Posts Tagged 'abundance'

Effect of different pCO2 concentrations in seawater on meiofauna: abundance of communities in sediment and survival rate of harpacticoid copepods

The amount of CO2 dissolved in the ocean has been increasing continuously, and the results using climate change models show that the CO2 concentration of the ocean will increase by over 1000 ppm by 2100. Ocean acidification is expected to have a considerable impact on marine ecosystems. To find out about the impacts of ocean acidification on meiofaunal communities and copepod groups, we analyzed the differences in the abundance of meiofauna communities in sediment and the survival rate of harpacticoid copepod assemblages separated from the sediment, between 400 and 1000 ppm pCO2 for a short period of 5 days. In experiments with communities in sediments exposed to different pCO2 concentrations, there was no significant difference in the abundance of total meiofauna and nematodes. However, the abundance of the harpacticoid copepod community was significantly lower at 1000 ppm than that at 400 ppm pCO2. On the other hand, in experiments with assemblages of harpacticoid copepods directly exposed to seawater, there was no significant difference in their survival rates between the two concentrations. Our findings suggest that a CO2 concentration of 1000 ppm in seawater can cause changes in the abundance of specific taxa such as harpacticoid copepods among the meiofauna communities in sediments.

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Schizosphaerella size and abundance variations across the Toarcian Oceanic Anoxic Event in the Sogno Core (Lombardy Basin, Southern Alps)

Highlights

  • Schizospharella spp. size and abundance variations during the Jenkyns event.
  • Abundance drop caused by the failure of S. punctulata > 7 μm.
  • Size decrease due to the relative increase in abundance of small specimens.
  • Drop in abundance and size consequence of ocean acidification and global warming.
  • Presence of diagenetic crust diagnostic to distinguish S. punctulata from S. astraea

Abstract

Abundance and size variations of nannofossil Schizosphaerella punctulata were quantified in the uppermost Pliensbachian–Lower Toarcian succession recovered with the Sogno Core (Lombardy Basin, Northern Italy). High-resolution nannofossil biostratigraphy and C-isotopic chemostratigraphy identified the Jenkyns Event within the Toarcian oceanic anoxic event (T-OAE) interval. Absolute abundances and morphometric changes of “small S. punctulata” (< 7 μm), S. punctulata (7–10 μm; 10–14 μm; > 14 μm) and “encrusted S. punctulata” (specimens with a fringing crust) show large fluctuations across the negative δ13C Jenkyns Event. The Schizosphaerella crisis is further characterized by a decrease in average valve size in the early–middle Jenkyns Event. The abundance fall was caused by the failure of S. punctulata specimens >7 μm and “encrusted S. punctulata” that along with the increased relative abundance of small specimens, produced the reduction of average dimensions also documented in the Lusitanian and Paris Basins, although with a diachronous inception. The average valve size from the Lombardy Basin is ~2 μm smaller than in these other basins. Hyperthermal conditions associated with excess CO2 and ocean acidification possibly forced the drastic reduction of S. punctulata abundance/size. In the pelagic succession of the Sogno Core there is a strong positive correlation between the S. punctulata (> 7 μm) absolute abundance/size and the CaCO3 content, with a negligible contribution by small specimens (< 7 μm). Encrusted specimens testify selective neomorphic processes: the diagenetic crust seems diagnostic to separate S. punctulata from S. astraea.

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Whole community and functional gene changes of biofilms on marine plastic debris in response to ocean acidification

Plastics are accumulating in the world’s oceans, while ocean waters are becoming acidified by increased CO2. We compared metagenome of biofilms on tethered plastic bottles in subtidal waters off Japan naturally enriched in CO2, compared to normal ambient CO2 levels. Extending from an earlier amplicon study of bacteria, we used metagenomics to provide direct insights into changes in the full range of functional genes and the entire taxonomic tree of life in the context of the changing plastisphere. We found changes in the taxonomic community composition of all branches of life. This included a large increase in diatom relative abundance across the treatments but a decrease in diatom diversity. Network complexity among families decreased with acidification, showing overall simplification of biofilm integration. With acidification, there was decreased prevalence of genes associated with cell–cell interactions and antibiotic resistance, decreased detoxification genes, and increased stress tolerance genes. There were few nutrient cycling gene changes, suggesting that the role of plastisphere biofilms in nutrient processes within an acidified ocean may not change greatly. Our results suggest that as ocean CO2 increases, the plastisphere will undergo broad-ranging changes in both functional and taxonomic composition, especially the ecologically important diatom group, with possible wider implications for ocean ecology.

