Posts Tagged 'morphology'

Influence of seagrass on juvenile Pacific oyster growth in two US west coast estuaries with different environmental gradients

Ocean acidification threatens many marine organisms, including oysters. Seagrass habitat has been suggested as a potential refuge for oysters because it may ameliorate stressful carbonate chemistry and augment food availability. We conducted an in situ study to investigate whether eelgrass Zostera marina habitat affects the growth of juvenile Pacific oysters Crassostrea gigas and influences local carbonate chemistry or food quantity at sites where we expected contrasting conditions in two US west coast estuaries. Juvenile oysters were out-planted in typical intertidal on-bottom (just above sediment) and off-bottom (45 cm above sediment) culture positions and in adjacent eelgrass and unvegetated habitats from June to September 2019. Water quality was measured with sondes for 24 h periods each month, and discrete water samples were collected in conjuncture. Results show that eelgrass habitat did not alter average local carbonate chemistry (pH, pCO2, Ωcalcite), but consistently reduced available food (relative chlorophyll a). Eelgrass habitat had little to no effect on the shell or tissue growth of juvenile oysters but may have influenced their energy allocation; oysters displayed a 16% higher ratio of shell to tissue growth in eelgrass compared to unvegetated habitat when cultured on-bottom. At the seascape scale, average site-level pH was negatively correlated with shell to tissue growth but not with shell growth alone. Overall, these findings suggest that juvenile oysters may display a compensatory response and allocate more energy to shell than tissue growth under stressful conditions like acidic water and/or altered food supply due to reduced immersion or eelgrass presence.

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The effect of ocean acidification on otolith morphology in larvae of a tropical, epipelagic fish species, yellowfin tuna (Thunnus albacares)

Increasing ocean acidification is a concern due to its potential effects on the growth, development, and survival of early life stages of tuna in oceanic habitats and on the spatial extent of their suitable nursery habitat. To investigate the potential effects of increasing CO2 on otolith calcification of 9-day old pre-flexion stage yellowfin tuna (Thunnus albacares), an experiment was conducted at the Inter-American Tropical Tuna Commission’s Achotines Laboratory in Panama during 2011. Fertilized eggs and larvae were exposed to mean pCO2 levels that ranged from present day (355 μatm) to two levels predicted to occur in some areas of the Pacific in the near future (2013 and 3321 μatm), and to an extreme value equivalent to long-term projections for 300 years in the future (9624 μatm). The results indicated significantly larger otoliths (in area and perimeter) with significant, and increasing, fluctuating asymmetry at acidification levels similar to those projected for the near future and long-term. Otoliths increased significantly in size despite a significant decrease in somatic length with increasing pCO2. A consistent correlation between otolith and somatic growth of yellowfin tuna larvae among treatments was evident (i.e., larger otoliths were still associated with larger larvae within a treatment). The observed changes in otolith morphology with increasing ocean acidification have the potential to indirectly affect larval survival through dysfunction of the mechanosensory organs, but this remains to be verified in yellowfin tuna larvae.

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Seasonality of marine calcifiers in the northern Barents Sea: spatiotemporal distribution of planktonic foraminifers and shelled pteropods and their contribution to carbon dynamics


  • In the northern Barents Sea there is a seasonal pattern of production and size distribution of planktonic foraminifers and pteropods, increasing from winter (March) to summer (July–August) and late autumn (December).
  • In general, pteropods dominate over planktonic foraminifera in the Arctic influenced stations.
  • In the study area, pteropods contribute the most (>80%) to carbon standing stocks and export production.
  • The highest values of carbon standing stocks and export production were found in the seasonal ice zone during all seasons.


