Posts Tagged 'respiration'

The potential of kelp Saccharina japonica in shielding Pacific oyster Crassostrea gigas from elevated seawater pCO2 stress

Ocean acidification (OA) caused by elevated atmospheric CO2 concentration is predicted to have negative impacts on marine bivalves in aquaculture. However, to date, most of our knowledge is derived from short-term laboratory-based experiments, which are difficult to scale to real-world production. Therefore, field experiments, such as this study, are critical for improving ecological relevance. Due to the ability of seaweed to absorb dissolved carbon dioxide from the surrounding seawater through photosynthesis, seaweed has gained theoretical attention as a potential partner of bivalves in integrated aquaculture to help mitigate the adverse effects of OA. Consequently, this study investigates the impact of elevated pCO2 on the physiological responses of the Pacific oyster Crassostrea gigas in the presence and absence of kelp (Saccharina japonica) using in situ mesocosms. For 30 days, mesocosms were exposed to six treatments, consisting of two pCO2 treatments (500 and 900 μatm) combined with three biotic treatments (oyster alone, kelp alone, and integrated kelp and oyster aquaculture). Results showed that the clearance rate (CR) and scope for growth (SfG) of C. gigas were significantly reduced by elevated pCO2, whereas respiration rates (MO2) and ammonium excretion rates (ER) were significantly increased. However, food absorption efficiency (AE) was not significantly affected by elevated pCO2. The presence of S. japonica changed the daytime pHNBS of experimental units by ~0.16 units in the elevated pCO2 treatment. As a consequence, CR and SfG significantly increased and MO2 and ER decreased compared to C. gigas exposed to elevated pCO2 without S. japonica. These findings indicate that the presence of S. japonica in integrated aquaculture may help shield C. gigas from the negative effects of elevated seawater pCO2.

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Natural analogues in pH variability and predictability across the coastal Pacific estuaries: extrapolation of the increased oyster dissolution under increased pH amplitude and low predictability related to ocean acidification

Coastal-estuarine habitats are rapidly changing due to global climate change, with impacts influenced by the variability of carbonate chemistry conditions. However, our understanding of the responses of ecologically and economically important calcifiers to pH variability and temporal variation is limited, particularly with respect to shell-building processes. We investigated the mechanisms driving biomineralogical and physiological responses in juveniles of introduced (Pacific; Crassostrea gigas) and native (Olympia; Ostrea lurida) oysters under flow-through experimental conditions over a six-week period that simulate current and future conditions: static control and low pH (8.0 and 7.7); low pH with fluctuating (24-h) amplitude (7.7 ± 0.2 and 7.7 ± 0.5); and high-frequency (12-h) fluctuating (8.0 ± 0.2) treatment. The oysters showed physiological tolerance in vital processes, including calcification, respiration, clearance, and survival. However, shell dissolution significantly increased with larger amplitudes of pH variability compared to static pH conditions, attributable to the longer cumulative exposure to lower pH conditions, with the dissolution threshold of pH 7.7 with 0.2 amplitude. Moreover, the high-frequency treatment triggered significantly greater dissolution, likely because of the oyster’s inability to respond to the unpredictable frequency of variations. The experimental findings were extrapolated to provide context for conditions existing in several Pacific coastal estuaries, with time series analyses demonstrating unique signatures of pH predictability and variability in these habitats, indicating potentially benefiting effects on fitness in these habitats. These implications are crucial for evaluating the suitability of coastal habitats for aquaculture, adaptation, and carbon dioxide removal strategies.

Continue reading ‘Natural analogues in pH variability and predictability across the coastal Pacific estuaries: extrapolation of the increased oyster dissolution under increased pH amplitude and low predictability related to ocean acidification’

Effects of seawater pCO2 on the skeletal morphology of massive Porites spp. corals

Ocean acidification alters the dissolved inorganic carbon chemistry of seawater and can reduce the calcification rates of tropical corals. Here we explore the effect of altering seawater pCO2 on the skeletal morphology of 4 genotypes of massive Porites spp. which display widely different calcification rates. Increasing seawater pCO2 causes significant changes in in the skeletal morphology of all Porites spp. studied regardless of whether or not calcification was significantly affected by seawater pCO2. Both the median calyx size and the proportion of skeletal surface occupied by the calices decreased significantly at 750 µatm compared to 400 µatm indicating that polyp size shrinks in this genus in response to ocean acidification. The coenosteum, connecting calices, expands to occupy a larger proportion of the coral surface to compensate for this decrease in calyx area. At high seawater pCO2 the spines deposited at the skeletal surface became more numerous and the trabeculae (vertical skeletal pillars) became significantly thinner in 2 of the 4 genotypes. The effect of high seawater pCO2 is most pronounced in the fastest growing coral and the regular placement of trabeculae and synapticulae is disturbed in this genotype resulting in a skeleton that is more randomly organised. The study demonstrates that ocean acidification decreases the polyp size and fundamentally alters the architecture of the skeleton in this major reef building species from the Indo-Pacific Ocean.

