Posts Tagged 'multiple factors'

The Arctic picoeukaryote Micromonas pusilla benefits synergistically from warming and ocean acidification (update)

In the Arctic Ocean, climate change effects such as warming and ocean acidification (OA) are manifesting faster than in other regions. Yet, we are lacking a mechanistic understanding of the interactive effects of these drivers on Arctic primary producers. In the current study, one of the most abundant species of the Arctic Ocean, the prasinophyte Micromonas pusilla, was exposed to a range of different pCO2 levels at two temperatures representing realistic current and future scenarios for nutrient-replete conditions. We observed that warming and OA synergistically increased growth rates at intermediate to high pCO2 levels. Furthermore, elevated temperatures shifted the pCO2 optimum of biomass production to higher levels. Based on changes in cellular composition and photophysiology, we hypothesise that the observed synergies can be explained by beneficial effects of warming on carbon fixation in combination with facilitated carbon acquisition under OA. Our findings help to understand the higher abundances of picoeukaryotes such as M. pusilla under OA, as has been observed in many mesocosm studies.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits synergistically from warming and ocean acidification (update)’

Additive effects of pCO2 and temperature on respiration rates of the Antarctic pteropod Limacina helicina antarctica

The Antarctic pteropod, Limacina helicina antarctica, is a dominant member of the zooplankton in the Ross Sea and supports the vast diversity of marine megafauna that designates this region as an internationally protected area. Here, we observed the response of respiration rate to abiotic stressors associated with global change—environmentally relevant temperature treatments (−0.8°C, 4°C) and pH treatments reflecting current-day and future modeled extremes (8.2, 7.95 and 7.7 pH at −0.8°C; 8.11, 7.95 and 7.7 pH at 4°C). Sampling repeatedly over a 14-day period in laboratory experiments and using microplate respirometry techniques, we found that the metabolic rate of juvenile pteropods increased in response to low-pH exposure (pH 7.7) at −0.8°C, a near-ambient temperature. Similarly, metabolic rate increased when pteropods were exposed simultaneously to multiple stressors: lowered pH conditions (pH 7.7) and a high temperature (4°C). Overall, the results showed that pCO2 and temperature interact additively to affect metabolic rates in pteropods. Furthermore, we found that L. h. antarctica can tolerate acute exposure to temperatures far beyond its maximal habitat temperature. Overall, L. h. antarctica appears to be susceptible to pH and temperature stress, two abiotic stressors which are expected to be especially deleterious for ectothermic marine metazoans in polar seas.

Continue reading ‘Additive effects of pCO2 and temperature on respiration rates of the Antarctic pteropod Limacina helicina antarctica’

Does nutrient availability regulate seagrass response to elevated CO2?

Future increases in oceanic carbon dioxide concentrations (CO2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO2(aq) effects on submerged vegetation. This study factorially manipulated CO2(aq) and nutrient availability, in situ, within a subtropical seagrass bed for 350 days, and examined treatment effects on leaf productivity, shoot density, above- and belowground biomass, nutrient content, carbohydrate storage, and sediment organic carbon (Corg). Clear, open-top chambers were used to replicate CO2(aq) forecasts for the year 2100, whereas nutrient availability was manipulated via sediment amendments of nitrogen (N) and phosphorus (P) fertilizer. We provide modest evidence of a CO2 effect, which increased seagrass aboveground biomass. CO2(aq) enrichment had no effect on nutrient content, carbohydrate storage, or sediment Corg content. Nutrient addition increased leaf productivity and leaf N content, however did not alter above- or belowground biomass, shoot density, carbohydrate storage, or Corg content. Treatment interactions were not significant, and thus NP availability did not influence seagrass responses to elevated CO2(aq). This study demonstrates that long-term carbon enrichment may alter the structure of shallow seagrass meadows, even in relatively nutrient-poor, oligotrophic systems.

Continue reading ‘Does nutrient availability regulate seagrass response to elevated CO2?’

Susceptibility of two co-existing mytilid species to simulated predation under projected climate change conditions

Properties of the shells and byssus filaments secreted by marine mussels are affected by environmental and biotic factors. In this study, we investigated the effects of pH and temperature on shell and byssus in artificially created monospecific and mixed aggregations of the indigenous mussel Mytilus galloprovincialis and the invasive mussel Xenostrobus securis. The variability in the response of the mussels was mainly explained by species-specific interactions derived from the type of aggregation. In the mixed groups, acidic conditions caused a decrease in byssus strength in M. galloprovincialis, but an increase in byssus strength in X. securis. Increased temperature positively affected shell strength in X. securis, but only in mixed aggregations. Interactive effects of acidification and warming were only detected in the organic matter of shells, the strength of which decreased in M. galloprovincialis in mixed aggregations. Although the invasive mussel may be able to take advantage of changed conditions by enhancing byssal attachment, the effects that acidification has on shells may make this species more vulnerable to some predators. The study findings provide some insight into the responses of protective and attachment structures of mussels to biotic and abiotic stressors, highlighting how species interactions may shape the future of mytilid populations.