The Barents Sea is presently undergoing rapid warming and the sea-ice edge and the productive zones are retreating northward at accelerating rates. Planktonic foraminifers and shelled pteropods are ubiquitous marine calcifiers that play an important role in the carbon budget and being particularly sensitive to ocean biogeochemical changes and ocean acidification. Their distribution at high latitudes have rarely been studied, and usually only for the summer season. Here we present results of their distribution patterns in the upper 300 m in the water column (individuals m−3), protein content and size distribution on a seasonal basis to estimate their inorganic and organic carbon standing stocks (µg m−3) and export production (mg m−2 d−1). The study area constitutes a latitudinal transect in the northern Barents Sea from 76˚ N to 82˚ N including seven stations through both Atlantic, Arctic, and Polar surface water regimes and the marginal and seasonal sea-ice zones. The transect was sampled in 2019 (August and December) and 2021 (March, May, and July). The highest carbon standing stocks and export production were found at the Polar seasonally sea-ice covered shelf stations with the contribution from shelled pteropods being significantly higher than planktonic foraminifers during all seasons. We recorded the highest production of foraminifers and pteropods in summer (August 2019 and July 2021) and autumn (December 2019) followed by spring (May 2021), and the lowest in winter (March 2021).

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Simultaneous warming and acidification limit population fitness and reveal phenotype costs for a marine copepod

Phenotypic plasticity and evolutionary adaptation allow populations to cope with global change, but limits and costs to adaptation under multiple stressors are insufficiently understood. We reared a foundational copepod species, Acartia hudsonica, under ambient (AM), ocean warming (OW), ocean acidification (OA), and combined ocean warming and acidification (OWA) conditions for 11 generations (approx. 1 year) and measured population fitness (net reproductive rate) derived from six life-history traits (egg production, hatching success, survival, development time, body size and sex ratio). Copepods under OW and OWA exhibited an initial approximately 40% fitness decline relative to AM, but fully recovered within four generations, consistent with an adaptive response and demonstrating synergy between stressors. At generation 11, however, fitness was approximately 24% lower for OWA compared with the AM lineage, consistent with the cost of producing OWA-adapted phenotypes. Fitness of the OWA lineage was not affected by reversal to AM or low food environments, indicating sustained phenotypic plasticity. These results mimic those of a congener, Acartia tonsa, while additionally suggesting that synergistic effects of simultaneous stressors exert costs that limit fitness recovery but can sustain plasticity. Thus, even when closely related species experience similar stressors, species-specific costs shape their unique adaptive responses.

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Differential reaction norms to ocean acidification in two oyster species from contrasting habitats

Ocean acidification (OA), a consequence of the increase in anthropogenic emissions of carbon dioxide, causes major changes in the chemistry of carbonates in the ocean with deleterious effects on calcifying organisms. The pH/pCO2 range to which species are exposed in nature is important to consider when interpreting the response of coastal organisms to OA. In this context, emerging approaches, which assess the reaction norms of organisms to a wide pH gradient, are improving our understanding of tolerance thresholds and acclimation potential to OA. In this study, we decipher the reaction norms of two oyster species living in contrasting habitats: the intertidal oyster Crassostrea gigas and the subtidal flat oyster Ostrea edulis, which are two economically and ecologically valuable species in temperate ecosystems. Six-month-old oysters of each species were exposed in common garden for 48 days to a pH gradient ranging from 7.7 to 6.4 (total scale). Both species are tolerant down to a pH of 6.6 with high plasticity in fitness-related traits such as survival and growth. However, oysters undergo remodelling of membrane fatty acids to cope with decreasing pH along with shell bleaching impairing shell integrity and consequently animal fitness. Finally, our work reveals species-specific physiological responses and highlights that intertidal C. gigas seems to have a better acclimation potential to rapid and extreme OA changes than O. edulis. Overall, our study provides important data about the phenotypic plasticity and its limits in two oyster species, which is essential for assessing the challenges posed to marine organisms by OA.

