The temporal variation of the carbonate system, air-sea CO2 fluxes and pH is analyzed in the Southern Indian Ocean, south of the Polar Front, based on in-situ data obtained from 1985 to 2021 at a fixed station (50°40’S–68°25’E) and results from a neural network model that reconstructs the fugacity of CO2 (fCO2) and fluxes at monthly scale. Anthropogenic CO2 (Cant) was estimated in the water column and detected down to the bottom (1600 m) in 1985 resulting in an aragonite saturation horizon at 600 m that migrated up to 400 m in 2021 due to the accumulation of Cant. In subsurface, the trend of Cant is estimated at +0.53 (±0.01) µmol.kg-1.yr-1 with a detectable increase in recent years. At the surface during austral winter the oceanic fCO2 increased at a rate close or slightly lower than in the atmosphere. To the contrary, in summer, we observed contrasting fCO2 and dissolved inorganic carbon (CT) trends depending on the decade and emphasizing the role of biological drivers on air-sea CO2 fluxes and pH inter-annual variability. The region moved from an annual source of 0.8 molC.m-2.yr-1 in 1985 to a sink of -0.5 molC.m-2.yr-1 in 2020. In 1985–2020, the annual pH trend in surface of -0.0165 (± 0.0040).decade-1 was mainly controlled by anthropogenic CO2 but the trend was modulated by natural processes. Using historical data from November 1962 we estimated the long-term trend for fCO2, CT and pH confirming that the progressive acidification was driven by atmospheric CO2 increase. In 59 years this leads to a diminution of 11 % for both aragonite and calcite saturation state. As atmospheric CO2 will desperately continue rising in the future, the pH and carbonate saturation state will decrease at a faster rate than observed in recent years. A projection of future CT concentrations for a high emission scenario (SSP5-8.5) indicates that the surface pH in 2100 would decrease to 7.32 in winter. This is up to -0.86 lower than pre-industrial pH and -0.71 lower than pH observed in 2020. The aragonite under-saturation in surface waters would be reached as soon as 2050 (scenario SSP5-8.5) and 20 years later for a stabilization scenario (SSP2-4.5) with potential impacts on phytoplankton species and higher trophic levels in the rich ecosystems of the Kerguelen Island area.
Continue reading ‘Anthropogenic CO2, air-sea CO2 fluxes and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51°S-68°E)’Posts Tagged 'Indian'
Anthropogenic CO2, air-sea CO2 fluxes and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51°S-68°E)
Published 20 November 2023 Science ClosedTags: biogeochemistry, chemistry, field, Indian, modeling, regionalmodeling
Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions
Published 17 November 2023 Science ClosedTags: biological response, BRcommunity, fish, Indian, laboratory, molecular biology, multiple factors, performance, physiology, temperature
Background
Mutualistic interactions, which constitute some of the most advantageous interactions among fish species, are highly vulnerable to environmental changes. A key mutualistic interaction is the cleaning service rendered by the cleaner wrasse, Labroides dimidiatus, which involves intricate processes of social behaviour to remove ectoparasites from client fish and can be altered in near-future environmental conditions. Here, we evaluated the neuromolecular mechanisms behind the behavioural disruption of cleaning interactions in response to future environments. We subjected cleaner wrasses and surgeonfish (Acanthurus leucosternon, serving as clients) to elevated temperature (warming, 32 °C), increased levels of CO2 (high CO2, 1000 ppm), and a combined condition of elevated CO2 and temperature (warming and high CO2, 32 °C, and 1000 ppm) for 28 days.
Results
Each of these conditions resulted in behavioural disruptions concerning the motivation to interact and the quality of interaction (high CO2 − 80.7%, warming − 92.6%, warming and high CO2 − 79.5%, p < 0.001). Using transcriptomics of the fore-, mid-, and hindbrain, we discovered that most transcriptional reprogramming in both species under warming conditions occurred primarily in the hind- and forebrain. The associated functions under warming were linked to stress, heat shock proteins, hypoxia, and behaviour. In contrast, elevated CO2 exposure affected a range of functions associated with GABA, behaviour, visual perception, thyroid hormones and circadian rhythm. Interestingly, in the combined warming and high CO2 condition, we did not observe any expression changes of behaviour. However, we did find signs of endoplasmic reticulum stress and apoptosis, suggesting not only an additive effect of the environmental conditions but also a trade-off between physiological performance and behaviour in the cleaner wrasse.
Conclusions
We show that impending environmental shifts can affect the behaviour and molecular processes that sustain mutualistic interactions between L. dimidiatus and its clients, which could have a cascading effect on their adaptation potential and possibly cause large-scale impacts on coral reef ecosystems.
