growth Archives - Ocean Acidification

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Influencing intertidal food web: implications of ocean acidification on the physiological energetics of key species the ‘wedge’ clam Donax faba

Published 26 April 2024 Science Leave a Comment
Tags: biological response, chemistry, growth, Indian, laboratory, mollusks, morphology, physiology

Highlights

Daily growth rate & calcium concentration have significantly decreased in acidified condition.
Total antioxidants and antioxidant enzymes showed an upward tendency.
Nutrient composition in clams has altered in acidified condition compared to control.
Prolonged exposure to OA will cause deleterious effects on clams thereby upsetting the intertidal food chain.

Abstract

Ocean acidification has become increasingly severe in coastal areas. It poses emerging threats to coastal organisms and influences ecological functioning. Donax faba, a dominant clam in the intertidal zone of the Bay of Bengal, plays an important role in the coastal food web. This clam has been widely consumed by the local communities and also acts as a staple diet for shorebirds and crustaceans. In this paper, we investigated how acidified conditions will influence the physiology, biochemical constituents, and energetics of Donax faba. Upon incubation for 2 months in lowered pH 7.7 ± 0.05 and control 8.1 ± 0.05 conditions, we found a delayed growth in the acidified conditions followed by decrease in calcium ions in the clam shell. Although not significant, we found the digestive enzymes showed a downward trend. Total antioxidant was significantly increased in the acidified condition compared to the control. Though not significant, the expression level of MDA and antioxidant enzymes (SOD, CAT, GST, GPX, and APX) showed increasing trend in acidified samples. Among nutrients such as amino acids and fatty acids, there was no significant difference between treatments, however, showed a downward trend in the acidified conditions compared to control. Among the minerals, iron and zinc showed significant increase in the acidified conditions. The above results suggest that the clam growth, and physiological energetics may have deleterious effects if exposed for longer durations at lowered pH condition thereby affecting the organisms involved in the coastal food web.

Continue reading ‘Influencing intertidal food web: implications of ocean acidification on the physiological energetics of key species the ‘wedge’ clam Donax faba’

Interactive effects of chronic ocean acidification and warming on the growth, survival, and physiological responses of adults of the temperate sea urchin Strongylocentrotus intermedius

Published 19 April 2024 Science Leave a Comment
Tags: biological response, chemistry, echinoderms, growth, laboratory, molecular biology, mortality, multiple factors, North Pacific, performance, physiology, temperature

Highlights

Ocean acidification and warming (OAW) repressed the survival and growth of Strongylocentrotus intermedius.
OAW altered the relative expression and activities of key metabolic enzymes of S. intermedius.
OAW attenuated the ATP production and antioxidant capability of S. intermedius.
Interactive effects of OAW on S. intermedius were analyzed in detail.

Abstract

To investigate the interactive effects of chronic ocean acidification and warming (OAW) on the growth, survival, and physiological responses of sea urchins, adults of the temperate sea urchin Strongylocentrotus intermedius were incubated separately/jointly in acidic (ΔpH_NBS = −0.5 units) and thermal (ΔT = +3.0 °C) seawater for 120 days under lab-controlled conditions based on the projected ocean pH and temperature for 2100 put forward by the Intergovernmental Panel on Climate Change (IPCC). Survival rate (SR), average food consumption rate (FCR), gut index (GuI), specific growth rate (SGR), digestive capability, energy production, and antioxidant capability were subsequently determined. The results showed that 1) the SR, FCR, GuI and SGR decreased sharply under OAW conditions. Significant interactive effects of OAW on SR and SGR were observed at 120 days post-incubation (dpi), and on FCR this occurred at 90 dpi. 2) OAW altered the activities of both digestive and antioxidant enzymes. There were significant interaction effects of OAW on the activities of amylase, trehalase, and superoxide dismutase. 3) The relative gene expression levels and activities of key enzymes involved in glycometabolism pathways (i.e., glycolysis and the tricarboxylic acid cycle) were significantly affected by OAW, resulting in an alteration of the total ATP content in the sea urchins. Interaction effects of OAW were observed in both relative gene expression and the activity of enzymes involved in glycolysis (hexokinase), the transformation of glycolysis end-products (lactate dehydrogenase), the tricarboxylic acid cycle (citrate synthetase), and ATP production (Na⁺/K⁺-ATPase). The data from this study will enrich our knowledge concerning the combined effects of global climate change on the survival, growth, and physiological responses of echinoderms.