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Response of foraminifera Ammonia confertitesta (T6) to ocean acidification, warming, and deoxygenation – an experimental approach

Ocean acidification, warmer temperatures, and the expansion of hypoxic zones in coastal areas are direct consequences of the increase in anthropogenic activities. However, so far, the combined effects of these stressors on calcium carbonate-secreting marine microorganisms – foraminifera are complex and poorly understood. This study reports the foraminiferal survival behavior, and geochemical trace elements incorporation measured from the shells of living cultured benthic foraminifera from the Gullmar fjord (Sweden) after exposure to warming, acidification, and hypoxic conditions. An experimental set-up was designed with two different temperatures (fjord’s in-situ 9 ˚C and 14 ˚C), two different oxygen concentrations (oxic versus hypoxic), and three different pH (control, medium, and low pH based on the IPCC scenario for the year 2100). Duplicate aquariums, meaning aquariums displaying the same conditions and same number of species, were employed for the controls and the two lower pH conditions at both temperatures. The stability of the aquariums was ensured by regular measurement of the water parameters and confirmed by statistical analysis. The species Ammonia confertitesta’s (T6) survival (CTB-labeled), shell calcification (calcein-labeled), and geochemical analyses (laser-ablation ICP-MS) were investigated at the end of the experimental period (48 days). Investigated trace elements (TE) ratios were Mg/Ca, Mn/Ca, Ba/Ca, and Sr/ Ca. Results show that A. confertitesta (T6) calcified chambers in all the experimental conditions except for the most severe combination of stressors (i.e., warm, hypoxic, low pH). Survival rates varied by up to a factor of two between duplicates for all conditions suggesting that foraminiferal response may not solely be driven by environmental conditions but also by internal or confounding factors (e.g., physiological stress). A large variability of all the TE/Ca values of foraminifera growing at low pH is observed suggesting that A. confertitesta (T6) may struggle to calcify in these conditions. Thus, this study demonstrates the vulnerability of a resilient species to the triple-stressor scenario in terms of survival, calcification, and trace element incorporation. Overall, the experimental set-up yielded coherent results compared to previous studies in terms of ontogeny, trace elements ratios, and partition coefficient making it advantageous for environmental reconstructions. 

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Anthropogenic acidification of surface waters drives decreased biogenic calcification in the Mediterranean Sea

Anthropogenic carbon dioxide emissions directly or indirectly drive ocean acidification, warming and enhanced stratification. The combined effects of these processes on marine planktic calcifiers at decadal to centennial timescales are poorly understood. Here, we analyze size normalized planktic foraminiferal shell weight, shell geochemistry, and supporting proxies from 3 sediment cores in the Mediterranean Sea spanning several centuries. Our results allow us to investigate the response of surface-dwelling planktic foraminifera to increases in atmospheric carbon dioxide. We find that increased anthropogenic carbon dioxide levels led to basin wide reductions in size normalized weights by modulating foraminiferal calcification. Carbon (δ13C) and boron (δ11B) isotopic compositions also indicate the increasing influence of fossil fuel derived carbon dioxide and decreasing pH, respectively. Alkenone concentrations and test accumulation rates indicate that warming and changes in biological productivity are insufficient to offset acidification effects. We suggest that further increases in atmospheric carbon dioxide will drive ongoing reductions in marine biogenic calcification in the Mediterranean Sea.

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Experimental ocean acidification and food limitation reveals altered energy budgets and synergistic effects on mortality of larvae of a coastal fish

Ocean acidification (OA) presents a unique challenge to early life stages of marine species. Developing organisms must balance the need to grow rapidly with the energetic demands of maintaining homeostasis. The small sizes of early life stages can make them highly sensitive to changes in environmental CO2 levels, but studies have found wide variation in responses to OA. Thus far most OA studies have manipulated CO2 only, and modifying factors need to be considered in greater detail. We investigated the effects of high pCO2 and food ration on rates of growth and mortality of a coastal fish, the California Grunion (Leuresthes tenuis). We also examined how CO2 and food levels affected feeding success, metabolic rate, and swimming activity – processes reflective of energy acquisition and expenditure. In general, exposure to high CO2 decreased energy intake by reducing feeding success, and increased energy expenditure by increasing metabolic rate and routine swimming speed, though the magnitudes of these effects varied somewhat with age. Despite these changes in energetics, growth of biomass was not affected significantly by pCO2 level but was reduced by low ration level, and we did not detect an interactive effect of food ration and pCO2 on growth. However, under OA conditions, larvae were in poorer condition (as evaluated by the mass to length ratio) by the end of the experiment and our analysis of mortality revealed a significant interaction in which the effects of OA were more lethal when food energy was limited. These results are consistent with the idea that although energy can be reallocated to preserve biomass growth, increased energetic demand under ocean acidification may draw energy away from maintenance, including those processes that foster homeostasis during development. Overall, these results highlight both the need to consider the availability of food energy as a force governing species’ responses to ocean acidification and the need to explicitly consider the energy allocated to both growth and maintenance as climate changes.

