Along with its impact on calcifying plankton, ocean acidification also affects benthic biogeochemistry and organisms. Compared to the overlying water, fluid composition in sediments is altered through the effect of the mineralization of organic matter, which can further lower both pH and the carbonate saturation state. This can potentially be counteracted by the addition of carbonate minerals to the sediment surface. To explore the biogeochemical effects of mineral additions to coastal sediments, we experimentally quantified carbonate mineral dissolution kinetics, and then integrated this data into a reactive transport model that represents early diagenetic cycling of C, O, N, S and Fe, and traces total alkalinity, pH and saturation state of CaCO3. Model simulations were carried out to delineate the impact of mineral type and amount added, porewater mixing and organic matter mineralization rates on sediment alkalinity and its flux to the overlying water. Model results showed that the added minerals undergo initial rapid dissolution and generate saturated conditions. Aragonite dissolution led to higher alkalinity concentrations than calcite. Simulations of carbonate mineral additions to sediment environments with low rates of organic matter mineralization exhibited a significant increase in mineral saturation state compared to sediments with high CO2 production rates, highlighting the environment-specific extent of the buffering effect. Our work indicates that carbonate additions have the potential to effectively buffer surficial sediments over multiple years, yielding biogeochemical conditions that counteract the detrimental effect of OA conditions on larval recruitment, and potentially increase benthic alkalinity fluxes to support marine carbon dioxide removal (mCDR) in the overlying water.
Continue reading ‘Countering the effect of ocean acidification in coastal sediments through carbonate mineral additions’Posts Tagged 'dissolution'
Countering the effect of ocean acidification in coastal sediments through carbonate mineral additions
Published 4 April 2024 Science ClosedTags: biogeochemistry, chemistry, dissolution, mitigation, modeling, mollusks, regionalmodeling, sediment
Archival records of the Antarctic clam shells from Marian Cove, King George Island suggest a protective mechanism against ocean acidification
Published 21 February 2024 Science ClosedTags: Antarctic, biological response, dissolution, field, mollusks, morphology, paleo, physiology, sediment
Abstract
Continuous emissions of anthropogenic CO2 are changing the atmospheric and oceanic environment. Although some species may have compensatory mechanisms to acclimatize or adapt to the changing environment, most marine organisms are negatively influenced by climate change. In this study, we aimed to understand the compensatory mechanisms of the Antarctic clam, Laternula elliptica, to climate-related stressors by using archived shells from 1995 to 2018. Principal component analysis revealed that seawater pCO2 and salinity in the Antarctic Ocean, which have increased since the 2000’s, are the most influential factors on the characteristics of the shell. The periostracum thickness ratio and nitrogen on the outermost surface have increased, and the dissolution area (%) has decreased. Furthermore, the calcium content and mechanical properties of the shells have not changed. The results suggest that L. elliptica retains the mechanism of protecting the shell from high pCO2 by thickening the periostracum as a phenotype plasticity.
Highlights
- We analyzed archival shells of the Antarctic clams in response to climate change.
- Seawater pCO2 and salinity in the Antarctic Ocean have increased since the 2000’s.
- Shell dissolution decreased over time while total shell thickness remained constant.
- The calcium content and mechanical properties of the shell remained unchanged.
- Shell integrity was retained by thickening the organic layer enriched with nitrogen.
Turf algae drives coral bioerosion under high CO2
Published 20 February 2024 Science ClosedTags: abundance, algae, biogeochemistry, biological response, BRcommunity, calcification, chemistry, communityMF, corals, dissolution, field, laboratory, morphology, multiple factors, North Pacific, otherprocess, photosynthesis, respiration, temperature, vents
Turf algal prevalence will increase in coral ecosystems under ocean acidification yet their contribution towards the ongoing and projected degradation of reefs is often overlooked. Turf algal settlement was induced on exposed coral skeleton adjacent to live coral tissue to investigate coral-turf algal interactions through a combination of laboratory and field transplantation (shallow volcanic CO2 seep) experiments across two temperature regimes. Here, we show that turf algae are competitively favored over corals under high pCO2 conditions. Turf algae-associated biological activity locally acidified the microenvironment overlying the exposed coral skeleton, leading to its bioerosion. Increases in coral-turf algal interactions could shift coral ecosystems towards net dissolution and should be integrated into global accretion models when considering future carbonate budgets under climate change.
