Gelatinous zooplankton are increasingly recognized to play a key role in the ocean’s biological carbon pump. Appendicularians, a class of pelagic tunicates, are among the most abundant gelatinous plankton in the ocean, but it is an open question how their contribution to carbon export might change in the future. Here, we conducted an experiment with large volume in situ mesocosms (~55–60 m3 and 21 m depth) to investigate how ocean acidification (OA) extreme events affect food web structure and carbon export in a natural plankton community, particularly focusing on the keystone species Oikopleura dioica, a globally abundant appendicularian. We found a profound influence of O. dioica on vertical carbon fluxes, particularly during a short but intense bloom period in the high CO2 treatment, during which carbon export was 42%–64% higher than under ambient conditions. This elevated flux was mostly driven by an almost twofold increase in O. dioica biomass under high CO2. This rapid population increase was linked to enhanced fecundity (+20%) that likely resulted from physiological benefits of low pH conditions. The resulting competitive advantage of O. dioica resulted in enhanced grazing on phytoplankton and transfer of this consumed biomass into sinking particles. Using a simple carbon flux model for O. dioica, we estimate that high CO2 doubled the carbon flux of discarded mucous houses and fecal pellets, accounting for up to 39% of total carbon export from the ecosystem during the bloom. Considering the wide geographic distribution of O. dioica, our findings suggest that appendicularians may become an increasingly important vector of carbon export with ongoing OA.
Continue reading ‘The appendicularian Oikopleura dioica can enhance carbon export in a high CO2 ocean’Posts Tagged 'zooplankton'
The appendicularian Oikopleura dioica can enhance carbon export in a high CO2 ocean
Published 22 November 2023 Science ClosedTags: abundance, biogeochemistry, biological response, BRcommunity, chemistry, communitymodeling, field, mesocosms, modeling, morphology, North Atlantic, otherprocess, photosynthesis, phytoplankton, reproduction, zooplankton
Global synthesis of the status and trends of ocean acidification impacts on shelled pteropods
Published 13 November 2023 Science ClosedTags: Antarctic, Arctic, biological response, chemistry, mollusks, morphology, North Pacific, physiology, zooplankton
The accumulation of anthropogenic CO₂ in the ocean has major ecological, socioeconomic, and biogeochemical impacts, with repercussions for the ocean as a critical carbon sink. Ocean acidification (OA) disproportionately affects marine calcifiers, among which pelagic zooplanktonic pteropods play a significant role in carbonate export. The pteropod, due to the susceptibility of its aragonite shell to rapid dissolution, is one of most vulnerable groups and a key indicator for OA regional monitoring, but its regional sensitivities have not yet been extrapolated over global scales. To delineate spatial and temporal changes in pteropod shell dissolution, global OA status and the OA rate of change were evaluated, based on gridded climatologies of observations and using a Regional Ocean Modeling System (ROMS) biogeochemical/ecosystem model. Pteropods, which dominate in the polar and subpolar regions, are characterized by low aragonite saturation state and low buffering capacity, where extended pteropod subsurface dissolution is projected. We show that pteropods are most susceptible to OA in the polar regions, subpolar North Pacific, and eastern boundary upwelling system regions, particularly the California and Humboldt Current Systems. Rates of acidification and corresponding increases in pteropod shell dissolution are projected to be the fastest in the North and South Equatorial Currents. These are the regions with the greatest impacts on pteropods and biogeochemical implications.