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Coral calcification mechanisms in a warming ocean and the interactive effects of temperature and light

Ocean warming is transforming the world’s coral reefs, which are governed by the growth of marine calcifiers, most notably branching corals. Critical to skeletal growth is the corals’ regulation of their internal chemistry to promote calcification. Here we investigate the effects of temperature and light on the calcifying fluid chemistry (using boron isotope systematics), calcification rates, metabolic rates and photo-physiology of Acropora nasuta during two mesocosm experiments simulating seasonal and static temperature and light regimes. Under the seasonal regime, coral calcification rates, calcifying fluid carbonate chemistry, photo-physiology and metabolic productivity responded to both changes in temperature and light. However, under static conditions the artificially prolonged exposure to summer temperatures resulted in heat stress and a heightened sensitivity to light. Our results indicate that temperature and light effects on coral physiology and calcification mechanisms are interactive and context-specific, making it essential to conduct realistic multi-variate dynamic experiments in order to predict how coral calcification will respond to ocean warming.

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The combined effects of ocean acidification and copper on the physiological responses of the tropical coral Stylophora pistillata


  • Exposure to increased Cu concentrations suppressed coral calcification.
  • Calcification was suppressed further when exposed to Cu under high pCO2.
  • Respiration decreased after two weeks when stressors were applied in combination.


A decrease in ocean pH of 0.3 units will likely double the proportion of dissolved copper (Cu) present as the free metal ion, Cu2+, the most bioavailable form of Cu, and one of the most common marine pollutants. We assess the impact of ocean acidification and Cu, separately and in combination, on calcification, photosynthesis and respiration of sub-colonies of a single tropical Stylophora pistillata colony. After 15 days of treatment, total calcification rates were significantly decreased in corals exposed to high seawater pCO2 (∼1000-μatm, 2100 scenario) and at both ambient (1.6–1.9 nmols) and high (2.5–3.6 nmols) dissolved Cu concentrations compared to controls. The effect was increased when both stressors were combined. Coral respiration rates were significantly reduced by the combined stressors after 2 weeks of exposure, indicating the importance of experiment duration. It is therefore likely rising atmospheric CO2 will exacerbate the negative effects of Cu pollution to S. pistillata.

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Response of Cymodocea nodosa to ocean acidification and warming in the Canary Islands: direct and indirect effects


  • Ocean acidification increase growth and gross primary production of Cymodocea nodosa.
  • The rise of temperature limited the net and gross primary production of Cymodocea nodosa.
  • A positive effect of decrased pH on greater vulnerability to consumption by Paracentrotus lividus.
  • A future scenario of climate change will affect metabolic rates of C.nodosa.
  • Different responses to climate change have been observed by C. nodosa from Canary Islands.


As detected in warming and ocean acidification, global change can have profound impact on marine life. Its effects on seagrasses are becoming increasingly well-known, since several studies have focused on the responses of these species to global change conditions. However a few studies have assessed the combined effect of temperature and acidification on seagrasses. Overall in this study, the combined effects of increased ocean temperature and pH levels expected at the end of this century (+5 °C and pH 7.5) on Cymodocea nodosa from Canary Islands, were evaluated for one month through manipulative laboratory experiments. Growth, net production, respiration, gross primary production, chlorophyll-a concentration and its vulnerability to herbivory were quantified. Results showed a positive effect of decreased pH on growth and gross primary production, as well as greater vulnerability to consumption by the sea urchin Paracentrotus lividus. In contrast, increased temperature limited net and gross primary production. This study shows than in future scenarios, C. nodosa from the Canary Islands may be a losing species in the global change stakes.

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Temperature effects on leaf and epiphyte photosynthesis, bicarbonate use and diel O2 budgets of the seagrass Zostera marina L.

