Posts Tagged 'zooplankton'

Influence of environmental conditions on the toxicokinetics of cadmium in the marine copepod Acartia tonsa

Marine and estuarine ecosystems are highly productive areas that often act as a final sink for several pollutants, such as cadmium. Environmental conditions in these habitats can affect metal speciation, as well as its uptake and depuration by living organisms. The aim of this study was to assess cadmium uptake and depuration rates in the euryhaline calanoid copepod Acartia tonsa under different pH, salinity and temperature conditions. Cadmium speciation did not vary with changing pH or temperature, but varied with salinity. Free Cd2+ ion activity increased with decreasing salinities resulting in increased cadmium concentrations in A. tonsa. However, uptake rate, derived using free Cd2+ ion activity, showed no significant differences at different salinities indicating a simultaneous combined effect of Cd2+ speciation and metabolic rates for osmoregulation. Cadmium concentration in A. tonsa and uptake rate increased with increasing pH, showing a peak at the intermediate pH of 7.5, while depuration rate fluctuated, thus suggesting that both parameters are mediated by metabolic processes (to maintain homeostasis at pH levels lower than normal) and ion competition at membrane binding sites. Cadmium concentration in A. tonsa, uptake and depuration rates increased with increasing temperature, a trend that can be attributed to an increase in metabolic energy demand at higher temperatures. The present study shows that cadmium uptake and depuration rates in the marine copepod A. tonsa is mostly affected by biological processes, mainly driven by metabolic mechanisms, and to a lesser extent by metal speciation in the exposure medium.

Continue reading ‘Influence of environmental conditions on the toxicokinetics of cadmium in the marine copepod Acartia tonsa’

Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as one of the species most susceptible to ocean acidification (OA). Yet, little is known about their capacity to acclimatize to such conditions. We collected pteropods in the California Current Ecosystem (CCE) that differed in the severity of exposure to Ωar conditions in the natural environment. Combining field observations, high-CO2 perturbation experiment results, and retrospective ocean transport simulations, we investigated biological responses based on histories of magnitude and duration of exposure to Ωar < 1. Our results suggest that both exposure magnitude and duration affect pteropod responses in the natural environment. However, observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Pteropods from the coastal CCE appear to be at or near the limit of their physiological capacity, and consequently, are already at extinction risk under projected acceleration of OA over the next 30 years. Our results demonstrate that Ωar exposure history largely determines pteropod response to experimental conditions and is essential to the interpretation of biological observations and experimental results.

Continue reading ‘Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast’

Potential impact of carbonate chemistry change (pCO2) on krill and krill-based food chain in the Southern Ocean with emphasis on embryogenesis of Antarctic krill

In the Southern Ocean, it is still not certain that overall krill biomass may decline because of drastic increase in pCO2, and consequent decline in pH. However, there is evidence that ecological vacuums created by krill population collapses caused by ecosystem shifts in Western Antarctic Peninsula (WAP) region led to replacement of Antarctic krill Euphausia superba by soft-bodied salps Salpa thomsoni. There is yet another questionable hypothesis that by the end of 21st century, ocean acidification stress, coupled with thermal increase, may synergistically induce physiologically critical stress to Antarctic krill in some areas of the Southern Ocean, egg development of krill may drastically decrease and in the 23rd century krill may even become extinct. I have earlier reported on normal krill egg development in relation to thermal change and high pressure (George and Stromberg, 1985). Recent experiments on krill development under different pCO2 conditions by Kawaguchi et al. (2011, 2013) suggest that we may witness 20 to 70 % reduction in Antarctic Krill by 2100 as direct consequence of pH decline. Such a scenario may lead to demise of krill-eating top-predators like baleen whales, seals and different species of Antarctic penguin populations. We now know that Adelaide penguins are decreasing in Bransfield Strait region off of the Western Antarctic Peninsula but increasing in Ross Sea region. Such a shift in breeding colonies moving from northern to southern WAP region and Ross Sea areas is not attributed to any decline in krill biomass but recent decadal melting of sea-ice as documented by remote sensing (George and Hayden, 2017). In this paper the main focus revolves around implications of changing chemistry of the Southern Ocean caused by absorption of anthropogenic carbon dioxide.
Continue reading ‘Potential impact of carbonate chemistry change (pCO2) on krill and krill-based food chain in the Southern Ocean with emphasis on embryogenesis of Antarctic krill’

Pteropod shell condition, locomotion, and long-term population trends in the context of ocean acidification and environmental change

Thecosome pteropods are planktonic mollusks that form aragonite shells and that may experience increased dissolution and other adverse effects due to ocean acidification. This thesis focuses on assessing the possible biological effects of ocean acidification on the shells and locomotion of pteropods and examining the response of a local pteropod population to environmental change over time. I analyzed shell condition after exposing pteropods to elevated CO2 as well as in natural populations to investigate the sensitivity of the shells of different species to aragonite saturation state (ΩA). The pteropods (Limacina retroversa) from laboratory experiments showed the clearest pattern of shell dissolution in response to decreased ΩA, while wild populations either had non-significant regional trends in shell condition (Clio pyramidata) or variability in shell condition that did not match expectations due to regional variability in ΩA (Limacina helicina). At locations with intermediate ΩA (1.5-2.5) the variability seen in L. helicina shell condition might be affected by food availability more than ΩA. I examined sinking and swimming behaviors in the laboratory in order to investigate a possible fitness effect of ocean acidification on pteropods. The sinking rates of L. retroversa from elevated CO2 treatments were slower in conjunction with worsened shell condition. These changes could increase their vulnerability to predators in the wild. Swimming ability was mostly unchanged by elevated CO2 after experiments that were up to three weeks in duration. I used a long-term dataset of pteropods in the Gulf of Maine to directly test whether there has been a population effect of environmental change over the past several decades. I did not observe a population decline between 1977 and 2015, and L. retroversa abundance in the fall actually increased over the time series. Analysis of the habitat use of L. retroversa revealed seasonal associations with temperature, salinity, and bottom depths. The combination of laboratory experiments and field surveys helped to address gaps in knowledge about pteropod ecology and improve our understanding of the effects of ocean acidification on pteropods.