Continue reading ‘Interactive effects of chronic ocean acidification and warming on the growth, survival, and physiological responses of adults of the temperate sea urchin Strongylocentrotus intermedius’

Effects of CO2 on the nitrogen isotopic composition of Trichodesmium and Crocosphaera

Published 11 April 2024 Science Closed
Tags: biogeochemistry, biological response, chemistry, growth, laboratory, nitrogen fixation, physiology, prokaryotes

Biological nitrogen (N₂) fixation is the main input of fixed nitrogen to ecosystems on Earth. Nitrogen isotope fractionation during this process is a key parameter for understanding the nitrogen cycle, however, relatively little is known about its regulatory mechanisms. Here we examine the effects of varying CO₂ concentrations on biomass δ¹⁵N signatures of the cyanobacterial diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii. We show that these organisms produce biomass up to ~3 ‰ lower in δ¹⁵N under either decreased (~180 µatm) or elevated (~1400 µatm) CO₂concentrations in comparison to modern levels (~380 µatm). Our results pointed towards changes in nitrogenase enzyme efficiency in response to CO₂ perturbations impacting isotopic fractionation during N₂ fixation and thus the biomass δ¹⁵N. This study contributes to an improved interpretation of the observed fluctuations in the δ¹⁵N records, and thus the past nitrogen cycle on Earth.

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Narrowed gene functions and enhanced transposon activity are associated with high tolerance to ocean acidification in a juvenile subarctic crustacean

Published 11 April 2024 Science Closed
Tags: biological response, chemistry, crustaceans, growth, laboratory, molecular biology, morphology, mortality, North Pacific, physiology, reproduction

Ocean acidification (OA) threatens marine crustaceans, particularly those at high latitudes where conditions are rapidly changing. Red king crab (RKC) support important fisheries in Alaskan waters. RKC early life stages are sensitive to OA when exposure occurs as embryos and juveniles. However, in a supporting study, RKC were surprisingly tolerant of varying OA conditions (pH 7.5, 7.8, & 8.0) when reared long-term from larval hatching to the first crab stage (C1). Here, we examined gene expression in the C1 juveniles to characterize transcriptional activity of these OA-tolerant crabs. Expression of nearly half of all genes (44%) correlated with OA treatment, suggesting a strong molecular response to OA, contrary to the phenotypic results. Downregulated functions were numerous in response to OA, and included reduced energy production, biosynthesis, immune function, and notably lipid and carbohydrate metabolic processes, which suggest a shift in metabolic strategy to protein catabolism, possibly to reduce CO₂ production and facilitate acid/base regulation. Only a handful of functions were enriched in OA-induced genes, which were related to transcription regulation, control of growth and cell death, and signaling activity. Transposon activity was high in OA-reared crab, many of which were upregulated at consistent levels, suggesting that transposon mobilization may be a component of the RKC OA-response system. Genetic composition did not differ among OA treatments indicating that transcriptional differences in OA-reared crab were more likely attributed to phenotypic plasticity than selective mortality. Our results suggest that OA-reared RKC have a narrowed, possibly optimized, set of gene functions that enables OA-tolerance through the early juvenile stage. OA-exposure from hatch may benefit RKC and related species by “hardening” them against OA through physiological reprogramming. Future studies should test OA-hardened crabs in additional challenges, as metabolic and immune limitations may ultimately make them more vulnerable to infection or secondary stressors.

Continue reading ‘Narrowed gene functions and enhanced transposon activity are associated with high tolerance to ocean acidification in a juvenile subarctic crustacean’

Ocean acidification and desalination increase the growth and photosynthesis of the diatom Skeletonema costatum isolated from the coastal water of the Yellow Sea

Published 5 April 2024 Science Closed
Tags: biological response, growth, laboratory, multiple factors, North Pacific, photosynthesis, physiology, phytoplankton, salinity, temperature

Highlights

This study aims to investigate the combined effects of pH (400 μatm and 1000 μatm), temperature (10 °C, 20 °C), and salinity (20 psu, 30 psu) on the diatom S. costatum.
In this study, we investigated the effects of ocean acidification and seawater desalination on Skeletonema costatum in varying seasonal temperatures.
We found that ocean acidification and seawater desalination promoted the growth of S. costatum under the simulated conditions.

Abstract

Global climate changes induce substantial alterations in the marine system, including ocean acidification (OA), desalination and warming of surface seawater. Here, we examined the combined effects of OA and reduced salinity under different temperatures on the growth and photosynthesis of the diatom Skeletonema costatum. After having been acclimated to 2 CO₂ concentrations (400 μatm, 1000 μatm) and 2 salinity levels (20 psu, 30 psu) at temperature levels of 10 °C and 20 °C, the diatom showed enhanced growth rate at the lowered salinity and elevated pCO₂ irrespective of the temperature. The OA treatment increased the net photosynthetic rate and biogenic silica (Bsi) contents. Increasing the temperature from 10 to 20 °C raised the net photosynthetic rate by over twofold. The elevated pCO₂ increased the net and gross photosynthetic rates by 20%–40% and by 16%–32%, respectively, with the higher enhancement observed at the higher levels of salinity and temperature. Our results imply that OA and desalination along with warming to the levels tested can enhance S. costatum‘s competitiveness in coastal phytoplankton communities under influence of future climate changes.

