The study to examine the calcification rate, adaptation, and the biotic response of three tropical coccolithophorids (Emiliania huxleyi, Gephyrocapsa oceanica, and Ochosphaera sp) to changes in CO2 concentration. Three selected calcifying coccolitophorids were grown at batch culture with CO2 system at two levels of CO2 (385 and 1000 ppm) and two light dark periods. The parameters measured and calculation including growth rate, particulate organic carbon content, particulate inorganic carbon content, chlorophyll a, cell size, photosynthetic, organic, inorganic carbon production, photosynthesis, and calcification rate. The results showed that there was a different response to carbonate chemistry changes and dark and light periods in any of the analyzed parameters. The growth rate of three selected calcifying microalgae tested was decreasing significantly at high concentrations of CO2 (1000 ppm) treatment on 14:10 hour light: dark periods. However, there was no significant difference between the two CO2 concentrations where they were illuminated by 24 hours light in growth rate. The increasing CO2 concentration and light-dark periods were species-specific responses to photosynthesis and calcification rate for three selected calcifying microalgae.
Continue reading ‘Interaction of CO2 and light availability on photophysiology of tropical coccolithophorids (Emiliania huxleyi, Gephyrocapsa oceanica, and Ochosphaera sp.)’Posts Tagged 'calcification'
Interaction of CO2 and light availability on photophysiology of tropical coccolithophorids (Emiliania huxleyi, Gephyrocapsa oceanica, and Ochosphaera sp.)
Published 28 February 2023 Science ClosedTags: biological response, calcification, growth, laboratory, light, morphology, multiple factors, photosynthesis, physiology, phytoplankton
Sensitivity of the grooved carpet shell clam, Ruditapes decussatus (Linnaeus, 1758), to ocean acidification
Published 21 February 2023 Science ClosedTags: biological response, calcification, laboratory, mollusks, morphology, physiology
This research investigated the possible impacts of ocean acidification on the grooved carpet shell clam Ruditapes decussatus as a model for commercially crucial marine bivalve species. Clams were collected from Lake Timsah on the Suez Canal coast, Ismailia, Egypt. They were then incubated in CO2-enriched seawater manipulated at four different CO2 concentrations: 420 ppm (ambient control) and 550, 750, and 1050 ppm. Calcification analysis was carried out using XRD and scanning electron microscope (SEM), highlighting a trend towards noticeable physical sensitivity to acidification. The antioxidant enzymatic activities [catalase (CAT)] were significantly different among different pCO2 (~ 20–23 µmol min−1 mg prot−1). Lipid peroxidation [malondialdehyde (MDA)] also showed a significant difference among treatments (0.21–0.23 nmol TBARS mg prot−1). Shell microstructure analysis showed periostracum distortion in the clam shell as pCO2 concentration increased at 1050 ppm. These results indicate that ocean acidification may exert an additional stress on bivalves through weakening their calcified shell making them more vulnerable to predators and affect their health and survival reducing production and economic value.
Continue reading ‘Sensitivity of the grooved carpet shell clam, Ruditapes decussatus (Linnaeus, 1758), to ocean acidification’Testing hypotheses on the calcification in scleractinian corals using a spatio-temporal model that shows a high degree of robustness
Published 27 January 2023 Science ClosedTags: biological response, calcification, chemistry, corals, individualmodeling, modeling, photosynthesis
Highlights
- Several hypotheses on coral calcification are tested using a computational model.
- The model is able to reproduce the experimental data of three separate studies.
- The model finds that paracellular ion transport into the ECM plays a minor role.
- Implementing OA in the model increased the calcification rate and ATP consumption.
- In the model, LEC is the result of increased metabolism and Ca2＋-ATPase activity.
Abstract
Calcification in photosynthetic scleractinian corals is a complicated process that involves many different biological, chemical, and physical sub-processes that happen within and around the coral tissue. Identifying and quantifying the role of separate processes in vivo or in vitro is difficult or not possible. A computational model can facilitate this research by simulating the sub-processes independently. This study presents a spatio-temporal model of the calcification physiology, which is based on processes that are considered essential for calcification: respiration, photosynthesis, Ca2＋-ATPase, carbonic anhydrase. The model is used to test different hypotheses considering ion transport across the calicoblastic cells and Light Enhanced Calcification (LEC). It is also used to quantify the effect of ocean acidification (OA) on the Extracellular Calcifying Medium (ECM) and ATP-consumption of Ca2＋-ATPase. It was able to reproduce the experimental data of three separate studies and finds that paracellular transport plays a minor role compared to transcellular transport. In the model, LEC results from increased Ca2＋-ATPase activity in combination with increased metabolism. Implementing OA increases the concentration of CO2 throughout the entire tissue, thereby increasing the availability of CO3− in the ECM. As a result, the model finds that calcification becomes more energy-demanding and the calcification rate increases.