Continue reading ‘Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions’Coupling between chromophoric dissolved organic matter and dissolved inorganic carbon in Indian estuaries
Published 7 November 2023 Science ClosedTags: chemistry, field, Indian
Highlights
- CDOM in estuaries, mostly humic/fulvic, may indicate DOM alkalinity.
- Combined with pH, CDOM fits into eqn. for DIC; accounts up to 22 % of DIC.
- Without CDOM, pH would rise by 0.67 in EC and 0.38 in WC Indian estuaries.
- High SR of CDOM is a marker of anthropogenic organic inputs to estuary.
- (TA-DIC) vs pH25 plot identifies buffering by CDOM.
Abstract
This study investigates the coupling between Chromophoric Dissolved Organic Matter (CDOM) and Dissolved Inorganic Carbon (DIC) in eighteen Indian estuaries across salinity gradient of the east and west coasts during the monsoon season, characterized by significant river discharge. The hypothesis that humic acids (HA) and fulvic acids (FA), prominent in estuarine CDOM, closely correspond to the ‘organic alkalinity’ (Aorg) component of total alkalinity is examined. In most estuaries, specifically those along the northeast coast (NE) and southwest coast (SW), a significant linear relationship exists between DIC, CDOM abundance, and pH level. Notably, minor estuaries along the southeast coast (SE) and northwest coast (NW) exhibit elevated DIC levels beyond what this relationship predicts. These estuaries also reveal heightened ammonium levels, increased δ15N values, and decreased δ13C values, indicative of anthropogenic influence. CDOM properties, such as spectral slope (S300–500) and spectral slope ratio (SR, S275–295:S350–400), align with these findings, with SE and NW estuaries displaying higher values. On average, CDOM contributes 110.5 μM (6.8 %) to DIC in NE, 390.7 μM (11 %) in SE, 24.4 μM (4.8 %) in SW, and 122.2 μM (4 %) in NW estuaries. The relationship between total alkalinity minus DIC (TA-DIC) and pH25 suggests that CDOM, mediated by HA/FA, buffers the inorganic carbon system in estuaries. This buffering capacity weakens at elevated DIC levels, and this condition is marked by anomalous SR values compared to the baseline salinity-SR linear regression. This Study suggests that estuarine CDOM could largely represent “organic alkalinity” and could help monitor acidification in estuaries.
Continue reading ‘Coupling between chromophoric dissolved organic matter and dissolved inorganic carbon in Indian estuaries’The impact of ocean acidification and cadmium toxicity in the marine crab Scylla serrata: biological indices and oxidative stress responses
Published 23 October 2023 Science ClosedTags: biological response, crustaceans, Indian, laboratory, metals, morphology, mortality, multiple factors, performance, physiology, toxicants
Highlights
- Growth, food index, ALP, and heamocytes of crabs were decreased in OA + Cd exposure.
- Antioxidants and metabolic enzymes were elevated in crabs under OA + Cd treatments.
- Bioaccumulation of Cd was more in crabs subjected to OA + Cd.
- OA + Cd interaction was higher on growth, protein, amino acid, and heamocytes of crabs.
Abstract
Ocean acidification (OA) and heavy metals pollution in marine environments are potentially threatening marine life. The interactive effect of OA and heavy metals could be more vulnerable to marine organisms than individual exposures. In the current study, the effect of OA on the toxicity of cadmium (Cd) in the crab Scylla serrata was evaluated. Crab instars (0.07 cm length and 0.1 g weight) were subjected to pH 8.2, 7.8, 7.6, 7.4, 7.2, and 7.0 with and without 0.01 mg l−1 of Cd for 60 days. We notice a significant decrease in growth, molting, protein, carbohydrate, amino acid, lipid, alkaline phosphatase, and haemocytes of crabs under OA + Cd compared to OA treatment. In contrast, the growth, protein, amino acid, and haemocyte levels were significantly affected by OA, Cd, and its interactions (OA + Cd). However, superoxide dismutase, catalase, lipid peroxidation, glutamic oxaloacetate transaminase, glutamic pyruvate transaminase, and accumulation of Cd in crabs were considerably elevated in OA + Cd treatments compared to OA alone treatments. The present investigation showed that the effect of Cd toxicity might be raised under OA on S. serrata. Our study demonstrated that ocean acidification significantly affects the biological indices and oxidative stress responses of S. serrata exposed to Cd toxicity.
Continue reading ‘The impact of ocean acidification and cadmium toxicity in the marine crab Scylla serrata: biological indices and oxidative stress responses’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’Rapid climate change alters the environment and biological production of the Indian Ocean
Published 6 October 2023 Science ClosedTags: biological response, chemistry, field, fisheries, Indian, modeling, policy, regionalmodeling, review
Highlights
- Indian Ocean experiences unprecedented warming with +1.7–3.8 °C century predictions.