Continue reading ‘Turf algae drives coral bioerosion under high CO2’Effects of year-long exposure to elevated pCO2 on the metabolism of back reef and fore reef communities
Published 16 February 2024 Science ClosedTags: abundance, biological response, BRcommunity, calcification, corals, dissolution, field, otherprocess, primary production, South Pacific
The implications of ocean acidification are acute for calcifying organisms, notably tropical reef corals, for which accretion generally is depressed and dissolution enhanced at reduced seawater pH. We describe year-long experiments in which back reef and fore reef (17-m depth) communities from Moorea, French Polynesia, were incubated outdoors under pCO2 regimes reflecting endpoints of representative concentration pathways (RCPs) expected by the end the century. Incubations were completed in three to four flumes (5.0 × 0.3 m, 500 L) in which seawater was refreshed and circulated at 0.1 m s−1, and the response of the communities was evaluated monthly by measurements of net community calcification (NCC) and net community productivity (NCP). For both communities, NCC (but not NCP) was affected by treatments and time, with NCC declining with increasing pCO2, and for the fore reef, becoming negative (i.e., dissolution was occurring) at the highest pCO2 (1067–1433 μatm, RCP8.5). There was scant evidence of community adjustment to reduce the negative effects of ocean acidification, and inhibition of NCC intensified in the back reef as the abundance of massive Porites spp. declined. These results highlight the risks of dissolution under ocean acidification for coral reefs and suggest these effects will be most acute in fore reef habitats. Without signs of amelioration of the negative effects of ocean acidification during year-long experiments, it is reasonable to expect that the future of coral reefs in acidic seas can be predicted from their current known susceptibility to ocean acidification.
Continue reading ‘Effects of year-long exposure to elevated pCO2 on the metabolism of back reef and fore reef communities’Interactive effects of ocean acidification and water flow on growth and recruitment of early successional coralline algal communities
Published 16 November 2023 Science ClosedTags: algae, biological response, BRcommunity, dissolution, laboratory, morphology, otherprocess, reproduction
Coralline algae play crucial roles in near-shore ecosystems but are susceptible to ocean acidification (OA). It has been hypothesized that low water velocity, allowing localized photosynthesis-driven pH-increases in the coralline surface boundary layer, could buffer against the negative impacts of OA. To test how water motion affected the sensitivity of coralline algae to OA, coralline communities (from 2 m and 10 m depth) were grown for 220 days at two pH levels (present-day: pH 8.03, OA: pH 7.65) under differing inflow rates (400, 200 and 100 ml min–1) providing water velocities of 2.7, 5.9 and 7.8 cm s–1. Communities from both depths were grown together, photographed to assess growth, and the resulting recruitment was evaluated at the experiment’s conclusion. Low seawater pH reduced growth by c. 11% (highest flow), further decreased by >23% under the lowest flow. This reduction resulted in differential outcomes for the two depths, with skeletal net-dissolution under the combination of low flow and pH 7.65 for 10 m communities. Furthermore, there was a synergistic interaction between the effects of flow and pH, whereby the negative effect of OA strengthened under low flow, with recruitment halved at pH 7.65. This demonstrates that OA impacts can be modulated by the flow environment. Surprisingly, increased flow rates/water velocities reduced negative impacts of low pH, thus further challenging the notion that slow flow habitats offer protection from OA. The observed interactions between water flow and OA on early successional communities and their recruits may hold implications for the future of rocky reef systems dominated by these communities.
Continue reading ‘Interactive effects of ocean acidification and water flow on growth and recruitment of early successional coralline algal communities’Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools (update)
Published 26 October 2023 Science ClosedTags: algae, biological response, BRcommunity, calcification, chemistry, dissolution, field, North Atlantic, primary production, respiration
Human CO2 emissions are modifying ocean carbonate chemistry, causing ocean acidification and likely already impacting marine ecosystems. In particular, there is concern that coastal, benthic calcifying organisms will be negatively affected by ocean acidification, a hypothesis largely supported by laboratory studies. The inter-relationships between carbonate chemistry and marine calcifying communities in situ are complex, and natural mesocosms such as tidal pools can provide useful community-level insights. In this study, we manipulated the carbonate chemistry of intertidal pools to investigate the influence of future ocean acidification on net community production (NCP) and calcification (NCC) at emersion. Adding CO2 at the start of the tidal emersion to simulate future acidification (+1500 µatm pCO2, target pH 7.5) modified net production and calcification rates in the pools. By day, pools were fertilized by the increased CO2 (+20 % increase in NCP, from 10 to 12 mmol O2 m−2 h−1), while there was no measurable impact on NCC. During the night, pools experienced net community dissolution (NCC < 0), even under present-day conditions, when waters were supersaturated with regard to aragonite. Adding CO2 to the pools increased nocturnal dissolution rates by 40 % (from −0.7 to −1.0 mmol CaCO3 m−2 h−1) with no consistent impact on nocturnal community respiration. Our results suggest that ocean acidification is likely to alter temperate intertidal community metabolism on sub-daily timescales, enhancing both diurnal community production and nocturnal calcium carbonate dissolution.
