Posts Tagged 'respiration'

Physiological and biochemical impacts induced by mercury pollution and seawater acidification in Hediste diversicolor

The present study evaluated the impacts of predicted seawater acidification and Hg pollution, when stressors were acting alone and in combination, on the polychaete Hediste diversicolor. Polychaetes were exposed during 28 days to low pH (7.5), Hg (5 μg/L) and pH 7.5 + Hg, and physiological alterations (respiration rate), biochemical markers related to metabolic potential (glycogen and protein content, electron transport system activity) and oxidative status (activity of antioxidant and biotransformation enzymes, lipid peroxidation) were evaluated. The results obtained clearly showed that polychaetes were sensitive to low pH and Hg contamination, both acting alone or in combination. Organisms used their energy reserves under stressful conditions, which decreased by up to half of the control content, probably to fuel defence mechanisms. Our findings further demonstrated that polychaetes exposed to these stressors presented increased antioxidant defence mechanisms (3 fold compared to control). However, organisms were not able to prevent cellular damage, especially noticed at Hg exposure and pH 7.5. Overall, although all the tested conditions induced oxidative stress in Hediste diversicolor, the combined effect of seawater acidification and Hg contamination did not induce higher impacts in polychaetes than single stressor exposures. These findings may indicate that predicted climate change scenarios may not increase Hediste diversicolor sensitivity towards Hg and may not significantly change the toxicity of this contaminant to this polychaete species.

Continue reading ‘Physiological and biochemical impacts induced by mercury pollution and seawater acidification in Hediste diversicolor’

Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment

Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.

Continue reading ‘Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment’

Aerobic and behavioral flexibility allow estuarine gastropods to flourish in rapidly changing and extreme pH conditions

Despite efforts to understand marine organismal responses to ocean acidification (gradual change in pH/ pCO2pCO2 over decades), there is a lack of information about the capabilities of coastal organisms to endure rapid and extreme pH change (often full units within hours). We predicted that gastropods faced with estuarine acidification avoid extreme pH exposure through isolation and/or escape behavior, and energetically compensate for feeding and energy uptake limitations by facultative metabolic depression (FMD). To test this, we studied behavioral (organism activity) and aerobic (cardiac performance) responses to acidification in two closely related tropical intertidal species, the estuarine Indothais gradata (two populations) and the open-shore Reishia bitubercularis. Snails were exposed in the laboratory to either acutely declining or stable low pH conditions, using two acidification modes (HNO3-acidification and CO2-aeration). Under acutely declining pH, aerobic performance was regulated to unexpectedly low pH levels (4.5), effectively extending the field pH range for activity. This pH performance threshold marked the onset of behavioral isolation and FMD (as opposed to respiratory stress) and was lower in Indothais than Reishia snails during mineral acidification. Behavioral (in isolated gastropods) and environmental hypercapnic acidosis complicates interpretation of lowered metabolic performance. Stable reduced pH exposures resulted in different behavioral and physiological responses by the Indothais populations, including more prominent escape from water in the seaward population. Overall, these results suggest that aerobic and behavioral flexibility are crucial to organismal fitness in widely fluctuating pH circumstances. They further warn against overgeneralizing marine acidification consequences across physiological dispositions, taxonomic levels, and ecological systems.

Continue reading ‘Aerobic and behavioral flexibility allow estuarine gastropods to flourish in rapidly changing and extreme pH conditions’

Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxide

Marine phytoplankton are expected to benefit from enhanced carbon dioxide (CO2), attributable largely to down-regulation of the CO2 concentrating mechanism (CCM) which saves energy resources for other cellular processes. However, the nitrogen (N) nutritional condition (N-replete vs. N-limiting) of phytoplankton may affect the responses of their intracellular metabolic processes to elevated CO2. We cultured the model diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Thalassiosira weissflogii at ambient and elevated CO2 levels under N-replete and N-limiting conditions. Key metabolic processes, including light harvesting, C fixation, photorespiration, respiration, and N assimilation, were assessed systematically and then incorporated into an energy budget to compare the effects of CO2 on the metabolic pathways and the consequent changes in photosynthesis and C fixation as a result of energy reallocation under the different N nutritional conditions. Under the N-replete condition, down-regulation of the CCM at high CO2 was the primary contributor to increased photosynthesis rates of the diatoms. Under N-limiting conditions, elevated CO2 significantly affected the photosynthetic photon flux and respiration, in addition to CCM down-regulation and declines in photorespiration, resulting in an increase of the C:N ratio in all 3 diatom species. In T. pseudonana and T. weissflogii, the elevated C:N ratio was driven largely by an increased cellular C quota, whereas in P. tricornutum it resulted primarily from a decreased cellular N quota. The N-limited diatoms therefore could fix more C per unit of N in response to elevated CO2, which could potentially provide a negative feedback to the ongoing increase in atmospheric CO2.

