Editorial

5 pages, 215 KiB

Open AccessEditorial

The Effect of Ocean Acidification on Skeletal Structures

by Hildegard Westphal, Justin B. Ries and Steve S. Doo

J. Mar. Sci. Eng. 2022, 10(6), 786; https://doi.org/10.3390/jmse10060786 - 08 Jun 2022

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It is well known that the increasing partial pressure of atmospheric CO₂ (pCO₂) is reducing surface ocean pH, a process known as ocean acidification (OA) [...] Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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21 pages, 4676 KiB

Open AccessFeature PaperArticle

Why Do Bio-Carbonates Exist?

by Luis Pomar, Pamela Hallock, Guillem Mateu-Vicens and Juan I. Baceta

J. Mar. Sci. Eng. 2022, 10(11), 1648; https://doi.org/10.3390/jmse10111648 - 03 Nov 2022

Cited by 1 | Viewed by 2115

Abstract

Calcium carbonate precipitation associated with biotic activity is first recorded in Archaean rocks. The oldest putative fossils related to hydrothermal vents have been dated at ~3.77 Ga (possibly 4.29 Ga). Stromatolites, the oldest dated at 3.70 Ga, have since occurred through Earth history, [...] Read more.

Calcium carbonate precipitation associated with biotic activity is first recorded in Archaean rocks. The oldest putative fossils related to hydrothermal vents have been dated at ~3.77 Ga (possibly 4.29 Ga). Stromatolites, the oldest dated at 3.70 Ga, have since occurred through Earth history, despite dramatic changes in physical and chemical conditions in aquatic environments. A key question is: what advantages do photosynthesizing aquatic prokaryotes and algae gain by precipitating carbonates? We propose the Phosphate Extraction Mechanism (PEM) to explain the benefits of biomineralization in warm, oligotrophic, alkaline, euphotic environments. Carbonate precipitation enhances access to otherwise limited carbon dioxide and phosphate in such environments. This mechanism also provides an explanation for prolific production of carbonates during times of elevated atmospheric carbon dioxide at intervals in the Phanerozoic. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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23 pages, 3156 KiB

Open AccessArticle

Impacts of Warming and Acidification on Coral Calcification Linked to Photosymbiont Loss and Deregulation of Calcifying Fluid pH

by Louise P. Cameron, Claire E. Reymond, Jelle Bijma, Janina V. Büscher, Dirk De Beer, Maxence Guillermic, Robert A. Eagle, John Gunnell, Fiona Müller-Lundin, Gertraud M. Schmidt-Grieb, Isaac Westfield, Hildegard Westphal and Justin B. Ries

J. Mar. Sci. Eng. 2022, 10(8), 1106; https://doi.org/10.3390/jmse10081106 - 12 Aug 2022

Cited by 6 | Viewed by 2868

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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26 pages, 2745 KiB

Open AccessArticle

Physicochemical Control of Caribbean Coral Calcification Linked to Host and Symbiont Responses to Varying pCO₂ and Temperature

by Robert A. Eagle, Maxence Guillermic, Illian De Corte, Blanca Alvarez Caraveo, Colleen B. Bove, Sambuddha Misra, Louise P. Cameron, Karl D. Castillo and Justin B. Ries

J. Mar. Sci. Eng. 2022, 10(8), 1075; https://doi.org/10.3390/jmse10081075 - 05 Aug 2022

Cited by 1 | Viewed by 2407

Abstract

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 (pH_CF) and other carbonate chemistry parameters ([CO₃²⁻] [...] Read more.

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 (pH_CF) and other carbonate chemistry parameters ([CO₃²⁻]_CF, DIC_CF, and Ω_CF) 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 pH_CF, [CO₃²⁻]_CF, and DIC_CF regulation in these corals, and δ¹³C to track changes in the sources of carbon for calcification. Temperature was found to not influence pH_CF 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. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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11 pages, 1734 KiB

Open AccessArticle

Responses of Freshwater Calcifiers to Carbon-Dioxide-Induced Acidification

by Aaron T. Ninokawa and Justin Ries

J. Mar. Sci. Eng. 2022, 10(8), 1068; https://doi.org/10.3390/jmse10081068 - 04 Aug 2022

Cited by 3 | Viewed by 1821

Abstract

Increased anthropogenic carbon dioxide (CO₂) in the atmosphere can enter surface waters and depress pH. In marine systems, this phenomenon, termed ocean acidification (OA), can modify a variety of physiological, ecological, and chemical processes. Shell-forming organisms are particularly sensitive to this [...] Read more.

