Posts Tagged 'physiology'

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Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)

Published 30 August 2023 Science Closed
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Highlights

  • Salinity and pH tolerance ranges were identified for Mactra chinensis Philippi juveniles in laboratory tests.
  • Survival rates were significantly reduced at extreme pH and salinity.
  • Low pH and salinity induced oxidative stress, decreasing antioxidant enzyme activities.

Abstract

The study investigated the impact of salinity and pH changes on the survival, growth, and antioxidant enzyme activity in Mactra chinensis Philippi (1.00 ± 0.10 cm shell length, 0.75±0.04 cm shell height), a marine clam species. Juveniles were exposed to various pH levels (5.4 – 9.6) and salinities (5 – 35 psu) for up to 20 days at 19 ± 0.5 ˚C. The individual effect of salinity and pH on juveniles were evaluated under pH 8.0 and salinity 30 psu, respectively. The results indicated that the highest survival rates were observed at pH 8.0 (85%, salinity = 30 psu) and salinity 30 psu (95%, pH = 8.0). The survival rates were significantly reduced at extreme pH (≤ 7.2; ≥ 8.4) and salinities (≤ 15; 35 psu). Additionally, oxidative stress was observed in clams exposed to low pH and salinity as indicated by the decreased activities of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). Notably, no significant difference in relative growth rates was observed between salinity 25 and 30 psu, between pH 7.8/8.4 and pH 8.0. Our results provide information on potential impact of pH and salinity changes on economically important bivalve species and may be used to optimize pH and salinity in aquaculture.

Continue reading ‘Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)’

Molecular responses in an Antarctic bivalve and an ascidian to ocean acidification

Published 29 August 2023 Science Closed
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Highlights

  • The non-calcifying species Cnemidocarpa verrucosa sp. A showed a greater number of differentially expressed genes than the calcifying Aequiyoldia eightsii.
  • The Ocean Acidification caused an upregulation of genes involved in the immune system and antioxidant response in the ascidian Cnemidocarpa verrucosa sp. A.
  • The abundance of the key marine organisms (such as Cnemidocarpa verrucosa), could be affected by Ocean Acidification if pH predictions for polar regions come true.
  • Contrary to expected, Ocean Acidification could not affect the mollusk Aequiyoldia eightsii compared to the non-calcifying species.

Abstract

Southern Ocean organisms are considered particularly vulnerable to Ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. It is also generally assumed that OA would affect calcifying animals more than non-calcifying animals. In this context, we aimed to study the impact of reduced pH on both types of species: the ascidian Cnemidocarpa verrucosa sp. A, and the bivalve Aequiyoldia eightsii, from an Antarctic fjord. We used gene expression profiling and enzyme activity to study the responses of these two Antarctic benthic species to OA. We report the results of an experiment lasting 66 days, comparing the molecular mechanisms underlying responses under two pCO2 treatments (ambient and elevated pCO2). We observed 224 up-regulated and 111 down-regulated genes (FC ≥ 2; p-value ≤ 0.05) in the ascidian. In particular, the decrease in pH caused an upregulation of genes involved in the immune system and antioxidant response. While fewer differentially expressed (DE) genes were observed in the infaunal bivalve, 34 genes were up-regulated, and 69 genes were downregulated (FC ≥ 2; p-value ≤ 0.05) in response to OA. We found downregulated genes involved in the oxidoreductase pathway (such as glucose dehydrogenase and trimethyl lysine dioxygenase), while the heat shock protein 70 was up-regulated. This work addresses the effect of OA in two common, widely distributed Antarctic species, showing striking results. Our major finding highlights the impact of OA on the non-calcifying species, results that differ from the general trend, in which one remarks the higher impact on calcifying species. Our result proposes a deep discussion about the potential effect on non-calcifying species, such as ascidians, a diverse and abundant group, that form extended three-dimensional clusters in the shallow waters and shelf areas along the Southern Ocean.