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Experimentally decomposing phytoplankton community change into ecological and evolutionary contributions

  1. Shifts in microbial communities and their functioning in response to environmental change result from contemporary interspecific and intraspecific diversity changes. Interspecific changes are driven by ecological shifts in species composition, while intraspecific changes are here assumed to be dominated by evolutionary shifts in genotype frequency. Quantifying the relative contributions of interspecific and intraspecific diversity shifts to community change thus addresses the essential, yet understudied question as to how important ecological and evolutionary contributions are to total community changes. This debate is to date practically constrained by (a) a lack of studies integrating across organizational levels and (b) a mismatch between data requirements of existing partitioning metrics and the feasibility to collect such data, especially in microscopic organisms like phytoplankton.
  2. We experimentally assessed the relative ecological and evolutionary contributions to total phytoplankton community changes using a new design and validated its functionality by comparisons to established partitioning metrics. We used a community of coexisting Emiliania huxleyi and Chaetoceros affinis with initially nine genotypes each. First, we exposed the community to elevated CO2 concentration for 80 days (~50 generations) to induce interspecific and intraspecific diversity changes and a total abundance change. Second, we independently manipulated the induced interspecific and intraspecific diversity changes in an assay to quantify the corresponding ecological and evolutionary contributions to the total change. Third, we applied existing partitioning metrics to our experimental data and compared the outcomes.
  3. Total phytoplankton abundance declined to one-fifth in the high CO2 exposed community compared to ambient conditions. Consistently across all applied partitioning metrics, the abundance decline could predominantly be explained by ecological shifts and to a low extent by evolutionary changes.
  4. We discuss potential consequences of the observed community changes on ecosystem functioning. Furthermore, we explain that the low evolutionary contributions likely resulted of intraspecific diversity changes that occurred irrespectively of CO2. We discuss how the assay could be upscaled to more realistic settings, including more species and drivers. Overall, the presented calculations of eco-evolutionary contributions to phytoplankton community changes constitute another important step towards understanding future phytoplankton shifts, and eco-evolutionary dynamics in general.
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The Bouraké semi-enclosed lagoon (New Caledonia) – a natural laboratory to study the lifelong adaptation of a coral reef ecosystem to extreme environmental conditions (update)

According to current experimental evidence, coral reefs could disappear within the century if CO2 emissions remain unabated. However, recent discoveries of diverse and high cover reefs that already live under extreme conditions suggest that some corals might thrive well under hot, high-pCO2, and deoxygenated seawater. Volcanic CO2 vents, semi-enclosed lagoons, and mangrove estuaries are unique study sites where one or more ecologically relevant parameters for life in the oceans are close to or even worse than currently projected for the year 2100. Although they do not perfectly mimic future conditions, these natural laboratories offer unique opportunities to explore the mechanisms that reef species could use to keep pace with climate change. To achieve this, it is essential to characterize their environment as a whole and accurately consider all possible environmental factors that may differ from what is expected in the future, possibly altering the ecosystem response.

This study focuses on the semi-enclosed lagoon of Bouraké (New Caledonia, southwest Pacific Ocean) where a healthy reef ecosystem thrives in warm, acidified, and deoxygenated water. We used a multi-scale approach to characterize the main physical-chemical parameters and mapped the benthic community composition (i.e., corals, sponges, and macroalgae). The data revealed that most physical and chemical parameters are regulated by the tide, strongly fluctuate three to four times a day, and are entirely predictable. The seawater pH and dissolved oxygen decrease during falling tide and reach extreme low values at low tide (7.2 pHT and 1.9 mg O2 L−1 at Bouraké vs. 7.9 pHT and 5.5 mg O2 L−1 at reference reefs). Dissolved oxygen, temperature, and pH fluctuate according to the tide by up to 4.91 mg O2 L−1, 6.50 C, and 0.69 pHT units on a single day. Furthermore, the concentration of most of the chemical parameters was 1 to 5 times higher at the Bouraké lagoon, particularly for organic and inorganic carbon and nitrogen but also for some nutrients, notably silicates. Surprisingly, despite extreme environmental conditions and altered seawater chemical composition measured at Bouraké, our results reveal a diverse and high cover community of macroalgae, sponges, and corals accounting for 28, 11, and 66 species, respectively. Both environmental variability and nutrient imbalance might contribute to their survival under such extreme environmental conditions. We describe the natural dynamics of the Bouraké ecosystem and its relevance as a natural laboratory to investigate the benthic organism’s adaptive responses to multiple extreme environmental conditions.