Ocean warming along with nutrient enrichment are major stressors causing global seagrass decline. While the effects of global warming on metabolic parameters in seagrasses are well described, the effect of increasing temperature on the epiphytic overgrowth of seagrass leaves and the consequences for the seagrass plant are poorly understood. Here, we investigated the effects of elevating temperature on the photosynthetic efficiency of the seagrass species Zostera marina L. and its associated epiphytes, to explore how ocean warming might affect epiphytism in seagrasses. Gas exchange and final pH measurements on bare seagrass leaves, leaves with epiphytes, and epiphytes separated from seagrass leaves were used to quantify photosynthesis and respiration rates, and the inorganic carbon extraction capacity of leaves and epiphytes as a function of photon scalar irradiance and temperature (12, 17, 22, and 27°C). Seagrass without epiphytic biofilm had a high ability to exploit the incoming irradiance regardless of the light intensity and temperature, shown as continuously high light use efficiency and maximum net photosynthesis rates. The presence of epiphytic biofilm on the seagrass leaves impaired plant photosynthesis by increasing light requirements and reducing the photosynthetic efficiency (especially at 27°C). Epiphytes showed the lowest respiration rates in darkness and had the highest oxygen surplus over diel cycles up to 22°C, whereas bare leaves had the highest diel oxygen surplus at 27°C. Both bare leaves and epiphytes lost the ability to utilize bicarbonate at 27°C, and epiphytes also did not show use of bicarbonate at 12°C. Our results indicate a competitive advantage for epiphytes in cold CO2-rich environments, whereas seagrass with bare leaves could be less affected under elevated seawater temperatures.

Continue reading ‘Temperature effects on leaf and epiphyte photosynthesis, bicarbonate use and diel O2 budgets of the seagrass Zostera marina L.’

Physiological acclimatization in Hawaiian corals following a 22-month shift in baseline seawater temperature and pH

Climate change poses a major threat to coral reefs. We conducted an outdoor 22-month experiment to investigate if coral could not just survive, but also physiologically cope, with chronic ocean warming and acidification conditions expected later this century under the Paris Climate Agreement. We recorded survivorship and measured eleven phenotypic traits to evaluate the holobiont responses of Hawaiian coral: color, Symbiodiniaceae density, calcification, photosynthesis, respiration, total organic carbon flux, carbon budget, biomass, lipids, protein, and maximum Artemia capture rate. Survivorship was lowest in Montipora capitata and only some survivors were able to meet metabolic demand and physiologically cope with future ocean conditions. Most M. capitata survivors bleached through loss of chlorophyll pigments and simultaneously experienced increased respiration rates and negative carbon budgets due to a 236% increase in total organic carbon losses under combined future ocean conditions. Porites compressa and Porites lobata had the highest survivorship and coped well under future ocean conditions with positive calcification and increased biomass, maintenance of lipids, and the capacity to exceed their metabolic demand through photosynthesis and heterotrophy. Thus, our findings show that significant biological diversity within resilient corals like Porites, and some genotypes of sensitive species, will persist this century provided atmospheric carbon dioxide levels are controlled. Since Porites corals are ubiquitous throughout the world’s oceans and often major reef builders, the persistence of this resilient genus provides hope for future reef ecosystem function globally.

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Coupled changes in pH, temperature and dissolved oxygen impact the physiology and ecology of herbivorous kelp forest grazers

Understanding species’ responses to upwelling may be especially important in light of ongoing environmental change. Upwelling frequency and intensity are expected to increase in the future, while ocean acidification and deoxygenation are expected to decrease the pH and dissolved oxygen of upwelled waters. However, the acute effects of a single upwelling event and the integrated effects of multiple upwelling events on marine organisms are poorly understood. Here, we use in situ measurements of pH, temperature, and dissolved oxygen to characterize the covariance of environmental conditions within upwelling-dominated kelp forest ecosystems. We then test the effects of acute (0-3 days) and chronic (1-3 month) upwelling on the performance of two species of kelp forest grazers, the echinoderm, Mesocentrotus franciscanus, and the gastropod, Promartynia pulligo. We exposed organisms to static conditions in a regression design to determine the shape of the relationship between upwelling and performance and provide insights into the potential effects in a variable environment. We found that respiration, grazing, growth, and net calcification decline linearly with increasing upwelling intensity for M. francicanus over both acute and chronic timescales. Promartynia pulligo exhibited decreased respiration, grazing, and net calcification with increased upwelling intensity after chronic exposure, but we did not detect an effect over acute timescales or on growth after chronic exposure. Given the highly correlated nature of pH, temperature, and dissolved oxygen in the California Current, our results suggest the relationship between upwelling intensity and growth in the 3-month trial could potentially be used to estimate growth integrated over long-term dynamic oceanographic conditions for M. franciscanus. Together, these results indicate current exposure to upwelling may reduce species performance and predicted future increases in upwelling frequency and intensity could affect ecosystem function by modifying the ecological roles of key species.

