ALBERT

Description: The large benthic foraminifera Amphistegina lobifera, collected from the Gulf of Aqaba, Red Sea, in Eilat, Israel, were cultured under three pCO2 conditions (492, 963, 3182 ppm) crossed with two temperature conditions (28°C, 31°C) for two months. Patterns in protein abundance (supplementary tables of publication) were linked to the organisms' physiological responses (i.e. mortality frequency, growth rates, coloration on the L*a*b* color scale, chlorophyll a content, average pore size, pH at the foraminiferal surface during dark and light compared to seawater pH, and the resulting ∆[H+]).

Description: It is thought that the active physiological regulation of the chemistry of a parent fluid is an important process in the biomineralization of scleractinian corals. Biological regulation of calcification fluid pH (pHCF) and other carbonate chemistry parameters ([CO32−]CF, DICCF, and ΩCF) may be challenged by CO2 driven acidification and temperature. Here, we examine the combined influence of changing temperature and CO2 on calcifying fluid regulation in four common Caribbean coral species—Porites astreoides, Pseudodiploria strigosa, Undaria tenuifolia, and Siderastrea siderea. We utilize skeletal boron geochemistry (B/Ca and δ11B) to probe the pHCF, [CO32−]CF, and DICCF regulation in these corals, and δ13C to track changes in the sources of carbon for calcification. Temperature was found to not influence pHCF regulation across all pCO2 treatments in these corals, in contrast to recent studies on Indo-Pacific pocilloporid corals. We find that [DIC]CF is significantly lower at higher temperatures in all the corals, and that the higher temperature was associated with depletion of host energy reserves, suggesting [DIC]CF reductions may result from reduced input of respired CO2 to the DIC pool for calcification. In addition, δ13C data suggest that under high temperature and CO2 conditions, algal symbiont photosynthesis continues to influence the calcification pool and is associated with low [DIC]CF in P. strigosa and P. astreoides. In P. astreoides this effect is also associated with an increase in chlorophyll a concentration in coral tissues at higher temperatures. These observations collectively support the assertion that physicochemical control over coral calcifying fluid chemistry is coupled to host and symbiont physiological responses to environmental change, and reveals interspecific differences in the extent and nature of this coupling.

Description: Corals are globally important calcifiers that exhibit complex responses to anthropogenic warming and acidification. Although coral calcification is supported by high seawater pH, photosynthesis by the algal symbionts of zooxanthellate corals can be promoted by elevated pCO2. To investigate the mechanisms underlying corals' complex responses to global change, three species of tropical zooxanthellate corals (Stylophora pistillata, Pocillopora damicornis, and Seriatopora hystrix) and one species of asymbiotic cold-water coral (Desmophyllum pertusum, syn. Lophelia pertusa) were cultured under a range of ocean acidification and warming scenarios. Under control temperatures, all tropical species exhibited increased calcification rates in response to increasing pCO2. However, the tropical species' response to increasing pCO2 flattened when they lost symbionts (i.e., bleached) under the high-temperature treatments—suggesting that the loss of symbionts neutralized the benefit of increased pCO2 on calcification rate. Notably, the cold-water species that lacks symbionts exhibited a negative calcification response to increasing pCO2, although this negative response was partially ameliorated under elevated temperature. All four species elevated their calcifying fluid pH relative to seawater pH under all pCO2 treatments, and the magnitude of this offset (Δ[H+]) increased with increasing pCO2. Furthermore, calcifying fluid pH decreased along with symbiont abundance under thermal stress for the one species in which calcifying fluid pH was measured under both temperature treatments. This observation suggests a mechanistic link between photosymbiont loss ('bleaching') and impairment of zooxanthellate corals' ability to elevate calcifying fluid pH in support of calcification under heat stress. This study supports the assertion that thermally induced loss of photosymbionts impairs tropical zooxanthellate corals' ability to cope with CO2-induced ocean acidification.

Description: A dynamic energy budget (DEB) model integrating pCO2 was used to describe ocean acidification (OA) effects on Atlantic surfclam, Spisula solidissima, bioenergetics. Effects of elevated pCO2 on ingestion and somatic maintenance costs were simulated, validated, and adapted in the DEB model based upon growth and biological rates acquired during a 12-week laboratory experiment. Temperature and pCO2 were projected for the next 100 years following the intergovernmental panel on climate change representative concentration pathways scenarios (2.6, 6.0, and 8.5) and used as forcing variables to project surfclam growth and reproduction. End-of-century water warming and acidification conditions resulted in simulated faster growth for young surfclams and more energy allocated to reproduction until the beginning of the 22nd century when a reduction in maximum shell length and energy allocated to reproduction was observed for the RCP 8.5 scenario.