Continue reading ‘Global synthesis of the status and trends of ocean acidification impacts on shelled pteropods’Prepared microplastics interaction with Artemia salina under low pH conditions representing ocean acidification; a simulated environmental exposure
Published 31 October 2023 Science ClosedTags: biological response, crustaceans, laboratory, multiple factors, physiology, reproduction, toxicants, zooplankton
Ocean acidification and microplastic pollution are two of the major ecological concerns. The distribution of large quantities of plastic debris and microplastics all across the oceans emphasises the need to determine the influence of microplastics in ocean acidification and to evaluate its concomitant toxicological effects on aquatic life forms. Studies on the combined impact of both the stressors are very limited, but much needed in the current scenario. Where most of the present-day research use purchased microplastics of defined size and morphology (microspheres, fibres, rods, etc.), the present study employs prepared “true to life microplastics” that resemble the environmental microplastic pollutants in morphology and size heterogeneity. The present study focusses on evaluating the fate and impact of oceanic microplastics on the physiology and development of Artemia salina (Brine shrimp), one among the most ecologically significant zooplankton species. Natural sea water was acidified by controlled perturbation of carbon dioxide using a valve system. The hatching rate of A. salina cysts receded significantly (p < 0.05) upon singular exposures to microplastics and low pH (7.80), whereas combined effect was insignificant. The reactive oxygen species (ROS) elevated as a result of individual exposures to microplastics and low pH. However, only in 0.5 mg mL−1 PE treatments at pH 7.80, an additive impact was reported for ROS activity (p < 0.05). The SOD activities increased significantly but it can be attributed as the individual responses towards exposure to both the stressors. A significant additive impact was not observed for SOD activity (p > 0.05). But during the development, significant morphological anomalies were observed. Changes in the appendages of nauplii and juveniles as a result of combined exposure to microplastics and low pH treatments are significant findings. Our observations suggest that coupled exposure to microplastics and low pH could induce significant oxidative stress in the marine zooplanktons and also adversely affect their normal development. Findings from the current study emphasise the need for further research to understand the coupled toxicological impacts of ocean acidification and predominant pollutants such as microplastics to other marine animals as well.
Continue reading ‘Prepared microplastics interaction with Artemia salina under low pH conditions representing ocean acidification; a simulated environmental exposure’Interactive effects of ocean acidification and temperature on oxygen uptake rates in Calanus hyperboreus nauplii
Published 30 October 2023 Science ClosedTags: Antarctic, biological response, crustaceans, laboratory, multiple factors, physiology, respiration, temperature, zooplankton
The Arctic region is undergoing rapid and significant changes, characterized by high rates of acidification and warming. These transformations prompt critical questions about the resilience of marine communities in the face of environmental change. In the Arctic, marine zooplankton and in particular calanoid copepods play a vital role in the food web. Changes in environmental conditions could disrupt zooplankton communities, posing detrimental consequences for the entire ecosystem. Copepod early-life stages have been shown to be particularly sensitive to environmental stressors since they represent a bottleneck in the life cycle. Here, we investigated the responses of 4-day old Calanus hyperboreus nauplii when exposed to acidification (pH 7.5 and 8.1) and warming (0 and 3°C), both independently and in combination. Naupliar respiration rates increased when exposed to a combination of acidification and warming, but not when exposed to the stressors individually. Moreover, we found no discernible differences in lipid content and fatty acid (FA) composition of the nauplii across the different experimental treatments. Wax esters accounted for approximately 75% of the lipid reserves, and high amounts of long chain fatty acids 20:1 and 22:1, crucial for the reproduction cycle in copepods, were also detected. Our results indicate a sensitivity of these nauplii to a combination of acidification and warming, but not to the individual stressors, aligning with a growing body of evidence from related studies. This study sheds light on the potential implications of global change for Arctic copepod populations by elucidating the responses of early-life stages to these environmental stressors.
Continue reading ‘Interactive effects of ocean acidification and temperature on oxygen uptake rates in Calanus hyperboreus nauplii’The transcriptome profile of the marine Calanoid copepod Parvocalanus crassirostris isolated from Kuwait territorial waters and generations cultured under different ocean acidification scenarios
Published 16 October 2023 Science ClosedTags: biological response, crustaceans, Indian, laboratory, molecular biology, zooplankton
Copepods are primary consumers, amounting to about 70 % of the metazoans in the marine environment, and are fundamental to marine food webs. Ocean acidification (OA) and ocean warming (OW) significantly affect the copepod community leading to the severe consequences of an ecological imbalance. Molecular resources are minimal for copepods and call for transcriptome profiling to better understand their responses under changing environmental conditions. This manuscript describes the de novo transcriptome of Parvocalanus crassirostris, a common inhabitant of coastal waters. RNA sequencing (RNAseq) was performed on whole organisms. Raw reads assembled through Trinity comprised 344,652 transcripts and 249,255 unigenes. Bench-marking-universal-single-copy-orthologs (BUSCO) analysis identified 86.6 % (C:86.9 % [S: 78 %, D: 8.6 %], M: 3.5 %, F: 9.9 %) of the assembly to be complete. Approximately 40 % and 12 % of unigenes were functionally annotated against the gene ontologies (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The dominant GO categories were cellular (58.20 %) > metabolic (55.91 %) > catalytic activity (50.12 %) > binding (45.55 %) > cellular anatomical entity (39.36 %) > and intracellular binding (21.68 %). In contrast, signal transduction pathways were the dominant pathways under the environment information processing of the KEGG category. Differential gene expression analysis was performed on different generations of copepods under progressively lower pH. Over 99,117 unigenes were discovered, of which 53,044 were upregulated and 46,073 downregulated. Gene ontologies enrichment analysis revealed significantly different functional pathways at a false discovery rate (FDR) of q< 0.05 (COP1-COP2: 15; COP1-COP3: 47; COP2-COP3: 22). The KEGG enrichment informed genes associated with 17 pathways to be upregulated while 31 pathways to be downregulated. This investigation provides an important genomic resource of P. crassirostris under ambient conditions and in future climate scenarios in response to OA.
