Posts Tagged 'otherprocess'



Impact of ocean acidification and high solar radiation on productivity and species composition of a late summer phytoplankton community of the coastal Western Antarctic Peninsula

The Western Antarctic Peninsula (WAP), one of the most productive regions of the Southern Ocean, is currently undergoing rapid environmental changes such as ocean acidification (OA) and increased daily irradiances from enhanced surface‐water stratification. To assess the potential for future biological CO2 sequestration of this region, we incubated a natural phytoplankton assemblage from Ryder Bay, WAP, under a range of pCO2 levels (180 μatm, 450 μatm, and 1000 μatm) combined with either moderate or high natural solar radiation (MSR: 124 μmol photons m−2 s−1 and HSR: 435 μmol photons m−2 s−1, respectively). The initial and final phytoplankton communities were numerically dominated by the prymnesiophyte Phaeocystis antarctica, with the single cells initially being predominant and solitary and colonial cells reaching similar high abundances by the end. Only when communities were grown under ambient pCO2 in conjunction with HSR did the small diatom Fragilariopsis pseudonana outcompete P. antarctica at the end of the experiment. Such positive light‐dependent growth response of the diatom was, however, dampened by OA. These changes in community composition were caused by an enhanced photosensitivity of diatoms, especially F. pseudonana, under OA and HSR, reducing thereby their competitiveness toward P. antarctica. Moreover, community primary production (PP) of all treatments yielded similar high rates at the start and the end of the experiment, but with the main contributors shifting from initially large to small cells toward the end. Even though community PP of Ryder Bay phytoplankton was insensitive to the changes in light and CO2 availability, the observed size‐dependent shift in productivity could, however, weaken the biological CO2 sequestration potential of this region in the future.

Continue reading ‘Impact of ocean acidification and high solar radiation on productivity and species composition of a late summer phytoplankton community of the coastal Western Antarctic Peninsula’

Effects of elevated CO2 on a natural diatom community in the subtropical NE Atlantic

Diatoms are silicifying phytoplankton contributing about one quarter to primary production on Earth. Ocean acidification (OA) could alter the competitiveness of diatoms relative to other taxa and/or lead to shifts among diatom species. In spring 2016, we set up a plankton community experiment at the coast of Gran Canaria (Canary Islands, Spain) to investigate the response of subtropical diatom assemblages to elevated seawater pCO2. Therefore, natural plankton communities were enclosed for 32 days in in situ mesocosms (∼8 m3 volume) with a pCO2 gradient ranging from 380 to 1140 μatm. Halfway through the study we added nutrients to all mesocosms (N, P, Si) to simulate injections through eddy-induced upwelling which frequently occurs in the region. We found that the total diatom biomass remained unaffected during oligotrophic conditions but was significantly positively affected by high CO2 after nutrient enrichment. The average cell volume and carbon content of the diatom community increased with CO2. CO2 effects on diatom biomass and species composition were weak during oligotrophic conditions but became quite strong above ∼620 μatm after the nutrient enrichment. We hypothesize that the proliferation of diatoms under high CO2 may have been caused by a fertilization effect on photosynthesis in combination with reduced grazing pressure. Our results suggest that OA in the subtropics may strengthen the competitiveness of (large) diatoms and cause changes in diatom community composition, mostly under conditions when nutrients are injected into oligotrophic systems.

