Posts Tagged 'Antarctic'

Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the oceans. Seawater pH levels have already decreased by 0.1 and are predicted to decline by ~ 0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). These negative effects may become even exacerbated by increasing sea temperatures. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make predictions about how OA might affect different taxa. We consider their geographic range, skeletal mineralogy, biological traits and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate shows response variation depending on mineralogical composition. Species-specific responses due to mineralogical composition suggest taxa with calcitic, aragonitic and HMC skeletons may be more vulnerable to the expected carbonate chemistry alterations, and low magnesium calcite (LMC) species may be mostly resilient. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits and physiological processes are also expected to influence species specific responses.

Continue reading ‘Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean’

Ocean freshening and acidification differentially influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica

Highlights

  • Glacial retreat induced by global warming can decrease salinity and pH of the Antarctic ocean.
  • The Antarctic amphipod Gondogeneia antarctica was exposed to low salinity (27 psu) and low pH (7.6) conditions.
  • Low salinity increased cannibalism and induced adjusted swimming.
  • Low pH increased mortality, impaired food detection and reduced daytime shelter use.
  • Ocean freshening and acidification act as independent stressors influencing behavior and physiology of Antarctic amphipods.

Abstract

The Western Antarctic Peninsula (WAP) has experienced rapid atmospheric and ocean warming over the past few decades and many marine-terminating glaciers have considerably retreated. Glacial retreat is accompanied by fresh meltwater intrusion, which may result in the freshening and acidification of coastal waters. Marian Cove (MC), on King George Island in the WAP, undergoes one of the highest rates of glacial retreat. Intertidal and shallow subtidal waters are likely more susceptible to these processes, and sensitive biological responses are expected from the organisms inhabiting this area. The gammarid amphipod Gondogeneia antarctica is one of the most abundant species in the shallow, nearshore Antarctic waters, and it occupies an essential ecological niche in the coastal marine WAP ecosystem. In this study, we tested the sensitivity of G. antarctica to lowered salinity and pH by meltwater intrusion following glacial retreat. We exposed G. antarctica to four different treatments combining two salinities (34 and 27 psu) and pH (8.0 and 7.6) levels for 26 days. Mortality, excluding cannibalized individuals, increased under low pH but decreased under low salinity conditions. Meanwhile, low salinity increased cannibalism, whereas low pH reduced food detection. Shelter use during the daytime decreased under each low salinity and pH condition, indicating that the two stressors act as disruptors of amphipod behavior. Under low salinity conditions, swimming increased during the daytime but decreased at night. Although interactions between low salinity and low pH were not observed during the experiment, the results suggest that each stressor, likely induced by glacial melting, causes altered behaviors in amphipods. These environmental factors may threaten population persistence in Marian Cove and possibly other similar glacial embayments.

Continue reading ‘Ocean freshening and acidification differentially influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica’

Effects of low pH and low salinity induced by meltwater inflow on the behavior and physical condition of the Antarctic limpet, Nacella concinna

Seawater acidification and freshening in the intertidal zone of Marian Cove, Antarctica, which occurs by the freshwater inflow from snow fields and glaciers, could affect the physiology and behavior of intertidal marine organisms. In this study, we exposed Antarctic limpets, Nacella concinna, to two different pH (8.00 and 7.55) and salinity (34.0 and 27.0 psu) levels and measured their righting ability after being flipped over, mortality, condition factor, and shell dissolution. During the 35-day exposure, there was no significant difference in behavior and mortality between different treatments. However, the condition factor was negatively affected by low salinity. Both low pH and low salinity negatively influenced shell formation by decreasing the aragonite saturation state (Ωarg) and enhancing shell dissolution. Our results suggest that, though limpets can tolerate short-term low pH and salinity conditions, intrusions of meltwater accompanied by the glacial retreat may act as a serious threat to the population of N. concinna.

Continue reading ‘Effects of low pH and low salinity induced by meltwater inflow on the behavior and physical condition of the Antarctic limpet, Nacella concinna’

Effects of ocean acidification on acid-base physiology, skeleton properties, and metal contamination in two echinoderms from vent sites in Deception Island, Antarctica

Highlights

  • Acid-base characteristics of adult Antarctic echinoderms are similar to those of tropical and temperate echionderms
  • Skeleton properties of both species were weaker than those of tropical and temperate echinoderms
  • Reduced seawater pH and metals had no impact on the skeleton mechanical properties of the two investigated species
  • Reduced pH was correlated to increased contamination by most metals but this relation was weak