Continue reading ‘Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools (update)’The effect of total alkalinity on growth performance and calcification in juvenile Pacific abalone Haliotis discus hannai
Published 5 October 2023 Science ClosedTags: biological response, calcification, dissolution, laboratory, mollusks, morphology, North Pacific, physiology
A 45-day trial was conducted to study the effect of seawater total alkalinity (TA) level up- and downregulation on the growth performance and calcification of Haliotis discus hannai Ino, while seawater pH was maintained at pHNBS = 8.1. Although seawater was not acidified, the results showed that TA downregulation caused a significant reduction (P < 0.05) in the somatic tissue growth of juvenile abalone, while TA upregulation significantly increased growth performance (P < 0.05). Similar to the impacts of pH reduction, TA downregulation also induces a decline in CO2 buffering capacity, which may be the reason why somatic tissue growth was reduced, as lowered CO2 buffering capacity was reported to shift the acid-base balancing of abalone. Parts of the periostracum layer weremissing and exposed the inner shell layers of the individuals from the TA-downregulated group. Scanning electron microscopy (SEM) results showed calcium carbonate densely deposited onto the inner shell in the control and TA-upregulated groups, while sparsely deposited calcium carbonate was observed in the TA-downregulated group. The C: N ratio in the shell of individuals from the TA-downregulated group was significantly lower than that of the other two groups, indicating that less inorganic carbon was added to the shell. As a result, abalone grew lighter and thinner shells in TA-downregulated seawater. Although seawater was not acidified, TA downregulation also caused a reduction in the calcium carbonate saturation state (Ω), which induced the erosion of the surface shell and the interruption of calcium carbonate generation. In conclusion, although seawater pH remained at ambient levels, the lowered CO2 buffering capacity and Ω induced by seawater TA downregulation also showed a detrimental effect on the growth and calcification of Pacific abalone. The impact of ocean acidification on the growth of abalone should not be assessed using only seawater pH and/or pCO2 but rather taking into account all of carbonate chemistry, particularly the CO2 buffering capacity. Abalone cultivation is suggested to be carried out in seawater with a higher level of CO2 buffering capacity and Ω, which can be achieved through integrated culture with seaweed or increasing the seawater TA level.
Continue reading ‘The effect of total alkalinity on growth performance and calcification in juvenile Pacific abalone Haliotis discus hannai’Ocean acidification influences the gene expression and physiology of two Caribbean bioeroding sponges
Published 5 September 2023 Science ClosedTags: biological response, dissolution, laboratory, molecular biology, North Atlantic, porifera
Introduction: Coral reef ecosystems are experiencing increased rates of carbonate dissolution due to losses in live coral cover coupled with the impacts of ocean acidification (OA) on coral reef calcifiers and bioeroders. While the stimulating effect of OA on bioerosion has been demonstrated experimentally, predominantly in the Pacific, the underlying physiological and molecular mechanisms behind the response are still poorly understood.
Methods: To address this, we subjected common zooxanthellate (Cliona varians) and azooxanthellate (Pione lampa) Caribbean sponges to pre-industrial (8.15 pH), present-day (8.05 pH), and two future OA scenarios (moderate OA, 7.85 pH; extreme OA, 7.75 pH) and evaluated their physiological and transcriptomic responses.
Results: The influence of OA on sponge bioerosion was nonlinear for both species, with the greatest total bioerosion and chemical dissolution rates found in the 7.85 pH treatment, then not increasing further under the more extreme 7.75 pH conditions. A trend towards reduced bioerosion rates in the 7.75 pH treatment occurred regardless of the presence of algal symbionts and suggests that the sponges may become physiologically impaired under prolonged OA exposure, resulting in diminished bioerosion potential. These findings were supported by the RNA-seq analysis, which revealed differentially expressed genes involved in a stress response to OA, in particular, suppressed metabolism.
Discussion: This may indicate that the sponges had reallocated energy resources towards more critical physiological needs in response to OA as a survival mechanism under stressful conditions. These data reveal that while the bioerosion rates of excavating sponges in Caribbean reef ecosystems may increase under moderate OA scenarios, this OA-stimulation may plateau or be lost at extreme end-of-century pH conditions, with implications for the dissolution and long-term persistence of reef habitat structures.