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Disparate response of decapods to low pH: a meta-analysis of life history, physiology and behavior traits across life stages and environments

Published 5 April 2024 Science Closed
Tags: biological response, calcification, crustaceans, growth, mortality, performance, physiology, reproduction, review

Highlights

Predicted level of ocean acidification is a threat for calcifier marine invertebrates.
Decapods, thought debatable, are presumably resilient.
Our meta-analysis revealed few impacts that mainly vary across biological traits.
Effect sizes little vary depending on the life stages and environments.

Abstract

We employed a meta-analysis to determine if the presumed resilience of decapods to ocean acidification extends to all biological aspects, environments, and life stages. Most response categories appeared unaffected by acidification. However, certain fitness-related traits (growth, survival, and, to some extent, calcification) were impacted. Acid-base balance and stress response scaled positively with reductions in pH, which maintains homeostasis, possibly at the cost of other processes. Juveniles were the only stage impacted by acidification, which is believed to reduce recruitment. We observed few differences in responses to acidification among decapods inhabiting contrasting environments. Our meta-analysis shows decapods as a group slightly to moderately sensitive to low pH, with impacts on some biological aspects rather than on all specific life stages or habitats. Although extreme pH scenarios may not occur in the open ocean, coastal and estuarine areas might experience lower pH levels in the near to medium future, posing potential challenges for decapods.

Continue reading ‘Disparate response of decapods to low pH: a meta-analysis of life history, physiology and behavior traits across life stages and environments’

Examining the effects of elevated CO2 on the growth kinetics of two microalgae, Skeletonema dohrnii (Bacillariophyceae) and Heterosigma akashiwo (Raphidophyceae)

Published 26 March 2024 Science Closed
Tags: abundance, algae, biological response, growth, North Pacific, otherprocess, photosynthesis, phytoplankton

Carbon dioxide (CO₂) serves as the primary substrate for the photosynthesis of phytoplankton, forming the foundation of marine food webs and mediating the biogeochemical cycling of C and N. We studied the effects of CO₂ variation on the Michaelis-Menten equations and elemental composition of Skeletonema dohrnii and Heterosigma akashiwo. CO₂ functional response curves were conducted from 100 to 2000 ppm. The growth of both phytoplankton was significantly affected by CO₂, but in different trends. The growth rate of S. dohrnii increased as CO₂ levels rose up to 400 ppm before reaching saturation. In contrast to S. dohrnii, the growth rate of H. akashiwo increased with CO₂ increasing up to 1000 ppm, and then CO₂ saturated. In addition, H. akashiwo showed a slower growth rate than S. dohrnii for all CO₂ concentrations, aside from 1000 ppm, and the Michaelis-Menten equations revealed that the half-saturation constant of H. akashiwo was higher than S. dohrnii. An increase in CO₂ concentration was seen to significantly affected the POC: Chl-a of both S. dohrnii and H. akashiwo, however, the effects on their elemental composition were minimal. Overall, our findings indicate that H. akashiwo had a more positive reaction to elevated CO₂ than S. dohrnii, and with higher nutrient utilization efficiency, while S. dohrnii exhibited higher carbon fixation efficiency, which is in line with their respective carbon concentrating mechanisms. Consequently, elevated CO₂, either alone or in combination with other limiting factors, may significantly alter the relative relationships between these two harmful algal blooms (HAB) species over the next century.

Continue reading ‘Examining the effects of elevated CO2 on the growth kinetics of two microalgae, Skeletonema dohrnii (Bacillariophyceae) and Heterosigma akashiwo (Raphidophyceae)’

Trade-off between growth and reproduction in Argopecten purpuratus (L.) scallops exposed to medium-term hypoxia and acidification

Published 25 March 2024 Science Closed
Tags: biological response, calcification, growth, laboratory, mollusks, mortality, multiple factors, physiology, reproduction, South Pacific

Highlights

•Scallops showed physiological adaptations to survive and reproduce under medium-term exposure.
•The most pronounced impact of hypoxia and low pH were on clearance and calcification rates.
•The combined effect of hypoxia and low pH produced relatively high survival (>70%).
•Hypoxia and low pH generated early gonad development and high reproductive potential.