Increased anthropogenic carbon dioxide (CO₂) in the atmosphere can enter surface waters and depress pH. In marine systems, this phenomenon, termed ocean acidification (OA), can modify a variety of physiological, ecological, and chemical processes. Shell-forming organisms are particularly sensitive to this chemical shift, though responses vary amongst taxa. Although analogous chemical changes occur in freshwater systems via absorption of CO₂ into lakes, rivers, and streams, effects on freshwater calcifiers have received far less attention, despite the ecological importance of these organisms to freshwater systems. We exposed four common and widespread species of freshwater calcifiers to a range of pCO₂ conditions to determine how CO₂-induced reductions in freshwater pH impact calcium carbonate shell formation. We incubated the signal crayfish, Pacifastacus leniusculus, the Asian clam, Corbicula fluminea, the montane pea clam, Pisidium sp., and the eastern pearlshell mussel, Margaritifera margaritifera, under low pCO₂ conditions (pCO₂ = 616 ± 151 µatm; pH = 7.91 ± 0.11), under moderately elevated pCO₂ conditions (pCO₂ = 1026 ± 239 uatm; pH = 7.67 ± 0.10), and under extremely elevated pCO₂ conditions (pCO₂ = 2380 ± 693 uatm; pH = 7.32 ± 0.12). Three of these species exhibited a negative linear response to increasing pCO₂ (decreasing pH), while the fourth, the pea clam, exhibited a parabolic response. Additional experiments revealed that feeding rates of the crayfish decreased under the highest pCO₂ treatment, potentially contributing to or driving the negative calcification response of the crayfish to elevated pCO₂ by depriving them of energy needed for biocalcification. These results highlight the potential for freshwater taxa to be deleteriously impacted by increased atmospheric pCO₂, the variable nature of these responses, and the need for further study of this process in freshwater systems. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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18 pages, 5233 KiB

Open AccessArticle

Ocean Warming Amplifies the Effects of Ocean Acidification on Skeletal Mineralogy and Microstructure in the Asterinid Starfish Aquilonastra yairi

by Munawar Khalil, Steve S. Doo, Marleen Stuhr and Hildegard Westphal

J. Mar. Sci. Eng. 2022, 10(8), 1065; https://doi.org/10.3390/jmse10081065 - 03 Aug 2022

Cited by 4 | Viewed by 2428

Abstract

Ocean acidification and ocean warming compromise the capacity of calcifying marine organisms to generate and maintain their skeletons. While many marine calcifying organisms precipitate low-Mg calcite or aragonite, the skeleton of echinoderms consists of more soluble Mg-calcite. To assess the impact of exposure [...] Read more.

Ocean acidification and ocean warming compromise the capacity of calcifying marine organisms to generate and maintain their skeletons. While many marine calcifying organisms precipitate low-Mg calcite or aragonite, the skeleton of echinoderms consists of more soluble Mg-calcite. To assess the impact of exposure to elevated temperature and increased pCO₂ on the skeleton of echinoderms, in particular the mineralogy and microstructure, the starfish Aquilonastra yairi (Echinodermata: Asteroidea) was exposed for 90 days to simulated ocean warming (27 °C and 32 °C) and ocean acidification (455 µatm, 1052 µatm, 2066 µatm) conditions. The results indicate that temperature is the major factor controlling the skeletal Mg (Mg/Ca ratio and Mg_norm ratio), but not for skeletal Sr (Sr/Ca ratio and Sr_norm ratio) and skeletal Ca (Ca_norm ratio) in A. yairi. Nevertheless, inter-individual variability in skeletal Sr and Ca ratios increased with higher temperature. Elevated pCO₂ did not induce any statistically significant element alterations of the skeleton in all treatments over the incubation time, but increased pCO₂ concentrations might possess an indirect effect on skeletal mineral ratio alteration. The influence of increased pCO₂ was more relevant than that of increased temperature on skeletal microstructures. pCO₂ as a sole stressor caused alterations on stereom structure and degradation on the skeletal structure of A. yairi, whereas temperature did not; however, skeletons exposed to elevated pCO₂ and high temperature show a strongly altered skeleton structure compared to ambient temperature. These results indicate that ocean warming might exacerbate the skeletal maintaining mechanisms of the starfish in a high pCO₂ environment and could potentially modify the morphology and functions of the starfish skeleton. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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19 pages, 5587 KiB