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Physiological responses of scallops and mussels to environmental variability: implications for future shellfish aquaculture


  • High acclimatization capability in mussels and scallops
  • Growth rates, δ13C, δ15N, and shell strength differed between seasons and depths.
  • Mussels and scallops had higher growth rates at 5 m than 30 m.
  • Shell strength changed with depth in mussels but not in the scallops.
  • Differences in nutritional sources between depths are higher in winter than spring.


Puget Sound (Washington, USA) is a large estuary, known for its profitable shellfish aquaculture industry. However, in the past decade, scientists have observed strong acidification, hypoxia, and temperature anomalies in Puget Sound. These co-occurring environmental stressors are a threat to marine ecosystems and shellfish aquaculture. Our research assesses how environmental variability in Puget Sound impacts two ecologically and economically important bivalves, the purple-hinge rock scallop (Crassodoma gigantea) and Mediterranean mussel (Mytilus galloprovincialis). Our study examines the effect of depth and seasonality on the physiology of these two important bivalves to gain insight into ideal grow-out conditions in an aquaculture setting, improving the yield and quality of this sustainable protein source. To do this, we used Hood Canal (located in Puget Sound) as a natural multiple-stressor laboratory, which allowed us to study acclimatization capacity of shellfish in their natural habitat and provide the aquaculture industry information about differences in growth rate, shell strength, and nutritional sources across depths and seasons. Bivalves were outplanted at two depths (5 and 30 m) and collected after 3.5 and 7.5 months. To maximize mussel and scallop growth potential in an aquaculture setting, our results suggest outplanting at 5 m depth, with more favorable oxygen and pH levels. Mussel shell integrity can be improved by placing out at 5 m, regardless of season, however, there were no notable differences in shell strength between depths in scallops. For both species, δ13C values were lowest at 5 m in the winter and δ15N was highest at 30 m regardless of season. Puget Sound’s combination of naturally and anthropogenically acidified conditions is already proving to be a challenge for shellfish farmers. Our study provides crucial information to farmers to optimize aquaculture grow-out as we begin to navigate the impacts of climate change.

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From individual to ecosystem: multi-stressor effects of acidification and warming on the physiological responses of coastal marine invertebrates

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).

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How does ocean acidification affect Zostera marina during a marine heatwave?


  • Under extreme conditions Z. marina grows in both leaf length and wet mass.
  • Increasing CO2 levels for Z. marina at high temperatures may stimulate growth.
  • Extremely high temperatures inhibit sucrose and starch synthesis in Z. marina.
  • Out of 223 identified differentially expressed genes 70 were upregulated.
  • Glycolysis and the TCA cycle controlling genes and metabolites were upregulated.


Extreme ocean events caused by global warming, such as marine heatwaves (MHWs) and ocean acidification (OA), are projected to intensify. A combination of extreme events may have severe consequences for marine ecosystemsZostera marina was selected to understand how seagrass adapts to OA in extremely hot conditions. By combining morphology, transcriptomics, and metabolomics under mesoscale experimental conditions, we systematically investigated the response characteristics of Z. marina. Extremely high temperatures had a pronounced effect on growth, and the combined effect of OA mitigated the inhibitory effect of MHW. Both transcriptomic and metabolomic results showed that Z. marina resisted OA and MHW by upregulating the TCA cycle, glycolysis, amino acid metabolism, and relevant genes, as well as by activating the antioxidant system. The results of this study serve to improve our understanding of dual effects of factors of climate change on seagrass and may be used to direct future management and conservation efforts.