Continue reading ‘The transcriptome profile of the marine Calanoid copepod Parvocalanus crassirostris isolated from Kuwait territorial waters and generations cultured under different ocean acidification scenarios’Transgenerational adaptation to ocean acidification determines the susceptibility of filter-feeding rotifers to nanoplastics
Published 26 September 2023 Science ClosedTags: biological response, laboratory, molecular biology, multiple factors, North Pacific, performance, physiology, toxicants, zooplankton
The adaptation of marine organisms to the impending challenges presented by ocean acidification (OA) is essential for their future survival, and mechanisms underlying OA adaptation have been reported in several marine organisms. In the natural environment, however, marine organisms are often exposed to a combination of environmental stressors, and the interactions between adaptive responses have yet to be elucidated. Here, we investigated the susceptibility of filter-feeding rotifers to short-term (ST) and long-term (LT) (≥180 generations) high CO2 conditions coupled with nanoplastic (NPs) exposure (ST+ and LT+). Adaptation of rotifers to elevated CO2 caused differences in ingestion and accumulation of NPs, resulting in a significantly different mode of action on in vivo endpoints between the ST+ and LT+ groups. Moreover, microRNA-mediated epigenetic regulation was strongly correlated with the varied adaptive responses between the ST+ and LT+ groups, revealing novel regulatory targets and pathways. Our results indicate that pre-exposure history to increased CO2 levels is an important factor in the susceptibility of rotifers to NPs.
Continue reading ‘Transgenerational adaptation to ocean acidification determines the susceptibility of filter-feeding rotifers to nanoplastics’Simultaneous warming and acidification limit population fitness and reveal phenotype costs for a marine copepod
Published 8 September 2023 Science ClosedTags: adaptation, biological response, crustaceans, laboratory, morphology, mortality, multiple factors, otherprocess, reproduction, temperature, zooplankton
Phenotypic plasticity and evolutionary adaptation allow populations to cope with global change, but limits and costs to adaptation under multiple stressors are insufficiently understood. We reared a foundational copepod species, Acartia hudsonica, under ambient (AM), ocean warming (OW), ocean acidification (OA), and combined ocean warming and acidification (OWA) conditions for 11 generations (approx. 1 year) and measured population fitness (net reproductive rate) derived from six life-history traits (egg production, hatching success, survival, development time, body size and sex ratio). Copepods under OW and OWA exhibited an initial approximately 40% fitness decline relative to AM, but fully recovered within four generations, consistent with an adaptive response and demonstrating synergy between stressors. At generation 11, however, fitness was approximately 24% lower for OWA compared with the AM lineage, consistent with the cost of producing OWA-adapted phenotypes. Fitness of the OWA lineage was not affected by reversal to AM or low food environments, indicating sustained phenotypic plasticity. These results mimic those of a congener, Acartia tonsa, while additionally suggesting that synergistic effects of simultaneous stressors exert costs that limit fitness recovery but can sustain plasticity. Thus, even when closely related species experience similar stressors, species-specific costs shape their unique adaptive responses.