Abstract

Antarctic surface waters are expected to be the first to experience severe ocean acidification (OA) with carbonate undersaturation and large decreases in pH forecasted before the end of this century. Due to the long stability in environmental conditions and the relatively low daily and seasonal variations to which they are exposed, Antarctic marine organisms, especially those with a supposedly poor machinery to eliminate CO2 and protons and with a heavily calcified skeleton like echinoderms, are hypothesized as highly vulnerable to these environmental shifts. The opportunities offered by the natural pH gradient generated by vent activities in Deception Island caldera, Western Antarctic Peninsula, were used to investigate for the first time the acid-base physiologies, the impact of OA on the skeleton and the impact of pH on metal accumulation in the Antarctic sea star Odontaster validus and sea urchin Sterechinus neumayeri. The two species were sampled in four stations within the caldera, two at pH (total scale) 8.0- 8.1 and two at reduced pH 7.8. Measured variables were pH, alkalinity, and dissolved inorganic carbon of the coelomic fluid; characteristic fracture force, stress and Young’s modulus using Weibull statistics and Cd, Cu, Fe, Pb and Zn concentrations in the integument, gonads and digestive system. Recorded acid-base characteristics of both studied species fit in the general picture deduced from temperate and tropical sea stars and sea urchins but conditions and possibly confounding factors, principally food availability and quality, in the studied stations prevented definitive conclusions. Reduced seawater pH 7.8 and metals had almost no impact on the skeleton mechanical properties of the two investigated species despite very high Cd concentrations in O. validus integument. Reduced pH was correlated to increased contamination by most metals but this relation was weak. Translocation and caging experiments taking into account food parameters are proposed to better understand future processes linked to ocean acidification and metal contamination in Antarctic echinoderms.

Continue reading ‘Effects of ocean acidification on acid-base physiology, skeleton properties, and metal contamination in two echinoderms from vent sites in Deception Island, Antarctica’

Seasonal variability of net sea-air CO2 fluxes in a coastal region of the northern Antarctic peninsula

We show an annual overview of the sea-air CO2 exchanges and primary drivers in the Gerlache Strait, a hotspot for climate change that is ecologically important in the northern Antarctic Peninsula. In autumn and winter, episodic upwelling events increase the remineralized carbon in the sea surface, leading the region to act as a moderate or strong CO2 source to the atmosphere of up to 40 mmol m–2 day–1. During summer and late spring, photosynthesis decreases the CO2 partial pressure in the surface seawater, enhancing ocean CO2 uptake, which reaches values higher than − 40 mmol m–2 day–1. Thus, autumn/winter CO2 outgassing is nearly balanced by an only 4-month period of intense ocean CO2 ingassing during summer/spring. Hence, the estimated annual net sea-air CO2 flux from 2002 to 2017 was 1.24 ± 4.33 mmol m–2 day–1, opposing the common CO2 sink behaviour observed in other coastal regions around Antarctica. The main drivers of changes in the surface CO2 system in this region were total dissolved inorganic carbon and total alkalinity, revealing dominant influences of both physical and biological processes. These findings demonstrate the importance of Antarctica coastal zones as summer carbon sinks and emphasize the need to better understand local/regional seasonal sensitivity to the net CO2 flux effect on the Southern Ocean carbon cycle, especially considering the impacts caused by climate change.

Continue reading ‘Seasonal variability of net sea-air CO2 fluxes in a coastal region of the northern Antarctic peninsula’

Effects of temperature and food concentration on pteropod metabolism along the Western Antarctic Peninsula

Highlights

  • Measured respiration and excretion of the Antarctic pteropod Limacina.
  • Analyzed effects of future temperature and food conditions on pteropod metabolism.
  • Highest metabolism occurred under higher temperatures with less response to food.
  • Metabolic ratios of C, N, and P were all below the canonical Redfield ratio.
  • Pteropod metabolism responsive to ocean change, affecting biogeochemical cycles.