Continue reading ‘Susceptibility of two co-existing mytilid species to simulated predation under projected climate change conditions’

Variable metabolic responses of Skagerrak invertebrates to low O2 and high CO2 scenarios (update)

Coastal hypoxia is a problem that is predicted to increase rapidly in the future. At the same time, we are facing rising atmospheric CO2 concentrations, which are increasing the pCO2 and acidity of coastal waters. These two drivers are well studied in isolation; however, the coupling of low O2 and pH is likely to provide a more significant respiratory challenge for slow moving and sessile invertebrates than is currently predicted. The Gullmar Fjord in Sweden is home to a range of habitats, such as sand and mud flats, seagrass beds, exposed and protected shorelines and rocky bottoms. Moreover, it has a history of both natural and anthropogenically enhanced hypoxia as well as North Sea upwelling, where salty water reaches the surface towards the end of summer and early autumn. A total of 11 species (Crustacean, Chordate, Echinoderm and Mollusc) of these ecosystems were exposed to four different treatments (high or low oxygen and low or high CO2; varying pCO2 of 450 and 1300 µatm and O2 concentrations of 2–3.5 and 9–10 mg L−1) and respiration measured after 3 and 6 days, respectively. This allowed us to evaluate respiration responses of species of contrasting habitats to single and multiple stressors. Results show that respiratory responses were highly species specific as we observed both synergetic as well as antagonistic responses, and neither phylum nor habitat explained trends in respiratory responses. Management plans should avoid the generalized assumption that combined stressors will result in multiplicative effects and focus attention on alleviating hypoxia in the region.

Continue reading ‘Variable metabolic responses of Skagerrak invertebrates to low O2 and high CO2 scenarios (update)’

Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)

Predicted ocean acidification and warming for the end of the century may have drastic consequences on the structure and functioning of marine ecosystems. However, a lack of knowledge persists on the impact of future changes on the response of marine communities. This thesis aims to provide new understanding of the impact of ocean acidification and warming at the community level. For this, two ecosystems have been considered: rockpools, characterized by high physico-chemical variations, and maerl beds, with smaller variations. In the laboratory, artificial assemblages were created from the main calcareous and fleshy macroalgal and grazer species present in these two ecosystems. Created assemblages have been subjected to ambient and future temperature and pCO2 conditions. Ocean acidification and warming altered the structure and functioning of maerl bed assemblages, through an increase in the productivity of non-calcareous macroalgae and a decline in maërl calcification rates. The physiology of grazers is negatively impacted by future changes, which altered assemblages’ trophic structure. On the other hand, ocean acidification and warming had no effect on the productivity of rockpool assemblages. The highly variable environment may thus increase the resistance of rockpool communities to future changes, compared to communities from more stable environments, such as maerl beds.

Continue reading ‘Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)’

Juvenile rockfish show resilience to CO2-acidification and hypoxia across multiple biological scales

California’s coastal ecosystems are forecasted to undergo shifting ocean conditions due to climate change, some of which may negatively impact recreational and commercial fish populations. To understand if fish populations have the capacity to respond to multiple stressors, it is critical to examine interactive effects across multiple biological scales, from cellular metabolism to species interactions. This study examined the effects of CO2-acidification and hypoxia on two naturally co-occurring species, juvenile rockfish (genus Sebastes) and a known predator, cabezon (Scorpaenichthys marmoratus). Fishes were exposed to two PCO2 levels at two dissolved oxygen (DO) levels: ~600 (ambient) and ~1600 (high) μatm PCO2 and 8.0 (normoxic) and 4.5 mg l−1 DO (hypoxic) and assessments of cellular metabolism, prey behavior and predation mortality rates were quantified after 1 and 3 weeks. Physiologically, rockfish showed acute alterations in cellular metabolic enzyme activity after 1 week of acclimation to elevated PCO2 and hypoxia that were not evident in cabezon. Alterations in rockfish energy metabolism were driven by increases in anaerobic LDH activity, and adjustments in enzyme activity ratios of cytochrome c oxidase and citrate synthase and LDH:CS. Correlated changes in rockfish behavior were also apparent after 1 week of acclimation to elevated PCO2 and hypoxia. Exploration behavior increased in rockfish exposed to elevated PCO2 and spatial analysis of activity indicated short-term interference with anti-predator responses. Predation rate after 1 week increased with elevated PCO2; however, no mortality was observed under the multiple-stressor treatment suggesting negative effects on cabezon predators. Most noteworthy, metabolic and behavioral changes were moderately compensated after 3 weeks of acclimation, and predation mortality rates also decreased suggesting that these rockfish may be resilient to changes in environmental stressors predicted by climate models. Linking physiological and behavioral responses to multiple stressors is vital to understand impacts on populations and community dynamics.

Continue reading ‘Juvenile rockfish show resilience to CO2-acidification and hypoxia across multiple biological scales’


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Ocean acidification in the IPCC AR5 WG II

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