- Significant decreases in pH and aragonite levels observed during last four decades.
- Decreasing primary productivity in the north with varying model predictions
- Importance of establishing biological time series for fisheries management
- Importance of safeguarding biodiversity in marine protected and other vital areas
Abstract
We synthesize and review the impacts of climate change on the physical, chemical, and biological environments of the Indian Ocean and discuss mitigating actions and knowledge gaps. The most recent climate scenarios identify with high certainty that the Indian Ocean (IO) is experiencing one of the fastest surface warming among the world’s oceans. The area of surface waters of >28 °C (IO Warm Pool) has significantly increased during 2012–2021 by expanding into the northern-central basins. A significant decrease in pH and aragonite (building blocks of calcified organisms) levels in the IO was observed from 1981 to 2020 due to an increase in atmospheric CO2 concentrations. There are also signals of decreasing trends in primary productivity in the north, likely related to enhanced stratification and nutrient depletion. Further, the rapid warming of the IO will manifest more extreme weather conditions along its adjacent continents and oceans, including marine heat waves that are likely to reshape biodiversity. However, the impact of climate change beyond the unprecedented warming, increase in marine heat waves, expansion of the IO Warm Pool, and decrease in pH, remains uncertain for many other key variables in the IO including changes in salinity, oxygen, and net primary production. Understanding the response of these physical, chemical, and biological variables to climate change is vital to project future changes in regional fisheries and identify mitigation actions. We accordingly conclude by identifying knowledge gaps and recommending directions for sustainable fisheries and climate impact studies.
Continue reading ‘Rapid climate change alters the environment and biological production of the Indian Ocean’Impact of ocean acidification on bioactive compounds production by marine phytoplankton, Off Visakhapatnam, Bay of Bengal
Published 27 September 2023 Science ClosedTags: biological response, Indian, laboratory, mesocosms, nitrogen fixation, photosynthesis, physiology, phytoplankton
Shallow coastal regions face heightened vulnerability due to human development, making them susceptible to substantial influxes of human-caused inputs alongside waters with low pH levels. This research delved into a microcosm pH alteration experiment to explore the impact of pH reduction on the generation of bioactive substances by marine phytoplankton in the eutrophic coastal waters of the Bay of Bengal. Initially, the prevalent compounds in the surface seawater were fucoxanthin at 75%, zeaxanthin at 10%, and other bioactive elements like diadinoxanthin, diatoxanthin, and β-carotene collectively contributing to around 15%. Notably, all bioactive compounds and Chl-a concentrations significantly favored the control container (ranging from 35–70%), while the least growth occurred in the more acidified experimental containers (15–40%).
In alignment with the above findings, the nutrient uptake rates were comparably diminished in the acidified experimental containers compared to the control group. The ratio between protective bioactive compounds (Diato + Diadino + Zea + β-Car) and synthetic bioactive compounds (Fuco + Chl-a) varied from 0.03 to 0.8, with the control container exhibiting the lowest values, and the more acidified experimental containers displaying the highest values of significance. Similarly, the DT index (diatoxanthin / (diatoxanthin + diadinoxanthin)) ratios followed a parallel pattern, with the control container showing the lowest average ratios and the acidified experimental containers displaying the highest ratios. Furthermore, based on our current study, we postulated that acidified water stimulates the proliferation of carotenoid-based bioactive compounds in marine regions more prominently than their synthetic counterparts. Mainly, the production of bioactive compounds in these experiments could also be influenced by our acidification method.
Continue reading ‘Impact of ocean acidification on bioactive compounds production by marine phytoplankton, Off Visakhapatnam, Bay of Bengal’Ocean acidification reduces iodide production by the marine diatom Chaetoceros sp. (CCMP 1690)
Published 13 September 2023 Science ClosedTags: biological response, growth, Indian, laboratory, physiology, phytoplankton
Highlights
- Ocean acidification had no effect on growth rates of the diatom Chaetoceros sp. CCMP (1690) but higher cell yield under high CO2.
- Ocean acidifcation has the potential to inhibit the diatom-mediated iodate to iodide reduction process.
- Iodide production was decoupled from iodate uptake and refute the proposed link between iodide produced and cell membrane permeability.