Continue reading ‘Testing hypotheses on the calcification in scleractinian corals using a spatio-temporal model that shows a high degree of robustness’Population-specific vulnerability to ocean change in a multistressor environment
Published 26 January 2023 Science ClosedTags: biological response, calcification, chemistry, echinoderms, field, laboratory, mesocosms, morphology, mortality, multiple factors, North Pacific, oxygen, physiology, respiration, temperature
Variation in environmental conditions across a species’ range can alter their responses to environmental change through local adaptation and acclimation. Evolutionary responses, however, may be challenged in ecosystems with tightly coupled environmental conditions, where changes in the covariance of environmental factors may make it more difficult for species to adapt to global change. Here, we conduct a 3-month-long mesocosm experiment and find evidence for local adaptation/acclimation in populations of red sea urchins, Mesocentrotus franciscanus, to multiple environmental drivers. Moreover, populations differ in their response to projected concurrent changes in pH, temperature, and dissolved oxygen. Our results highlight the potential for local adaptation/acclimation to multivariate environmental regimes but suggest that thresholds in responses to a single environmental variable, such as temperature, may be more important than changes to environmental covariance. Therefore, identifying physiological thresholds in key environmental drivers may be particularly useful for preserving biodiversity and ecosystem functioning.
Continue reading ‘Population-specific vulnerability to ocean change in a multistressor environment’Evaluation of the current understanding of the impact of climate change on coral physiology after three decades of experimental research
Published 24 January 2023 Science ClosedTags: biological response, BRcommunity, calcification, chemistry, community composition, corals, field, laboratory, mesocosms, multiple factors, North Pacific, oxygen, photosynthesis, physiology, temperature
After three decades of coral research on the impacts of climate change, there is a wide consensus on the adverse effects of heat-stress, but the impacts of ocean acidification (OA) are not well established. Using a review of published studies and an experimental analysis, we confirm the large species-specific component of the OA response, which predicts moderate impacts on coral physiology and pigmentation by 2100 (scenario-B1 or SSP2-4.5), in contrast with the severe disturbances induced by only +2 °C of thermal anomaly. Accordingly, global warming represents a greater threat for coral calcification than OA. The incomplete understanding of the moderate OA response relies on insufficient attention to key regulatory processes of these symbioses, particularly the metabolic dependence of coral calcification on algal photosynthesis and host respiration. Our capacity to predict the future of coral reefs depends on a correct identification of the main targets and/or processes impacted by climate change stressors.
Continue reading ‘Evaluation of the current understanding of the impact of climate change on coral physiology after three decades of experimental research’Seasonal net calcification by secondary calcifiers in coral reefs of the Eastern Tropical Pacific Ocean
Published 19 January 2023 Science ClosedTags: abundance, biological response, BRcommunity, calcification, community composition, corals, field, multiple factors, North Pacific, otherprocess, temperature
This study assesses whether secondary calcification is driven by a contrasting seasonal pattern (rainy vs dry) that occurs in the Eastern Tropical Pacific (ETP). Secondary calcifiers net calcification rates and coverage were measured in two reefs: the semi-enclosed Bahía Tiburón reef (BT [21°52′30 “N, 105°54/54 “W]) and the open Las Monas fringing reef (LM [21°51ʹ00ʹʹN, 105°52ʹ45ʹʹW]). Measurements were made from 2013 to 2016 using Calcification Accretion Units (CAUs). Seawater temperature, illuminance, pCO2, pH, ΩCa, and ΩAr were also measured. Low means of pCO2, and high means of ΩCa and ΩAr, were measured during the rainy season. At Las Monas, the composition of the calcifier community differed between seasons. A seasonal effect on net calcification was recorded in the semi-enclosed reef and in the exposed microhabitat of both reefs. Overall, net calcification (mean ± SD) was 1.17 ± 1.13 g·CaCO3·m−2·day−1. Calcification in the open fringing reef (1.51 ± 1.32 g·CaCO3·m−2·day−1) was almost double that in the semi-enclosed reef (0.83 ± 0.78 g·CaCO3·m−2·day−1). Calcification also decreased dramatically between 2014 (1.57 g·CaCO3·m−2·day−1) and 2016 (0.99 g·CaCO3·m−2·day−1). The ENSO event of 2015 raised the water temperature almost 1 °C above the decadal average, which led to a mass coral bleaching in both reefs. That thermal stress might explain the calcification decline in 2015–2016, but probably also obscured a clearer seasonal pattern in net calcification. This study is the first to show that anomalous and persistent high seawater temperatures can affect carbonate production by secondary calcifiers.