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Long-term preconditioning of the coral Pocillopora acuta does not restore performance in future ocean conditions

Published 28 August 2023 Science Closed
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There is overwhelming evidence that tropical coral reefs are severely impacted by human induced climate change. Assessing the capability of reef-building corals to expand their tolerance limits to survive projected climate trajectories is critical for their protection and management. Acclimation mechanisms such as developmental plasticity may provide one means by which corals could cope with projected ocean warming and acidification. To assess the potential of preconditioning to enhance thermal tolerance in the coral Pocillopora acuta, colonies were kept under three different scenarios from settlement to 17 months old: present day (0.9 °C-weeks (Degree Heating Weeks), + 0.75 °C annual, 400 ppm pCO2) mid-century (2.5 °C-weeks, + 1.5 °C annual, 685 ppm pCO2) and end of century (5 °C-weeks, + 2 °C annual, 900 ppm pCO2) conditions. Colonies from the present-day scenario were subsequently introduced to the mid-century and end of century conditions for six weeks during summer thermal maxima to examine if preconditioned colonies (reared under these elevated conditions) had a higher physiological performance compared to naive individuals. Symbiodiniaceae density and chlorophyll a concentrations were significantly lower in mid-century and end of century preconditioned groups, and declines in symbiont density were observed over the six-week accumulated heat stress in all treatments. Maximum photosynthetic rate was significantly suppressed in mid-century and end of century preconditioned groups, while minimum saturating irradiances were highest for 2050 pre-exposed individuals with parents originating from specific populations. The results of this study indicate preconditioning to elevated temperature and pCO2 for 17 months did not enhance the physiological performance in P. acuta. However, variations in trait responses and effects on tolerance found among treatment groups provides evidence for differential capacity for phenotypic plasticity among populations which could have valuable applications for future restoration efforts.

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

Published 22 August 2023 Science Closed
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Highlights

  • 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.

Abstract

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 ecosystems. Zostera 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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Short-term exposure to independent and combined acidification and warming elicits differential responses from two tropical seagrass-associated invertebrate grazers

Published 18 August 2023 Science Closed
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Ocean acidification and warming could affect animal physiology, key trophic interactions and ecosystem functioning in the long term. This study investigates the effects of four pH−temperature combination treatments simulating ocean acidification (OA), ocean warming (OW) and combined OA and OW conditions (FUTURE) relative to ambient present-day conditions (PRESENT) on the grazing of the juveniles of two seagrass-associated invertebrates namely the sea cucumber Stichopus cf. horrens and topshell Trochus maculatus over a 5-day exposure period. Diel and feeding activity of both species increased under OW and FUTURE to some extent, while the nighttime activity of Trochus but not Stichopus decreased under OA relative to PRESENT during the first 2 days. Fecal production of Stichopus did not differ among treatments, while the lowest fecal production of Trochus was observed under OA during the first 24 h of grazing. These responses suggest that Trochus may be initially more sensitive to OA compared with Stichopus. Interestingly, fecal production of Trochus in FUTURE was significantly higher than OA, suggesting that warming may ameliorate the negative effect of acidification. Diel activity, feeding and fecal production after 5 days did not differ among treatments for both species, suggesting acclimation to the acute changes in temperature and pH after a few days, although Stichopus acclimated rapidly than Trochus. The ability of the two juvenile invertebrate grazers to rapidly acclimate to increased temperature and lowered pH conditions after short-term exposure may favor their survival under projected changes in ocean conditions.

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Using meta-analysis to explore the roles of global upwelling exposure and experimental design in bivalve responses to low pH

Published 16 August 2023 Science Closed
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Highlights

  • Meta-analysis was used to assess bivalve responses to low pH.
  • Strong upwelling regions may yield bivalves that are less sensitive to low pH.
  • Upwelling explains up to 49 % variability of bivalve metabolic responses to low pH.
  • Larger carbonate chemistry deltas in experiments yield stronger responses.