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Impact of dust addition on Mediterranean plankton communities under present and future conditions of pH and temperature: an experimental overview (update)

In low-nutrient low-chlorophyll areas, such as the Mediterranean Sea, atmospheric fluxes represent a considerable external source of nutrients likely supporting primary production, especially during periods of stratification. These areas are expected to expand in the future due to lower nutrient supply from sub-surface waters caused by climate-driven enhanced stratification, likely further increasing the role of atmospheric deposition as a source of new nutrients to surface waters. Whether plankton communities will react differently to dust deposition in a warmer and acidified environment remains; however, an open question. The potential impact of dust deposition both in present and future climate conditions was investigated in three perturbation experiments in the open Mediterranean Sea. Climate reactors (300 L) were filled with surface water collected in the Tyrrhenian Sea, Ionian Sea and in the Algerian basin during a cruise conducted in the frame of the PEACETIME project in May–June 2017. The experiments comprised two unmodified control tanks, two tanks enriched with a Saharan dust analogue and two tanks enriched with the dust analogue and maintained under warmer (+3 C) and acidified (−0.3 pH unit) conditions. Samples for the analysis of an extensive number of biogeochemical parameters and processes were taken over the duration (3–4 d) of the experiments. Dust addition led to a rapid release of nitrate and phosphate, however, nitrate inputs were much higher than phosphate. Our results showed that the impacts of Saharan dust deposition in three different basins of the open northwestern Mediterranean Sea are at least as strong as those observed previously, all performed in coastal waters. The effects of dust deposition on biological stocks were different for the three investigated stations and could not be attributed to differences in their degree of oligotrophy but rather to the initial metabolic state of the community. Ocean acidification and warming did not drastically modify the composition of the autotrophic assemblage, with all groups positively impacted by warming and acidification. Although autotrophic biomass was more positively impacted than heterotrophic biomass under future environmental conditions, a stronger impact of warming and acidification on mineralization processes suggests a decreased capacity of Mediterranean surface plankton communities to sequester atmospheric CO2 following the deposition of atmospheric particles.

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Experimental reef communities persist under future ocean acidification and warming

Coral reefs are among the most sensitive ecosystems affected by ocean acidification and warming, and are predicted to shift from net accreting calcifier-dominated systems to net eroding algal-dominated systems over the coming decades. Here we present a long-term experimental study examining the responses of entire mesocosm coral reef communities to acidification (-0.2 pH units), warming (+ 2°C), and combined future ocean (-0.2 pH, + 2°C) treatments. We show that under future ocean conditions, net calcification rates declined yet remained positive, corals showed reduced abundance yet were not extirpated, and community composition shifted while species richness was maintained. Our results suggest that under Paris Climate Agreement targets, coral reefs could persist in an altered functional state rather than collapse.

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Elevated pCO2 impedes succession of phytoplankton community from diatoms to dinoflagellates along with increased abundance of viruses and bacteria

Eutrophic coastal regions are highly productive and greatly influenced by human activities. Primary production supporting the coastal ecosystems is supposed to be affected by progressive ocean acidification driven by increasing CO2 emissions. In order to investigate the effects of high pCO2 (HC) on eutrophic plankton community structure and ecological functions, we employed 9 mesocosms and carried out an experiment under ambient (∼410 ppmv) and future high (1000 ppmv) atmospheric pCO2 conditions, using in situ plankton community in Wuyuan Bay, East China Sea. Our results showed that HC along with natural seawater temperature rise significantly boosted biomass of diatoms with decreased abundance of dinoflagellates in the late stage of the experiment, demonstrating that HC repressed the succession from diatoms to dinoflagellates, a phenomenon observed during algal blooms in the East China Sea. HC did not significantly influence the primary production or biogenic silica contents of the phytoplankton assemblages. However, the HC treatments increased the abundance of viruses and heterotrophic bacteria, reflecting a refueling of nutrients for phytoplankton growth from virus-mediated cell lysis and bacterial degradation of organic matters. Conclusively, our results suggest that increasing CO2 concentrations can modulate plankton structure including the succession of phytoplankton community and the abundance of viruses and bacteria in eutrophic coastal waters, which may lead to altered biogeochemical cycles of carbon and nutrients.