Continue reading ‘Ocean acidification influences the gene expression and physiology of two Caribbean bioeroding sponges’From individual to ecosystem: multi-stressor effects of acidification and warming on the physiological responses of coastal marine invertebrates
Published 24 August 2023 Science ClosedTags: biological response, BRcommunity, calcification, dissolution, field, mesocosms, mollusks, morphology, multiple factors, North Pacific, temperature
Climate change is directly impacting the services humans derive from the sea at an accelerated rate. Ocean warming and acidification (i.e., a decrease in ocean pH) are leading to modifications in population sizes and ecosystem functioning. The observed shifts in these higher order processes are a direct result of individuals’ responses (i.e., physiology, including metabolism, growth, calcification, and survival) occurring within communities. Natural variation in past environmental exposure experienced by individuals may lead to greater population resilience, or it may push individuals past physiological thresholds leading to increased sensitivity and vulnerability to climate change. Thus, we need to determine how individual-level physiological responses to climate change scale up to influence marine ecosystems. Rocky intertidal habitats are an ideal study system for evaluating the relationships between individual physiological responses, ecosystem functioning, and climate change. Tide pools possess unique thermal and pH environments and can be monitored under natural conditions or manipulated with field-experiments over daily and seasonal time scales, creating natural “experimental mesocosms”. In addition, many species within rocky intertidal habitats are exposed to environmental conditions close to their tolerance limits, increasing their potential vulnerability to climate change. In Chapter 1, by utilizing the unique thermal environments of tide pools, I showed that across small spatial scales (pools), thermal history influences thermal sensitivity of marine invertebrates for short-term time intervals (1-week and 1-day) and that this relationship differs seasonally and between species with differing traits, including mobility. This suggests that variability in thermal responses among individuals may allow for a natural buffer at a population level in response to climate change. Multiple stressors may affect individuals independently or interactively, amplifying or mitigating effects. Thus, to determine the impacts of climate change, in Chapter 2, I used a 6-month long field manipulation of ocean warming and acidification in tide pools. I examined the combined effects of warming and acidification on the shell structure (shell thickness and corrosion) and functional properties (shell strength) of the ecologically critical species, the Pacific blue mussel (Mytilus trossulus). Acidification led to thinner, weaker, and more corroded shells whereas combined warming and acidification resulted in an increase in shell strength. My results suggest that to some degree, warming may mitigate the negative impacts of acidification on this mollusk species. Lastly, in Chapter 3, I characterize how warming and acidification, individually and interactively, impact net ecosystem calcification and the individual and population-level mechanisms driving impacts on net ecosystem calcification. Net ecosystem calcification tended to increase during the day and decrease at night; however, addition of CO2 during the hottest months led to decreased net ecosystem calcification and increased dissolution during both day and night. I found that individual mussel metabolic rates increased significantly in the presence of elevated CO2 and increased daily maximum of pool temperatures. Through this individual-level pathway, pH and temperature had a strong impact on the metabolic rates of individuals ultimately resulting in changes in net ecosystem calcification. On the other hand, greater mussel abundance was associated with increased net ecosystem calcification. Yet, with the addition of CO2, calcification decreased even in pools with the highest abundance of mussels, indicating that there are other pathways by which changes in pH can drive alterations in net ecosystem calcification. My dissertation reveals how species’ traits and natural thermal variation from short-term to seasonal time scales influence metabolic sensitivity to future warming among individuals (Ch. 1), independent climate stressors can negatively impact shellfish in situ, whereas the combined interactive effects between multiple stressors can lead to mitigation of the negative impacts of a single stressor alone (Ch. 2), and that ecosystem-level consequences of climate change are mediated by the abundance of dominant calcifiers and that this effect is dependent on the magnitude of acidification and warming (Ch. 3).
Continue reading ‘From individual to ecosystem: multi-stressor effects of acidification and warming on the physiological responses of coastal marine invertebrates’Pacific oysters do not compensate growth retardation following extreme acidification events
Published 21 August 2023 Science ClosedTags: biological response, dissolution, laboratory, mollusks, morphology
Ocean acidification caused by anthropogenic carbon dioxide emissions alters the growth of marine calcifiers. Although the immediate effects of acidification from global ocean models have been well studied on calcifiers, their recovery capacity over a wide range of pH has never been evaluated. This aspect is crucial because acidification events that arise in coastal areas can far exceed global ocean predictions. However, such acidification events could occur transiently, allowing for recovery periods during which the effects on growth would be compensated, maintained or amplified. Here we evaluated the recovery capacity of a model calcifier, the Pacific oyster Crassostrea gigas. We exposed juveniles to 15 pH conditions between 6.4 and 7.8 for 14 days. Oyster growth was retarded below pH 7.1 while shells were corroded at pH 6.5. We then placed the oysters under ambient pH > 7.8 for 42 days. Growth retardation persisted at pH levels below pH 7.1 even after the stress was removed. However, despite persistent retardation, growth has resumed rapidly suggesting that the oysters can recover from extreme acidification. Yet we found that the differences in individual weight between pH conditions below 7.1 increased over time, and thus the growth retardation cannot be compensated and may affect the fitness of the bivalves.