Abstract

Low pH conditions, associated with ocean acidification, represent threats to many commercially and ecologically important organisms, including bivalves. However, there are knowledge gaps regarding factors explaining observed differences in biological responses to low pH in laboratory experiments. Specific sources of local adaptation such as upwelling exposure and the role of experimental design, such as carbonate chemistry parameter changes, should be considered. Linking upwelling exposure, as an individual oceanographic phenomenon, to responses measured in laboratory experiments may further our understanding of local adaptation to global change. Here, meta-analysis is used to test the hypotheses that upwelling exposure and experimental design affect outcomes of individual, laboratory-based studies that assess bivalve metabolic (clearance and respiration rate) responses to low pH. Results show that while bivalves generally decrease metabolic activity in response to low pH, upwelling exposure and experimental design can significantly impact outcomes. Bivalves from downwelling or weak upwelling areas decrease metabolic activity in response to low pH, but bivalves from strong upwelling areas increase or do not change metabolic activity in response to low pH. Furthermore, experimental temperature, exposure time and magnitude of the change in carbonate chemistry parameters all significantly affect outcomes. These results suggest that bivalves from strong upwelling areas may be less sensitive to low pH. This furthers our understanding of local adaptation to global change by demonstrating that upwelling alone can explain up to 49 % of the variability associated with bivalve metabolic responses to low pH. Furthermore, when interpreting outcomes of individual, laboratory experiments, scientists should be aware that higher temperatures, shorter exposure times and larger changes in carbonate chemistry parameters may increase the chance of suppressed metabolic activity.

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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

Published 10 August 2023 Science Closed
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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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Short-term exposure to combined condition of low salinity and pH affects ROS-mediated stress in disk abalone (Haliotis discus hannai)

Published 3 August 2023 Science Closed
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Climate change due to global warming can alter the salinity and pH in aquatic ecosystems. Low salinity (LS) and ocean acidification (OA) are stressors involved in osmotic regulation and can alter the antioxidant capacity of the body. In this study, we observed Na+/K+-ATPase (NKA) expression and activity in disk abalone gill tissue and changes in hemolymph osmolarity in relation to osmotic regulation over a short period (5 days). To confirm the degree of oxidative stress caused by changes in salinity and pH, changes in H2O2 levels, reactive oxygen species (ROS) levels, antioxidant enzyme (superoxide dismutase [SOD] and catalase [CAT]) expression, and caspase-7 expression were investigated at the molecular level. The degree of DNA damage was evaluated using the comet assay. mRNA expression, activity of gill NKA, and osmolarity of the hemolymph were significantly decreased in the LS group. Nonetheless, no noteworthy distinction was observed in mRNA expression or NKA activity between the control group and OA group. Hemolymph H2O2 levels and mRNA expression of SOD, CAT, and caspase-7 were significantly higher under the LS + OA condition than under single conditions of LS and OA. Further, caspase-7 mRNA expression and DNA damage increased with increasing exposure time. The group exposed to LS + OA showed the highest levels of caspase-7 expression and DNA damage. These results indicate that a combination of low salinity and pH induces more stress than a single condition does. Unmanageable ROS-mediated stress caused by environmental changes can lead to cell death and DNA damage.

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Northern shrimp from multiple origins show similar sensitivity to global change drivers, but different cellular energetic capacity

Published 3 August 2023 Science Closed
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Species with a wide distribution can experience regionally a wide range of environmental conditions, to which they can acclimatize or adapt. Consequently, the geographic origin of an organism can influence its responses to environmental changes, and therefore its sensitivity to combined global change drivers. This study aimed at determining the physiological responses of the northern shrimp Pandalus borealis, at different levels of biological organization and from four different geographic origins, exposed to elevated temperature and low pH to define its sensitivity to future ocean warming (OW) and acidification (OA). Shrimp sampled within the northwest Atlantic, were exposed for 30 days to combinations of three temperature (2, 6 or 10 °C) and two pH levels (7.75 or 7.40). Survival, metabolic rates, whole-organism aerobic performance and cellular energetic capacity were assessed at the end of the exposure. Our results show that shrimp survival was negatively affected by temperature above 6 °C and low pH, regardless of their origin. Additionally, shrimp from different origins show overall similar whole-organism performances: aerobic scope increasing with increasing temperature and decreasing with decreasing pH. Finally, the stability of aerobic metabolism appears to be related to cellular adjustments specific to shrimp origin. Our results show that the level of intraspecific variation differs among levels of biological organization: different cellular capacities lead to similar individual performances. Thus, the northern shrimp sensitivity to OW and OA is overall comparable among origins. Nonetheless, shrimp vulnerability to predicted global change scenarios for 2100 could differ among origins due to different regional environmental conditions.