Abstract
Phytoplankton in marine surface waters play a key role in the global iodine cycle. The biologically-mediated iodide production under future scenarios is limited. Here we compare growth, iodate to iodide conversion rate and membrane permeability in the diatom Chaetoceros sp. (CCMP 1690) grown under seawater carbonate chemistry conditions projected for 2100 (1000 ppm) and pre-industrial (280 ppm) conditions. We found no effect of CO2 on growth rates, but a significantly higher cell yield under high CO2, suggesting sustained growth from relief from carbon limitation. Cell normalised iodate uptake (16.73 ± 0.92 amol IO3− cell−1) and iodide production (8.61 ± 0.15 amol I− cell−1) was lower in cultures grown at high pCO2 than those exposed to pre-industrial conditions (21.29 ± 2.37 amol IO3− cell−1, 11.91 ± 1.49 amol I− cell−1, respectively). Correlating these measurements with membrane permeability, we were able to ascertain that iodide conversion rates were not linked to cell permeability and that the processes of mediated iodate loss and diatom-iodide formation are decoupled. These findings are the first to implicate OA in driving a potential shift in diatom-mediated iodate reduction. If our results are indicative of diatom-mediated iodine cycling in 2100, future surface ocean conditions could experience reduced rates of iodide production by Chaetoceros spp., potentially lowering iodide concentrations in ocean regions dominated by this group. These changes have the potential to impact ozone cycling and new particle formation in the atmosphere.
Continue reading ‘Ocean acidification reduces iodide production by the marine diatom Chaetoceros sp. (CCMP 1690)’Prolonged deep-ocean carbonate chemistry recovery after the Paleocene-Eocene Thermal Maximum
Published 5 September 2023 Science ClosedTags: chemistry, field, Indian, North Atlantic, paleo, South Atlantic
Highlights
- N. truempyi B/Ca can be used to reconstruct the Early Cenozoic deep-water Ω.
- PETM deep-water Ω recovery is slower than suggested by sedimentary %CaCO3.
- PETM Ω recovery implies sustained carbon injection into the ocean-atmosphere system.
Abstract
The Paleocene-Eocene Thermal Maximum (PETM) is a hyperthermal event at ∼56 Ma ago, caused by rapid and massive carbon releases into the ocean-atmosphere system. Currently, the PETM ocean acidification is mainly quantified in the surface ocean. By contrast, PETM carbonate chemistry changes of the deep ocean, a larger carbon reservoir, are largely qualitatively constrained by sedimentary calcium carbonate contents (%CaCO3). Here, we revisit a previously proposed method for quantifying Early Cenozoic deep-water carbonate chemistry, using boron to calcium ratios (B/Ca) in extinct benthic foraminifera Nuttallides truempyi (Brown et al., 2011). We show that calibrating core-top B/Ca in the extant relative of N. truempyi against deep-water calcite saturation degree (Ω, Ω = [CO32−] /[CO32−]saturated), rather than calcite saturation state (Δ[CO32−], Δ[CO32−] = [CO32−] – [CO32−]saturated) as originally proposed better reflects Early Cenozoic carbonate chemistry changes. Furthermore, we provide multiple deep-water Ω reconstructions paired with benthic foraminiferal carbon isotopes during the PETM. At two sites, deep-water Ω recovered synchronously with carbon isotopes but lagged the sedimentary %CaCO3 rebound, indicating a slower post-PETM deep-water Ω recovery than previously thought. This may imply that during the PETM recovery phase, carbon could have been injected into the ocean-atmosphere system, despite net carbon loss, over a prolonged period after the initial release. If so, during this period, carbon removal from the ocean via calcite burial on the seafloor in response to enhanced silicate weathering may be weakened, suggesting that more carbon was sequestered via other processes such as those related to organic carbon burial.
Continue reading ‘Prolonged deep-ocean carbonate chemistry recovery after the Paleocene-Eocene Thermal Maximum’A synthesis of SNAPO-CO2 ocean total alkalinity and total dissolved inorganic carbon measurements from 1993 to 2022
Published 23 August 2023 Science ClosedTags: Antarctic, chemistry, field, Indian, Mediterranean, North Atlantic, North Pacific, South Atlantic, South Pacific
Total alkalinity (AT) and total dissolved inorganic carbon (CT) in the oceans are important properties to understand the ocean carbon cycle and its link with climate change (ocean carbon sinks and sources) or global change (ocean acidification). We present a data-base of more than 44 400 AT and CT observations in various ocean regions obtained since 1993 mainly in the frame of French projects. This includes both surface and water columns data acquired in open oceans, coastal zones and in the Mediterranean Sea and either from time-series or punctual cruises. Most AT and CT data in this synthesis were measured from discrete samples using the same closed-cell potentiometric titration calibrated with Certified Reference Material, with an overall accuracy of ± 4 µmol kg-1 for both AT and CT. Given the lack of observations in the Indian and Southern Oceans, we added sea surface underway AT and CT data obtained in 1998–2018 in the frame of OISO cruises and in 2019 during the CLIM-EPARSES cruise measured onboard using the same technique. Separate datasets for the global ocean, and for the Mediterranean Sea are provided in a single format (https://doi.org/10.17882/95414, Metzl et al., 2023) that offers a direct use for regional or global purposes, e.g. AT/Salinity relationships, long-term CT estimates, constraint and validation of diagnostics CT–AT reconstructed fields or ocean carbon and coupled climate/carbon models simulations, as well as data derived from BG-ARGO floats. When associated with other properties, these data can also be used to calculate pH, fugacity of CO2 (fCO2) and other carbon systems properties to derive ocean acidification rates or air-sea CO2 fluxes.