Continue reading ‘Pacific oysters do not compensate growth retardation following extreme acidification events’Seasonal production dynamics of high latitude seaweeds in a changing ocean: implications for bottom-up effects on temperate coastal food webs
Published 10 August 2023 Science ClosedTags: algae, biological response, BRcommunity, calcification, chemistry, dissolution, field, growth, laboratory, light, morphology, multiple factors, North Pacific, otherprocess, phanerogams, photosynthesis, physiology, primary production, temperature
As the oceans absorb excess heat and CO2 from the atmosphere, marine primary producers face significant changes to their abiotic environments and their biotic interactions with other species. Understanding the bottom-up consequences of these effects on marine food webs is essential to informing adaptive management plans that can sustain ecosystem and cultural services. In response to this need, this dissertation provides an in-depth consideration of the effects of global change on foundational macroalgal (seaweed) species in a poorly studied, yet highly productive region of our world’s oceans. To explore how seaweeds within seasonally dynamic giant kelp forest ecosystems will respond to ocean warming and acidification, I employ a variety of methods: year-round environmental monitoring using an in situ sensor array, monthly subtidal community surveys, and a series of manipulative experiments. I find that a complementary phenology of macroalgal production currently characterizes these communities, providing complex habitat and a nutritionally diverse energy supply to support higher trophic levels throughout the year. I also find that future ocean warming and acidification will lead to substantial shifts in the phenology, quantity and quality of macroalgal production in these systems. My results suggest that the giant kelp Macrocystis pyrifera may be relatively resilient to the effects of global change in future winter and summer seasons at high latitudes. In contrast, the calcifying coralline algae Bossiella orbigniana and Crusticorallina spp. and the understory kelps Hedophyllum nigripes and Neoagarum fimbriatum will experience a suite of negative impacts, especially in future winter conditions. The resulting indirect effects on macroalgal-supported coastal food webs will be profound, with projected reductions in habitat and seasonal food supply on rocky reefs. Coming at a time of heightened interest in seaweed production potential at high latitudes, this dissertation provides a comprehensive evaluation of the future of these foundational organisms in a changing environment.
Continue reading ‘Seasonal production dynamics of high latitude seaweeds in a changing ocean: implications for bottom-up effects on temperate coastal food webs’Constraining oceanic carbonate chemistry evolution during the Cretaceous-Paleogene transition: combined benthic and planktonic calcium isotope records from the equatorial Pacific Ocean
Published 1 August 2023 Science ClosedTags: biological response, calcification, dissolution, field, North Pacific, paleo, phytoplankton, protists, sediment
The Mesozoic-Cenozoic transition is a period of biogeochemical cycle perturbations. The strongest of them is the Cretaceous-Paleogene boundary (K-Pg) crisis, characterized by one of the most important extinctions of planktonic marine calcifiers in Earth’s history. One of the primary drivers of this biocalcification crisis is thought to be the increase in atmospheric CO2 concentration and ocean acidification triggered by the Chicxulub Impact, and/or Deccan volcanism. Because it reflects changes of the calcium cycle and/or depends on parameters of the carbonate system, the Ca isotope composition of carbonate minerals precipitated from seawater (44/40Ca) offers the potential to reconstruct some of the environmental changes that occurred. Here we present new high-resolution planktonic and benthic foraminiferal 44/40Ca, 18O, 13C, and Sr/Ca records across the K-Pg transition from Shatsky rise (Leg 198; ODP Site 1209, Hole C). The 44/40Ca record displays a succession of rapid shifts of ca. ‰−0.4‰ across the K-Pg transition. They are similar though not identical between the planktonic and benthic records. These shifts took place on a timescale significantly shorter than the residence time of Ca in the oceans and are therefore unlikely to result from global disequilibrium in the oceanic Ca budget. Instead, changes in the fractionation factor between carbonate minerals and seawater in response to changes in precipitation rates may explain the observed 44/40Ca and Sr/Ca record. The benthic and planktonic 44/40Ca records show a late Maastrichtian and an early Danian negative excursions best explained by a succession of episodes of ocean alkalinity increase related to increased continental weathering caused by CO2 emissions from Deccan volcanism and the aftermath of the K-Pg biocalcification crisis. Carbonate compensation via carbonate sediment dissolution, biological carbonate compensation via reduction of biocalcification, and/or an increase in continental weathering must have occurred to offset the excess CO2, ultimately resulting in rapid changes in ocean carbonate chemistry, in combination with reduced surface alkalinity export in response to the early Paleogene planktonic biomineralization crisis.
Continue reading ‘Constraining oceanic carbonate chemistry evolution during the Cretaceous-Paleogene transition: combined benthic and planktonic calcium isotope records from the equatorial Pacific Ocean’The effects of ocean change drivers on the ecophysiology of the mottled brittle star Ophionereis fasciata
Published 18 July 2023 Science ClosedTags: biological response, calcification, dissolution, echinoderms, growth, laboratory, mesocosms, mortality, multiple factors, performance, physiology, South Pacific, temperature
Global ocean environments are rapidly changing, posing a substantial threat to the viability of marine populations due to the co-occurrence of different changing ocean (CO) drivers, such as ocean warming (OW) and ocean acidification (OA). In order to persist, marine species undergo some combination of acclimation and adaptation in response to these changes. Understanding such responses is essential to measure and predict the magnitude and direction of environmental changes, leading to the development of different approaches to understanding the links and interactions between biological processes and abiotic environmental conditions. A series of long-term mesocosm experiments have been conducted using adult Ophionereis fasciata as a model to investigate the physiological response and trade-offs of marine organisms to ocean acidification, ocean warming and the combined effect of both drivers. A scenario-based approach was adopted to elucidate the primary physiological responses to conditions currently experienced by this species in its tidally influenced habitat (21-24°C and pH 7.75-7.4) as well as changes expected to occur in the near future due to CO (+2.5 ℃ and -0.36 pH by 2100). Long-term exposure to OW and OA conditions affected survival, metabolic rate, regeneration and growth rates, calcification/dissolution and the righting response of O. fasciata. Temperature changes clearly impacted these aspects of the mottled brittle star, while changes in pH had more subtle or no effect. Our results indicate that for most of the assessed ecophysiological traits, there are no significant interactive effects of OA and OW. Moreover, temperature was the dominant driver, with a greater impact regarding the magnitude and quantity of the affected processes. However, the exposure to a combination of high temperature and low pH produced complex responses in terms of survival and calcification/dissolution. Finally, we documented the first report of symbionts associated with O. fasciata: an obligate amphipod parasite and a facultative commensal polychaete. Our findings indicate that the mottled brittle star will need to cope with CO conditions in context with the predictions made for New Zealand waters, with a potential impact on its performance and survival, as well as its distribution and ecological interactions.