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Genomic signatures suggesting adaptation to ocean acidification in a coral holobiont from volcanic CO2 seeps

Published 25 July 2023 Science Closed
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Ocean acidification, caused by anthropogenic CO2 emissions, is predicted to have major consequences for reef-building corals, jeopardizing the scaffolding of the most biodiverse marine habitats. However, whether corals can adapt to ocean acidification and how remains unclear. We addressed these questions by re-examining transcriptome and genome data of Acropora millepora coral holobionts from volcanic CO2 seeps with end-of-century pH levels. We show that adaptation to ocean acidification is a wholistic process involving the three main compartments of the coral holobiont. We identified 441 coral host candidate adaptive genes involved in calcification, response to acidification, and symbiosis; population genetic differentiation in dinoflagellate photosymbionts; and consistent transcriptional microbiome activity despite microbial community shifts. Coral holobionts from natural analogues to future ocean conditions harbor beneficial genetic variants with far-reaching rapid adaptation potential. In the face of climate change, these populations require immediate conservation strategies as they could become key to coral reef survival.

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

Published 24 July 2023 Science Closed
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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.

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Whole-genome methylation sequencing of large yellow croaker (Larimichthys crocea) liver under hypoxia and acidification stress

Published 21 July 2023 Science Closed
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Large yellow croaker (Larimichthys crocea) is an important aquaculture species in China. This study analysed whole-genome methylation differences in liver tissues of young fish under different hypoxic and acidification conditions. Differentially methylated regions (DMRs) and differentially methylated genes (DMGs) were identified. Gene ontology (GO) and Kyoto encyclopaedia of genes and genomes (KEGG) enrichment analyses of DMGs were conducted to explore the mechanism of coping with hypoxic acidification. The main methylation type was CG, accounting for > 70% of total methylation, significantly higher than CHG and CHH methylation types. GO enrichment analysis of DMGs revealed strong enrichment of nervous system development, cell periphery, plasma membrane, cell junction organisation, cell junction, signalling receptor activity, molecular sensor activity, cell-linked tissue junction organisation, cell–cell adhesion and nervous system development. KEGG enrichment analysis of DMR-related genes identified cell adhesion molecules, cortisol synthesis and secretion and aldosterone synthesis and secretion as the three key pathways regulating the physiological responses to hypoxia and acidification. Long-term hypoxic and acidification stress affected the immune system, nervous system and stress responses of large yellow croaker. Whole-genome sequencing analysis of exposed tissues was used to investigate changes that occur in L. crocea in response to hypoxic and acidic conditions at the DNA methylation level. The findings contribute to our comprehensive understanding of functional methylation in large yellow croaker and will support future research on the response mechanisms of this species under different environmental pressures.

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Seagrass Thalassia hemprichii and associated bacteria co-response to the synergistic stress of ocean warming and ocean acidification