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The impact of oyster aquaculture on the estuarine carbonate system

Many studies have examined the vulnerability of calcifying organisms, such as the eastern oyster (Crassostrea virginica), to externally forced ocean acidification, but the opposite interaction whereby oysters alter their local carbonate conditions has received far less attention. We present an exploratory model for isolating the impact that net calcification and respiration of aquacultured eastern oysters can have on calcite and aragonite saturation states, in the context of varying temperature, ocean-estuary mixing, and air-sea gas exchange. We apply the model to the Damariscotta River Estuary in Maine which has experienced rapid expansion of oyster aquaculture in the last decade. Our model uses oyster shell growth over the summer season and a previously derived relationship between net calcification and respiration to quantify impacts of net oyster calcification and gross metabolism on carbonate saturation states in open tidal waters. Under 2018 industry size and climate conditions, we estimate that oysters can lower carbonate saturation states by up to 5% (i.e., 0.17 and 0.11 units on calcite and aragonite saturation states, respectively) per day in late summer, with an average of 3% over the growing season. Perturbations from temperature and air-sea exchange are similar in magnitude. Under 2050 climate conditions and 2018 industry size, calcite saturation state will decrease by up to an additional 0.54 units. If the industry expands 3-fold by 2050, the calcite and aragonite saturation states may decrease by 0.73 and 0.47 units, respectively, on average for the latter half of the growing season when compared to 2018 climate conditions and industry size. Collectively, our results indicate that dense aggregations of oysters can have a significant role on estuarine carbonate chemistry.

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Heterogeneous environmental seascape across a biogeographic break influences the thermal physiology and tolerances to ocean acidification in an ecosystem engineer


Understanding how spatio-temporal environmental variability influences stress tolerance, local adaptation and phenotypic variation among populations is a key challenge for evolutionary ecology and climate change biology. Coastal biogeographic breaks are natural laboratories to explore this fundamental research question due to the contrasting environmental conditions experienced by natural populations across these regions.


In the South East Pacific (SEP) coast, a major break (30º-32ºS) is characterized by extreme natural variability in sea surface temperature (SST) and carbonate chemistry parameters related to temporal and spatial dynamics in upwelling events. Calcifying organisms inhibiting this zone are exposed to marked fluctuations and clines in SST that together with naturally acidified waters can impact their metabolism, calcification and fitness, making them particularly prone to the effects of climate change (e.g. ocean acidification, OA). We investigated to what extent the spatial and temporal environmental variability (in SST and seawater carbonate conditions) that characterizes the biogeographic break in the SEP influences intra-specific differences in the thermal ecology and the tolerances to OA of the limpet Scurria araucana.


During two years, we conducted field surveys of limpet populations at sites across the SEP break (27ºS, 30ºS and 32ºS). We collected individuals from each population to test for geographic differences in morphometric (e.g. total buoyancy weight, shell length) and physiological (e.g. oxygen consumption rate, cardiac activity and thermal performance curves; TPC) responses to local environmental conditions (Tº and pH/pCO2) and to simulated OA scenarios.


Populations of SAraucana exhibit high tolerance to OA with no signal of geographic influence on this attribute. However, inter-population differences in thermal physiology (metabolic rates and performances) were found across the biogeographic break in the SEP coast. Limpets from the central part of the break (30ºS) exhibit higher thermal performance compared to limpets from populations at both sides of the break.

Main conclusions

Variation in SST has a greater effect shaping inter-population differences in thermal physiology of the limpet Saraucana. These physiological differences are aligned the thermal heterogenous seascape along the biogeographic break in the SEP. Contrarily, temporal and spatial variation in seawater carbonate conditions does not influence inter-population differences in phenotypic response populations, but an overall high tolerance to OA.