Open AccessArticle

Artificial Intelligence as a Tool to Study the 3D Skeletal Architecture in Newly Settled Coral Recruits: Insights into the Effects of Ocean Acidification on Coral Biomineralization

by Federica Scucchia, Katrein Sauer, Paul Zaslansky and Tali Mass

J. Mar. Sci. Eng. 2022, 10(3), 391; https://doi.org/10.3390/jmse10030391 - 09 Mar 2022

Cited by 3 | Viewed by 3655

Abstract

Understanding the formation of the coral skeleton has been a common subject uniting various marine and materials study fields. Two main regions dominate coral skeleton growth: Rapid Accretion Deposits (RADs) and Thickening Deposits (TDs). These have been extensively characterized at the 2D level, [...] Read more.

Understanding the formation of the coral skeleton has been a common subject uniting various marine and materials study fields. Two main regions dominate coral skeleton growth: Rapid Accretion Deposits (RADs) and Thickening Deposits (TDs). These have been extensively characterized at the 2D level, but their 3D characteristics are still poorly described. Here, we present an innovative approach to combine synchrotron phase contrast-enhanced microCT (PCE-CT) with artificial intelligence (AI) to explore the 3D architecture of RADs and TDs within the coral skeleton. As a reference study system, we used recruits of the stony coral Stylophora pistillata from the Red Sea, grown under both natural and simulated ocean acidification conditions. We thus studied the recruit’s skeleton under both regular and morphologically-altered acidic conditions. By imaging the corals with PCE-CT, we revealed the interwoven morphologies of RADs and TDs. Deep-learning neural networks were invoked to explore AI segmentation of these regions, to overcome limitations of common segmentation techniques. This analysis yielded highly-detailed 3D information about the RAD’s and TD’s architecture. Our results demonstrate how AI can be used as a powerful tool to obtain 3D data essential for studying coral biomineralization and for exploring the effects of environmental change on coral growth. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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20 pages, 28330 KiB

Open AccessArticle

Mussels Repair Shell Damage despite Limitations Imposed by Ocean Acidification

by Matthew N. George, Michael J. O’Donnell, Michael Concodello and Emily Carrington

J. Mar. Sci. Eng. 2022, 10(3), 359; https://doi.org/10.3390/jmse10030359 - 03 Mar 2022

Cited by 6 | Viewed by 3466

Abstract

Bivalves frequently withstand shell damage that must be quickly repaired to ensure survival. While the processes that underlie larval shell development have been extensively studied within the context of ocean acidification (OA), it remains unclear whether shell repair is impacted by elevated p [...] Read more.

Bivalves frequently withstand shell damage that must be quickly repaired to ensure survival. While the processes that underlie larval shell development have been extensively studied within the context of ocean acidification (OA), it remains unclear whether shell repair is impacted by elevated pCO₂. To better understand the stereotypical shell repair process, we monitored mussels (Mytilus edulis) with sublethal shell damage that breached the mantle cavity within both field and laboratory conditions to characterize the deposition rate, composition, and integrity of repaired shell. Results were then compared with a laboratory experiment wherein mussels (Mytilus trossulus) repaired shell damage in one of seven pCO₂ treatments (400–2500 µatm). Shell repair proceeded through distinct stages; an organic membrane first covered the damaged area (days 1–15), followed by the deposition of calcite crystals (days 22–43) and aragonite tablets (days 51–69). OA did not impact the ability of mussels to close drill holes, nor the microstructure, composition, or integrity of end-point repaired shell after 10 weeks, as measured by µCT and SEM imaging, energy-dispersive X-ray (EDX) analysis, and mechanical testing. However, significant interactions between pCO₂, the length of exposure to treatment conditions, the strength and inorganic content of shell, and the physiological condition of mussels within OA treatments were observed. These results suggest that while OA does not prevent adult mussels from repairing or mineralizing shell, both OA and shell damage may elicit stress responses that impose energetic constraints on mussel physiology. Full article

(This article belongs to the Special Issue The Effect of Ocean Acidification on Skeletal Structures)

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