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Short-term effects of winter warming and acidification on phytoplankton growth and mortality: more losers than winners in a temperate coastal lagoon

Changes in temperature and CO2 are typically associated with climate change, but they also act on shorter time scales, leading to alterations in phytoplankton physiology and community structure. Interactions among stressors may cause synergistic or antagonistic effects on phytoplankton dynamics. Therefore, the main goal of this work is to understand the short-term isolated and interactive effects of warming and high CO2 on phytoplankton nutrient consumption, growth, production, and community structure in the Ria Formosa coastal lagoon (southern Portugal). We performed microcosm experiments with temperature and CO2 manipulation, and dilution experiments under temperature increase, using winter phytoplankton assemblages. Phytoplankton responses were evaluated using inverted and epifluorescence microscopy. Overall, phytoplankton growth and microzooplankton grazing on phytoplankton decreased with warming. Negative antagonist interactions with CO2 alleviated the negative effect of temperature on phytoplankton and cryptophytes. In contrast, higher temperature benefited smaller-sized phytoplankton, namely cyanobacteria and eukaryotic picophytoplankton. Diatom growth was not affected by temperature, probably due to nutrient limitation, but high CO2 had a positive effect on diatoms, alleviating the effect of nutrient limitation. Results suggest that this winter phytoplankton assemblage is well acclimated to ambient conditions, and short-term increases in temperature are detrimental, but can be alleviated by high CO2.

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The effect of global warming and ocean acidification on Halichondira panicea bacteria

Marine sponges are becoming an increasing source of novel biomedical and antibacterial compounds. Many of these compounds are synthesized as secondary metabolites from symbiotic bacteria and have immense potential in the pharmaceutical industry. However, climate change may pose a threat to the viability of marine sponges and result in the loss of future medical discoveries. Therefore, this paper looks at the effect climate change may have on marine sponges by subjecting fragments of the marine sponge, Halichondria panicea, into aquaria representing different climate change scenarios to study the effect that global warming and ocean acidification may have on its symbiotic bacteria. To model climate change towards the end of the 21st century, conditions from the IPCC’s 2014 climate change report were simulated to determine specific growth conditions. The fragments were placed in the different RCP growth conditions for two weeks, then dissociated, filtered, and the extracts incubated on Hektoen enteric agar for 48 hours. The results showed that climate change has adverse effects on the marine sponge, Halichondria panicea, by decreasing their symbiotic bacterial population by around 18 %

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Characterization of the abiotic drivers of abundance of nearshore Arctic fishes

Fish are critical ecologically and socioeconomically for subsistence economies in the Arctic, an ecosystem undergoing unprecedented environmental change. Our understanding of the responses of nearshore Arctic fishes to environmental change is inadequate because of limited research on the physicochemical drivers of abundance occurring at a fine scale. Here, high-frequency in situ measurements of pH, temperature, salinity, and dissolved oxygen were paired with daily fish catches in nearshore Alaskan waters of the Beaufort Sea. Due to the threat that climate change poses to high-latitude marine ecosystems, our main objective was to characterize the abiotic drivers of abundance and elucidate how nearshore fish communities may change in the future. We used generalized additive models (GAMs) to describe responses to the nearshore environment for 18 fish species. Relationships between abundance and the physicochemical environment were variable between species and reflected life history. Each abiotic covariate was significant in at least one GAM, exhibiting both nonlinear and linear associations with abundance. Temperature was the most important predictor of abundance and was significant in GAMs for 11 species. Notably, pH was a significant predictor of abundance for six species: Arctic cod (Boreogadus saida), broad whitefish (Coregonus nasus), Dolly Varden (Salvelinus malma), ninespine stickleback (Pungitius pungitius), saffron cod (Eleginus gracilis), and whitespotted greenling (Hexagrammos stelleri). Broad whitefish and whitespotted greenling abundance was positively associated with pH, while Arctic cod and saffron cod abundance was negatively associated with pH. These results may be a bellwether for future nearshore Arctic fish community change by providing a foundational characterization of the relationships between abundance and the abiotic environment, particularly in regard to pH, and demonstrate the importance of including a wider range of physicochemical habitat covariates in future research.