Published 21 July 2023 Science Closed
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Seagrass meadows play vital ecological roles in the marine ecosystem. Global climate change poses considerable threats to seagrass survival. However, it is unclear how seagrass and its associated bacteria will respond under future complex climate change scenarios. This study explored the effects of ocean warming (+2 °C) and ocean acidification (−0.4 units) on seagrass physiological indexes and bacterial communities (sediment and rhizosphere bacteria) of the seagrass Thalassia hemprichii during an experimental exposure of 30 days. Results demonstrated that the synergistic effect of ocean warming and ocean acidification differed from that of one single factor on seagrass and the associated bacterial community. The seagrass showed a weak resistance to ocean warming and ocean acidification, which manifested through the increase in the activity of typical oxidoreductase enzymes. Moreover, the synergistic effect of ocean warming and ocean acidification caused a significant decrease in seagrass’s chlorophyll content. Although the bacterial community diversity exhibited higher resistance to ocean warming and ocean acidification, further bacterial functional analysis revealed the synergistic effect of ocean warming and ocean acidification led to significant increases in SOX-related genes abundance which potentially supported the seagrass in resisting climate stress by producing sulfates and oxidizing hydrogen sulfide. More stable bacterial communities were detected in the seagrass rhizosphere under combined ocean warming and ocean acidification. While for one single environmental stress, simpler networks were detected in the rhizosphere. In addition, the observed significant correlations between several modules of the bacterial community and the physiological indexes of the seagrass indicate the possible intimate interaction between seagrass and bacteria under ocean warming and ocean acidification. This study extends our understanding regarding the role of seagrass associated bacterial communities and sheds light on both the prediction and preservation of the seagrass meadow ecosystems in response to global climate change.

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

Published 21 July 2023 Science Closed
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Highlights

  • 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.

Abstract

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 clam, Ruditapes 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.

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The effect of differences pH of waters on the growth rate of seagrass of Cymodocea rotundata (in Indonesian)

Published 20 July 2023 Science Closed
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The continued use of fossil fuels will increase the concentration of carbon dioxide (CO2) in the atmosphere. Ocean acidification occurs due to CO2 in the atmosphere diffusing into the oceans. The oceans are able to absorb CO2 in the atmosphere as much as 35 % more which causes a decrease in ocean pH. Seagrass Cymodocea rotundata is a type of seagrass that can be found growing in tropical waters. This situation raises concerns about the possible impact on the growth of seagrass C. rotundata. This study aims to analyze the content of nitrate, phosphate and potassium and the growth of seagrass C. rotundata which includes the growth of leaves, rhizomes and roots of C. rotundata against differences in pH. The study used an experimental method with a completely randomized design using a random table. A total of 15 jars with a diameter of 20 cm and a height of 25 cm were used with 3 treatments, each treatment was repeated 5 times. The results of the linear regression test showed that pH had an effect on nitrate concentrations, and had a strong effect on phosphate and potassium concentrations. The highest growth rate of C. rotundata seagrass leaves in the control ranged from 0.50–1.29 mm/day while the lowest at low pH ranged from 0.07–0.73 mm/day. The growth rate of seagrass rhizomes horizontally and vertically was highest at low pH while the lowest was at control pH. The highest growth rate of seagrass roots at low pH ranged from 0.20–0.90 mm/day. while the lowest was in the control ranged from 0.13–0.43 mm/day. pH also affects the growth rate of leaves, rhizomes and seagrass roots of C. rotundata. The lower the pH, the lower the leaf growth rate, in contrast to rhizomes and roots, the lower the pH, the higher the growth rate.

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Effects of climate change and eutrophication on photosynthesis and carbon-concentrating mechanisms: surprising diversity among reef algae

Published 19 July 2023 Science Closed
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Increased anthropogenic CO2 emission since the start of the Industrial Revolution has brought a changing climate and various threats to coastal ecosystems including ocean warming, ocean acidification (OA), and sea level rise. Coral reef ecosystems are especially vulnerable to the climate change, because ocean warming and acidification decrease calcification and increase bleaching in coral. In addition to these impacts of climate change, coastal ecosystems are already experiencing local anthropogenic impacts such as chronic eutrophication and continuing arrival of new invasive species. In Hawai‘i, large-scale blooms of both native and invasive macroalgae are often observed in the region with coastal eutrophication by land-based anthropogenic nutrient input. Predicting the effects of OA (increased CO2 concentration in the ocean) on algae is not straightforward because many algae are already equipped with carbon-concentrating mechanisms (CCMs) with which algae can increase their internal CO2 concentration for photosynthesis. Further, nutrient availability especially that of the macronutrient, nitrogen (N) could alter the operation of algal CCMs because CCMs involve specific, large proteins such as ribulose-1,5-biphosphate carboxylase-oxygenase (RUBISCO) and carbonic anhydrases (CA). This study experimentally investigated how OA and eutrophication, independently and synergistically, affect photosynthesis and CCMs in common Hawaiian reef algae. Algae can quickly change their maximum photosynthetic rates and CCMs when grown under elevated CO2 and N. Further, we found a surprising diversity among reef algae in how they react to elevated CO2 and N with their CCMs. The results of this study suggest that many Hawaiian algae will thrive under future climate change conditions, and OA and eutrophication will likely work in their favor, accelerating the phase shift from coral-dominated to macroalgal-dominated reefs in unpredictably faster paces and with players that are not easily predicted.