Description: Increasing anthropogenic carbon dioxide is predicted to cause declines in ocean pH and calcium carbonate saturation state over the coming centuries, making it potentially harder for marine calcifiers to build their shells and skeletons. One mechanism of resilience to ocean acidification is an organism's ability to regulate pH and, thus, calcium carbonate saturation state, at its site of calcification. This mechanism has received detailed study in scleractinian corals but is relatively understudied in other taxonomic groups that are vulnerable to ocean acidification, such as bivalves. Here, the results of a 74-day controlled laboratory experiment investigating the impact of ocean acidification on the extrapallial fluid (EPF; the bivalve calcifying fluid) pH, calcification rate, and condition factor of the king scallop Pecten maximus at their average spring and summer temperatures (362 ppm/9.0°C, 454 ppm/12.3°C; 860 ppm/9.0°C, 946 ppm/12.3°C; 2,639 ppm/8.9°C, 2,750 ppm/12.1°C) are presented. Scallop EPF pH was lower than seawater pH in all treatments and declined with increasing pCO2 under the spring temperature (9°C) but was uncorrelated with pCO2 under the summer temperature (12°C). Furthermore, king scallop calcification rate and EPF pH were inversely correlated at 9°C and uncorrelated at 12°C. This inverse correlation between EPF pH and scallop calcification rate, combined with the observation that scallop EPF pH is consistently lower than seawater pH, suggests that pH regulation is not the sole mechanism by which scallops concentrate carbonate ions for calcification within their EPF. Calcification trends contrasted most other published studies on bivalves, increasing with ocean acidification under spring temperature and exhibiting no response to ocean acidification under summer temperature. Scallop condition factor exhibited no response to ocean acidification under spring temperature but increased with ocean acidification under summer temperature-exactly the opposite of their calcification response to ocean acidification. These results suggest that king scallops are relatively resilient to CO2-induced ocean acidification, but that their allocation of resources between tissue and shell production in response to this stressor varies seasonally.

Description: Corals are globally important calcifiers that exhibit complex responses to anthropogenic warming and acidification. Although coral calcification is supported by high seawater pH, photosynthesis by the algal symbionts of zooxanthellate corals can be promoted by elevated pCO2. To investigate the mechanisms underlying corals’ complex responses to global change, three species of tropical zooxanthellate corals (Stylophora pistillata, Pocillopora damicornis, and Seriatopora hystrix) and one species of asymbiotic cold-water coral (Desmophyllum pertusum, syn. Lophelia pertusa) were cultured under a range of ocean acidification and warming scenarios. Under control temperatures, all tropical species exhibited increased calcification rates in response to increasing pCO2. However, the tropical species’ response to increasing pCO2 flattened when they lost symbionts (i.e., bleached) under the high-temperature treatments—suggesting that the loss of symbionts neutralized the benefit of increased pCO2 on calcification rate. Notably, the cold-water species that lacks symbionts exhibited a negative calcification response to increasing pCO2, although this negative response was partially ameliorated under elevated temperature. All four species elevated their calcifying fluid pH relative to seawater pH under all pCO2 treatments, and the magnitude of this offset (Δ[H+]) increased with increasing pCO2. Furthermore, calcifying fluid pH decreased along with symbiont abundance under thermal stress for the one species in which calcifying fluid pH was measured under both temperature treatments. This observation suggests a mechanistic link between photosymbiont loss (‘bleaching’) and impairment of zooxanthellate corals’ ability to elevate calcifying fluid pH in support of calcification under heat stress. This study supports the assertion that thermally induced loss of photosymbionts impairs tropical zooxanthellate corals’ ability to cope with CO2-induced ocean acidification.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Guillermic, M., Cameron, L. P., De Corte, I., Misra, S., Bijma, J., de Beer, D., Reymond, C. E., Westphal, H., Ries, J. B., & Eagle, R. A. Thermal stress reduces pocilloporid coral resilience to ocean acidification by impairing control over calcifying fluid chemistry. Science Advances, 7(2), (2021): eaba9958, https://doi.org/10.1126/sciadv.aba9958.

Description: The combination of thermal stress and ocean acidification (OA) can more negatively affect coral calcification than an individual stressors, but the mechanism behind this interaction is unknown. We used two independent methods (microelectrode and boron geochemistry) to measure calcifying fluid pH (pHcf) and carbonate chemistry of the corals Pocillopora damicornis and Stylophora pistillata grown under various temperature and pCO2 conditions. Although these approaches demonstrate that they record pHcf over different time scales, they reveal that both species can cope with OA under optimal temperatures (28°C) by elevating pHcf and aragonite saturation state (Ωcf) in support of calcification. At 31°C, neither species elevated these parameters as they did at 28°C and, likewise, could not maintain substantially positive calcification rates under any pH treatment. These results reveal a previously uncharacterized influence of temperature on coral pHcf regulation—the apparent mechanism behind the negative interaction between thermal stress and OA on coral calcification.

Description: R.A.E. and J.B.R. acknowledge support from National Science Foundation grants OCE-1437166 and OCE-1437371. The work was also supported by the “Laboratoire d’Excellence” LabexMER (ANR-10-LABX-19), cofunded by a grant from the French government under the program “Investissements d’Avenir,” and an IAGC student grant 2017. R.A.E. acknowledges financial and logistical support from the Pritzker Endowment to UCLA IoES, and J.B.R. acknowledges support from the ZMT and the Hanse-Wissenschaftskolleg Fellowship Program and the NSF OCE award #1437371.