Abstract

Peruvian bays that are home to aquatic organisms of commercial interest are increasingly affected by hypoxia and low pH events. These stressors produce unfavorable conditions for the aquatic fauna, leading to mass mortality events. In this study, we evaluated the ecophysiological responses of the scallop Argopecten purpuratus exposed to moderate hypoxia (20% DO saturation) and low pH (OA, pH 7.4) using a 2 × 2 factorial design. We found that a 51-day exposure to low pH (OA treatment) had greater negative effects on A. purpuratus performances than hypoxia (lower survival and decreased clearance and calcification rates), but stimulated early gonad maturation. The survival rate was 1.3-fold higher under hypoxia than under acidic treatment. The interaction between hypoxia and low pH had an antagonistic effect on survival, since the combined treatment (HOA) resulted in lower scallop mortality than the single stress treatments. Calcification was negatively affected by all stress treatments, whereas hypoxia and OA both stimulated gametogenesis. OA treatment resulted in higher frequencies of previtellogenic and vitellogenic oocytes, greater gonad coverage area, and lower frequency of atretic oocytes, suggesting higher reproductive potential. HOA was positively related to oocyte development and high frequency of post-vitellogenic and atretic oocytes. These results suggest that, due to hypoxia and low pH, feeding is reduced and energy allocation prioritizes scallop gonad maturation. This trend would have negative effects on scallop growth and calcification, while increased reproduction under environmental stress could mitigate the effect on recruitment.

Continue reading ‘Trade-off between growth and reproduction in Argopecten purpuratus (L.) scallops exposed to medium-term hypoxia and acidification’

Short periods of decreased water flow may modulate long-term ocean acidification in reef-building corals

Published 14 March 2024 Science Closed
Tags: biological response, chemistry, corals, flow, growth, laboratory, morphology, multiple factors, photosynthesis, physiology, respiration

Ocean acidification (OA) poses a major threat to reef-building corals. Although water flow variability is common in coral reefs and modulates coral physiology, the interactive effects of flow and OA on corals remain poorly understood. Therefore, we performed a three-month OA experiment investigating the effect of changes in flow on coral physiology. We exposed the reef-building corals Acropora cytherea, Pocillopora verrucosa, and Porites cylindrica to control (pH 8.0) and OA (pH 7.8) conditions at moderate flow (6 cm s^-1) and monitored OA effects on growth. Throughout the experiment, we intermittently exposed all corals to low flow (2 cm s^-1) for 1.5 h and measured their photosynthesis:photosynthesis (P:R) ratio under low and moderate flow. On average, corals under OA calcified 18 % less and grew 23 % less in surface area than those at ambient pH. We observed species-specific interactive effects of OA and flow on coral physiology. P:R ratios decreased after 12 weeks of OA in A. cytherea (22 %) and P. cylindrica (28 %) under moderate flow, but were unaffected by OA under low flow. P:R ratios were stable in P. verrucosa. These results suggest that short periods of decreased water flow may modulate OA effects on some coral species, indicating that flow variability is a factor to consider when assessing long-term effects of climate change.

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The tolerance of two marine diatoms to diurnal pH fluctuation under dynamic light condition and ocean acidification scenario

Published 14 March 2024 Science Closed
Tags: biological response, growth, laboratory, North Atlantic, North Pacific, photosynthesis, physiology, phytoplankton

Highlights

Growth rates of two diatoms remained insensitive to fluctuating pH or seawater acidification.
Fluctuating pH enhanced the light-saturated photosynthetic rate of the diatom Thalassiosira weissflogii by 20%.
Photosynthetic rates of two diatoms remained unaltered in response to acute pH changes ranging from 7.2 to 8.4.

Abstract

Coastal waters undergo dynamic changes in seawater carbonate chemistry due to natural and anthropogenic factors. Despite this, our current understanding of how coastal phytoplankton respond to fluctuating pH is limited. In the present study, we investigated the physiological responses of two coastal diatoms Thalassiosira pseudonana and Thalassiosira weissflogii to seawater acidification and diurnally fluctuating pH under natural solar irradiance. Seawater acidification did not significantly impact the growth, maximum and effective quantum yield of PSII, and photosynthetic rates of the two species. However, it did increase the maximum relative electron transport rate of T. weissflogii by 11%. Overall, fluctuating pH had neutral or positive effects on both species. It enhanced the light-saturated photosynthetic rate of T. weissflogii by 20% compared to cells grown under seawater acidification condition. Results from the short-term pH exposure experiment revealed that the photosynthetic rates of both species remained unaffected by acute pH changes, indicating their tolerance to varying pH. Nevertheless, it is crucial to consider dynamic pH when predicting changes in primary production in coastal waters, given the interplay of various environmental drivers.