Continue reading ‘Seasonal net calcification by secondary calcifiers in coral reefs of the Eastern Tropical Pacific Ocean’A space-time mosaic of seawater carbonate chemistry conditions in the north-shore Moorea coral reef system
Published 13 January 2023 Science ClosedTags: biological response, calcification, chemistry, corals, modeling, photosynthesis, physiology, regionalmodeling, South Pacific
The interplay between ocean circulation and coral metabolism creates highly variable biogeochemical conditions in space and time across tropical coral reefs. Yet, relatively little is known quantitatively about the spatiotemporal structure of these variations. To address this gap, we use the Coupled Ocean Atmosphere Wave and Sediment Transport (COAWST) model, to which we added the Biogeochemical Elemental Cycling (BEC) model computing the biogeochemical processes in the water column, and a coral polyp physiology module that interactively simulates coral photosynthesis, respiration and calcification. The coupled model, configured for the north-shore of Moorea Island, successfully simulates the observed (i) circulation across the wave regimes, (ii) magnitude of the metabolic rates, and (iii) large gradients in biogeochemical conditions across the reef. Owing to the interaction between coral net community production (NCP) and coral calcification, the model simulates distinct day versus night gradients, especially for pH and the saturation state of seawater with respect to aragonite (Ωα). The strength of the gradients depends non-linearly on the wave regime and the resulting residence time of water over the reef with the low wave regime creating conditions that are considered as “extremely marginal” for corals. With the average water parcel passing more than twice over the reef, recirculation contributes further to the accumulation of these metabolic signals. We find diverging temporal and spatial relationships between total alkalinity (TA) and dissolved inorganic carbon (DIC) (≈ 0.16 for the temporal vs. ≈ 1.8 for the spatial relationship), indicating the importance of scale of analysis for this metric. Distinct biogeochemical niches emerge from the simulated variability, i.e., regions where the mean and variance of the conditions are considerably different from each other. Such biogeochemical niches might cause large differences in the exposure of individual corals to the stresses associated with e.g., ocean acidification. At the same time, corals living in the different biogeochemical niches might have adapted to the differing conditions, making the reef, perhaps, more resilient to change. Thus, a better understanding of the mosaic of conditions in a coral reef might be useful to assess the health of a coral reef and to develop improved management strategies.
Continue reading ‘A space-time mosaic of seawater carbonate chemistry conditions in the north-shore Moorea coral reef system’Climate change impacts on the coral reefs of the UK Overseas Territory of the Pitcairn Islands: resilience and adaptation considerations
Published 3 January 2023 Science ClosedTags: biological response, calcification, corals, mitigation, multiple factors, review, South Pacific, temperature
The coral reefs of the Pitcairn Islands are in one of the most remote areas of the Pacific Ocean, and yet they are exposed to the impacts of anthropogenic climate change. The Pitcairn Islands Marine Protected Area was designated in 2016 and is one of the largest in the world, but the marine environment around these highly isolated islands remains poorly documented. Evidence collated here indicates that while the Pitcairn Islands’ reefs have thus far been relatively sheltered from the effect of warming sea temperatures, there is substantial risk of future coral decalcification due to ocean acidification. The projected acceleration in the rate of sea level rise, and the reefs’ exposure to risks from distant ocean swells and cold-water intrusions, add further uncertainty as to whether these islands and their reefs will continue to adapt and persist into the future. Coordinated action within the context of the Pitcairn Islands Marine Protected Area can help enhance the resilience of the reefs in the Pitcairn Islands. Options include management of other human pressures, control of invasive species and active reef interventions. More research, however, is needed in order to better assess what are the most appropriate and feasible options to protect these reefs.