Continue reading ‘Heterogeneous environmental seascape across a biogeographic break influences the thermal physiology and tolerances to ocean acidification in an ecosystem engineer’

Attributing controlling factors of acidification and hypoxia in a deep, nutrient-enriched estuarine embayment

Measuring and attributing controlling factors of acidification and hypoxia are essential for management of coastal ecosystems affected by those stressors. We address this using surveys in the Firth of Thames, a deep, seasonally stratified estuarine embayment adjoing the Hauraki Gulf in northern Aotearoa/New Zealand. The Firth’s catchment has undergone historic land-use intensification transforming it from native forest cover to dominance by pastoral use, increasing its riverine total nitrogen loading by ∼82% over natural levels and switching it’s predominate loading source from offshore to the catchment. We hypothesised that seasonal variation in net ecosystem metabolism [NEM: dissolved inorganic carbon (DIC) uptake/release] will be a primary factor determining carbonate and oxic responses in the Firth, and that organic matter involved in the metabolism will originate primarily by fixation within the Firth system and be driven by catchment dissolved inorganic nitrogen (DIN) loading. Seasonal ship-based and biophysical mooring surveys across the Hauraki Gulf and Firth showed depressed pH and O2 reaching pH ∼7.8 and O2 ∼4.8 mg L–1 in autumn in the inner Firth, matched by shoreward increasing nutrient loading, phytoplankton, organic matter, gross primary production (GPP) and apparent O2 utilization. A carbonate system deconvolution of the ship survey data, combined with other ship survey and mooring results, showed how CO2 partial pressure responded to seasonal shifts in temperature, NEM, phytoplankton sinking and mineralisation and water column stratification, that underlay the late-season expression of acidification and hypoxia. This aligned with seasonal shifts in net DIC fluxes determined in a coincident nutrient mass-balance analysis, showing near-neutral fluxes from spring to summer, but respiratory NEM from summer to autumn. Particulate C:N and ratios of organic C fixed by Firth GPP to that from river inputs (∼29- to 100-fold in summer and autumn) showed that the dominant source of organic matter fuelling heterotrophy in autumn was autochthonous GPP, driven by riverine DIN loading. The results signified the sensitivity of deep, long-residence time, seasonally stratifying estuaries to acidification and hypoxia, and are important for coastal resource management, including aquaculture developments and catchment runoff limit-setting for maintenance of ecosystem health.

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The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord

In the North Patagonian fjord region, the cold-water coral (CWC) Desmophyllum dianthus occurs in high densities, in spite of low pH and aragonite saturation. If and how these conditions affect the energy demand of the corals is so far unknown. In a laboratory experiment, we investigated the carbon and nitrogen (C, N) budget of D. dianthus from Comau Fjord under three feeding scenarios: (1) live fjord zooplankton (100–2,300 µm), (2) live fjord zooplankton plus krill (>7 mm), and (3) four-day food deprivation. In closed incubations, C and N budgets were derived from the difference between C and N uptake during feeding and subsequent C and N loss through respiration, ammonium excretion, release of particulate organic carbon and nitrogen (POC, PON). Additional feeding with krill significantly increased coral respiration (35%), excretion (131%), and POC release (67%) compared to feeding on zooplankton only. Nevertheless, the higher C and N losses were overcompensated by the threefold higher C and N uptake, indicating a high assimilation and growth efficiency for the krill plus zooplankton diet. In contrast, short food deprivation caused a substantial reduction in respiration (59%), excretion (54%), release of POC (73%) and PON (87%) compared to feeding on zooplankton, suggesting a high potential to acclimatize to food scarcity (e.g., in winter). Notwithstanding, unfed corals ‘lost’ 2% of their tissue-C and 1.2% of their tissue-N per day in terms of metabolism and released particulate organic matter (likely mucus). To balance the C (N) losses, each D. dianthus polyp has to consume around 700 (400) zooplankters per day. The capture of a single, large krill individual, however, provides enough C and N to compensate daily C and N losses and grow tissue reserves, suggesting that krill plays an important nutritional role for the fjord corals. Efficient krill and zooplankton capture, as well as dietary and metabolic flexibility, may enable D. dianthus to thrive under adverse environmental conditions in its fjord habitat; however, it is not known how combined anthropogenic warming, acidification and eutrophication jeopardize the energy balance of this important habitat-building species.