Continue reading ‘Simultaneous warming and acidification limit population fitness and reveal phenotype costs for a marine copepod’The reproductive capacities of the calanoid copepods Parvocalanus crassirostis and Acartia pacifica under different pH and temperature conditions
Published 4 August 2023 Science ClosedTags: biological response, crustaceans, Indian, laboratory, multiple factors, reproduction, temperature, zooplankton
The increasing atmospheric CO2 concentrations and warming of marine waters have encouraged experiments on multi-stressor interactions in marine organisms. We conducted a multigenerational experiment to assess reproductive capacities regarding egg production in calanoid copepods Parvocalanus crassirostis and Acartia pacifica under different pH and temperature conditions. The experimental set-up allowed assessing the tandem effect of warming and acidification on the number of eggs produced by healthy copepod pairs under two pH conditions of 8.20 and 7.50 (hard selection) as well as with a gradual reduction of 0.05 pH units at each generation (soft selection). The results are quite interesting, with very diverse performance across temperatures. The number of eggs produced under hard selection was higher at pH 8.20 compared to pH 7.50 for both species, with the maximum number of eggs produced at 24–28 °C, whereas under soft selection, there was no significant difference in the egg production rate at 24–28 °C across generations and there was an improvement in the number of eggs produced at 8–16 °C. The results provide evidence that in a future ocean scenario of lower pH and higher temperature, the two species, and possibly the copepod population at large, might not decrease. Copepod populations might be resilient, and the transcriptomic evidence of adaptation to increased temperature and lower pH is a ray of hope. We believe further studies are needed to provide more robust datasets to underpin the hypothesis of adaptation to climate change.
Continue reading ‘The reproductive capacities of the calanoid copepods Parvocalanus crassirostis and Acartia pacifica under different pH and temperature conditions’Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification
Published 14 July 2023 Science ClosedTags: biogeochemistry, BRcommunity, communitymodeling, modeling, phytoplankton, protists, zooplankton
Plankton phototrophy consumes CO2, increasing seawater pH, while heterotrophy does the converse. Elevation of pH (>8.5) during coastal blooms becomes increasingly deleterious for plankton. Mixoplankton, which can be important bloom-formers, engage in both photoautotrophy and phagoheterotrophy; in theory, this activity could create a relatively stable pH environment for plankton growth. Using a systems biology modelling approach, we explored whether different mixoplankton functional groups could modulate the environmental pH compared to the extreme activities of phototrophic phytoplankton and heterotrophic zooplankton. Activities by most mixoplankton groups do not stabilize seawater pH. Through access to additional nutrient streams from internal recycling with phagotrophy, mixoplankton phototrophy is enhanced, elevating pH; this is especially so for constitutive and plastidic specialist non-constitutive mixoplankton. Mixoplankton blooms can exceed the size of phytoplankton blooms; the synergisms of mixoplankton physiology, accessing nutrition via phagotrophy as well as from inorganic sources, enhance or augment primary production rather than depressing it. Ocean acidification will thus enable larger coastal mixoplankton blooms to form before basification becomes detrimental. The dynamics of such bloom developments will depend on whether the mixoplankton are consuming heterotrophs and/or phototrophs and how the plankton community succession evolves.
Continue reading ‘Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification’The roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification
Published 27 June 2023 Science ClosedTags: biogeochemistry, biological response, individualmodeling, modeling, multiple factors, physiology, reproduction, respiration, review, temperature, zooplankton
Two ocean acidification studies about egg hatching success (HS) in geographically important marine copepods, Calanus finmarchicus and C. helgolandicus, were reanalyzed with improved statistical procedures. The new results at low and moderate levels of seawater acidification showed no HS inhibition at normal habitat temperatures but statistically significant inhibition at warmer and colder temperatures. These HS results were compared with seawater carbonate system and borate concentrations from precise seawater measurements. The temperature dependent differences in HS could not be directly explained by changes in the seawater concentrations of either H+, bicarbonate (HCO3−), or CO2* (CO2* being the sum of unhydrated CO2 and H2CO3). In contrast, HS differences did match trends in seawater carbonate (CO32−) concentrations. A numerical model was developed which evaluates the concentrations of O2 or CO2*, HCO3−, and CO32− at the cellular level across an egg and embryo