Continue reading ‘Effects of elevated CO2 on a natural diatom community in the subtropical NE Atlantic’

Biogenic habitat shifts under long-term ocean acidification show nonlinear community responses and unbalanced functions of associated invertebrates

Experiments have shown that increasing dissolved CO2 concentrations (i.e. Ocean Acidification, OA) in marine ecosystems may act as nutrient for primary producers (e.g. fleshy algae) or a stressor for calcifying species (e.g., coralline algae, corals, molluscs). For the first time, rapid habitat dominance shifts and altered competitive replacement from a reef-forming to a non-reef-forming biogenic habitat were documented over one-year exposure to low pH/high CO2 through a transplant experiment off Vulcano Island CO2 seeps (NE Sicily, Italy). Ocean acidification decreased vermetid reefs complexity via a reduction in the reef-building species density, boosted canopy macroalgae and led to changes in composition, structure and functional diversity of the associated benthic assemblages. OA effects on invertebrate richness and abundance were nonlinear, being maximal at intermediate complexity levels of vermetid reefs and canopy forming algae. Abundance of higher order consumers (e.g. carnivores, suspension feeders) decreased under elevated CO2 levels. Herbivores were non-linearly related to OA conditions, with increasing competitive release only of minor intertidal grazers (e.g. amphipods) under elevated CO2 levels.
Our results support the dual role of CO2 (as a stressor and as a resource) in disrupting the state of rocky shore communities, and raise specific concerns about the future of intertidal reef ecosystem under increasing CO2 emissions. We contribute to inform predictions of the complex and nonlinear community effects of OA on biogenic habitats, but at the same time encourage the use of multiple natural CO2 gradients in providing quantitative data on changing community responses to long-term CO2 exposure.

Continue reading ‘Biogenic habitat shifts under long-term ocean acidification show nonlinear community responses and unbalanced functions of associated invertebrates’

Ichthyotoxicity of the dinoflagellate Karlodinium veneficum in response to changes in seawater pH

The ichthyotoxic dinoflagellate Karlodinium veneficum has a worldwide distribution and produces highly potent lytic toxins (karlotoxins) that have been associated with massive fish kill events in coastal environments. The capacity of K. veneficum to gain energy from photosynthesis as well as phagotrophy enables cellular maintenance, growth and dispersal under a broad range of environmental conditions. Coastal ecosystems are highly dynamic in light of the prevailing physicochemical conditions, such as seawater carbonate speciation (CO2, HCO3−, and CO32−) and pH. Here, we monitored the growth rate and ichthyotoxicity of K. veneficum in response to a seawater pH gradient. K. veneficum exhibited a significant linear reduction in growth rate with elevated seawater acidity [pH(totalscale) from 8.05 to 7.50]. Ichthyotoxicity was assessed by exposing fish gill cells to K. veneficum extracts and subsequent quantification of gill cell viability via resorufin fluorescence. Extracts of K. veneficum indicated increased toxicity when derived from elevated pH treatments. The variation in growth rate and toxin production per cell in regard to seawater pH implies that (1) future alteration of seawater carbonate speciation, due to anthropogenic ocean acidification, may negatively influence physiological performance and ecosystem interactions of K. veneficum and (2) elevated seawater pH values (>8.0) represent favorable conditions for K. veneficum growth and toxicity. This suggests that prey of K. veneficum may be exposed to increased karlotoxin concentrations at conditions when nutrients are scarce and seawater pH has been elevated due to high photosynthetic activity from prior autotrophic phytoplankton blooms.

Continue reading ‘Ichthyotoxicity of the dinoflagellate Karlodinium veneficum in response to changes in seawater pH’

In-situ behavioural and physiological responses of Antarctic microphytobenthos to ocean acidification

Ocean acidification (OA) is predicted to alter benthic marine community structure and function, however, there is a paucity of field experiments in benthic soft sediment communities and ecosystems. Benthic diatoms are important components of Antarctic coastal ecosystems, however very little is known of how they will respond to ocean acidification. Ocean acidification conditions were maintained by incremental computer controlled addition of high fCO2 seawater representing OA conditions predicted for the year 2100. Respiration chambers and PAM fluorescence techniques were used to investigate acute behavioural, photosynthetic and net production responses of benthic microalgae communities to OA in in-situ field experiments. We demonstrate how OA can modify behavioural ecology, which changes photo-physiology and net production of benthic microalgae. Ocean acidification treatments significantly altered behavioural ecology, which in turn altered photo-physiology. The ecological trends presented here have the potential to manifest into significant ecological change over longer time periods.