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Pacific oysters do not compensate growth retardation following extreme acidification events

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.

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Large-scale culturing of Neogloboquadrina pachyderma, its growth in, and tolerance of, variable environmental conditions

The planktic foraminifera Neogloboquadrina pachyderma is a calcifying marine protist and the dominant planktic foraminifera species in the polar oceans, making it a key species in marine polar ecosystems. The calcium carbonate shells of foraminifera are widely used in palaeoclimate studies because their chemical composition reflects the seawater conditions in which they grow. This species provides unique proxy data for past surface ocean hydrography, which can provide valuable insight to future climate scenarios. However, little is known about the response of N. pachyderma to variable and changing environmental conditions.Here, we present observations from large-scale culturing experiments where temperature, salinity and carbonate chemistry were altered independently. We observed overall low mortality, calcification of new chambers and addition of secondary calcite crust in all our treatments. In-culture asexual reproduction events also allowed us to monitor the variable growth of N. pachyderma’s offspring. Several specimens had extended periods of dormancy or inactivity after which they recovered. These observations suggest that N. pachyderma can tolerate, adapt to and calcify within a wide range of environmental conditions. This has implications for the species-level response to ocean warming and acidification, for future studies aiming to culture N. pachyderma and use in palaeoenvironmental reconstruction.

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Seasonal production dynamics of high latitude seaweeds in a changing ocean: implications for bottom-up effects on temperate coastal food webs

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.

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The response of coral skeletal nano structure and hardness to ocean acidification conditions

Ocean acidification typically reduces coral calcification rates and can fundamentally alter skeletal morphology. We use atomic force microscopy (AFM) and microindentation to determine how seawater pCO2 affects skeletal structure and Vickers hardness in a Porites lutea coral. At 400 µatm, the skeletal fasciculi are composed of tightly packed bundles of acicular crystals composed of quadrilateral nanograins, approximately 80–300 nm in dimensions. We interpret high adhesion at the nanograin edges as an organic coating. At 750 µatm the crystals are less regular in width and orientation and composed of either smaller/more rounded nanograins than observed at 400 µatm or of larger areas with little variation in adhesion. Coral aragonite may form via ion-by-ion attachment to the existing skeleton or via conversion of amorphous calcium carbonate precursors. Changes in nanoparticle morphology could reflect variations in the sizes of nanoparticles produced by each crystallization pathway or in the contributions of each pathway to biomineralization. We observe no significant variation in Vickers hardness between skeletons cultured at different seawater pCO2. Either the nanograin size does not affect skeletal hardness or the effect is offset by other changes in the skeleton, e.g. increases in skeletal organic material as reported in previous studies.

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Water quality and the CO2-carbonate system during the preconditioning of Pacific oyster (Crassostrea gigas) in a recirculating aquaculture system

The continued increase of the demand for seed of the Pacific oyster (Crassostrea gigas) has driven the aquaculture industry to produce land-based hatcheries using broodstock conditioning. This has led to the need to create closed systems to control the main factors involved in reproduction (temperature and food). Additionally, reproductive synchronization of broodstocks may be considered to ensure homogeneous maturation and spawning among the organisms. In this work, we synchronized the broodstock reproductive stage of Pacific oysters in a recirculating aquaculture system (RAS) using a “preconditioning” process and evaluated the effect of the water quality and the CO2-carbonate system on preconditioned broodstock. The oysters were kept at 12 °C for 45 days in a RAS containing a calcium reactor (C2) or without a calcium reactor (C1, control). Water quality parameters were measured daily, and the oyster’s condition and reproductive development were monitored using condition index, biometrics, and histology, on Days 0, 20, and 45. C1 and C2 systems kept the water quality within the ranges reported as favorable for bivalves. The calcium reactor kept the pH (8.03–8.10), alkalinity (200 mg/L as CaCO3), CO32− (≤ 80 µmol/kg), and Ω aragonite (≤ 1) closer to the ranges reported as optimal for bivalves. However, no significant differences were detected in the total weight and the condition index in C1 and C2. The preconditioning allowed to maintain the organisms in early reproductive development, allowing gametogenesis synchronization to start maturation.