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Ocean acidification and food availability impacts on the metabolism and grazing in a cosmopolitan herbivorous protist Oxyrrhis marina

Published 8 March 2024 Science Closed
Tags: abundance, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, otherprocess, performance, physiology, primary production, protists, respiration, zooplankton

The heterotrophic dinoflagellate Oxyrrhis marina is an essential microzooplankton in coastal waters, linking the energy transfer from phytoplankton to higher trophic levels. It is of general significance to investigate how it responds and acclimates to ocean acidification (OA), especially under varied availabilities of food. Here, O. marina was exposed and acclimated to three pCO₂ levels (LC: 415, MC:1000, HC:1500 μatm) for 60 days, and then was further grown under the CO₂ levels with different levels of food (the microalgae Dunaliella salina) availability for about 8 generations. The OA treatments did not significantly hamper its growth and ingestion rates even under the reduced food availability and starvation (deprived of the microalgae), which significantly reduced its growth rate. While the impacts of OA on the growth and ingestion rates of O. marina were insignificant, the OA treatments appeared to have resulted in a faster decline of the heterotrophic dinoflagellate cells during the starvation period. Nevertheless, the acidic stress under the elevated pCO₂ of 1000 or 1500 μatm decreased its respiration by about 53% or 59% with the high and by about 26% or 23% with the low food availability, respectively. Such OA-repressed respiration was also significant during the starvation period. On the other hand, the OA treatments and deprivation of the microalgae synergistically reduced the cellular quota of particulate organic C, N and P, resulting in a reduction of food value of the heterotrophic dinoflagellate as prey. In conclusion, our results show that O. marina is highly resilient to future ocean acidification by reducing its respiration and sustaining its ingestion of microalgae.

Continue reading ‘Ocean acidification and food availability impacts on the metabolism and grazing in a cosmopolitan herbivorous protist Oxyrrhis marina’

Marine phytoplankton and heterotrophic bacteria rapidly adapt to future pCO2 conditions in experimental co-cultures

Published 7 March 2024 Science Closed
Tags: abundance, biological response, BRcommunity, community composition, growth, laboratory, molecular biology, otherprocess, phytoplankton, prokaryotes

The CO₂ content of Earth’s atmosphere is rapidly increasing due to human consumption of fossil fuels. Models based on short-term culture experiments predict that major changes will occur in marine phytoplankton communities in the future ocean, but these models rarely consider how the evolutionary potential of phytoplankton or interactions within marine microbial communities may influence these changes. Here we experimentally evolved representatives of four phytoplankton functional types (silicifiers, calcifiers, coastal cyanobacteria, and oligotrophic cyanobacteria) in co-culture with a heterotrophic bacterium, Alteromonas, under either present-day or predicted future pCO₂ conditions. Growth rates of cyanobacteria generally increased under both conditions, and the growth defects observed in ancestral Prochlorococcus cultures at elevated pCO₂ and in axenic culture were diminished after evolution, possibly due to regulatory mutations in antioxidant genes. Except for Prochlorococcus, mutational profiles suggested phytoplankton experienced primarily purifying selection, but most Alteromonas lineages showed evidence of directional selection, especially when co-cultured with eukaryotic phytoplankton, where evolution appeared to favor a broad metabolic switch from growth on small organic acids to catabolism of more complex carbon substrates. Evolved Alteromonas were also poorer “helpers” for Prochlorococcus, supporting the assertion that the interaction between Prochlorococcus and heterotrophic bacteria is not a true mutualism but rather a competitive interaction stabilized by Black Queen processes. This work provides new insights on how phytoplankton will respond to anthropogenic change and on the evolutionary mechanisms governing the structure and function of marine microbial communities.

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Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming

Published 4 March 2024 Science Closed
Tags: algae, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, photosynthesis, physiology, temperature