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Major loss of coralline algal diversity in response to ocean acidification

Calcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO2 conditions. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition; it is less diverse today and was the most sensitive to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO2; it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO2 highlighted their lower fitness in response to ocean acidification. Reductions in CO2 emissions are needed to limit the risk of losing coralline algal diversity.

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Impact of anthropogenic pH perturbation on dimethyl sulfide cycling: a peek into the microbial black box

The objective of this study was to assess experimentally the potential impact of anthropogenic pH perturbation (ApHP) on concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as processes governing the microbial cycling of sulfur compounds. A summer planktonic community from surface waters of the Lower St. Lawrence Estuary was monitored in microcosms over 12 days under three pCO2 targets: 1 × pCO2 (775 µatm), 2 × pCO2 (1,850 µatm), and 3 × pCO2 (2,700 µatm). A mixed phytoplankton bloom comprised of diatoms and unidentified flagellates developed over the course of the experiment. The magnitude and timing of biomass buildup, measured by chlorophyll a concentration, changed in the 3 × pCO2 treatment, reaching about half the peak chlorophyll a concentration measured in the 1 × pCO2 treatment, with a 2-day lag. Doubling and tripling the pCO2 resulted in a 15% and 40% decline in average concentrations of DMS compared to the control. Results from 35S-DMSPd uptake assays indicated that neither concentrations nor microbial scavenging efficiency of dissolved DMSP was affected by increased pCO2. However, our results show a reduction of the mean microbial yield of DMS by 34% and 61% in the 2 × pCO2 and 3 × pCO2 treatments, respectively. DMS concentrations correlated positively with microbial yields of DMS (Spearman’s ρ = 0.65; P < 0.001), suggesting that the impact of ApHP on concentrations of DMS in diatom-dominated systems may be strongly linked with alterations of the microbial breakdown of dissolved DMSP. Findings from this study provide further empirical evidence of the sensitivity of the microbial DMSP switch under ApHP. Because even small modifications in microbial regulatory mechanisms of DMSP can elicit changes in atmospheric chemistry via dampened efflux of DMS, results from this study may contribute to a better comprehension of Earth’s future climate.

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Exposure duration modulates the response of Caribbean corals to global change stressors

Global change, including rising temperatures and acidification, threatens corals globally. Although bleaching events reveal fine-scale patterns of resilience, traits enabling persistence under global change remain elusive. We conducted a 95-d controlled-laboratory experiment investigating how duration of exposure to warming (~28, 31°C), acidification (pCO2 ~ 343 [present day], ~663 [end of century], ~3109 [extreme] μatm), and their combination influences physiology of reef-building corals (Siderastrea sidereaPseudodiploria strigosa) from two reef zones on the Belize Mesoamerican Barrier Reef System. Every 30 d, net calcification rate, host protein and carbohydrate, chlorophyll a, and symbiont density were quantified for the same coral individual to characterize acclimation potential under global change. Coral physiologies of the two species were differentially affected by stressors and exposure duration was found to modulate these responses. Siderastrea siderea exhibited resistance to end of century pCO2 and temperature stress, but calcification was negatively affected by extreme pCO2. However, S. siderea calcification rates remained positive after 95 d of extreme pCO2 conditions, suggesting acclimation. In contrast, P. strigosa was more negatively influenced by elevated temperatures, which reduced most physiological parameters. An exception was nearshore P. strigosa, which maintained calcification rates under elevated temperature, suggesting local adaptation to the warmer environment of their natal reef zone. This work highlights how tracking coral physiology across various exposure durations can capture acclimatory responses to global change stressors.

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Ocean acidification amplifies multi-stressor impacts on global marine invertebrate fisheries

Elevated atmospheric carbon dioxide (CO2) is causing global ocean changes and drives changes in organism physiology, life-history traits, and population dynamics of natural marine resources. However, our knowledge of the mechanisms and consequences of ocean acidification (OA) – in combination with other climatic drivers (i.e., warming, deoxygenation) – on organisms and downstream effects on marine fisheries is limited. Here, we explored how the direct effects of multiple changes in ocean conditions on organism aerobic performance scales up to spatial impacts on fisheries catch of 210 commercially exploited marine invertebrates, known to be susceptible to OA. Under the highest CO2 trajectory, we show that global fisheries catch potential declines by as much as 12% by the year 2100 relative to present, of which 3.4% was attributed to OA. Moreover, OA effects are exacerbated in regions with greater changes in pH (e.g., West Arctic basin), but are reduced in tropical areas where the effects of ocean warming and deoxygenation are more pronounced (e.g., Indo-Pacific). Our results enhance our knowledge on multi-stressor effects on marine resources and how they can be scaled from physiology to population dynamics. Furthermore, it underscores variability of responses to OA and identifies vulnerable regions and species.