Continue reading ‘Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxide’

Elevated pCO2 enhances bacterioplankton removal of organic carbon

Factors that affect the removal of organic carbon by heterotrophic bacterioplankton can impact the rate and magnitude of organic carbon loss in the ocean through the conversion of a portion of consumed organic carbon to CO2. Through enhanced rates of consumption, surface bacterioplankton communities can also reduce the amount of dissolved organic carbon (DOC) available for export from the surface ocean. The present study investigated the direct effects of elevated pCO2 on bacterioplankton removal of several forms of DOC ranging from glucose to complex phytoplankton exudate and lysate, and naturally occurring DOC. Elevated pCO2 (1000–1500 ppm) enhanced both the rate and magnitude of organic carbon removal by bacterioplankton communities compared to low (pre-industrial and ambient) pCO2 (250 –~400 ppm). The increased removal was largely due to enhanced respiration, rather than enhanced production of bacterioplankton biomass. The results suggest that elevated pCO2 can increase DOC consumption and decrease bacterioplankton growth efficiency, ultimately decreasing the amount of DOC available for vertical export and increasing the production of CO2 in the surface ocean.

Continue reading ‘Elevated pCO2 enhances bacterioplankton removal of organic carbon’

Ocean acidification changes abiotic processes but not biotic processes in coral reef sediments

In coral reefs, sediments play a crucial role in element cycling by contributing to primary production and the remineralization of organic matter. We studied how future ocean acidification (OA) will affect biotic and abiotic processes in sediments from two coral reefs of the Great Barrier Reef, Australia. This was investigated in the laboratory under conditions where water-sediment exchange was dominated by molecular diffusion (Magnetic Island) or by porewater advection (Davies Reef). OA conditions (+ΔpCO2: 170–900 µatm, -ΔpH: 0.1–0.4) did not affect photosynthesis, aerobic and anaerobic organic matter remineralization and growth of microphytobenthos. However, microsensor measurements showed that OA conditions reduced the porewater pH. Under diffusive conditions these changes were limited to the upper sediment layers. In contrast, advective conditions caused a deeper penetration of low pH water into the sediment resulting in an earlier pH buffering by dissolution of calcium carbonate (CaCO3). This increased the dissolution of Davis Reef sediments turning them from net precipitating (-0.8 g CaCO3 m-2 d-1) under ambient to net dissolving (1 g CaCO3 m-2 d-1) under OA conditions. Comparisons with in-situ studies on other reef sediments show that our dissolution rates are reasonable estimates for field settings. We estimate that enhanced dissolution due to OA will only have a minor effect on net ecosystem calcification of the Davies Reef flat (< 4%). However, it could decrease recent sediment accumulation rates in the lagoon by up to 31% (by 0.2–0.4 mm year-1), reducing valuable reef space. Furthermore, our results indicate that high-magnesium calcite is predominantly dissolving in the studied sediments and a drastic reduction in this mineral can be expected on Davis Reef lagoon in the near future, leaving sediments of an altered mineral composition. This study demonstrates that biotic sediment processes will likely not directly be affected by OA. Ensuing indirect effects of OA-induced sediment dissolution on biotic processes are discussed.

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The acclimation process of phytoplankton biomass, carbon fixation and respiration to the combined effects of elevated temperature and pCO2 in the northern South China Sea

We conducted shipboard microcosm experiments at both off-shore (SEATS) and near-shore (D001) stations in the northern South China Sea (NSCS) under three treatments, low temperature and low pCO2 (LTLC), high temperature and low pCO2 (HTLC), and high temperature and high pCO2 (HTHC). Biomass of phytoplankton at both stations were enhanced by HT. HTHC did not affect phytoplankton biomass at station D001 but decreased it at station SEATS. HT alone increased net primary productivity by 234% at station SEATS and by 67% at station D001 but the stimulating effect disappeared when HC was combined. HT also increased respiration rate by 236% at station SEATS and by 87% at station D001 whereas HTHC reduced it by 61% at station SEATS and did not affect it at station D001. Overall, our findings indicate that the positive effect of ocean warming on phytoplankton assemblages in NSCS could be damped or offset by ocean acidification.

Continue reading ‘The acclimation process of phytoplankton biomass, carbon fixation and respiration to the combined effects of elevated temperature and pCO2 in the northern South China Sea’


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Ocean acidification in the IPCC AR5 WG II

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