Continue reading ‘The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord’

Climate change effects on the ecophysiology and ecological functioning of an offshore wind farm artificial hard substrate community


  • Local effects of offshore wind farms add to and interact with global climate change.
  • Species-specific effects on artificial hard substrate colonising community.
  • Mortality, feeding and metabolism generally increased with temperature and lower pH.
  • Temperature and pH had antagonistic effect on growth.
  • Maximised cumulative clearance potential significantly increased by climate change.


In the effort towards a decarbonised future, the local effects of a proliferating offshore wind farm (OWF) industry add to and interact with the global effects of marine climate change. This study aimed to quantify potential ecophysiological effects of ocean warming and acidification and to estimate and compare the cumulative clearance potential of suspended food items by OWF epifauna under current and future climate conditions. To this end, this study combined ecophysiological responses to ocean warming and acidification of three dominant colonising species on OWF artificial hard substrates (the blue mussel Mytilus edulis, the tube-building amphipod Jassa herdmani and the plumose anemone Metridium senile). In general, mortality, respiration rate and clearance rate increased during 3- to 6-week experimental exposures across all three species, except for M. senile, who exhibited a lower clearance rate in the warmed treatments (+3 °C) and an insensitivity to lowered pH (−0.3 pH units) in terms of survival and respiration rate. Ocean warming and acidification affected growth antagonistically, with elevated temperature being beneficial for M. edulis and lowered pH being beneficial for M. senile. The seawater volume potentially cleared from suspended food particles by this AHS colonising community increased significantly, extending the affected distance around an OWF foundation by 9.2% in a future climate scenario. By using an experimental multi-stressor approach, this study thus demonstrates how ecophysiology underpins functional responses to climate change in these environments, highlighting for the first time the integrated, cascading potential effects of OWFs and climate change on the marine ecosystem.

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Effects of ocean acidification on the performance and interaction of fleshy macroalgae and a grazing sea urchin


  • We investigated the direct and indirect effects of CO2 on an urchin and macroalgae.
  • Elevated CO2 increased production of fleshy macroalgae biomass but not photosynthesis.
  • Urchin respiration, biomass, righting time, and consumption rate were unaffected.
  • Reduced algal nutrition interacted with impaired chemosensing to preserve foraging.
  • Foraging and consumption suggest sustained trophic interactions under acidification.


When predicting the response of marine ecosystems to climate change, it is increasingly recognized that understanding the indirect effects of ocean acidification on trophic interactions is as important as studying direct effects on organism physiology. Furthermore, comprehensive studies that examine these effects simultaneously are needed to identify and link the underlying mechanisms driving changes in species interactions. Using an onshore ocean acidification simulator system, we investigated the direct and indirect effects of elevated seawater pCO2 on the physiology and trophic interaction of fleshy macroalgae and the grazing sea urchin Lytechinus variegatus. Macroalgal (Dictyota spp.) biomass increased despite decreased photosynthetic rates after two-week exposure to elevated pCO2. Algal tissue carbon content remained constant, suggesting the use of alternative carbon acquisition pathways beneficial to growth under acidification. Higher C:N ratios driven by a slight reduction in N content in algae exposed to elevated pCO2 suggest a decrease in nutritional content under acidification. Urchin (L. variegatus) respiration, biomass, and righting time did not change significantly after six-week exposure to elevated pCO2, indicating that physiological stress and changes in metabolism are not mechanisms through which the trophic interaction was impacted. Correspondingly, urchin consumption rates of untreated macroalgae (Caulerpa racemosa) were not significantly affected by pCO2. In contrast, exposure of urchins to elevated pCO2 significantly reduced the number of correct foraging choices for ambient macroalgae (Dictyota spp.), indicating impairment of urchin chemical sensing under acidification. However, exposure of algae to elevated pCO2 returned the number of correct foraging choices in similarly exposed urchins to ambient levels, suggesting alongside higher C:N ratios that algal nutritional content was altered in a way detectable by the urchins under acidification. These results highlight the importance of studying the indirect effects of acidification on trophic interactions simultaneously with direct effects on physiology. Together, these results suggest that changes to urchin chemical sensing and algal nutritional quality are the driving mechanisms behind surprisingly unaltered urchin foraging behavior for fleshy macroalgae under joint exposure to ocean acidification. Consistent foraging behavior and consumption rates suggest that the trophic interaction between L. variegatus and fleshy macroalgae may be sustained under future acidification. However, increases in fleshy macroalgal biomass driven by opportunistic carbon acquisition strategies have the potential to cause ecological change, depending on how grazer populations respond. Additional field research is needed to determine the outcome of these results over time and under a wider range of environmental conditions.

