons. The permanence of coral reef ecosystems is therefore closely related to OA stress as habitat-forming corals will exhibit reduced calcification and growth. Relatively little is known concerning the fate of other constituent taxa which may either suffer concomitant declines or be competitively favoured in acidified waters. Here, we experimentally (49 d) test the effects of next century predictions for OA (pH = 7.75, pCO(2) = 1081 mu atm) vs. near-present-day conditions (pH = 8.01, pCO(2) = 498 mu atm) on the common Caribbean octocoral Eunicea flexuosa. We measure linear extension of this octocoral and use a novel technique, high-resolution micro-computed tomography, to measure potential differences in the morphology of calcified internal skeletal structures (sclerites) in a 2 mm apical section of each branch. Despite the use of highly accurate procedures, we found no significant differences between treatments in either the growth of E. flexuosa branches or the structure of their sclerites. Our results suggest a degree of resilience to OA stress and provide evidence that this octocoral species may persist on Caribbean coral reefs, despite global change.
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Koch, M., Bowes, G., Ross, C., & Zhang, X. - H. (2013). Climate change and ocean acidification effects on seagrasses and marine macroalgae. Glob Change Biol, 19(1), 103–132.
Abstract: Although seagrasses and marine macroalgae (macro-autotrophs) play critical ecological roles in reef, lagoon, coastal and open-water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro-autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO2], and lower carbonate [CO32-] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO2]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro-autotroph photosynthesis is overwhelmingly C3 (= 85%) with most species capable of utilizing HCO3-; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO2-only users, lead us to conclude that photosynthetic and growth rates of marine macro-autotrophs are likely to increase under elevated [CO2] similar to terrestrial C3 species. In the tropics, many species live close to their thermal limits and will have to up-regulate stress-response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO2] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO2] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO2] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H+ and DIC. These fluxes control micro-environments that promote calcification over dissolution and may be more important than CaCO3 mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO2 ocean; therefore, it is critical to elucidate the research gaps identified in this review.
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Okazaki, R. R., Towle, E. K., van Hooidonk, R., Mor, C., Winter, R. N., Piggot, A. M., et al. (2017). Species-specific responses to climate change and community composition determine future calcification rates of Florida Keys reefs. Glob Change Biol, 23(3), 1023–1035.
Abstract: Anthropogenic climate change compromises reef growth as a result of increasing temperatures and ocean acidification. Scleractinian corals vary in their sensitivity to these variables, suggesting species composition will influence how reef communities respond to future climate change. Because data are lacking for many species, most studies that model future reef growth rely on uniform scleractinian calcification sensitivities to temperature and ocean acidification. To address this knowledge gap, calcification of twelve common and understudied Caribbean coral species was measured for two months under crossed temperatures (27, 30.3 °C) and CO2 partial pressures (pCO2) (400, 900, 1300 μatm). Mixed-effects models of calcification for each species were then used to project community-level scleractinian calcification using Florida Keys reef composition data and IPCC AR5 ensemble climate model data. Three of the four most abundant species, Orbicella faveolata, Montastraea cavernosa, and Porites astreoides, had negative calcification responses to both elevated temperature and pCO2. In the business-as-usual CO2 emissions scenario, reefs with high abundances of these species had projected end-of-century declines in scleractinian calcification of >50% relative to present-day rates. Siderastrea siderea, the other most common species, was insensitive to both temperature and pCO2 within the levels tested here. Reefs dominated by this species had the most stable end-of-century growth. Under more optimistic scenarios of reduced CO2 emissions, calcification rates throughout the Florida Keys declined <20% by 2100. Under the most extreme emissions scenario, projected declines were highly variable among reefs, ranging 10�100%. Without considering bleaching, reef growth will likely decline on most reefs, especially where resistant species like S. siderea are not already dominant. This study demonstrates how species composition influences reef community responses to climate change and how reduced CO2 emissions can limit future declines in reef calcification.
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Towle, E., Baker, A., & Langdon, C. (2016). Preconditioning to high CO2 exacerbates the response of the Caribbean branching coral Porites porites to high temperature stress. Mar. Ecol. Prog. Ser., 546, 75–84.
Abstract: Climate change stress on coral reefs occurs as a result of increased temperature and ocean acidification. However, these stressors do not act uniformly: acidification is a ‘press’ disturbance characterized by chronic increases in CO2, whereas thermal stress is a ‘pulse’ disturbance characterized by acute episodes of anomalously warm temperatures. Therefore future episodes of thermal stress will develop within the context of pre-existing acidification. Many studies have investigated the effect of combined temperature and CO2 on corals, but no study has yet investigated whether pre-exposing corals to elevated CO2 affects their response to high temperature. We investigated this for the first time using replicate fragments of the Caribbean coral Porites porites preconditioned to either 390 ppm or 900 ppm CO2 at 26°C for 3 mo. After this period, half of the corals from each CO2 level were exposed to 31°C (i.e. 31°C/390 ppm or 31°C/900 ppm) for 2 mo, while the other half were maintained in their original treatments (26°C/390 ppm or 26°C/900 ppm). Calcification, feeding rate, and photochemical efficiency were measured. Corals preconditioned to high CO2 before thermal stress (i.e. 31°C/900 ppm) showed 44% lower calcification rates than the control group, but single stress treatment groups did not experience significant growth reductions. Feeding rates increased for corals exposed to either high CO2 or high temperature singularly, but not when thermal stress was applied following CO2 preconditioning. Photochemical efficiency decreased by 25% for all treatment groups compared to the control. Together, these data suggest that preconditioning to elevated CO2 worsens holobiont response to thermal stress, potentially exacerbating the effects of climate change stressors on coral reefs.
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Turk, D., Yates, K., Vega-Rodriguez, M., Toro-Farmer, G., L'Esperance, C., Melo, N., et al. (2015). Community metabolism in shallow coral reef and seagrass ecosystems, lower Florida Keys. Mar. Ecol. Prog. Ser., 538, 35–52.
Abstract: Diurnal variation of net community production (NEP) and net community calcification (NEC) were measured in coral reef and seagrass biomes during October 2012 in the lower Florida Keys using a mesocosm enclosure and the oxygen gradient flux technique. Seagrass and coral reef sites showed diurnal variations of NEP and NEC, with positive values at near-seafloor light levels > 100-300 mu Einstein m(-2) s(-1). During daylight hours, we detected an average NEP of 12.3 and 8.6 mmol O-2 m(-2) h(-1) at the seagrass and coral reef site, respectively. At night, NEP at the seagrass site was relatively constant, while on the coral reef, net respiration was highest immediately after dusk and decreased during the rest of the night. At the seagrass site, NEC values ranged from 0.20 g CaCO3 m(-2) h(-1) during daylight to -0.15 g CaCO3 m(-2) h(-1) at night, and from 0.17 to -0.10 g CaCO3 m(-2) h(-1) at the coral reef site. There were no significant differences in pH and aragonite saturation states (Omega(ar)) between the seagrass and coral reef sites. Decrease in light levels during thunderstorms significantly decreased NEP, transforming the system from net autotrophic to net heterotrophic.
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