Continue reading ‘In-situ behavioural and physiological responses of Antarctic microphytobenthos to ocean acidification’

The influence of simulated global ocean acidification on the toxic effects of carbon nanoparticles on polychaetes

Highlights

• Slighter aggregation and more suspended carbon nanomaterials in acidified seawater

• Under pH acidified both carbon nanomaterials generated greater oxidative stress in polychaetes.

• Functionalized carbon nanomaterials increased oxidative stress and neurotoxicity under both pHs.

• Ocean acidification may cause a higher risk of carbon nanomaterials to marine ecosystems.

Abstract

Ocean acidification events are recognized as important drivers of change in biological systems. Particularlly, the impacts of estuarine acidification are severe than surface ocean due to its shallowness, low buffering capacity, low salinity and high organic matter from land drainage. Moreover, because they are transitional areas, estuaries can be seriously impacted by any number of anthropogenic activities and in the last decades, carbon nanomaterials (CNMs) are considered as emerging contaminants in the estuarine ecosystem. Considering all these evidences, chronic experiment was carried out trying to understand the possible alteration on the chemical behaviour of two different CNMs (functionalized and pristine) in predicted climate change scenarios and consequently, how these alterations could modify the sensitivity of one the most common marine and estuarine organisms (the polychaeta Hediste diversicolor) assessing a set of biomarkers related to polychaetes oxidative status as well as the metabolic performance and neurotoxicity. Our results demonstrated that all enzymes worked together to counteract seawater acidification and CNMs, however oxidative stress in the exposed polychaetes to both CNMs, especially under ocean acidification conditions was enhanced. In fact, although the antioxidant enzymes tried to cope as compensatory response of cellular defense systems against oxidative stress, the synergistic interactive effects of pH and functionalized CNMs indicated that acidified pH significantly increased the oxidative damage (in terms of lipid peroxidation) in the cotaminated organisms. Different responses were observed in organisms submitted to pristine CNMs under pH control, where the lipid peroxidation did not increase along with the increasing exposure concentrations. The present results further demonstrated the neurotoxicity caused by both CNMs, especially noticeable at acidified conditions. The mechanism of enhanced toxicity could be attributed to slighter aggregation and more suspended NMs in acidified seawater (demonstrated in the DLS analysis). Therefore, ocean acidification may cause a higher risk of CNMs to marine ecosystems.

Continue reading ‘The influence of simulated global ocean acidification on the toxic effects of carbon nanoparticles on polychaetes’

Physical factors affecting oyster diversity and distribution in southern Thailand

Aim : Studies on oyster population dynamic is essential for effective oyster aquaculture.Bandon Bay in Southern Thailand is a major shellfish aquaculture site of high commercial value. The aim of this study was to evaluate the influence of environmental factors on oyster diversity and their distribution in Bandon Bay. Methodology: Adult oysters were collected from eight aquaculture sites during low tide and their body sizes were measured. Monthly, transparency, salinity, pH, dissolved oxygen, biochemical oxygen demand, alkalinity, ammonium (NH4-N),nitrite, nitrate and phosphate were recorded from Surat Thani Coastal Fisheries Research and Development Centre, Department of Fisheries. Results : Three oyster species were observed: Crassostrea belcheri, Crassostrea lugubris and Saccostrea forskalii, however, C. belcheri was most abundant at most locations. Oyster density in Bandon Bay was mostly influenced by alkalinity, followed by salinity, pH, NO3and NH4-N. Interpretation : Since oyster reproduction, survival and shell development depend on environmental factors, thus studies on relationships between environmental factors and oyster occurrence/density may provide a better understanding about the community structures and spatial dynamics of oysters, as well as how oysters respond to environmental changes.

Continue reading ‘Physical factors affecting oyster diversity and distribution in southern Thailand’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book