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The effects of ocean change drivers on the ecophysiology of the mottled brittle star Ophionereis fasciata

Published 18 July 2023 Science Closed
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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.

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Integrated assessment of CO2-induced acidification lethal and sub-lethal effects on tropical mussels Perna perna

Published 17 July 2023 Science Closed
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Leakages of CO2 capture and storage systems from the seabed are able to cause significant adverse biological effects in marine species. Adult mussels were exposed to different CO2 enrichment scenarios (pH from 8.3 to 6.0) for 96 h, and endpoints (lysosomal membrane deterioration, lipid peroxidation and primary damages in DNA) were assessed. Mortality and reduced health status can occur after short exposure of the tropical mussel Perna perna to pH levels lower than 7.5. Results pointed out cytogenotoxic effects in the hemolymph and gills after 48 and 96 h of exposure, respectively. These findings should be considered when environmental monitoring approaches are performed in tropical marine areas employing CCS strategies.

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Increased sensitivity of sea urchin larvae to metal toxicity as a consequence of the past two decades of climate change and ocean acidification in the Mediterranean Sea

Published 14 July 2023 Science Closed
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Highlights

  • Climate change and ocean acidification affect reproductive health of sea urchins.
  • Larvae ability to cope with copper deteriorated in the past 20 years.
  • Contribution of CO2, pH and temperature worsened in the past 7 years.

Abstract

The Mediterranean Sea represents a natural laboratory to infer the possible impacts of climate change and ocean acidification. In this article, we report the deteriorating ability of sea urchin larvae (Paracentrotus lividus) to cope with toxicity of a reference contaminant (Cu EC50) over the past 20 years and assessed the influence of 5 environmental factors from satellite measurements. This timeframe was divided in before and after January 2016 (46.57 μg/L vs 28.56 μg/L respectively, p < 0.001). In the second subset of data, correlation of the biological variable with CO2 and pH strengthened compared to the first part (rCO2-EC50: −0.21 vs −0.83 and rpH-EC50: 0.25 vs 0.87 respectively), with a causal link starting from one year and ending 4 months prior to EC50 measurements. Considering the continuous increase in CO2 concentrations recorded recently, this study could reveal a rapid deterioration of the health condition of this population of sea urchins in a coastal ecosystem.

Continue reading ‘Increased sensitivity of sea urchin larvae to metal toxicity as a consequence of the past two decades of climate change and ocean acidification in the Mediterranean Sea’

Surviving in an acidifying ocean: acid-base physiology and energetics of the sea urchin larva

Published 13 July 2023 Science Closed
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The sea urchin larva has been used by biologists for more than a century to study the development and evolution of animals. Surprisingly, very little information has been generated regarding the physiology of this small planktonic organism. However, in the context of anthropogenic CO2-driven ocean acidification (OA), the membrane transport physiology and energetics of this marine model organism have received considerable attention in the past decade. This has led to the discovery of new, exciting physiological systems, including a highly alkaline digestive tract and the calcifying primary mesenchyme cells that generate the larval skeleton. These physiological systems directly relate to the energetics of the organisms when challenged by OA. Here we review the latest membrane transport physiology and energetics in the sea urchin larva, we identify emerging questions, and we point to important future directions in the field of marine physiology in times of rapid climate change.

Continue reading ‘Surviving in an acidifying ocean: acid-base physiology and energetics of the sea urchin larva’
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