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Ontogenetic differences in the response of the cold-water coral Caryophyllia huinayensis to ocean acidification, warming and food availability


  • Response to multiple stressors differs between cold-water coral life stages.
  • Elevated temperature and reduced feeding have the strongest effect.
  • Highest mortality occurs in adult corals.
  • Calcification rates decrease the most in juvenile corals.
  • Three-month delay in response to changing environmental conditions.


Cold-water corals (CWCs) are considered vulnerable to environmental changes. However, previous studies have focused on adult CWCs and mainly investigated the short-term effects of single stressors. So far, the effects of environmental changes on different CWC life stages are unknown, both for single and multiple stressors and over long time periods. Therefore, we conducted a six-month aquarium experiment with three life stages of Caryophyllia huinayensis to study their physiological response (survival, somatic growth, calcification and respiration) to the interactive effects of aragonite saturation (0.8 and 2.5), temperature (11 and 15 °C) and food availability (8 and 87 μg C L−1). The response clearly differed between life stages and measured traits. Elevated temperature and reduced feeding had the greatest effects, pushing the corals to their physiological limits. Highest mortality was observed in adult corals, while calcification rates decreased the most in juveniles. We observed a three-month delay in response, presumably because energy reserves declined, suggesting that short-term experiments overestimate coral resilience. Elevated summer temperatures and reduced food supply are likely to have the greatest impact on live CWCs in the future, leading to reduced coral growth and population shifts due to delayed juvenile maturation and high adult mortality.

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Model development to assess carbon fluxes during shell formation in blue mussels

In order to quantify the amount of carbonate, precipitated as calcium-carbonate in the shells of blue mussel (Mytilus edulis) in a temperate climate, an existing Dynamic Energy Budget (DEB) model for the blue mussel was adapted by separating shell growth from soft tissue growth. Hereby, two parameters were added to the original DEB-model, a calcification cost [J/mgCaCO3] and an energy allocation fraction [-], which resulted in the energy allocated for structural growth being divided between shell and meat growth. As values for these new parameters were lacking, they were calibrated by fitting the model to field data. Calibration results showed that an Energy allocation fraction of 0.5 and a calcification cost of 0.9 J/mgCaCO3, resulted in the best fit when fitted on 2017 and 2018 field data separately. These values however, show the best fit for data obtained within the first couple of years of the shellfish life, and do not take later years into account. Also it could be discussed that some parameters vary throughout the lifespan of the species. The results were compared to a regular DEB model, where the shell output was calculated through a simple allometric relationship. It is sometimes assumed that the carbon storage in shell material as calcium carbonate could be regarded as a form of carbon sequestration, with a positive impact on the atmospheric CO2 concentrations. However, studies on the physical-chemical processes related to shell formation have shown that from an oceanographic perspective, shell formation should be regarded as a source of atmospheric CO2 rather than a sink. The removal of carbonates, through the biocalcification process, reduces the buffer capacity (alkalinity) of the water to store CO2. As a result CO2 is released from the water to the atmosphere when shell material is formed. The actual amount of CO2 that escapes from the water to the atmosphere as a result of biocalcification depends strongly on local water characteristics. In this study, the effect of calcification by mussels on the CO2 flux to the atmosphere is studied using an adapted DEB model where energy costs of calcification are modelled explicitly. The model was subsequently run under two future climate scenarios, (RCP 4.5 and RCP 8.3) with elevated temperature and decreased pH, and the total released CO2 as a result of shell formation was calculated with the SeaCarb model. This showed growth of mussels, under future climate conditions to be slower, and with that the cumulative shell mass and carbonate precipitated to CaCO3 to decrease. Yet the amount of CO2 released, due to biocalcification, increased. This is due to the fact that the amount of CO2 released/gr of CaCO3 precipitated will be higher, as a result of the decreased buffering capacity of seawater under future climatic environmental conditions.