Continue reading ‘The effects of ocean change drivers on the ecophysiology of the mottled brittle star Ophionereis fasciata’Organismal responses to coastal acidification informed by interrelating erosion, roundness and growth of gastropod shells
Published 28 June 2023 Science ClosedTags: biological response, dissolution, field, growth, mollusks, morphology, North Pacific
Current understanding of how calcifying organisms respond to externally forced oceanic and coastal acidification (OCA) is largely based on short-term, controlled laboratory or mesocosm experiments. Studies on organismal responses to acidification (reduced carbonate saturation and pH) in the wild, where animals simultaneously interact with a range of biotic and abiotic circumstances, are limited in scope and interpretation. The present study aimed to better understand the value of gastropod shell attributes and their interrelations in informing about responses to coastal acidification. We investigated shell chemical erosion, shell roundness, and growth rate of Planaxis sulcatus snails, which are locally exposed to acidified or non-acidified rocky intertidal water. We trialed a new approach to quantifying shell erosion based on the spiral suture length (EI, erosion index), and found that shell erosion mirrored field acidification conditions. Acidification caused shells to become rounder (width/length) compared to those of snails from a non-acidified shore. Field growth rate, determined from apertural margin extension of marked and later recaptured snails, was strongly negatively related to both shell erosion and shell roundness. Because the different shell attributes inform about different associations – shell erosion represents an extrinsic passive marker of acidification, and shell roundness and growth rate are intrinsic performance responders – their interrelations imply causation, infer predictive power and improve interpretation confidence. This study contributes to the methodology and interpretation of findings of trait-based field investigations to understand organismal responses to coastal acidification.
Continue reading ‘Organismal responses to coastal acidification informed by interrelating erosion, roundness and growth of gastropod shells’Costs and mechanisms associated with resilience to acidification in marine bivalves
Published 9 June 2023 Science ClosedTags: adaptation, biological response, dissolution, laboratory, molecular biology, mollusks, mortality, otherprocess, physiology
The unprecedented flux of CO2 into the ocean and the resulting chemical reactions has led to a reduction in pH, carbonate concentration, and saturation states of calcium carbonate, known as ocean acidification (OA). These conditions make it more difficult to precipitate biogenic calcium carbonate to mineralize shells because of the reduction in available carbonate ions. This represents a serious and growing threat to the future of commercially and ecologically important species, such as the northern quahog (Mercenaria mercenaria) and eastern oyster (Crassostrea virginica). But clams and oysters are found in heterogeneous coastal environments and are already exposed to reductions in pH surpassing predictions for the decrease in open ocean pH for the end of the century (with pH dropping below 7 under ambient conditions). These bivalves have shown high levels of resilience to fluctuations in pH and a capacity to respond to altered carbonate chemistry. However, the accelerated pace of these changes requires additional understanding of how or if species and populations will be able to acclimate or adapt to such swift environmental alterations. Future acidification might result in reduction in average pH, changes in the scale of variability, more occurrences of extreme acidification, and less periods of relief, exceeding thresholds of tolerance.
Thus far, the majority of studies have focused on the physiological effects of elevated pCO2 on bivalve larvae. While important, this leaves a substantial gap in knowledge of the molecular mechanisms of resilience to elevated pCO2 or the effect of acidification on different life history stages. To fill this gap in our understanding, this dissertation aims to uncover the mechanisms of resilience to elevated pCO2 in clams and oysters at different stages of their life.