Continue reading ‘A synthesis of SNAPO-CO2 ocean total alkalinity and total dissolved inorganic carbon measurements from 1993 to 2022’Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth
Published 22 August 2023 Science ClosedTags: Antarctic, Arctic, chemistry, Indian, modeling, North Atlantic, North Pacific, regionalmodeling, review, South Atlantic, South Pacific
Highlights
- Ocean acidification has caused the carbonate compensation depth (CCD) to rise by ~98 m.
- Seafloor area below the CCD has increased by 3.6% in the last 200 years.
- Risk of impact of rising CCD is greatest in the western equatorial Atlantic Ocean.
- Different geomorphic features impacted by rising CCD in different ocean areas.
Abstract
Due to burning of fossil fuels, carbon dioxide is being absorbed by the ocean where its chemical conversion to carbonic acid has already caused the surface ocean to become more acidic than it has been for at least the last 2 million years. Global ocean modeling suggests that the carbonate compensation depth (CCD) has already risen by nearly 100 m on average since pre-industrial times and will likely rise further by several hundred meters more this century. Potentially millions of square kilometres of ocean floor will undergo a rapid transition in terms of the overlying water chemistry whereby calcareous sediment will become unstable causing the carbonate “snow line” to rise.We carried out a spatial analysis of seafloor geomorphology to assess the area newly submerged below the rising CCD. We found that shoaling of the CCD since the industrial revolution has submerged 12,432,096 km2 of ocean floor (3.60% of total ocean area) below the CCD. Further hypothetical shoaling of the CCD by 100 m increments illustrated that the surface area of seafloor submerged below the CCD has risen by 14% with 300 m of shoaling, such that 51% of the ocean area will be below the CCD. All categories of geomorphic feature mapped in one global database intersect the lysocline and will be (or already are) submerged below the CCD with much regional variation since the rise in CCD depth during the last 150 years varies significantly between different ocean regions. For seamounts, the highest percentages of increase in area submerged below the CCD occurred in the Southern Indian Ocean and the South West Atlantic regions (6.3% and 5.9%, respectively). For submarine canyons we found the South West Atlantic increased from 3.9% in pre-industrial times to 8.0% at the present time, the highest percentage of canyons found below the CCD in any ocean region.We also carried out a relative risk assessment for future submergence of ocean floor below the CCD in 17 ocean regions. In our assessment we assumed that the change in CCD from pre-industrial times to the present is an indicator of the likelihood and the change in percentage of seafloor submerged below the CCD due to a hypothetical 300 m rise in the CCD is an indicator of the consequences. We found that the western equatorial Atlantic is at high risk and 9 other Ocean Regions are at moderate risk. Overall, geomorphic features in the Atlantic Ocean and southern Indian Ocean are at greater risk of impact from a rising CCD than Pacific and other Indian Ocean regions.A separate analysis of the Arctic Ocean points to the possible submergence of glacial troughs incised on the continental shelf within a mid-depth (400–800 m) acidified water mass. We also found that the area of national Exclusive Economic Zones submerged below the rising CCD exhibits extreme variability; with 300 m of CCD shoaling we found a > 12% increase in area submerged below the CCD for 23 national EEZs, whereas there was virtually no change for other countries.