Continue reading ‘Climate change impacts on the coral reefs of the UK Overseas Territory of the Pitcairn Islands: resilience and adaptation considerations’Responses of corals and coral reef ecosystems to ocean acidification under variable temperature and light
Published 19 December 2022 Science ClosedTags: biological response, BRcommunity, calcification, corals, field, growth, laboratory, light, molecular biology, mortality, multiple factors, photosynthesis, physiology, protists, temperature, vents
Coral reefs are under increasing pressure from ocean acidification. However, much of our understanding is based on single-species aquarium experiments made in isolation from realistic environmental parameters (e.g. light, water flow, food supply) and other co occurring stressors (e.g. increasing sea surface temperatures, reduced water clarity due to terrestrial runoff). In my PhD project I aimed to understand how ocean acidification affects the ecophysiology of reef corals and reef communities in natural settings, and how effects may differ with concurrent exposure to variable temperature and light. I used a combination of experimental and observational studies at unique field sites with naturally high levels of CO2 (CO2 seep sites), and multi-factor experiments in the aquarium facilities of The Australian Institute of Marine Science’s National Sea Simulator to address these questions.
In chapter 2, I investigated if corals can acclimate to ocean acidification by switching their photosymbionts to types that may be able to utilise the more abundant CO2 in photosynthesis. I used molecular techniques to investigate the dominant photosymbiont types in six species of coral from the field and found them to be highly conserved within species between CO2 seep and control sites. In chapter 3, I used a combination of field surveys and a multifactor laboratory experiment to investigate if elevated CO2 increased the severity of coral thermal bleaching. Field surveys during a bleaching event at the CO2 seeps, as well as the experimental study, both showed that corals were not significantly more susceptible to thermal stress under high CO2. In chapter 4, I used a multifactor laboratory experiment to investigate if reduced or variable daily light availability affected the responses of corals to high CO2. Here I found that reductions in light levels, regardless of the variability in daily light integrals, can reduce coral growth rates more than high CO2. In chapter 5, I followed the development of early successional coral reef benthic communities on settlement tiles along a gradient of CO2 exposure at the seep sites, and further measured rates of community metabolism. Here high CO2 strongly influenced the development of communities, shifting them away from a dominance of calcifying taxa under present day conditions to a range of non-calcifying algae as CO2 levels increased. These high CO2 communities progressively recorded lower rates of calcification and higher rates of hotosynthesis at high CO2.
Results from this thesis show that the considerable changes to the CO2 seep benthic communities are likely due to secondary ecological effects, rather than the physiological effects on corals alone. Moreover, the negative effects of cooccurring stressors on corals and coral reefs will also be substantial. Hence there is an immediate need to reduce atmospheric CO2 emissions and improve the management of local stressors to prevent further declines to the health and functioning of coral reef ecosystems.
Continue reading ‘Responses of corals and coral reef ecosystems to ocean acidification under variable temperature and light’Calcium isotope ratios of malformed foraminifera reveal biocalcification stress preceded Oceanic Anoxic Event 2
Published 16 December 2022 Science ClosedTags: biological response, calcification, field, laboratory, Mediterranean, morphology, paleo, protists
Ocean acidification causes biocalcification stress. The calcium isotope composition of carbonate producers can archive such stress because calcium isotope fractionation is sensitive to precipitation rate. Here, we synthesize morphometric observations of planktic foraminifera with multi-archive calcium isotope records from Gubbio, Italy and the Western Interior Seaway spanning Cretaceous Ocean Anoxic Event 2 (~94 million years ago). Calcium isotope ratios increase ~60 thousand years prior to the event. The increase coincides with foraminiferal abnormalities and correlates with existing proxy records for carbon dioxide release during large igneous province volcanism. The results highlight Ocean Anoxic Event 2 as a geologic ocean acidification analog. Moreover, decreasing calcium isotope ratios during the event provide evidence for ocean alkalinization, which could have shifted air-sea carbon dioxide partitioning. These data offer an explanation for the Plenus Cold Event and further have implications for refining ocean alkalinity enhancement, a leading anthropogenic carbon dioxide removal strategy.
