Posts Tagged 'communityMF'

Physiological and biochemical responses of a coralline alga and a sea urchin to climate change: Implications for herbivory

Highlights

• Algal metabolism and phenolic content were unaffected by CO2 and temperature treatments.
• CaCO3 content of algae decreased in high CO2 treatments.
• Total sugar content of algae was affected by both CO2 and temperature.
• Sea urchin respiration and feeding increased under high CO2, low temperature.
• Direct effects to sea urchin metabolism drove feeding more than algal palatability.

Abstract

Direct responses to rising temperatures and ocean acidification are increasingly well known for many single species, yet recent reviews have highlighted the need for climate change research to consider a broader range of species, how stressors may interact, and how stressors may affect species interactions. The latter point is important in the context of plant-herbivore interactions, as increasing evidence shows that increasing seawater temperature and/or acidification can alter algal traits that dictate their susceptibility to herbivores, and subsequently, community and ecosystem properties. To better understand how marine rocky shore environments will be affected by a changing ocean, in the present study we investigated the direct effects of short-term, co-occurring increased temperature and ocean acidification on a coralline alga (Jania rubens) and a sea urchin herbivore (Echinometra lucunter) and assessed the indirect effects of these factors on the algal-herbivore interaction. A 21-day mesocosm experiment was conducted with both algae and sea urchins exposed to ambient (24 °C, Low CO2), high-temperature (28 °C, Low CO2), acidified (24 °C, High CO2), or high-temperature plus acidified (28 °C, High CO2) conditions. Algal photosynthesis, respiration, and phenolic content were unaffected by increased temperature and CO2, but calcium carbonate content was reduced under high CO2 treatments in both temperatures, while total sugar content of the algae was reduced under acidified, lower temperature conditions. Metabolic rates of the sea urchin were elevated in the lower temperature, high CO2 treatment, and feeding assays showed that consumption rates also increased in this treatment. Despite some changes to algal chemical composition, it appears that at least under short-term exposure to climate change conditions, direct effects on herbivore metabolism dictated herbivory rates, while indirect effects caused by changes in algal palatability seemed to be of minor importance.

Continue reading ‘Physiological and biochemical responses of a coralline alga and a sea urchin to climate change: Implications for herbivory’

Comparative effects of seawater acidification on microalgae: Single and multispecies toxicity tests

Highlights

• Different responses were observed depending on the species.
• In this work N. gaditana was the most sensitive species to low pH.
• Effects of competence among species were observed in the multispecies control (pH 8.0).
• Effects of competence were eclipsed by the CO2 effects on cultures exposed to pH 6.0.

Abstract

In order to gain knowledge about the potential effects of acidification in aquatic ecosystems, global change research based on microalgae as sentinel species has been often developed. However, these studies are limited to single species tests and there is still a knowledge gap about the behaviour of microalgal communities under this environmental stressor. Thus, the aim of this study was to assess the negative effects of CO2 under an ecologically realistic scenario. To achieve this objective, two types of toxicity tests were developed; i) single toxicity tests and ii) multispecies toxicity tests, in order to evaluate the effects on each species as well as the interspecific competition. For this purpose, three microalgae species (Tetraselmis chuii, Phaeodactylum tricornutum and Nannochloropsis gaditana) were exposed to two selected pH levels (7.4, 6.0) and a control (pH 8.0). The pH values were choosen for testsing different scenarios of CO2 enrichment including the exchange atmosphere-ocean (pH 7.4) and natural or anthropogenic sources of CO2 (pH 6.0). The effects on growth, cell viability, oxidative stress, plus inherent cell properties (size, complexity and autofluorescence) were studied using flow cytometry (FCM). Results showed that T. chuii was the most resistant species to CO2 enrichment with less abrupt changes in terms of cell density, inherent cell properties, oxidative stress and cell viability. Although P. tricornutum was the dominant species in both single and multispecies tests, this species showed a higher decrease in cell density under pH 6.0. Effects of competence were recorded in the multispecies tests (pH 8, control) but this competence was eclipsed by the effects of low pH. The knowledge of biological interactions made by different microalgae species is a useful tool to extrapolate research data from laboratory to the field.

Continue reading ‘Comparative effects of seawater acidification on microalgae: Single and multispecies toxicity tests’

The bloom-forming macroalgae, Ulva, outcompetes the seagrass, Zostera marina, under high CO2 conditions

This study reports on experiments performed with a Northwest Atlantic species of the macroalgae, Ulva, and the seagrass, Zostera marina, grown under ambient and elevated levels of pCO2, and subjected to competition with each other. When grown individually, elevated pCO2 significantly increased growth rates and productivity of Ulva and Zostera, respectively, beyond control treatments (by threefold and 27%, respectively). For both primary producers, significant declines in tissue δ13C signatures suggested that increased growth and productivity were associated with a shift from use of HCO3 toward CO2 use. When grown under higher pCO2, Zostera experienced significant increases in leaf and rhizome carbon content as well as significant increases in leaf carbon-to-nitrogen ratios, while sediments within which high CO2 Zostera were grown had a significantly higher organic carbon content. When grown in the presence of Ulva; however, above- and below-ground productivity and tissue nitrogen content of Zostera were significantly lower, revealing an antagonistic interaction between elevated CO2 and the presence of Ulva. The presence of Zostera had no significant effect on the growth of Ulva. Collectively, this study demonstrates that while Ulva and Zostera can each individually benefit from elevated pCO2 levels, the ability of Ulva to grow more rapidly and inhibit seagrass productivity under elevated pCO2, coupled with accumulation of organic C in sediments, may offset the potential benefits for Zostera within high CO2 environments.