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Effect of coastal development on larval fish abundance in Klang Strait (Malaysia)

Highlights

  • BACI model detects larval fish abundance before and after 30 years of development.
  • Lower larval diversity and abundance at impact than at offshore control stations.
  • The inshore-offshore cline in abundance can be related to lower SST and higher pH.
  • Total larval fish abundance increased despite changes in zooplankton composition.
  • 1st and 2nd stage larvae of certain families increased after development impact.

Abstract

Changes in larval fish assemblages were studied before (1985-86) and after (2013–2014) rapid coastal development in the Klang Strait, Malaysia, based on a Before-After-Control-Impact (BACI) experimental design. Fish larvae were sampled by bongo-nets along an 18-km transect from the impact station at the Kapar power station (KPS) to four control stations in increasingly offshore waters. Families Gobiidae, Clupeidae, Sciaenidae and Engraulidae were most abundant at both sampling periods, demonstrating their adaptability and resilience to the natural and anthropogenic disturbances. Coastal development has reduced larval fish abundance at KPS, inevitably shifting higher larval abundance to the control stations. This shift is related to lower sea surface temperature and higher pH. Despite the coastal disturbances, there was an overall increase in total larval fish abundance attributed to the preflexion stage of the Gobiidae, Sciaenidae, Engraulidae, Cynoglossidae and Callionymidae, and the yolk-sac and preflexion larvae of unidentified taxa.

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Planktic foraminiferal and pteropod contributions to carbon dynamics in the Arctic Ocean (North Svalbard Margin)

Planktic foraminifera and shelled pteropods are some of the major producers of calcium carbonate (CaCO3) in the ocean. Their calcitic (foraminifera) and aragonitic (pteropods) shells are particularly sensitive to changes in the carbonate chemistry and play an important role for the inorganic and organic carbon pump of the ocean. Here, we have studied the abundance distribution of planktic foraminifera and pteropods (individuals m–3) and their contribution to the inorganic and organic carbon standing stocks (μg m–3) and export production (mg m–2 day–1) along a longitudinal transect north of Svalbard at 81° N, 22–32° E, in the Arctic Ocean. This transect, sampled in September 2018 consists of seven stations covering different oceanographic regimes, from the shelf to the slope and into the deep Nansen Basin. The sea surface temperature ranged between 1 and 5°C in the upper 300 m. Conditions were supersaturated with respect to CaCO3 (Ω > 1 for both calcite and aragonite). The abundance of planktic foraminifera ranged from 2.3 to 52.6 ind m–3 and pteropods from 0.1 to 21.3 ind m–3. The planktic foraminiferal population was composed mainly of the polar species Neogloboquadrina pachyderma (55.9%) and the subpolar species Turborotalita quinqueloba (21.7%), Neogloboquadrina incompta (13.5%) and Globigerina bulloides (5.2%). The pteropod population was dominated by the polar species Limacina helicina (99.6%). The rather high abundance of subpolar foraminiferal species is likely connected to the West Spitsbergen Current bringing warm Atlantic water to the study area. Pteropods dominated at the surface and subsurface. Below 100 m water depth, foraminifera predominated. Pteropods contribute 66–96% to the inorganic carbon standing stocks compared to 4–34% by the planktic foraminifera. The inorganic export production of planktic foraminifera and pteropods together exceeds their organic contribution by a factor of 3. The overall predominance of pteropods over foraminifera in this high Arctic region during the sampling period suggest that inorganic standing stocks and export production of biogenic carbonate would be reduced under the effects of ocean acidification.

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Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system

Significance

We conduct a modeling study of the effects of enhanced coastal nutrient export from human activities on the carbon, nitrogen, and oxygen cycles of the Southern California Bight, in the context of emerging global climate change. The modeling approach used is innovative in the breadth of its scope, and simulations are generally consistent with local measurements. The human effects on the regional ecosystem from coastal nitrogen inputs of 23 million people are substantial, leading to significant increases in the photosynthesis and biomass of phytoplankton and increased oxygen loss and acidification of the water column. These changes are likely to compress habitat for a variety of marine organisms, with cascading ecological effects and implications for marine resources and water-quality management.