by considering both gas diffusion with the seawater and respiration by the embryo. Again, temperature-dependent trends in HS could not be explained changes in intracellular CO2* or HCO3− concentrations, but HS did trend with the changes in intracellular CO32− concentrations. Carbonate ions form strong coordination complexes with metals, so acidification-driven decreases in external seawater carbonate concentrations, which are amplified at warmer temperatures, could release injurious metals, thus driving the HS inhibition at warmer temperatures. Increases in cytoplasmic carbonate concentrations at warmer temperatures caused by seawater acidification could complex with biochemically-needed nutrient-type metals within the cells, also causing the increased HS inhibition at warmer temperatures. Furthermore, boron is essential in chemically signaling within and between cells. Seawater borate concentrations were closely correlated with HS inhibition via Michaelis-Menton equations, suggesting that acidification-driven decreases in seawater borate concentrations may also inhibit HS. Finally, the acidification-driven increases in CO2 diffusion into cells dramatically increased intracellular bicarbonate concentrations. At mild levels of seawater acidification, an organism might compensate by exporting bicarbonate from the cells to the haemolymph and then to the seawater. Although the energetic cost, as percentage of ATP production, might be high, increased respiration rates at warmer temperatures might better allow the organism to survive. However, as temperature is lowered, the cellular respiration rate declines more rapidly with respect to temperature than does the gas diffusion coefficient. Consequently, bicarbonate accumulation driven by inward CO2 diffusion might overwhelm the egg’s bicarbonate export capacity at colder temperatures, explaining the colder temperature HS inhibition.
Continue reading ‘The roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification’Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea
Published 19 June 2023 Science ClosedTags: abundance, annelids, biological response, BRcommunity, chemistry, community composition, crustaceans, field, nematodes, North Pacific, otherprocess, protists, zooplankton
This study aimed to investigate the meiofauna community characteristics in coastal waters highly affected by ocean acidification. Therefore, the meiofauna communities in the coastal waters of Hupo in Uljin-gun, a county bordering the East Sea of Korea, were monitored over five years. During the study period, the mean abundance of total meiofauna communities expressed in population density was 614.4 individuals (Inds.)/10 cm2, similar to the reported meiofauna abundance in the subtidal zone in the Yellow Sea of Korea, an area with sandy sedimentary facies. The most dominant taxa were nematodes (65–70%) and harpacticoids (7–20%); these two taxa accounted for approximately 80% of the total meiofauna abundance. Among the stations studied, station (St.) 10 showed the lowest seawater pH value, and in 2011, when the measured pH was the lowest at 7.82, St. 10 showed the lowest abundance values for total meiofauna and harpacticoids in the 5-year period. To examine the effect of ocean acidification on meiofauna communities at the species level, species of nematodes, the most dominant taxon, were analyzed. The results indicated that the number of nematode species at St. 10 in 2009, when the pH value was low, was 8, which was very low compared to that in the other years of the study period. According to the feeding type, epistrate feeders (2A) accounted for a remarkably high proportion at St. 10, which showed a low pH. This study provides various data on meiobenthic community characteristics to understand the effects of ocean acidification on coastal ecosystems.
Continue reading ‘Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea’Evidence for an effective defence against ocean acidification in the key bioindicator pteropod Limacina helicina
Published 19 May 2023 Science ClosedTags: biological response, dissolution, laboratory, mollusks, morphology, mortality, North Pacific, performance, zooplankton
The pteropod Limacina helicina has become an important bioindicator species for the negative impacts of ocean acidification (OA) on marine ecosystems. However, pteropods diversified during earlier high CO2 periods in Earth history and currently inhabit regions that are naturally corrosive to their shells, suggesting that they possess mechanisms to survive unfavourable conditions. Recent work, which is still under considerable debate, has proposed that the periostracum, a thin organic coating on the outer shell, protects pteropods from shell dissolution. Here, we provide direct evidence that shows that damage to the L. helicina periostracum results in dissolution of the underlying shell when exposed to corrosive water for ∼8 d, while an intact periostracum protects the shell from dissolution under the same conditions. This important first line of defence suggests that pteropods are more resistant to OA-induced shell dissolution than is generally accepted.