Ocean acidification and warming caused by elevated CO₂ are urgent problems facing the marine ecological environment. With the strengthening of environmental governance in China, anthropogenic inputs of terrestrial phosphorus into the coastal ocean have drastically decreased, resulting in frequent phosphorus deficiency in seawater. These environmental factors in the future may affect algal growth, photosynthesis and yield. As an important economic macroalga suitable for large-scale cultivation, Gracilariopsis lemaneiformis is also potentially affected by the coupling of ocean acidification, warming and phosphorus deficiency. In this study, G. lemaneiformis was cultured outdoors under two pCO₂ levels (LC, 400 μatm; HC, 1000 μatm), two temperatures (LT, 20 ℃; HT, 24 ℃) and two phosphorus concentrations (LP, 0.1 μmol L⁻¹; HP, 10 μmol L⁻¹) to investigate its growth and photosynthetic performance. The results showed that LP significantly decreased the relative growth rates (RGR) and the maximum photosynthesis rate (P_m) of G. lemaneiformis both under LC and HC conditions. Under P depletion condition, the effects of warming and ocean acidification on the growth and photosynthetic performance of G. lemaneiformis showed an opposite trend, that is, HC caused a decrease in the growth, P_m, maximum relative electron transfer rate (rETR_max) and light utilization efficiency (α) from the rapid light response curve of G. lemaneiformis, and HT improved these parameters. Under LP condition, HC significantly inhibited the RGR of G. lemaneiformis in the LT group but had no significant effect on RGR in the HT group. Additionally, under LP condition, HC insignificantly affected PE and PC contents in the LT group, but significantly reduced these contents in the HT group. These findings suggest that phosphorus deficiency results in a decline in the growth of G. lemaneiformis and, under LP condition, the inhibition effect of ocean acidification on the growth of G. lemaneiformis could be mitigated by warming. This study provides scientific guidance for the field cultivation and selective breeding of G. lemaneiformis in phosphorus-deficient seawater under global climate change.

Continue reading ‘Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming’

Ocean acidification alters shellfish-algae nutritional value and delivery

Published 1 March 2024 Science Closed
Tags: biological response, BRcommunity, growth, laboratory, mollusks, morphology, multiple factors, North Pacific, nutrients, photosynthesis, physiology, phytoplankton

Highlights

Ocean acidification promotes microalgae growth.
The nutrient value of microalgae is positively altered under acidifying conditions.
Nutrient changes in primary producers can have indirect effects through trophic transfer.
Fatty acid content of food sources affects shellfish macromolecular ratios.

Abstract

The ecological effects of climate change and ocean acidification (OA) have been extensively studied. Various microalgae are ecologically important in the overall pelagic food web as key contributors to oceanic primary productivity. Additionally, no organism exists in isolation in a complex environment, and shifts in food quality may lead to indirect OA effects on consumers. This study aims to investigate the potential effects of OA on algal trophic composition and subsequent bivalve growth. Here, the growth and nutrient fractions of Chlorella sp., Phaeodactylum tricornutum and Chaetocetos muelleri were used to synthesize and assess the impact of OA on primary productivity. Total protein content, total phenolic compounds, and amino acid (AA) and fatty acid (FA) content were evaluated as nutritional indicators. The results demonstrated that the three microalgae responded positively to OA in the future environment, significantly enhancing growth performance and nutritional value as a food source. Additionally, certain macromolecular fractions found in consumers are closely linked to their dietary sources, such as phenylalanine, C14:0, C16:0, C16:1, C20:1n9, C18:0, and C18:3n. Our findings illustrate that OA affects a wide range of crucial primary producers in the oceans, which can disrupt nutrient delivery and have profound impacts on the entire marine ecosystem and human food health.

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Effect of increased pCO2 and temperature on the phytoplankton community in the coastal of Yellow Sea

Published 26 February 2024 Science Closed
Tags: abundance, biological response, BRcommunity, community composition, growth, laboratory, multiple factors, North Pacific, otherprocess, physiology, phytoplankton, primary production, temperature

Highlights

Elevated pCO₂ and temperature impact phytoplankton abundance and structure.
High temperature boosts phytoplankton growth.
Species vary in response to pCO₂ and temperature.

Abstract

In order to study the dynamics of marine phytoplankton communities in response to anticipated in temperature and CO₂, a shipboard continuous culture experiment (Ecostat) was conducted. The experiment involved simulations under current atmospheric CO₂ concentrations (400 ppm) and projected year-2100 CO₂ levels (1000 ppm), as well as varying temperature under present (22 °C) versus increased temperature (26 °C) in the Yellow Sea during the summer of 2020. The results showed that both the increased pCO₂ and temperature had significant effects on microphytoplankton and picophytoplankton, with the warming effect proving to be more significant. The different responses of various species to acidification and warming and their coupling effect led to the changes in microphytoplankton and picophytoplankton community structure. Elevated temperature and greenhouse treatments promoted the growth of dominant diatoms and Synechococcus, such as Guinardia flaccida and Pseudo-nitzschia delicatissima. This phenomenons widened the ecological niche, and the changes in the growth patterns of dominant species consequently influenced the content of cellular elements. Mantel’s analysis further demonstrated that both warming and greenhouse promoted the growth of diatoms and Synechococcus. Projections of marine phytoplankton community trends by the end of the century based on Growth Rate Ratio (GRR), indicated that not only would species with GRR < 1 decrease, but also numerous species with growth rates >1 at elevated pCO₂ levels would be ousted from competition. This experiment demonstrates the need to investigate whether extended exposure to increased pCO₂ and temperature over more extended time scales would similarly induce shifts in the biological and biogeochemical dynamics of the Yellow Sea.