Abstract

Global change is leading to warming, acidification, and oxygen loss in the ocean. In the Southern California Bight, an eastern boundary upwelling system, these stressors are exacerbated by the localized discharge of anthropogenically enhanced nutrients from a coastal population of 23 million people. Here, we use simulations with a high-resolution, physical–biogeochemical model to quantify the link between terrestrial and atmospheric nutrients, organic matter, and carbon inputs and biogeochemical change in the coastal waters of the Southern California Bight. The model is forced by large-scale climatic drivers and a reconstruction of local inputs via rivers, wastewater outfalls, and atmospheric deposition; it captures the fine scales of ocean circulation along the shelf; and it is validated against a large collection of physical and biogeochemical observations. Local land-based and atmospheric inputs, enhanced by anthropogenic sources, drive a 79% increase in phytoplankton biomass, a 23% increase in primary production, and a nearly 44% increase in subsurface respiration rates along the coast in summer, reshaping the biogeochemistry of the Southern California Bight. Seasonal reductions in subsurface oxygen, pH, and aragonite saturation state, by up to 50 mmol m−3, 0.09, and 0.47, respectively, rival or exceed the global open-ocean oxygen loss and acidification since the preindustrial period. The biological effects of these changes on local fisheries, proliferation of harmful algal blooms, water clarity, and submerged aquatic vegetation have yet to be fully explored.

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Dynamics of bacterial communities during a seasonal hypoxia at the Bohai Sea: coupling and response between abundant and rare populations

Marine bacterial community plays a vital role in the formation of the hypoxia zone in coastal oceans. Yet, their dynamics in the seasonal hypoxia zone of the Bohai Sea (BHS) are barely studied. Here, the 16S rRNA gene-based high-throughput sequencing was used to explore the dynamics of their diversity, structure, and function as well as driving factors during the gradual deoxygenation process in the BHS. Our results evinced that the bacterial community was dominated by Proteobacteria, followed by Bacteroidetes, Firmicutes, Actinobacteria, and Cyanobacteria, etc. The abundant subcommunity dominated in the number of sequences (49%) while the rare subcommunity dominated in the number of species (99.61%). Although abundant subcommunity accounted for most sequences, rare subcommunity possessed higher diversity, richness and their population dramatically changed (higher turnover) during the hypoxia transition. Further, co-occurrence network analysis proved the vital role of rare subcommunity in the process of community assembly. Additionally, beta diversity partition revealed that both subcommunities possessed a higher turnover component than nestedness and/or richness component, implying species replacement could explain a considerable percentage of community variation. This variation might be governed by both environmental selection and stochastic processes, and further, it influenced the nitrogen cycle (PICRUSt-based prediction) of the hypoxia zone. Overall, this study provides insight into the spatial-temporal heterogeneity of bacterial and their vital role in biogeochemical cycles in the hypoxia zone of the BHS. These findings will extend our horizons about the stabilization mechanism, feedback regulation, and interactive model inside the bacterial community under oxygen-depleted ecosystems.

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Comparative sensitivities of zooplankton to ocean acidification conditions in experimental and natural settings

Zooplankton can serve as indicators of ecosystem health, water quality, food web structure, and environmental change, including those associated with climate change and ocean acidification (OA). Laboratory studies demonstrate that low pH and high pCO2 associated with OA can significantly affect the physiology and survival of zooplankton, with differential responses among taxa. While laboratory studies can be indicative of zooplankton response to OA, in situ responses will ultimately determine the fate of populations and ecosystems. In this perspective, we compare expectations from experimental studies with observations made in Puget Sound (Washington, United States), a highly dynamic estuary with known vulnerabilities to low pH and high pCO2. We found little association between empirical measures of in situ pH and the abundance of sensitive taxa as revealed by meta-analysis, calling into question the coherence between experimental studies and field observations. The apparent mismatch between laboratory and field studies has important ramifications for the design of long-term monitoring programs and interpretation and use of the data produced. Important work remains to be done to connect traits that are sensitive to OA with those that are ecologically relevant and reliably observable in the field.

Continue reading ‘Comparative sensitivities of zooplankton to ocean acidification conditions in experimental and natural settings’

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