Continue reading ‘Evidence for an effective defence against ocean acidification in the key bioindicator pteropod Limacina helicina’Contrasting life cycles of Southern Ocean pteropods alter their vulnerability to climate change
Published 16 May 2023 Science ClosedTags: abundance, Antarctic, biological response, chemistry, community composition, field, mollusks, morphology, otherprocess, physiology, reproduction, zooplankton
Pteropods are a key part of biogeochemical cycling and epipelagic food webs in the Southern Ocean. However, shelled pteropods are vulnerable to climate change, due to their aragonite shells being particularly sensitive to ocean acidification. Currently our understanding of pteropod responses to environmental change is hindered by uncertainties surrounding their life cycles and population dynamics. In this study, we describe polar shelled pteropod diversity in the north-eastern Scotia Sea, inferring life history and population structures of the dominant pteropod species, Limacina rangii (formerly Limacina helicina antarctica) and Limacina retroversa. An annual timeseries of Limacina shell morphometrics was derived from individuals collected in a moored sediment trap at 400 m depth. We found that L. rangii and L. retroversa have contrasting life history strategies. L. rangii has a continuous spawning and recruitment period from November to March and can overwinter as juveniles and adults. L. retroversa has discrete spawning events from November to May, producing non–overlapping cohorts of juveniles and adults. Their development to the adult stage takes between two and five months, upon which they overwinter as adults. Our findings suggest different vulnerabilities of L. rangii and L. retroversa to a changing ocean. For example, since all life stages of L. rangii co-exist, vulnerability of one cohort is not detrimental to the stability of the overall population whereas, if one L. retroversa cohort fails to recruit, the entire population is threatened. Changes in pteropod populations could have cascading ramifications to Antarctic ecosystems and carbon cycling.
Continue reading ‘Contrasting life cycles of Southern Ocean pteropods alter their vulnerability to climate change’Ocean warming and CO2-driven acidification can alter the toxicity of metal-contaminated sediments to the meiofauna community
Published 8 May 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, crustaceans, laboratory, mesocosms, metals, multiple factors, nematodes, otherprocess, South Atlantic, temperature, toxicants, zooplankton
Highlights
- Contamination interacted with warming but the effect on density was taxon dependent.
- Warming increased metal effects in nematods and copepods, and decreased in acoelomorphs.
- Copepod densities were lower, and acoelomorphs higher, in the high CO2/low pH scenario.
- Global change studies should consider multispecies exposures in multi-stressor scenarios.
Abstract
Interactive effects of trace metal contamination, ocean warming, and CO2-driven acidification on the structure of a meiofaunal benthic community was assessed. Meiofauna microcosm bioassays were carried out in controlled conditions in a full factorial experimental design which included three fixed factors: metal contamination in the sediment (3 levels of a mixture of Cu, Pb, Zn, and Hg), temperature (26 and 28 °C) and pH (7.6 and 8.1). Metal contamination caused a sharp decrease in the densities of the most abundant meiobenthic groups and interacted with temperature rise, exacerbating deleterious effects for Nematoda and Copepoda, but mitigating effects for Acoelomorpha. CO2-driven acidification resulted in increased acoelomorphs density, but only in sediments with lower levels of metals. Copepod densities, in turn, were lower in the CO2-driven acidification scenario regardless of contamination or temperature. The results obtained in the present study showed that temperature rise and CO2-driven acidification of coastal ocean waters, at environmentally relevant levels, interacts with trace metals in marine sediments, differently affecting the major groups of benthic biota.
Continue reading ‘Ocean warming and CO2-driven acidification can alter the toxicity of metal-contaminated sediments to the meiofauna community’Projected effects of climate change on marine ecosystems in Southeast Asian seas
Published 17 April 2023 Science ClosedTags: biological response, BRcommunity, chemistry, corals, modeling, North Pacific, phytoplankton, primary production, regionalmodeling, South Pacific, zooplankton
The seas of Southeast Asia are home to some of the world’s most diverse ecosystems and resources that support the livelihoods of millions of people. Climate change will bring temperature changes, acidification and other environmental change, with uncertain consequences for human and natural systems, but there has been little regional-scale climate modelling of the marine ecosystem. We present initial dynamically downscaled projections using a biogeochemical model suitable for coastal and shelf seas. A coupled physical-biogeochemical model with a resolution of 0.1° (approximately 11 km) was used to create projections of future environmental conditions under moderate (RCP4.5) and high (RCP8.5) greenhouse gas scenarios. Changes for different parts of the region are presented, including four sensitive coastal sites of key importance for biodiversity and sustainable development: UNESCO Biosphere Reserves at Cu Lao Cham-Hoi An in Vietnam, Palawan in the Philippines and Taka Bonerate-Kepulauan Selayar in Indonesia, and coastal waters of Sabah, Malaysia, which include several marine parks. The projections show a sea that is warming by 1.1 to 2.9°C through the 21st century, with dissolved oxygen decreasing by 5 to 13 mmol m-3 and changes in many other environmental variables. The changes reach all parts of the water column and many places are projected to experience conditions well outside the range seen at the start of the century. The resulting damage to coral reefs and altered species distribution would have consequences for biodiversity, the livelihoods of small-scale fishers and the food security of coastal communities. Further work using a range of global models and regional models with different biogeochemical components is needed to provide confidence levels, and we suggest some ways forward. Projections of this type serve as a key tool for communities and policymakers as they plan how they will adapt to the challenge of climate change.