Continue reading ‘Calcium isotope ratios of malformed foraminifera reveal biocalcification stress preceded Oceanic Anoxic Event 2’Corals adapted to extreme and fluctuating seawater pH increase calcification rates and have unique symbiont communities
Published 7 December 2022 Science ClosedTags: biological response, BRcommunity, calcification, chemistry, corals, field, growth, laboratory, molecular biology, morphology, photosynthesis, physiology, protists, South Pacific
Ocean acidification (OA) is a severe threat to coral reefs mainly by reducing their calcification rate. Identifying the resilience factors of corals to decreasing seawater pH is of paramount importance to predict the survivability of coral reefs in the future. This study compared corals adapted to variable pH (i.e., 7.23-8.06 pH units) from the semi-enclosed lagoon of Bouraké, New Caledonia, to corals adapted to more stable seawater pH (i.e., 7.90-8.18 pH units). In a 100-day aquarium experiment, we examined the physiological response and genetic diversity of Symbiodiniaceae from three coral species ( Acropora tenuis , Montipora digitata and Porites sp.) from both sites under three stable pH conditions (i.e., 8.11, 7.76, 7.54 pH units) and fluctuating pH conditions (i.e., between 7.56 and 8.07 pH units). Bouraké corals consistently exhibited higher growth rates than corals from the stable pH environment, with specific ITS2 intragenomic variant profiles. While OA generally decreased coral calcification by ca. 16%, Bouraké coralsshowed higher growth rates (21 to 93% increase, depending on species with all pH conditions pooled) than those from the stable pH environment. This superior performance coincided with divergent ITS2-like profiles with better consistency for both variable and low pH conditions. This response was not gained by corals from the more stable environment exposed to variable pH during the four-month experiment, suggesting that such a kind of plasticity is time dependent. Future long-term experiments should address the exposure duration required to confer fitness benefits for sustained calcification, hopefully fast enough to cope with the ongoing rapid OA.
Continue reading ‘Corals adapted to extreme and fluctuating seawater pH increase calcification rates and have unique symbiont communities’Negative effects of a zoanthid competitor limit coral calcification more than ocean acidification
Published 6 December 2022 Science ClosedTags: abundance, biological response, BRcommunity, calcification, cnidaria, community composition, corals, field, laboratory, otherprocess, photosynthesis
Ocean acidification (OA) threatens the persistence of reef-building corals and the habitat they provide. While species-specific effects of OA on marine organisms could have cascading effects on ecological interactions like competition, few studies have identified how benthic reef competitors respond to OA. We explored how two common Caribbean competitors, branching Porites and a colonial zoanthid (Zoanthus), respond to the factorial combination of OA and competition. In the laboratory, we exposed corals, zoanthids and interacting corals and zoanthids to ambient (8.01 ± 0.03) and OA (7.68 ± 0.07) conditions for 60 days. The OA treatment had no measured effect on zoanthids or coral calcification but decreased Porites maximum PSII efficiency. Conversely, the competitive interaction significantly decreased Porites calcification but had minimal-to-no countereffects on the zoanthid. Although this interaction was not exacerbated by the 60-day OA exposure, environmental changes that enhance zoanthid performance could add to the dominance of zoanthids over corals. The lack of effects of OA on coral calcification indicates that near-term competitive interactions may have more immediate consequences for some corals than future global change scenarios. Disparate consequences of competition have implications for community structure and should be accounted for when evaluating local coral reef trajectories.
Continue reading ‘Negative effects of a zoanthid competitor limit coral calcification more than ocean acidification’Coral reef carbonate accretion rates track stable gradients in seawater carbonate chemistry across the U.S. Pacific Islands
Published 1 December 2022 Science ClosedTags: algae, biological response, BRcommunity, calcification, chemistry, community composition, corals, field, methods, North Pacific, otherprocess
The U.S. Pacific Islands span a dramatic natural gradient in climate and oceanographic conditions, and benthic community states vary significantly across the region’s coral reefs. Here we leverage a decade of integrated ecosystem monitoring data from American Samoa, the Mariana Archipelago, the main and Northwestern Hawaiian Islands, and the U.S. Pacific Remote Island Areas to evaluate coral reef community structure and reef processes across a strong natural gradient in pH and aragonite saturation state (Ωar). We assess spatial patterns and temporal trends in carbonate chemistry measured in situ at 37 islands and atolls between 2010 and 2019, and evaluate the relationship between long-term mean Ωar and benthic community cover and composition (benthic cover, coral genera, coral morphology) and reef process (net calcium carbonate accretion rates). We find that net carbonate accretion rates demonstrate significant sensitivity to declining Ωar, while most benthic ecological metrics show fewer direct responses to lower-Ωar conditions. These results indicate that metrics of coral reef net carbonate accretion provide a critical tool for monitoring the long-term impacts of ocean acidification that may not be visible by assessing benthic cover and composition alone. The perspectives gained from our long-term, in situ, and co-located coral reef environmental and ecological data sets provide unique insights into effective monitoring practices to identify potential for reef resilience to future ocean acidification and inform effective ecosystem-based management strategies under 21st century global change.