Continue reading ‘Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth’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’Variations in the Southern Ocean carbonate production, preservation, and hydrography for the past 41, 500 years: evidence from coccolith and CaCO3 records
Published 15 June 2023 Science ClosedTags: abundance, Antarctic, BRcommunity, community composition, Indian, otherprocess, paleo, phytoplankton, sediment
Changes in ocean alkalinity affect atmospheric pCO2 (i.e., higher alkalinity lowers atmospheric pCO2). Ocean alkalinity is partly determined by sedimentary burial of carbonates, which is primarily controlled by carbonate flux and the degree of deep ocean carbonate saturation. In this study, we investigate the factors determining the coccolith burial in subantarctic sediments and the surface ocean changes in the subtropical South Indian Ocean. The downcore coccolith records from the subantarctic region (SK200/22a) of the Indian sector of the Southern Ocean display low coccolith concentration during the glacial period. A possible explanation for this is, 1) the low glacial production of coccolithophores due to the competition from diatoms and 2) dilution by biogenic silica in the glacial sediments. Additionally, reduced carbonate burial owing to the low carbonate saturation of the deep-water accounts for the decline in glacial coccolith concentration. This also explains the low coccolith dissolution index and enrichment of the large dissolution-resistant coccolith species, Coccolithus pelagicus subsp. braarudii in the glacial sediments. The low carbonate saturation is attributed to, 1) the replacement of carbonate saturated, North Atlantic Deep Waters by the undersaturated southern sourced water masses and 2) increased storage of dissolved CO2 in the deep glacial Southern Ocean. Our study suggests that changes in coccolith production and the deep ocean carbonate saturation determine their burial in subantarctic sediments for the last 41,500 years. Other than these changes, the study region also records the changes in the Agulhas Return Current via variation in the proportion of tropical-subtropical coccolith assemblage.
Continue reading ‘Variations in the Southern Ocean carbonate production, preservation, and hydrography for the past 41, 500 years: evidence from coccolith and CaCO3 records’Assessment of water quality parameters in the Hooghly Estuary, India, using sentinel-3 and global biogeochemical analysis and forecasts products
Published 12 June 2023 Science ClosedTags: chemistry, field, Indian
The Hooghly Estuary is a source of livelihood for millions of people, along with the sustenance of marine biodiversity. The frequent estimation of the water quality is a vital process for the estuary, mainly because of global warming and the changes it brings. Sentinel-3 data and Global Biogeochemical Analysis and Forecast Products from Copernicus for the years 2021 and 2022 were used in this study to assess the different water quality parameters, namely, Chlorophyll-a, Total Suspended Matter (TSM), Kd490 as a proxy for turbidity, Adg443 for Coloured Detrital Organic Matter (CDOM) concentration, Sea surface temperature (SST), Nitrate, Phosphate, Silicate, pH, Dissolved Inorganic Carbon (DIC) and Molecular dissolved oxygen (DO2), in the Hooghly Estuary. The main changes were observed during the monsoon and post-monsoon due to heavy rainfall causing runoffs and an increase in sediments from land, along with nutrients in the estuary, with lower SST and increased chlorophyll-a, which could also lead to eutrophication and harmful algal blooms, depleting oxygen levels and causing harm to the aquatic biota. The effects of cyclonic storms were also observed during the pre-monsoon in 2021 and the post-monsoon in 2022. Satellite data was therefore found to be adequate but not fully accurate for the assessment of water quality parameters in the Hooghly Estuary.
Continue reading ‘Assessment of water quality parameters in the Hooghly Estuary, India, using sentinel-3 and global biogeochemical analysis and forecasts products’Marine macroinvertebrate ecosystem services under changing conditions of seagrasses and mangroves
Published 5 June 2023 Science ClosedTags: abundance, annelids, biological response, BRcommunity, chemistry, cnidaria, community composition, crustaceans, echinoderms, Indian, mollusks, otherprocess, phanerogams, phytoplankton, primary production, review, socio-economy
Highlights
- Overfishing and climate change show potential effects on MMI ES.
- MMI regulating ES can be quantified using species richness and functional traits.
- Digital platforms are valuable tools to retrieve data but have limitations.
- Baseline data and information on environmental changes and MMI ES is provided.
Abstract
This study aimed to investigate the impact of changing environmental conditions on MMI ES in seagrasses and mangroves. We used data from satellite and biodiversity platforms combined with field data to explore the links between ecosystem pressures (habitat conversion, overexploitation, climate change), conditions (environmental quality, ecosystem attributes), and MMI ES (provisioning, regulation, cultural). Both seagrass and mangrove extents increased significantly since 2016. While sea surface temperature showed no significant annual variation, sea surface partial pressure CO2, height above sea level and pH presented significant changes. Among the environmental quality variables only silicate, PO4 and phytoplankton showed significant annual varying trends. The MMI food provisioning increased significantly, indicating overexploitation that needs urgent attention. MMI regulation and cultural ES did not show significant trends overtime. Our results show that MMI ES are affected by multiple factors and their interactions can be complex and non-linear. We identified key research gaps and suggested future directions for research. We also provided relevant data that can support future ES assessments.