Continue reading ‘Projected effects of climate change on marine ecosystems in Southeast Asian seas’Hypoxia tolerance, but not low pH tolerance, is associated with a latitudinal cline across populations of Tigriopus californicus
Published 6 April 2023 Science ClosedTags: adaptation, biological response, crustaceans, field, laboratory, morphology, mortality, multiple factors, North Pacific, otherprocess, oxygen, zooplankton
Intertidal organisms must tolerate daily fluctuations in environmental parameters, and repeated exposure to co-occurring conditions may result in tolerance to multiple stressors correlating. The intertidal copepod Tigriopus californicus experiences diurnal variation in dissolved oxygen levels and pH as the opposing processes of photosynthesis and cellular respiration lead to coordinated highs during the day and lows at night. While environmental parameters with overlapping spatial gradients frequently result in correlated traits, less attention has been given to exploring temporally correlated stressors. We investigated whether hypoxia tolerance correlates with low pH tolerance by separately testing the hypoxia and low pH stress tolerance separately of 6 genetically differentiated populations of T. californicus. We independently checked for similarities in tolerance for each of the two stressors by latitude, sex, size, and time since collection as predictors. We found that although hypoxia tolerance correlated with latitude, low pH tolerance did not, and no predictor was significant for both stressors. We concluded that temporally coordinated exposure to low pH and low oxygen did not result in populations developing equivalent tolerance for both. Although climate change alters several environmental variables simultaneously, organisms’ abilities to tolerate these changes may not be similarly coupled.
Continue reading ‘Hypoxia tolerance, but not low pH tolerance, is associated with a latitudinal cline across populations of Tigriopus californicus’Assessing the impact of ocean acidification: a methods comparison of SEM, CT and light microscopy on pteropod shells
Published 31 March 2023 Science ClosedTags: biological response, dissolution, laboratory, methods, mollusks, morphology, North Atlantic, North Pacific, zooplankton
Since the onset of the Industrial Revolution, the world’s oceans have absorbed approximately one third of all anthropogenic CO2 emissions and are experiencing acidification as a result. Pteropods are a marine group of snails that are vulnerable to acidification due to their thin shells composed of aragonite, which is 50% more soluble than calcite. Due to their vulnerability and ubiquity throughout the world’s oceans, pteropods are considered bioindicators of ocean acidification; their responses include decreased size, reduced shell thickness, and increased shell dissolution. Shell dissolution has been measured using a variety of metrics involving light microscopy, scanning electron microscopy (SEM), and computed tomography (CT). Assessing which method(s) effectively capture acidification’s impact on pteropod shells is still an active area of research. While CT and SEM metrics offer high resolution imaging, these analyses are cost- and time-intensive relative to light microscopy analyses and may be inaccessible for ocean monitoring projects and research. This research compares light microscopy, CT, and SEM shell dissolution metrics across three pteropod species: Limacina helicina, Limacina retroversa, and Heliconoides inflatus. Sourced from multiple localities, these taxa lived in tropical to subpolar environments and were exposed to varying aragonite saturations states due to stark oceanographic differences in these environments. Specimens were evaluated using light microscopy for the Limacina Dissolution Index (LDX), using SEM for average and maximum dissolution type, and using CT for shell thickness. Spearman correlation tests were run among the dissolution metrics within each species dataset and significance was assessed both before and viii after Bonferroni correction. Before Bonferroni correction, LDX and SEM average dissolution type were highly correlated for both the Limacina retroversa (rho = 0.81, p > 0.001) and Heliconoides inflatus (rho = 0.79, p > 0.001) datasets, and remained significant after Bonferroni correction. For Limacina retroversa, LDX was also significantly correlated to SEM maximum dissolution type (rho = 0.77, p > 0.001). The CT metrics for shell thickness were not significantly correlated to any other dissolution metrics for any species. However, severely dissolved (type 3) areas apparent in SEM were also visually discernible in CT thickness heatmaps. Although the genera Heliconoides and Limacina have different shell microstructures, the relationship between LDX and SEM average dissolution type did not vary by species. Additionally, the Heliconoides inflatus specimens were sourced from both the aragonite-undersaturated California Current and the aragonite-oversaturated Cariaco Basin; however, the differing localities and their respective oceanographic conditions did not have a significant influence on the relationship between LDX and SEM average dissolution. Overall, these findings show that the cheaper and faster LDX method, which needs only a light microscope, is a promising method for detecting dissolution resulting from ocean acidification across multiple species and oceanographic conditions.