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Transgenerational effects decrease larval resilience to ocean acidification & warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic

The aim of this study was to investigate the effect of ocean acidification (OA) and warming (OW) as well as the transgenerational effect of OA on larval and juvenile growth and metabolism of a large economically important fish species with a long generation time. Therefore we incubated European sea bass from Brittany (France) for two generations (>5 years in total) under current and predicted OA conditions (PCO2: 650 and 1700 µatm). In the F1 generation both OA condition were crossed with OW (temperature: 15-18°C and 20-23°C). We found that OA alone did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine metabolic rate (RMR) and juvenile standard metabolic rate (SMR) were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA on RMR or SMR. Juvenile PO2crit was not affected by OA, OW or OAW in both generations.

We discuss the potential underlying mechanisms resulting in beneficial effects of OW on F1 larval growth and RMR and in resilience of F0 and F1 larvae and juveniles to OA, but on the other hand resulting in vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

Summary statement We found that OA did not affect developmental time, growth, RMR and SMR, while OW increased these traits. OAW decreased larval size at metamorphosis. We discuss underlying mechanisms and the ecological perspective resulting from these results and conclude that recruitment to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures in Atlantic waters.

Continue reading ‘Transgenerational effects decrease larval resilience to ocean acidification & warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic’

Predictive model for gross community production rate of coral reefs using ensemble learning methodologies

Coral reefs play a vital role in maintaining the ecological balance of the marine ecosystem. Various marine organisms depend on coral reefs for their existence and their natural processes. Coral reefs provide the necessary habitat for reproduction and growth for various exotic species of the marine ecosystem. In this article, we discuss the most important parameters which influence the lifecycle of coral and coral reefs such as ocean acidification, deoxygenation and other physical parameters such as flow rate and surface area. Ocean acidification depends on the amount of dissolved Carbon dioxide (CO2). This is due to the release of H+ ions upon the reaction of the dissolved CO2 gases with the calcium carbonate compounds in the ocean. Deoxygenation is another problem that leads to hypoxia which is characterized by a lesser amount of dissolved oxygen in water than the required amount for the existence of marine organisms. In this article, we highlight the importance of physical parameters such as flow rate which influence gas exchange, heat dissipation, bleaching sensitivity, nutrient supply, feeding, waste and sediment removal, growth and reproduction. In this paper, we also bring out these important parameters and propose an ensemble machine learning-based model for analyzing these parameters and provide better rates that can help us to understand and suitably improve the ocean composition which in turn can eminently improve the sustainability of the marine ecosystem, mainly the coral reefs

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Marine macrophytes as carbon sinks: comparison between seagrasses and the non-native alga Halimeda incrassata in the Western Mediterranean (Mallorca)

Seagrass species play a critical role in the mitigation of climate change by acting as valuable carbon sinks and storage sites. Another important ecosystem service of this coastal vegetation is nutrient removal. However, coastal ecosystems are under increasing pressure of global warming and associated establishment of invasive species. To elucidate the respective contributions of seagrass species Posidonia oceanica and Cymodocea nodosa and the non-native macroalga Halimeda incrassata as primary producers and nutrient sinks in coastal habitats we conducted in-situ incubations in the North-western Mediterranean Sea. Measured metabolic activity and nutrient removal as well as calcification rates in these habitats over a 24 h period in spring and summer confirmed that the endemic seagrass P. oceanica represents a valuable ecosystem with high O2 production and considerable carbon capture. The documented regression of P. oceanica meadows with higher temperatures and decline in autotrophy as measured here causes concern for the continuity of ecosystem services rendered by this habitat throughout the Mediterranean Sea with progressing climate warming. In contrast, the enhanced performance of C. nodosa and the calcifying alga H. incrassata with increasing temperatures, under expected rates of future warming is uncertain to mitigate loss of productivity in case of a potential shift in marine vegetation. This could ultimately lead to a decline in ecosystem services, decreased carbon storage and mitigation of climate change. Furthermore, this study provides a first estimate for the growth rate of H. incrassata in the Mediterranean Sea, supporting evidence for the mechanism of its rapid extension.