Continue reading ‘Coral reef carbonate accretion rates track stable gradients in seawater carbonate chemistry across the U.S. Pacific Islands’High sclerobiont calcification in marginal reefs of the eastern tropical Pacific
Published 8 November 2022 Science ClosedTags: annelids, biological response, BRcommunity, bryozoa, calcification, chemistry, community composition, field, mollusks, multiple factors, North Pacific, nutrients, otherprocess, protists, review
Graphical abstract.
A sclerobiont is any organism capable of fouling hard substrates. Sclerobionts have recently received attention due to their notable calcium carbonate contributions to reef structures and potential to offset drops in carbonate budgets in degraded reefs. However, due to their encrusting nature, it is difficult to quantify net calcium carbonate production at the level of individual taxonomic groups, and knowledge regarding the main environmental factors that regulate their spatial distributions is limited. In addition, the material types used to create experimental substrates, their orientations, and their overall deployment times can influence settlement and the composition of the resulting communities. Thus, comparative evaluations of these variables are necessary to improve future research efforts. In this study, we used calcification accretion units (CAUs) to quantify the calcium carbonate contributions of sclerobionts at the taxonomic group level and evaluated the effects of two frequently used materials [i.e., polyvinyl chloride (PVC) and terracotta (TCT) tiles] on the recruitment and calcification of the sclerobiont community in the tropical Mexican Pacific and the Midriff Island Region of the Gulf of California over 6 and 15 months [n = 40; 5 CAUs x site (2) x deployment time (2) x material type (2)]. The net sclerobiont calcification rate (mean ± SD) reached maximum values at six months and was higher in the Mexican Pacific (2.15 ± 0.99 kg m−2 y−1) than in the Gulf of California (1.70 ± 0.67 kg m−2 y−1). Moreover, the calcification rate was slightly higher on the PVC-CAUs compared to that of the TCT-CAUs, although these differences were not consistent at the group level. In addition, cryptic microhabitats showed low calcification rates when compared to those of exposed microhabitats. Crustosecoralline algae and barnacles dominated the exposed experimental surfaces, while bryozoans, mollusks, and serpulid polychaetes dominated cryptic surfaces. Regardless of the site, deployment time, or material type, barnacles made the greatest contributions to calcimass production (between 41 and 88%). Our results demonstrate that the orientation of the experimental substrate, and the material to a lesser extent, influence the sclerobiont community and the associated calcification rate. Upwelling-induced surface nutrient levels, low pH levels, and the aragonite saturation state (ΩAr) limit the early cementation of reef-building organisms in the tropical Mexican Pacific and promote high bioerosion rates in corals of the Gulf of California. Our findings demonstrate that sclerobionts significantly contribute to calcium carbonate production even under conditions of high environmental variability.
Continue reading ‘High sclerobiont calcification in marginal reefs of the eastern tropical Pacific’Climate change and species facilitation affect the recruitment of macroalgal marine forests
Published 3 November 2022 Science ClosedTags: biological response, calcification, laboratory, Mediterranean, morphology, multiple factors, phanerogams, protists, temperature
Marine forests are shrinking globally due to several anthropogenic impacts including climate change. Forest-forming macroalgae, such as Cystoseira s.l. species, can be particularly sensitive to environmental conditions (e.g. temperature increase, pollution or sedimentation), especially during early life stages. However, not much is known about their response to the interactive effects of ocean warming (OW) and acidification (OA). These drivers can also affect the performance and survival of crustose coralline algae, which are associated understory species likely playing a role in the recruitment of later successional species such as forest-forming macroalgae. We tested the interactive effects of elevated temperature, low pH and species facilitation on the recruitment of Cystoseira compressa. We demonstrate that the interactive effects of OW and OA negatively affect the recruitment of C. compressa and its associated coralline algae Neogoniolithon brassica-florida. The density of recruits was lower under the combinations OW and OA, while the size was negatively affected by the temperature increase but positively affected by the low pH. The results from this study show that the interactive effects of climate change and the presence of crustose coralline algae can have a negative impact on the recruitment of Cystoseira s.l. species. While new restoration techniques recently opened the door to marine forest restoration, our results show that the interactions of multiple drivers and species interactions have to be considered to achieve long-term population sustainability.