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Hidden cost of pH variability in seagrass beds on marine calcifiers under ocean acidification

Published 9 February 2024 Science Closed
Tags: biological response, calcification, chemistry, communityMF, echinoderms, growth, laboratory, light, mortality, multiple factors, North Atlantic

Highlights

The presence of seagrass creates variability in pH/pCO₂.
High pCO₂/low pH negatively impacts growth and calcification of sea urchin larvae.
The variability associated with the presence of seagrass negatively impacts growth under ocean acidification.
Two different calcification strategies are observed in presence and absence of seagrass.

Abstract

Coastal ecosystems experience large environmental variability leading to local adaptation. The key role of variability and adaptation in modulating the biological sensitivity to ocean acidification is increasingly acknowledged. Monitoring and understanding the ecological niche at the right spatio-temporal scale is key to understand the sensitivity of any organism and ecosystems. However, the role of the variability in relevant carbonate chemistry parameters as a driver is often overlooked. For example, the balance between photosynthesis and respiration over the day/night cycle is leading to high pH/pCO₂ variability in seagrass beds. We hypothesized that (i) the calcifying larvae of the sea urchin Echinus esculentus exposed to seagrass-driven variability would have some physiological mechanisms to respond to such variability; and (ii) these mechanisms would reach their limit under ocean acidification. We compared the presence and absence of the seagrass Zostera marina in flow through mesocosms fed with seawater with 4 pHs. The carbonate chemistry was monitored and biological response of a sea urchin larvae was documented over 3 weeks. Growth and net calcification rates were measured twice a day to encompass diurnal variability. Our results show that larvae growth rate significantly decreased with decreasing average pH_T in both absence and presence of seagrass. Moreover, sea urchin larvae showed a slower growth rate in presence of seagrass, only visible in the lowest pH conditions. In addition, larvae raised in presence of seagrass, maximized calcification during the day, and lower their calcification during the night. In contrast, no significant difference was observed between day and night for the net calcification rate in larvae raised in absence of seagrass. Our results demonstrate the limit of local adaptation to the present range of variability under ocean acidification conditions. It also demonstrates that photosynthetic ecosystems such as seagrass may not play a role of refuge against future ocean acidification.

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Reviews and syntheses: The clam before the storm – a meta-analysis showing the effect of combined climate change stressors on bivalves

Published 6 February 2024 Science Closed
Tags: biological response, growth, mollusks, morphology, multiple factors, oxygen, review, salinity, temperature

The impacts of climate change on marine organisms have been increasingly documented in laboratory and experimental studies. However, the use of different taxonomic groupings and the assessment of a range of processes make identifying overall trends challenging. Meta-analysis has been used to determine general trends, but coarse taxonomic granularity may mask phylogenetically specific responses. Bivalve molluscs are a data-rich clade of ecologically and economically important calcifying marine taxa that allow for the assessment of species-specific vulnerability across developmental stages. Drawing on the large body of available literature, we conduct a meta-analysis of 203 unique experimental set-ups in order to examine how bivalve growth responds to increased water temperature, acidity, deoxygenation, and changes in salinity in 10 climate change stressor combinations. This is the most complete examination of bivalve responses to date and shows that anthropogenic climate change will disproportionally affect particular families, suggesting taxonomic differentiation in climate change response. Specifically, Mytilidae, Ostreidae, and Pectinidae (67 % of experiments) respond with negative effect sizes for all individual stressors, whereas responses in Pinnidae, Tellinidae, and Veneridae are more complex. Our analysis shows that earlier studies reporting negative impacts on bivalves are driven by only three or four well-studied, commercially important families. Despite the taxonomic differentiation, almost all drivers and their combinations have significant negative effects on growth. The synergistic impacts of deoxygenation, acidification, and temperature result in the largest negative effect size. Infaunal taxa, including Tellinidae and Veneridae, appear more resistant to warming and oxygen reduction than epifaunal or motile taxa, but this difference between the two taxa is also based on a small number of data points. The current focus of experimental set-ups on commercially important taxa and families within a small geographic range creates gaps in the understanding of global impacts on these economically important foundation organisms.