Continue reading ‘Assessing the impact of ocean acidification: a methods comparison of SEM, CT and light microscopy on pteropod shells’Ocean acidification and warming modify stimulatory benthos effects on sediment functioning: an experimental study on two ecosystem engineers
Published 17 March 2023 Science ClosedTags: biological response, laboratory, mollusks, mortality, multiple factors, North Atlantic, physiology, sediment, temperature, zooplankton
Many macrofauna have a stimulatory effect on sediment functioning through their burrowing, feeding and irrigation activities. Here, we investigated the single and combined effect of ocean acidification and warming on the stimulatory effect of two key-species inhabiting sandy seabeds in the Southern Bight of the North Sea; the bivalve Abra alba and the polychaete Lanice conchilega. The species were separately incubated in natural sediment in the laboratory under ambient, low pH (pH: -0.3), warm (T: + 3°C) and mimicked climate change (pH: -0.3, T: +3°C) conditions. After six weeks of incubation, nutrient and oxygen exchange were measured at the sediment-water interface to estimate aerobic sediment metabolism and nitrogen cycling. Both species facilitate sediment community oxygen consumption, nitrification and denitrification under ambient conditions. The stimulatory effect of A. alba disappeared in a low pH environment and decreased over time in the warmer treatments along with increased mortality. In contrast, L. conchilega stimulated sediment biogeochemical cycling more when seawater becomes acidified (+ 8 to 41%, depending on the function) but warming had no effect. We explain these species-specific climate change effects by different behavioral and physiological coping strategies that cascade on to sediment biogeochemical cycling, especially through altered oxygenation the sediment matrix.
Continue reading ‘Ocean acidification and warming modify stimulatory benthos effects on sediment functioning: an experimental study on two ecosystem engineers’Nanoplastics induce epigenetic signatures of transgenerational impairments associated with reproduction in copepods under ocean acidification
Published 15 March 2023 Science ClosedTags: biological response, crustaceans, laboratory, molecular biology, multiple factors, North Pacific, reproduction, toxicants, zooplankton
Ocean acidification (OA) is one of many major global climate changes that pose a variety of risks to marine ecosystems in different ways. Meanwhile, there is growing concern about how nanoplastics (NPs) affect marine ecosystems. Combined exposure of marine organisms to OA and NPs is inevitable, but their interactive effects remain poorly understood. In this study, we investigated the multi- and transgenerational toxicity of NPs on copepods under OA conditions for ten generations. The findings revealed that OA and NPs have a synergistic negative effect on copepod reproduction across generations. In particular, the transgenerational groups showed reproductive impairments in the F1 and F2 generations (F1T and F2T), even though they were never exposed to NPs. Moreover, our epigenetic examinations demonstrated that the observed intergenerational reproductive impairments are associated with differential methylation patterns of specific genes, suggesting that the interaction of OA and NPs can pose a significant threat to the sustainability of copepod populations through epigenetic modifications. Overall, our findings provide valuable insight into the intergenerational toxicity and underlying molecular mechanisms of responses to NPs under OA conditions.
Continue reading ‘Nanoplastics induce epigenetic signatures of transgenerational impairments associated with reproduction in copepods under ocean acidification’