Continue reading ‘Climate change and species facilitation affect the recruitment of macroalgal marine forests’Physiologically mediated susceptibilities of coralline algae to ocean change
Published 13 October 2022 Science ClosedTags: biological response, calcification, corals, laboratory, light, molecular biology, multiple factors, physiology, South Pacific, temperature
Coralline algae are important foundation species in coastal ecosystems around the world but are threatened by ocean acidification (OA) and other anthropogenic stressors such as ocean warming (OW) and sedimentation. Physiological responses to ocean change are challenging to predict because the mechanisms that provide tolerance to different stressors are unknown and there is a lack of understanding of responses to multiple drivers. To address these issues, I conducted four experiments examining the physiological responses of multiple temperate coralline algal species to decreasing irradiance, declining pH, OW and marine heatwaves (MHWs), and a combination of OA, OW and reduced irradiance.
Coralline algal calcification generally responded parabolically to irradiance, but photosynthesis responded linearly. My results suggest that light enhanced calcification is the result of increased ion pumping rates to elevate the calcium carbonate saturation state in the calcifying fluid (CF) and a higher daytime pH in the diffusion boundary layer that raises pHCF. My results implied the existence of two calcification strategies in coralline algae that I discuss within the thesis.
Tolerance to OA was coupled to the species’ ability to maintain stable carbonate chemistry at the site of calcification to support calcification as seawater pH declined. Conversely, pronounced changes in internal calcium carbonate saturation state (ΩCF) and skeletal magnesium content were observed in the sensitive taxa. However, ΩCF did generally not decline but increase under OA. There was also slight OA-induced photodamage in sensitive taxa that could explain the inability to support ion-pumping and growth under OA.
Photo-physiology and calcification of coralline algae were generally unaffected by OW and MHWs implying a high thermo-tolerance. However, exposure to future ocean conditions (decreased irradiance+OW x OA) caused the most severe reductions in calcification. Single driver (OA and decreased irradiance+OW) impacts were smaller. Calcification responses were decoupled from ΩCF likely due to the effective control over the internal carbonate chemistry. However, calcification likely declined due to the increased energy expenditure of calcification or when energy supply was reduced. Indeed, variations in energy expenditure and photosynthesis could explain most of the observed calcification responses.
Overall, this thesis has increased our predictive understanding regarding the impact of ocean change on coralline algae by addressing several critical issues by providing a new mechanistic model that more accurately defines the role of irradiance in coralline algal calcification.
Continue reading ‘Physiologically mediated susceptibilities of coralline algae to ocean change’Cold-water coral ecosystems under future ocean change: live coral performance vs. framework dissolution and bioerosion
Published 23 September 2022 Science ClosedTags: biological response, calcification, corals, dissolution, growth, laboratory, morphology, mortality, multiple factors, North Atlantic, physiology, temperature
Physiological sensitivity of cold-water corals to ocean change is far less understood than of tropical corals and very little is known about the impacts of ocean acidification and warming on degradative processes of dead coral framework. In a 13-month laboratory experiment, we examined the interactive effects of gradually increasing temperature and pCO2 levels on survival, growth, and respiration of two prominent color morphotypes (colormorphs) of the framework-forming cold-water coral Lophelia pertusa, as well as bioerosion and dissolution of dead framework. Calcification rates tended to increase with warming, showing temperature optima at ~ 14°C (white colormorph) and 10–12°C (orange colormorph) and decreased with increasing pCO2. Net dissolution occurred at aragonite undersaturation (ΩAr < 1) at ~ 1000 μatm pCO2. Under combined warming and acidification, the negative effects of acidification on growth were initially mitigated, but at ~ 1600 μatm dissolution prevailed. Respiration rates increased with warming, more strongly in orange corals, while acidification slightly suppressed respiration. Calcification and respiration rates as well as polyp mortality were consistently higher in orange corals. Mortality increased considerably at 14–15°C in both colormorphs. Bioerosion/dissolution of dead framework was not affected by warming alone but was significantly enhanced by acidification. While live corals may cope with intermediate levels of elevated pCO2 and temperature, long-term impacts beyond levels projected for the end of this century will likely lead to skeletal dissolution and increased mortality. Our findings further suggest that acidification causes accelerated degradation of dead framework even at aragonite saturated conditions, which will eventually compromise the structural integrity of cold-water coral reefs.