Continue reading ‘Marine macroinvertebrate ecosystem services under changing conditions of seagrasses and mangroves’Acidification scenario of Cox’s Bazar coast of the Bay of Bengal, Bangladesh and its influence on fish larvae abundance
Published 3 May 2023 Science ClosedTags: abundance, biological response, chemistry, community composition, field, fish, Indian, otherprocess
Ocean acidification is caused mainly by atmospheric carbon dioxide stored in the ocean. Ocean acidification is considered a major threat to aquatic life, and how it influences the abundance of marine fish larvae is still unclear. This research was designed to measure the current ocean acidification scenario of the Cox’s Bazar coast of the Bay of Bengal, Bangladesh, and its probable influence on the abundance of fish larvae. Three research stations were selected: Bakkhali river estuary, Naf river estuary, and Rezu Khal. Monthly sampling was done, and larvae sample was collected from the surface water column (depth: 0.5 m) using a bongo net. Water parameters such as temperature, salinity, total alkalinity, and pH were determined using laboratory protocol. The seacarb package of the R programming language was used to determine ocean acidification factors. The Bakkhali river estuary showed the highest partial carbon dioxide (143.99 ± 102.27 μatm) and the lowest pH (8.27 ± 0.21). A total of 19 larvae families were identified, and the highest larval count was found in Rezu Khal (390 larvae/1000 m3), while the lowest was found in the Bakkhali river (3 larvae/1000 m3). Clupeidae, Myctophidae, and Engraulidae comprised more than 50% of the identified larvae. Blenniidae, Carangidae, Clupeidae, Engraulidae, and Gobiidae were found in all three seasons. Most of the larvae families showed the highest mean abundance under less pCO2. A negative correlation was observed between larvae and acidification factors such as pCO2, HCO3−, and dissolved inorganic carbon (DIC). The study revealed that acidification parameters of the Cox’s Bazar coast were not in an acute state for the aquatic organisms’ survival, but fish larvae abundance could be declined with raises in the partial carbon dioxide. The results of this study may aid in developing a management plan for conserving Bangladesh’s marine and coastal fish.
Continue reading ‘Acidification scenario of Cox’s Bazar coast of the Bay of Bengal, Bangladesh and its influence on fish larvae abundance’Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change
Published 18 April 2023 Science ClosedTags: adaptation, biogeochemistry, biological response, BRcommunity, communitymodeling, corals, Indian, modeling, multiple factors, North Atlantic, North Pacific, otherprocess, primary production, regionalmodeling, South Pacific, temperature
Projecting the effects of climate change on net reef calcium carbonate production is critical to understanding the future impacts on ecosystem function, but prior estimates have not included corals’ natural adaptive capacity to such change. Here we estimate how the ability of symbionts to evolve tolerance to heat stress, or for coral hosts to shuffle to favourable symbionts, and their combination, may influence responses to the combined impacts of ocean warming and acidification under three representative concentration pathway (RCP) emissions scenarios (RCP2.6, RCP4.5 and RCP8.5). We show that symbiont evolution and shuffling, both individually and when combined, favours persistent positive net reef calcium carbonate production. However, our projections of future net calcium carbonate production (NCCP) under climate change vary both spatially and by RCP. For example, 19%–35% of modelled coral reefs are still projected to have net positive NCCP by 2050 if symbionts can evolve increased thermal tolerance, depending on the RCP. Without symbiont adaptive capacity, the number of coral reefs with positive NCCP drops to 9%–13% by 2050. Accounting for both symbiont evolution and shuffling, we project median positive NCPP of coral reefs will still occur under low greenhouse emissions (RCP2.6) in the Indian Ocean, and even under moderate emissions (RCP4.5) in the Pacific Ocean. However, adaptive capacity will be insufficient to halt the transition of coral reefs globally into erosion by 2050 under severe emissions scenarios (RCP8.5).
Continue reading ‘Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change’Paris Agreement could prevent regional mass extinctions of coral species
Published 12 April 2023 Science ClosedTags: abundance, adaptation, biological response, corals, globalmodeling, Indian, modeling, multiple factors, North Atlantic, otherprocess, regionalmodeling, South Pacific, temperature
Coral reef ecosystems are expected to undergo significant declines over the coming decades as oceans become warmer and more acidic. We investigate the environmental tolerances of over 650 Scleractinian coral species based on the conditions found within their present-day ranges and in areas where they are currently absent but could potentially reach via larval dispersal. These “environmental envelopes” and connectivity constraints are then used to develop global forecasts for potential coral species richness under two emission scenarios, representing the Paris Agreement target (“SSP1-2.6”) and high levels of emissions (“SSP5-8.5”). Although we do not directly predict coral mortality or adaptation, the projected changes to environmental suitability suggest considerable potential declines in coral species richness for the majority of the world’s tropical coral reefs, with a net loss in average local richness of 73% (Paris Agreement) to 91% (High Emissions) by 2080-2090 and particularly large declines across sites in the Great Barrier Reef, Coral Sea, Western Indian Ocean and Caribbean. However, at the regional scale, we find that environmental suitability for the majority of coral species can be largely maintained under the Paris Agreement target, with 0-30% potential net species lost in most regions (increasing to 50% for the Great Barrier Reef) as opposed to 80-90% losses in most areas under High Emissions. Projections for sub-tropical areas suggest that range expansion will give rise to coral reefs with low species richness (typically 10-20 coral species per region) and will not meaningfully offset declines in the tropics. This work represents the first global projection of coral species richness under oceanic warming and acidification. Our results highlight the critical importance of mitigating climate change to avoid potentially massive extinctions of coral species.