Abstract

Pteropods (pelagic snails) are abundant zooplankton in the Southern Ocean where they are important grazers of phytoplankton, prey for higher trophic levels, and sensitive to environmental change. The Western Antarctic Peninsula (WAP) is a highly dynamic and productive region that has undergone rapid warming, but little is known about how environmental changes there will affect pteropod physiology. In this study, the effects of warming seawater temperatures and shifting food availability on Limacina helicina antarctica metabolism (respiration and excretion) were determined by conducting shipboard experiments that exposed pteropods to a range of temperatures and phytoplankton (food) concentrations. Highest respiration (up to 69 μmol O2 gDW−1 h−1) and usually highest excretion rates occurred under higher temperature with more limited metabolic response to food concentration, indicating these factors do not always have an additive effect on pteropod metabolism. The proportion of dissolved organic matter (DOM) to total organic and inorganic dissolved constituents was high and was also significantly affected by shifts in temperature and food. Dissolved organic carbon, nitrogen, and phosphorus (DOC, DON, and DOP) were on average 27, 51, and 11.5% of the total C, N, and P metabolized, respectively. The proportion of total N excreted as DON and the proportion of total P excreted as DOP were significantly affected by a combination of shifting temperature and food concentrations. There were no effects of temperature or food on DOC excretion (mean 8.79 μmol C gDW−1 h−1; range 0.44 to 44) as a proportion of total C metabolized. Metabolic O2:N ratio ranged from 2 to 9 and decreased significantly with increasing temperature and food, indicating a shift toward increased protein catabolism. Metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which has implications for phytoplankton nutrient uptake and bacterial production. Respiration rates at ambient conditions of other WAP pteropods, and excretion rates for Clio pyramidata, were also measured, with respiration rates ranging from 24.39 (Spongiobranchaea australis) to 28.86 (L. h. antarctica) μmol O2 gDW−1 h−1. Finally, a CO2 perturbation experiment measuring L. h. antarctica metabolism under pre-industrial and elevated dissolved pCO2 conditions showed no significant change in mean L. h. antarctica respiration or excretion rates with higher pCO2. These insights into the metabolic response of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.

Continue reading ‘Effects of temperature and food concentration on pteropod metabolism along the Western Antarctic Peninsula’

Environmental controls on pteropod ecology and physiology along the Western Antarctic Peninsula

Pteropods (pelagic snails) are ubiquitous zooplankton in the Southern Ocean and abundant along the Western Antarctic Peninsula (WAP), one of the most rapidly warming regions on the planet. They are important prey for higher trophic levels, grazers of phytoplankton, and contribute to particulate organic and inorganic carbon export. Pteropods are heralded as bioindicators of ecosystem health due to the vulnerability of their aragonitic shells under ocean acidification conditions, which could greatly affect their abundances in the future. Despite their importance within Antarctic food webs, few studies have analyzed the effects of climate change on pteropod physiology and biogeography in the Southern Ocean. I utilized zooplankton net tows and sediment trap samples collected as part of the Palmer Antarctica Long Term Ecological Research (PAL LTER) program to determine long-term changes in pteropod biogeography and phenology (life history). I also conducted shipboard experiments on PAL LTER research cruises to analyze the effects of shifting temperature and food conditions on pteropod metabolism. Lastly, to examine WAP pteropod feeding ecology, I utilized high-throughput sequencing techniques and analyzed pteropod gut contents at an unprecedented taxonomic resolution. Pteropod populations along the WAP from 1993-2017 either remained stable (shelled pteropods) or increased (non-shelled pteropods) and were most strongly controlled by La Niña conditions the year prior, which led to warmer, ice-free waters. There was a weak relationship between pteropod abundance and carbonate chemistry, and no detectable long-term trend in carbonate chemistry parameters (i.e., aragonite saturation), thus ocean acidification is not presently a factor influencing WAP pteropod abundance. More open-water areas the year prior also increased growth rates of the shelled pteropod, Limacina helicina antarctica, and caused earlier time of appearance in the PAL LTER sediment trap. There was considerable interannual variability in the time of appearance of a new pteropod cohort, which ranged from year day 22 to 255, but no long-term, directional change in time of appearance or growth rate. The effects of warming seawater temperatures and shifting food availability on L. h. antarctica metabolism revealed that highest respiration and usually highest excretion rates occurred under higher temperatures, but the effect of food concentration was more limited. The proportion of dissolved organic matter to total organic and inorganic dissolved constituents was high and the metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which can directly affect phytoplankton growth and bacterial production in the WAP. Analysis of L. h. antarctica gut contents revealed its microbiome for the first time with Mollicutes bacteria the most abundant prokaryote. Pteropods were mainly herbivorous in summer, consuming predominantly diatoms but also supplementing their diet with microzooplankton such as ciliates. My dissertation shows that pteropods along the WAP are sensitive to changes in the environment from daily to interannual time scales. These insights into the metabolic and ecologic responses of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.

Continue reading ‘Environmental controls on pteropod ecology and physiology along the Western Antarctic Peninsula’

Impact of climate change on the primary production and related biogeochemical cycles in the coastal and sea ice zone of the Southern Ocean

Highlights

• Changes in primary production in the Southern Ocean are analyzed in a comprehensive manner.

• General production increase is the sign of climate change in the Southern Ocean.

• Associated biogeochemical variables show regionally heterogenous signals of climate change.

• Sea ice affecting iron supply and stratification is a primary factor for CCSZ production change.

• Production change in SIZ is sensitive to change in iron supply arising from various mechanisms.