Continue reading ‘Cold-water coral ecosystems under future ocean change: live coral performance vs. framework dissolution and bioerosion’Environmental memory gained from exposure to extreme pCO2 variability promotes coral cellular acid–base homeostasis
Published 23 September 2022 Science ClosedTags: abundance, biological response, calcification, corals, field, laboratory, molecular biology, mortality, otherprocess, photosynthesis, physiology, protists, South Pacific
Ocean acidification is a growing threat to coral growth and the accretion of coral reef ecosystems. Corals inhabiting environments that already endure extreme diel pCO2 fluctuations, however, may represent acidification-resilient populations capable of persisting on future reefs. Here, we examined the impact of pCO2 variability on the reef-building coral Pocillopora damicornis originating from reefs with contrasting environmental histories (variable reef flat versus stable reef slope) following reciprocal exposure to stable (218 ± 9) or variable (911 ± 31) diel pCO2 amplitude (μtam) in aquaria over eight weeks. Endosymbiont density, photosynthesis and net calcification rates differed between origins but not treatment, whereas primary calcification (extension) was affected by both origin and acclimatization to novel pCO2 conditions. At the cellular level, corals from the variable reef flat exhibited less intracellular pH (pHi) acidosis and faster pHi recovery rates in response to experimental acidification stress (pH 7.40) than corals originating from the stable reef slope, suggesting environmental memory gained from lifelong exposure to pCO2 variability led to an improved ability to regulate acid–base homeostasis. These results highlight the role of cellular processes in maintaining acidification resilience and suggest that prior exposure to pCO2 variability may promote more acidification-resilient coral populations in a changing climate.
Continue reading ‘Environmental memory gained from exposure to extreme pCO2 variability promotes coral cellular acid–base homeostasis’Global change differentially modulates Caribbean coral physiology
Published 20 September 2022 Science ClosedTags: abundance, biological response, BRcommunity, calcification, corals, laboratory, morphology, multiple factors, North Atlantic, otherprocess, photosynthesis, physiology, protists, temperature
Global change driven by anthropogenic carbon emissions is altering ecosystems at unprecedented rates, especially coral reefs, whose symbiosis with algal symbionts is particularly vulnerable to increasing ocean temperatures and altered carbonate chemistry. Here, we assess the physiological responses of three Caribbean coral (animal host + algal symbiont) species from an inshore and offshore reef environment after exposure to simulated ocean warming (28, 31°C), acidification (300–3290 μatm), and the combination of stressors for 93 days. We used multidimensional analyses to assess how a variety of coral physiological parameters respond to ocean acidification and warming. Our results demonstrate reductions in coral health in Siderastrea siderea and Porites astreoides in response to projected ocean acidification, while future warming elicited severe declines in Pseudodiploria strigosa. Offshore S. siderea fragments exhibited higher physiological plasticity than inshore counterparts, suggesting that this offshore population was more susceptible to changing conditions. There were no plasticity differences in P. strigosa and P. astreoides between natal reef environments, however, temperature evoked stronger responses in both species. Interestingly, while each species exhibited unique physiological responses to ocean acidification and warming, when data from all three species are modelled together, convergent stress responses to these conditions are observed, highlighting the overall sensitivities of tropical corals to these stressors. Our results demonstrate that while ocean warming is a severe acute stressor that will have dire consequences for coral reefs globally, chronic exposure to acidification may also impact coral physiology to a greater extent in some species than previously assumed. Further, our study identifies S. siderea and P. astreoides as potential ‘winners’ on future Caribbean coral reefs due to their resilience under projected global change stressors, while P. strigosa will likely be a ‘loser’ due to their sensitivity to thermal stress events. Together, these species-specific responses to global change we observe will likely manifest in altered Caribbean reef assemblages in the future.
Continue reading ‘Global change differentially modulates Caribbean coral physiology’Impacts of warming and acidification on coral calcification linked to photosymbiont loss and deregulation of calcifying fluid pH
Published 14 September 2022 Science ClosedTags: biological response, BRcommunity, calcification, community composition, corals, laboratory, multiple factors, otherprocess, physiology, protists, South Pacific, temperature
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.
Continue reading ‘Impacts of warming and acidification on coral calcification linked to photosymbiont loss and deregulation of calcifying fluid pH’