Continue reading ‘Pteropod shell condition, locomotion, and long-term population trends in the context of ocean acidification and environmental change’

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

The Southern Ocean provides a vital service by absorbing about one sixth of humankind’s annual emissions of CO2. This comes with a cost – an increase in ocean acidity that is expected to have negative impacts on ocean ecosystems. The reduced ability of phytoplankton and zooplankton to precipitate carbonate shells is a clearly identified risk. The impact depends on the significance of these organisms in Southern Ocean ecosystems, but there is very little information on their abundance or distribution. To quantify their presence, we used coulometric measurement of particulate inorganic carbonate (PIC) on particles filtered from surface seawater into two size fractions: 50–1000 μm to capture foraminifera (the most important biogenic carbonate forming zooplankton) and 1–50 μm to capture coccolithophores (the most important biogenic carbonate forming phytoplankton). Ancillary measurements of biogenic silica (BSi) and particulate organic carbon (POC) provided context, as estimates of the abundance of diatoms (the most abundant phytoplankton in polar waters), and total microbial biomass, respectively. Results for 9 transects from Australia to Antarctica in 2008–2015 showed low levels of PIC compared to northern hemisphere polar waters. Coccolithophores slightly exceeded the biomass of diatoms in Subantarctic waters, but their abundance decreased more than 30-fold poleward, while diatom abundances increased, so that on a molar basis PIC was only 1 % of BSi in Antarctic waters. This limited importance of coccolithophores in the Southern Ocean is further emphasized in terms of their associated POC, representing less than 1 % of total POC in Antarctic waters and less than 10 % in Subantarctic waters. NASA satellite ocean colour based PIC estimates were in reasonable agreement with (though somewhat higher than) the shipboard results in Subantarctic waters, but greatly over-estimated PIC in Antarctic waters. Contrastingly, the NASA Ocean Biogeochemical Model (NOBM) shows coccolithophores as overly restricted to Subtropical and northern Subantarctic waters. The cause of the strong southward decrease in PIC abundance in the Southern Ocean is not yet clear. Poleward decrease in pH is small and while calcite saturation decreases strongly southward it remains well above saturation (> 2). Nitrate and phosphate variations would predict a poleward increase. Temperature and competition with diatoms for limiting iron appear likely to be important. While the future trajectory of coccolithophore distributions remains uncertain, their current low abundances suggest small impacts on overall Southern Ocean pelagic ecology.

Continue reading ‘Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment’

Spatial patterns of Anchoveta (Engraulis ringens) eggs and larvae in relation to pCO2 in the Peruvian upwelling system

Large and productive fisheries occur in regions experiencing or projected to experience ocean acidification. Anchoveta (Engraulis ringens) constitute the world’s largest single-species fishery and live in one of the ocean’s highest pCO2 regions. We investigated the relationship of the distribution and abundance of Anchoveta eggs and larvae to natural gradients in pCO2 in the Peruvian upwelling system. Eggs and larvae, zooplankton, and data on temperature, salinity, chlorophyll a and pCO2 were collected during a cruise off Peru in 2013. pCO2 ranged from 167–1392 µatm and explained variability in egg presence, an index of spawning habitat. Zooplankton abundance explained variability in the abundance of small larvae. Within the main spawning and larva habitats (6–10°S), eggs were found in cool, low-salinity, and both extremely low (less than 200 µatm) and high (more than 900 µatm) pCO2 waters, and larvae were collected in warmer, higher salinity, and moderate (400–600 µatm) pCO2 waters. Our data support the hypothesis that Anchoveta preferentially spawned at high pCO2 and these eggs had lower survival. Enhanced understanding of the influence of pCO2 on Anchoveta spawning and larva mortality, together with pCO2 measurements, may enable predictions of ocean acidification effects on Anchoveta and inform adaptive fisheries management.

Continue reading ‘Spatial patterns of Anchoveta (Engraulis ringens) eggs and larvae in relation to pCO2 in the Peruvian upwelling system’

Is the chemical composition of biomass the agent by which ocean acidification influences on zooplankton ecology?

Climate change impacts prevail on marine pelagic systems and food webs, including zooplankton, the key link between primary producers and fish. Several metabolic, physiological, and ecological responses of zooplankton species and communities to global stressors have recently been tested, with an emerging field in assessing effects of combined climate-related factors. Yet, integrative studies are needed to understand how ocean acidification interacts with global warming, mediating zooplankton body chemistry and ecology. Here, we tested the combined effects of global warming and ocean acidification, predicted for the year 2100, on a community of calanoid copepods, a ubiquitously important mesozooplankton compartment. Warming combined with tested pCO2 increase affected metabolism, altered stable isotope composition and fatty acid contents, and reduced zooplankton fitness, leading to lower copepodite abundances and decreased body sizes, and ultimately reduced survival. These interactive effects of temperature and acidification indicate that metabolism-driven chemical responses may be the underlying correlates of ecological effects observed in zooplankton communities, and highlight the importance of testing combined stressors with a regression approach when identifying possible effects on higher trophic levels.

Continue reading ‘Is the chemical composition of biomass the agent by which ocean acidification influences on zooplankton ecology?’


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Ocean acidification in the IPCC AR5 WG II

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