In summary the conclusions of the project were:

  • Biocalcification (shell formation) of marine organisms, such as bivalves, cannot be regarded as a process resulting in negative CO2 emission to the atmosphere;
  • The actual amount of CO2 that, due to biocalcification, is released from the water to the atmosphere depends on the physicochemical characteristics of the water, which are influenced by (future) climate conditions;
  • Our first model calculations suggest that at future climate conditions mussel’s grow rate will be somewhat reduced. While the amount of CO2 that due to biocalcification, escapes to the atmosphere during its life-time will slightly increase. Making the ratio of g CO2 release/g CaCO3 precipitated slightly higher;
  • Our model calculations should be considered an exercise rather than a definite prediction of how mussels will respond to future climate scenarios. Additional information/experimentation is strongly needed to validate the model settings, and to test the validity of the above mentioned outcome of the model.
Continue reading ‘Model development to assess carbon fluxes during shell formation in blue mussels’

Differences in carbonate chemistry up-regulation of long-lived reef-building corals

With climate projections questioning the future survival of stony corals and their dominance as tropical reef builders, it is critical to understand the adaptive capacity of corals to ongoing climate change. Biological mediation of the carbonate chemistry of the coral calcifying fluid is a fundamental component for assessing the response of corals to global threats. The Tara Pacific expedition (2016–2018) provided an opportunity to investigate calcification patterns in extant corals throughout the Pacific Ocean. Cores from colonies of the massive Porites and Diploastrea genera were collected from different environments to assess calcification parameters of long-lived reef-building corals. At the basin scale of the Pacific Ocean, we show that both genera systematically up-regulate their calcifying fluid pH and dissolved inorganic carbon to achieve efficient skeletal precipitation. However, while Porites corals increase the aragonite saturation state of the calcifying fluid (Ωcf) at higher temperatures to enhance their calcification capacity, Diploastrea show a steady homeostatic Ωcf across the Pacific temperature gradient. Thus, the extent to which Diploastrea responds to ocean warming and/or acidification is unclear, and it deserves further attention whether this is beneficial or detrimental to future survival of this coral genus.

Continue reading ‘Differences in carbonate chemistry up-regulation of long-lived reef-building corals’

Experimental determination of differential seasonal response in seed of the Manila clam, Ruditapes philippinarum, in context of climate change


  • Growth, feeding, burrowing and biomarkers respond to Climate Change (CC) in clams.
  • Spring and summer are the seasons when clams are more affected by CC.
  • In clams, pH induced more biochemical/physiological alterations than temperature.
  • Seasonality is an important factor to modulate physiological responses to CC in clams.


Marine bivalves are found as key components of coastal habitats and have several important roles, such as serving as a food source for human beings and aquatic organisms. In fact, as the world’s population continues to grow, bivalve aquaculture is expected to increase in importance as a means of addressing demands for animal protein; however, its growth may be possibly compromised by unfavourable climatic conditions. Thus, we assessed the effects of increased water temperature and acidification on the seeds of a bivalve of commercial importance, the Manila clamRuditapes philippinarum, in order to understand how this species may be affected by climate change at its early life stages. We examined the expected response of clams by experimentally mimicking seasonal conditions that could be forecasted to occur at the end of the twenty-first century. Different physiological responses were measured including growth rates, clearance rate, burrowing time and different biochemical biomarkers of metabolic stress. The results showed that growth decreased in acidic experimental conditions in spring, with a weak interaction with temperature. Clearance rate was negatively affected by a lower pH in spring and summer but, under extreme summer conditions, the effect of pH was overridden by the negative impact of a higher temperature. Burrowing rates were reduced by half under warm temperature conditions in spring and summer. In contrast, biochemical biomarkers were only significantly depicted under climate change conditions in autumn. Overall, this study demonstrates the need to consider seasonality when evaluating the potential effects of climate change on clam aquaculture in order to forecast consequences for biological production.

Continue reading ‘Experimental determination of differential seasonal response in seed of the Manila clam, Ruditapes philippinarum, in context of climate change’

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