Abstract

Climate change in the Southern Hemisphere has exerted impact on the primary production in the Southern Ocean (SO). Using a recently released reanalysis dataset on global biogeochemistry, a comprehensive analysis was conducted on the complex biogeochemical seasonal cycle and the impact of climate change with a focus in areas within the meridional excursion of the sea ice boundary—coastal and continental shelf zone (CCSZ) and seasonal sea ice zone (SIZ). The seasonal cycles of primary production and related nutrients are closely linked with the seasonal changes in sea ice and sea surface temperatures. As sea ice retreats and allows energy and gas exchange across the sea surface, phytoplankton growth is initiated, consuming accumulated nutrients within the shallow depth of ~40 m. The seasonal evolutions of physical, biological and chemical variables show both spatial and temporal consistency with each other. Climate change has altered the timing and amplitude of the seasonal cycle. While primary production has generally increased along with an intensified uptake of CO2, some areas show a reduction in production (e.g., Prydz Bay, eastern Indian Ocean). In the CCSZ, increased iron utilization and light availability allowed production to be increased. However, the mechanism by which these factors are altered varies from one location to another, including changes in sea ice cover, surface stratification, and downwelling/upwelling. In the SIZ, where iron is generally a limiting factor, iron supply is a key driver of changes in primary production regardless of other nutrients. There is a clear influence of climatic change on the biogeochemical cycle although the signal is still weak.

Continue reading ‘Impact of climate change on the primary production and related biogeochemical cycles in the coastal and sea ice zone of the Southern Ocean’

Understanding the metabolic capacity of Antarctic fishes to acclimate to future ocean conditions

Antarctic fishes have evolved under stable, extreme cold temperatures for millions of years. Adapted to thrive in the cold environment, their specialized phenotypes will likely render them particularly susceptible to future ocean warming and acidification as a result of climate change. Moving from a period of stability to one of environmental change, species persistence will depend on maintaining energetic equilibrium, or sustaining the increased energy demand without compromising important biological functions such as growth and reproduction. Metabolic capacity to acclimate, marked by a return to metabolic equilibrium through physiological compensation of resting metabolic rate (RMR), will likely determine which species will be better poised to cope with shifts in environmental conditions. Focusing on the suborder Notothenioidei, a dominant group of Antarctic fishes, and in particular 4 well-studied species, Trematomus bernacchii, Pagothenia borchgrevinki, Notothenia rossii and N. coriiceps, we discuss metabolic acclimation potential to warming and CO2-acidification using an integrative and comparative framework. There are species-specific differences in the physiological compensation of RMR during warming and the duration of acclimation time required to achieve compensation; for some species RMR fully recovered within 3.5 weeks of exposure, such as P. borchgrevinki, while for other species, such as N. coriiceps, RMR remained significantly elevated past 9 weeks of exposure. In all instances, added exposure to increased PCO2, further compromised the ability of species to return RMR to pre-exposure levels. The period of metabolic imbalance, marked by elevated RMR, was underlined by energetic disturbance and elevated energetic costs, which shifted energy away from fitness-related functions, such as growth. In T. bernacchii and N. coriiceps, long duration of elevated RMR impacted condition factor and/or growth rate. Low growth rate can affect development and ultimately the timing of reproduction, severely compromising the species’ survival potential and the biodiversity of the notothenioid lineage. Therefore, the ability to achieve full compensation of RMR, and in a short-time frame, in order to avoid long term consequences of metabolic imbalance, will likely be an important determinant in a species’ capacity to persist in a changing environment. Much work is still required to develop our understanding of the bioenergetics of Antarctic fishes in the face of environmental change, and a targeted approach of nesting a mechanistic focus in an ecological and comparative framework will better aid our predictions on the effect of global climate change on species persistence in the polar regions.

Continue reading ‘Understanding the metabolic capacity of Antarctic fishes to acclimate to future ocean conditions’

Ocean acidification reduces growth and grazing impact of Antarctic heterotrophic nanoflagellates

High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing fCO2 on the growth of heterotrophic nanoflagellates (HNFs), nano- and picophytoplankton, and prokaryotes (heterotrophic Bacteria and Archaea) in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO2 levels ≥634 µatm, HNF abundance was reduced, coinciding with increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNFs. Nanophytoplankton abundance was elevated in the 634 µatm treatment, suggesting that moderate increases in CO2 may stimulate growth. The taxonomic and morphological differences in CO2 tolerance we observed are likely to favour dominance of microbial communities by prokaryotes, nanophytoplankton, and picophytoplankton. Such changes in predator–prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean, intensifying organic-matter recycling in surface waters; reducing vertical carbon flux; and reducing the quality, quantity, and availability of food for higher trophic levels.

Continue reading ‘Ocean acidification reduces growth and grazing impact of Antarctic heterotrophic nanoflagellates’


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