This study combined physiological assays with ‘omic’ approaches (transcriptomics, genomics, proteomics) to assess the susceptibility of clams and oysters to acidification and the factors conferring resilience. Mechanisms enabling bivalves to respond to elevated pCO2 (from the organism level to individual genes) were investigated, taking into consideration the potential costs of resilience to elevated pCO2. Gene silencing experiments (RNAi) and chemical inhibition were used to confirm the protective role of candidate genes (perlucin and carbonic anhydrase, respectively) associated with resilience to elevated pCO2. While there were consequences for surviving under stressful acidification conditions, demonstrated by a marked reduction in immunity, depletion of energy resources, and inability to remineralize damaged shell, M. mercenaria and C. virginica, having already been exposed to natural fluctuations in pH and carbonate chemistry for generations, appear to be capable of implementing strategies to mitigate the negative impacts of elevated pCO2 (acclimation). While acclimation can be costly, the potential for adaptation was also investigated, and there was evidence to suggest genetic selection for OA-resilient genotypes enabling clams and oysters to persist under future climate regimes.
Continue reading ‘Costs and mechanisms associated with resilience to acidification in marine bivalves’The Paleocene-Eocene transition in the Gulf of Guinea: evidence of the Petm in the Douala Basin, Cameroon
Published 1 June 2023 Science ClosedTags: biological response, crustaceans, dissolution, field, morphology, North Atlantic, paleo, protists, sediment
The Paleocene-Eocene Thermal Maximum (PETM) was identified for the first time in two sections (Bongue and Dibamba) from the Douala sub-basin located in the Gulf of Guinea, Cameroon. This discovery was based on a multi-disciplinary approach including benthic and planktic foraminifera, ostracods, major and trace elements, mercury, carbon stable isotope (δ13C values), total organic carbon (TOC), whole-rock and clay mineralogy. A combination of lithology, microfossil assemblage, and carbon isotope data indicate zone P5 and the top of the Paleocene enabling the definition of the Paleocene-Eocene boundary (PEB). A negative carbon-isotope excursion (CIE) spanning from the uppermost Paleocene deposits to the earliest Eocene sediments (PETM interval) shows a shift in δ13Corg values of 1.5 ‰ in Bongue and 3.0 ‰ in Dibamba. In both sections, this interval is affected by widespread acidification, as revealed by carbonate dissolution and microfossil preservation (i.e., species are dwarfed, broken, thin shelled, and with holes). The very low carbonate content and the scarcity of microfauna indicate the severity of acidification during the PETM, especially in the early Eocene where only one species was identified (Igorina broedermanni). Mercury anomalies, TOC contents, and trace element concentration ratios, point to volcanic activity linked to the Cameroon Volcanic Line (CVL) intrusive magma, and a decrease in productivity prior to the PETM. In addition to climate change, our geochemical and mineralogical data support the hypothesis that other environmental perturbations such as an increase in productivity and detrital input, as well as a decrease in bottom water oxygenation occurred during the PETM in the Douala sub-basin.
Continue reading ‘The Paleocene-Eocene transition in the Gulf of Guinea: evidence of the Petm in the Douala Basin, Cameroon’Foraminiferal assemblages and test characteristics associated with natural low pH waters at Puerto Morelos reef lagoon springs, QR Mexico
Published 26 May 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, dissolution, laboratory, morphology, North Pacific, otherprocess, protists, sediment
Ocean acidification is expected to negatively affect many ecologically important organisms. Here we explored the response of Caribbean benthic foraminiferal assemblages to naturally discharging low-pH waters similar to expected future projections for the end of the 21st century. At low pH (~7.7 pH units) and low calcite saturation, agglutinated and symbiont-bearing species were relatively more abundant, indicating higher resistance to potential carbonate chemistry changes. Diversity and other taxonomical metrics declined steeply with decreasing pH, despite exposure of this ecosystem for millennia to low pH conditions, suggesting that tropical foraminifera communities will be negatively impacted under acidification scenarios SSP3-7.0 and SSP5-8.5. The species Archaias angulatus, a major contributor to sediment production in the Caribbean, was able to calcify at conditions more extreme than those projected for the late 21st century (7.1 pH units), but the calcified tests were of lower density than those exposed to higher-pH ambient conditions (7.96 pH units), indicating that reef foraminiferal carbonate budget might decrease. Smaller foraminifera were highly sensitive to decreasing pH and our results demonstrate their potential as indicators to monitor increasing OA conditions.
Continue reading ‘Foraminiferal assemblages and test characteristics associated with natural low pH waters at Puerto Morelos reef lagoon springs, QR Mexico’Taphonomy and dissolution rates of the razor clam Ensis magnus shells: current status and projected acidification scenarios
Published 25 May 2023 Science ClosedTags: biological response, chemistry, dissolution, field, laboratory, modeling, mollusks, morphology, multiple factors, North Atlantic, regionalmodeling, temperature
Highlights
- Natural variability of seawater (Ta, Ωaragonite and pCO2) revealed an increase of acidification though such change did not suppose abrupt detrimental effects for taphonomic characteristics of shells (length, thickness, organic content or strength).
- Temperature affected negatively shell strength and thickness, although the large correlation between the environmental variables would disturb the individual characterization of environmental parameters.
- Dissolution rates of shells subjected to projected laboratory scenarios were significantly greater for cold-acidic environment (more corrosive) as compared to warm-acidic. Mean dissolution time (DT50) for cold-acidic scenario was reduced by half (15 years) as compared to current water chemistry conditions (30 years).