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Effects of diel pCO₂ fluctuations on coral reef fishes now and into the future

The uptake of anthropogenic carbon dioxide from the atmosphere has increased the partial pressure of carbon dioxide (pCO2) and decreased the pH of the oceans, termed ocean acidification (OA). The majority of the models predicting future OA conditions are based on the open ocean, where pCO2 and pH are relatively stable. However, pCO2 fluctuates at a variety of temporal scales in coastal ecosystems. Coral reefs possess a daily cycle, where the pCO2 is elevated at night and lower during the day, mainly due to the photosynthesis, respiration, and calcification cycle of benthic reef organisms. Moreover, the magnitude of pCO2 fluctuations is projected to increase in the future as OA advances. To date, most studies on the effects of elevated pCO2 on reef fishes have used stable CO2 treatments, which may not accurately represent physiological responses under predicted future fluctuation in pCO2. In this thesis, I aim to examine fluctuations of pCO2 on coral reefs and how fishes will be affected in the future by these conditions.

While coral reef pCO2 is known to fluctuate on a daily cycle, much less is known about pCO2 variation at the microhabitat scale that animals occupy. Therefore, in Chapter 2 I investigate the pH/pCO2 variability of three different reefs and three coral reef microhabitats (hard coral, soft coral, and sand). I found typical diel variation in pCO2 associated with photosynthesis and respiration cycles. These fluctuations differed between reefs more than between the microhabitats within a reef. The variation was likely influenced by water flow and wind speed. These results fall within the normal range of coral reef diel variation and suggest that it is important to consider physical and hydrodynamic factors when projecting future pCO2 variation. Data from Chapter 2 on the current-day natural fluctuations of pCO2 in the environment can be used to inform ecologically relevant pCO2 treatments to measure how fishes and other coral reef organisms will be affected by OA in the future.

Elevated pCO2 has the potential to negatively impact fishes due to the increased costs of acid-base regulation. In Chapter 3, I explored the effects of an 8 h exposure to one of four pCO2 treatments, two stable (ambient and stable elevated) or two fluctuating levels of pCO2 (increasing, and decreasing) on two species of damselfishes, Acanthochromis polyacanthus and Amblyglyphidodon curacao. Acanthochromis polyacanthus required more energy upon exposure to both stable pCO2 treatments during the 8 h trial compared to fish exposed to the fluctuating pCO2 treatments. However, there was no effect of pCO2 treatment on the swimming or oxygen uptake rates of A. curacao. This suggests that, for some species of coral reef fishes, performing under fluctuating pCO2 conditions may be less energetically-costly than performing under stable pCO2 conditions. Moreover, these results highlight the importance of ecologically relevant pCO2 treatments when testing how fishes will perform in future OA conditions.

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Near future ocean acidification modulates the physiological impact of fluoxetine at environmental concentration on larval urchins


  • We exposed larval urchins to environmentally-relevant fluoxetine and future pH.
  • Acidification and FX exposure had an interactive effect on larval physiologies.
  • Multistressors and environmentally-relevant conditions are vital for predictions.


Pharmaceuticals found in human wastes are emergent pollutants that are continuously released into aquatic systems. While exposure to pharmaceuticals alone could adversely impact aquatic organisms, few studies have considered the interactive effects of pharmaceuticals and the future environmental conditions, such as decreasing pH due to ocean acidification. Given the bioavailability of many pharmaceuticals is dependent on these physical conditions, we investigated the effect of environmentally-relevant concentrations of fluoxetine (10 and 100 ng L−1) under ambient (pH 8.0) and reduced pH conditions (pH 7.7) on physiology, behavior, and DNA integrity of larval sea urchins (Heliocidaris crassispina). Notably, the negative impacts of fluoxetine exposure were attenuated by reduced pH. Larvae exposed to both reduced pH and fluoxetine exhibited lower levels of DNA damage compared to those exposed to only one of the stressors. Similar antagonistic interactions were observed at the organismal level: for example, fluoxetine exposure at 10 ng L−1 under ambient pH increased the percentage of embryos at later developmental stages, but such effects of fluoxetine were absent at pH 7.7. However, despite the modulation of fluoxetine impacts under ocean acidification, control larvae performed better than those exposed to either stressor, alone or in combination. We also observed that pH alone impacted organismal behaviors, as larvae swam slower at reduced pH regardless of fluoxetine exposure. Our findings highlight the need to consider multi-stressor interactions when determining future organismal performance and that multiple metrics are needed to paint a fuller picture of ecological risks.

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