Continue reading ‘Paris Agreement could prevent regional mass extinctions of coral species’Nutrient diversity over Gujarat coastal water, the Northeast Arabian Sea
Published 12 April 2023 Science ClosedTags: biogeochemistry, chemistry, field, Indian
The Gujarat coast has a variety of topographical factors that influence the spectrum of nutrients. Over various periods, the team of researchers analyzed the nutrients in seawater from over 75 stations in a total of 5 places across the northeast Arabian sea. Nitrate, Silicate, Orthophosphate, and Ammonia concentrations (µmol/L) of surface seawater were measured in situ. The result shows that southern Gujarat had a considerably higher range of nitrate, silicate, and orthophosphate concentrations which may be due to nitrification and eutrophication because of the gulf, estuary zone, heavy sedimentation, and industrial fluxes. A total of 43 stations/part A near the Gulf of Khambhat compared to 32 stations/part B from the northwest Gujarat coast, shows remarkably different results. Southern Gujarat supports different kinds of water with lower pH and high TSM range and muddy seawater color, remote sensing reflectance also supports the same. Satellite-based chlorophyll concentration supports the high range of Chl in southern Gujarat. The range of Nitrate, Ammonia, Silicate, and Orthophosphate for all stations is 3.9–62.5 µmol/L, 2.8-63.65 µmol/L, 0.5–160 µmol/L, 0.4-5 µmol/L respectively. Nitrate, Phosphate, and Silicate concentration follow the polynomial trend from the southern to the northern coast of Gujarat. The publication recommends researchers conduct more research on eutrophication in the southern Gujarat coastal region since it is linked to primary production and other elements of the marine ecosystem.
Continue reading ‘Nutrient diversity over Gujarat coastal water, the Northeast Arabian Sea’Tidal cycle and time of day control pH levels in coastal habitats of the western Indian Ocean: the case of Mnazi and Chwaka Bays in Tanzania
Published 4 April 2023 Science ClosedTags: chemistry, field, Indian
Ocean acidification, a progressive decrease in the pH and change in the carbonate chemistry of seawater caused by the uptake of carbon dioxide (CO2) from the atmosphere, is a growing crisis that threatens marine species. pH data relevant to a species’ natural habitat in the coastal waters of the western Indian Ocean (WIO) is still sparse, limiting the capacity to undertake manipulative studies to better understand the impacts of ocean acidification on marine species. This study investigated tidal and day-night pH variations in mangrove, seagrass, and coral reef habitats of the WIO by using Tanzania as a case study. The mean pH of the studied coastal habitats was highest in seagrass (8.49 ± 0.29), followed by coral reef (8.33 ± 0.06), and lowest in mangrove (8.20 ± 0.17). Seagrass habitats had the highest pH (9.06) during the day at low spring tides, mangrove habitats had the highest pH (8.45) during the day at high spring tides, and coral reef habitats had the highest pH (8.47) during the day at low tides. Seagrass habitats had the widest pH range (1.03), followed by mangrove habitats (0.54), while coral reef habitats had the narrowest range (0.23). The water with the highest pH during the day was transported to nearby mangrove habitats during incoming tides and to coral reef habitats during outgoing tides, resulting in the highest mean pH in mangrove and coral reef habitats during spring high and low tides, respectively. pH within the seagrass habitats correlated strongly and positively with changes in temperature (r=0.80), dissolved oxygen (r=0.84), and salinity (r=0.72), while pH in mangrove habitats correlated moderately and positively with dissolved oxygen (r=0.59). This study provides in-situ evidence on the pH fluctuations in the WIO’s coastal habitats over time and space, with water from seagrass habitats capable of raising the pH of water in nearby mangrove and coral reef habitats during the day, thereby potentially helping in the mitigation of the effects of ocean acidification on these habitats.
Continue reading ‘Tidal cycle and time of day control pH levels in coastal habitats of the western Indian Ocean: the case of Mnazi and Chwaka Bays in Tanzania’