- More recent shells are being secreted in a progressively less saturated carbonate environment (at an annual rate of change of −0.0127 for Ωaragonite) and accordingly, were more prone to suffer dissolution (and weakening) in projected laboratory scenarios.
- Marine shells support ecosystem services including refuge for multiple species, substrate to attach and settle of fauna that may change in future environments or may bring changes in the ecological interactions of our coastal areas affecting biodiversity and optimal functioning of the ecosystem services.
Abstract
The analysis of the natural variability of seawater (Ta, Ωaragonite and pCO2) at Rodas Beach (NW Iberian Peninsula, Spain) revealed an increase of acidification. However, such pH change was not linked to any detrimental effect of the shell taphonomic characteristics of live razor clams harvested during distinct temporal series (length, thickness, organic content or strength). Temperature affected negatively shell strength and thickness, although the large correlation between the environmental variables would limit the individual characterization. Modelled trends in pH (and Ωaragonite) showed a significant decrease in the last 20 years, despite Ω > 1. Therefore, more recent shells are being secreted in a progressively less saturated carbonate environment and, consequently, more prone to suffer dissolution (and weakening) in projected climatic scenarios. When shells of harvested razor clams were exposed to projected climatic scenarios in the laboratory, dissolution rates were significantly greater for cold-acidic scenarios (more corrosive) as compared to warm-acidic. The median dissolution time (DT50) for shells under the cold-acidic scenario was reduced by half (15 years) when compared to the values observed for shells under current water chemistry conditions (30 years).
Galician coastline, often characterised by pCO2-rich and cold waters due to upwelling system, would represent the most corrosive scenario for the shells according to the responses monitored in our survey which highlight future compromise for the ecosystem services supplied by these hard skeletons. Future climate scenarios might condition performance of bivalves but also more complex processes related to carbonate structures. Local biodiversity may be lowered which may reduce the possibility that many species find shelter and feeding grounds, diminishing the optimal substrate for other organisms as needed elements for optimal services in the ecosystems.
Continue reading ‘Taphonomy and dissolution rates of the razor clam Ensis magnus shells: current status and projected acidification scenarios’Evidence for an effective defence against ocean acidification in the key bioindicator pteropod Limacina helicina
Published 19 May 2023 Science ClosedTags: biological response, dissolution, laboratory, mollusks, morphology, mortality, North Pacific, performance, zooplankton
The pteropod Limacina helicina has become an important bioindicator species for the negative impacts of ocean acidification (OA) on marine ecosystems. However, pteropods diversified during earlier high CO2 periods in Earth history and currently inhabit regions that are naturally corrosive to their shells, suggesting that they possess mechanisms to survive unfavourable conditions. Recent work, which is still under considerable debate, has proposed that the periostracum, a thin organic coating on the outer shell, protects pteropods from shell dissolution. Here, we provide direct evidence that shows that damage to the L. helicina periostracum results in dissolution of the underlying shell when exposed to corrosive water for ∼8 d, while an intact periostracum protects the shell from dissolution under the same conditions. This important first line of defence suggests that pteropods are more resistant to OA-induced shell dissolution than is generally accepted.
Continue reading ‘Evidence for an effective defence against ocean acidification in the key bioindicator pteropod Limacina helicina’Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools
Published 18 May 2023 Science ClosedTags: algae, biological response, BRcommunity, calcification, chemistry, dissolution, field, North Atlantic, primary production, respiration
Human CO2 emissions are modifying ocean carbonate chemistry, causing ocean acidification, and likely already impacting marine ecosystems. In particular, there is concern that coastal, benthic calcifying organisms will be negatively affected by ocean acidification, a hypothesis largely supported by laboratory studies. The inter-relationships between carbonate chemistry and marine calcifying communities in situ are complex and natural mesocosms such as tidal pools can provide useful community-level insights. In this study, we manipulated the carbonate chemistry of intertidal pools to investigate the influence of future ocean acidification on net community production (NCP) and calcification (NCC) at emersion. Adding CO2 at the start of the tidal emersion to simulate future acidification (+1500 μatm pCO2, target pH: 7.5) modified net production and calcification rates in the pools. By day, pools were fertilized by the increased CO2 (+20 % increase in NCP, from 10 to 12 mmol O2 m−2 hr−1), while there was no measurable impact on NCC. During the night, pools experienced net community dissolution (NCC < 0), even in present-day conditions, when waters were supersaturated with regards to aragonite. Adding CO2 in the pools increased nocturnal dissolution rates by 40 % (from −0.7 to −1.0 mmol CaCO3 m−2 hr−1) with no consistent impact on night community respiration. Our results suggest that ocean acidification is likely to alter temperate intertidal community metabolism on sub-daily timescales, enhancing both diurnal community production and nocturnal calcium carbonate dissolution.
Continue reading ‘Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools’