Continue reading ‘Reviews and syntheses: The clam before the storm – a meta-analysis showing the effect of combined climate change stressors on bivalves’

Physiological responses of Caulerpa spp. (with different dissolved inorganic carbon physiologies) to ocean acidification

Published 1 February 2024 Science Closed
Tags: algae, biological response, growth, laboratory, photosynthesis, physiology, primary production, South Pacific

Caulerpa is a widely distributed genus of chlorophytes (green macroalgae) which are important for their dietary, social and coastal ecosystem value. Ocean acidification (OA) threatens the future of marine ecosystems, favouring macroalgal species that could benefit from increased seawater carbon dioxide (CO₂) concentrations. Most macroalgae species possess CO₂ concentrating mechanisms (CCMs) that allow active uptake of bicarbonate (HCO₃⁻). Those species without CCMs are restricted to using CO₂, which is currently the least abundant species of dissolved inorganic carbon (DIC) in seawater. Thus, macroalgae without CCMs are predicted to be likely benefit from OA. Caulerpa is one of the rare few genera that have species both with and without CCMs. The two most common Caulerpa species in New Zealand are C. geminata (possesses a CCM) and C. brownii (non-CCM). We investigated the responses of growth, photo-physiology and DIC utilisation of C. geminata and C. brownii to four mean seawater pH treatments (8.03, 7.93, 7.83 and 7.63) that correspond to changes in pH driven by increases in pCO₂ simulating future OA. There was a tendency for the mean growth rates for C. brownii (non-CCM) to increase under lower pH, and the growth rates of C. geminata (CCM) to decline with lower pH, although this was not statistically significant. However, this is likely because variability in growth rates also increased as seawater pH declined. There were few other differences in physiology of both species with pH, although there was tendency for greater preference for CO₂ over HCO₃⁻ uptake in the CCM species with declining seawater pH. This study demonstrates that DIC-use alone does not predict macroalgal responses to OA.

Continue reading ‘Physiological responses of Caulerpa spp. (with different dissolved inorganic carbon physiologies) to ocean acidification’

Season influences interspecific responses of canopy-forming kelps to future warming and acidification at high latitude

Published 26 January 2024 Science Closed
Tags: algae, biological response, growth, laboratory, morphology, multiple factors, North Pacific, performance, physiology, temperature

Variability in primary producers’ responses to environmental change may buffer higher trophic levels against shifts in basal resource composition. Then again, in instances where there is a lack of functional redundancy because consumers rely on a few species to meet their energetic requirements at specific times of the year, altered community production dynamics may significantly impact food web resilience. In high-latitude kelp forests, a complementary annual phenology of seaweed production supports coastal marine consumers’ metabolic needs across large seasonal variations in their environment. Yet, marine consumers in these systems may face significant metabolic stress under the pronounced low pH conditions expected in future winters, particularly if they lack the resources to support their increased energetic demands. In this study, we investigate how the growth and nutritional value of three dominant, coexisting macroalgal species found in subpolar kelp forests will respond to ocean acidification and warming in future winter and summer seasons. We find that the three kelps Macrocystis pyrifera, Hedophyllum nigripes, and Neoagarum fimbriatum differ in their vulnerability to future environmental conditions, and that the seasonal environmental context of nutrient and light availability shapes these responses. Our results suggest that poleward fringe populations of M. pyrifera may be relatively resilient to anticipated ocean warming and acidification. In contrast, ocean warming conditions caused a decrease in the biomass and nutritional quality of both understory kelps. Considering the unique production phenology of H. nigripes, we emphasize that negative impacts on this species in future winters may be of consequence to consumer energetics in this system. This work highlights how interspecific variation in autotrophs’ responses to global change can disrupt the diversity and phenological structure of energy supply available to higher trophic levels.

Continue reading ‘Season influences interspecific responses of canopy-forming kelps to future warming and acidification at high latitude’

Functional changes across marine habitats due to ocean acidification

Published 15 January 2024 Science Closed
Tags: abundance, biological response, BRcommunity, calcification, chemistry, community composition, communitymodeling, field, growth, Mediterranean, modeling, otherprocess, performance, photosynthesis, reproduction, vents

Global environmental change drives diversity loss and shifts in community structure. A key challenge is to better understand the impacts on ecosystem function and to connect species and trait diversity of assemblages with ecosystem properties that are in turn linked to ecosystem functioning. Here we quantify shifts in species composition and trait diversity associated with ocean acidification (OA) by using field measurements at marine CO₂ vent systems spanning four reef habitats across different depths in a temperate coastal ecosystem. We find that both species and trait diversity decreased, and that ecosystem properties (understood as the interplay between species, traits, and ecosystem function) shifted with acidification. Furthermore, shifts in trait categories such as autotrophs, filter feeders, herbivores, and habitat-forming species were habitat-specific, indicating that OA may produce divergent responses across habitats and depths. Combined, these findings reveal the importance of connecting species and trait diversity of marine benthic habitats with key ecosystem properties to anticipate the impacts of global environmental change. Our results also generate new insights on the predicted general and habitat-specific ecological consequences of OA.

Continue reading ‘Functional changes across marine habitats due to ocean acidification’

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