Continue reading ‘The bloom-forming macroalgae, Ulva, outcompetes the seagrass, Zostera marina, under high CO2 conditions’

Interactive effects of ocean acidification with other environmental drivers on marine plankton

Planktonic organisms form the base of the marine food web and may be impacted by environmental change in many ways. The interactive effects of multiple, simultaneous climate-driven changes on these organisms are not well understood. This dissertation examined the impacts of ocean acidification in combination with other environmental stressors on marine plankton and determined spatial patterns of one of these potential interactive drivers. Chapter 2 investigated the synergistic effects of ocean acidification and hypoxia on the harmful dinoflagellate Amphidinium carterae. Findings indicated that empirical studies may be crucial to accurately predict organismal responses to multi-stressors. Results also suggested that photorespiration may serve a previously unrecognized role in dinoflagellate metabolism. Chapter 3 examined the combined effects of ocean acidification and lithogenic trace metals on the growth of another harmful dinoflagellate, Cochlodinium polykrikoides. Results indicated that high suspended sediment loads may deliver toxic concentrations of trace elements to marine phytoplankton in acidified coastal ecosystems. Chapter 4 examined the interactive effects of ocean acidification and bacteria on the severity and extent of dissolution in the shells of larval gastropods and the adult pteropod Limacina helicina. Research findings indicated that microbial communities on the shell surfaces of some planktonic molluscs may mediate certain types of shell dissolution in acidified, upwelled waters. Chapter 5 explored the use of thorium isotope fluxes as a proxy for dust and lithogenic iron in the Indian Ocean. Results suggested that the gradient of dust fluxes in the region could impose thresholds for biological productivity. Together, these interdisciplinary studies demonstrate coupled biological and chemical changes in marine ecosystems as a result of increased anthropogenic environmental change.

Continue reading ‘Interactive effects of ocean acidification with other environmental drivers on marine plankton’

The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In 6 of 7 experiments, exposure to elevated pCO2 levels (~ 1,700 µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions (p < 0.05) whereas rates were significantly higher in the presence of Ulva in all experiments (p < 0.05). In many cases, the co-exposure elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification only treatment (p < 0.05). Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates (p < 0.05). Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

Continue reading ‘The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve’

Competitive interactions moderate the effects of elevated temperature and atmospheric CO2 on the health and functioning of oysters

Global increases in sea temperatures and atmospheric concentrations of CO2 may affect the health of calcifying shellfish. Little is known, however, about how competitive interactions within and between species may influence how species respond to multiple stressors. We experimentally assessed separate and combined effects of temperature (12 or 16°C) and atmospheric CO2 concentrations (400 and 1000 ppm) on the health and biological functioning of native (Ostrea edulis) and invasive (Crassostrea gigas) oysters held alone and in intraspecific or interspecific mixtures. We found evidence of reduced phagocytosis under elevated CO2 and, when combined with increased temperature, a reduction in the number of circulating haemocytes. Generally, C. gigas showed lower respiration rates relative to O. edulis when the species were in intraspecific or interspecific mixtures. In contrast, O. edulis showed a higher respiration rate relative to C. gigas when held in an interspecific mixture and exhibited lower clearance rates when held in intraspecific or interspecific mixtures. Overall, clearance rates of C. gigas were consistently greater than those of O. edulis. Collectively, our findings indicate that a species’ ability to adapt metabolic processes to environmental conditions can be modified by biotic context and may make some species (here, C. gigas) competitively superior and less vulnerable to future climatic scenarios at local scales. If these conclusions are generic, the relative role of species interactions, and other biotic parameters, in altering the outcomes of climate change will require much greater research emphasis.

Continue reading ‘Competitive interactions moderate the effects of elevated temperature and atmospheric CO2 on the health and functioning of oysters’

Divergent responses in growth and nutritional quality of coastal macroalgae to the combination of increased pCO2 and nutrients

Highlights

  • Growth rates and tissue quality of two common macroalgal species were assessed under conditions of high pCO2 and nutrient loading under monoculture and biculture.
  • Ephemeral macroalgae exhibited significant increases in growth under high pCO2 and high nutrients.
  • Growth rates of perennial macroalgae were unaffected by environmental treatments.
  • Tissue quality of both species increased via decreases in C:N when nutrients were increased.
  • Biculture appears to impact resource acquisition of perennial macroalgae as evidence of higher tissue C:N when compared to monoculture tissue.

Abstract

Coastal ecosystems are subjected to global and local environmental stressors, including increased atmospheric carbon dioxide (CO2) (and subsequent ocean acidification) and nutrient loading. Here, we tested how two common macroalgal species in the Northwest Atlantic (Ulva spp. and Fucus vesiculosus Linneaus) respond to the combination of increased CO2 and nutrient loading. We utilized two levels of pCO2 with two levels of nutrients in a full factorial design, testing the growth rates and tissue quality of Ulva and Fucus grown for 21 days in monoculture and biculture. We found that the opportunistic, fast-growing Ulva exhibited increased growth rates under high pCO2 and high nutrients, with growth rates increasing three-fold above Ulva grown in ambient pCO2 and ambient nutrients. By contrast, Fucus growth rates were not impacted by either environmental factor. Both species exhibited a decline in carbon to nitrogen ratios (C:N) with elevated nutrients, but pCO2 concentration did not alter tissue quality in either species. Species grown in biculture exhibited similar growth rates to those in monoculture conditions, but Fucus C:N increased significantly when grown with Ulva, indicating an effect of the presence of Ulva on Fucus. Our results suggest that the combination of ocean acidification and nutrients will enhance abundance of opportunistic algal species in coastal systems and will likely drive macroalgal community shifts, based on species-specific responses to future conditions.

Continue reading ‘Divergent responses in growth and nutritional quality of coastal macroalgae to the combination of increased pCO2 and nutrients’


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Ocean acidification in the IPCC AR5 WG II

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