Posts Tagged 'communityMF'

Predator populations differ in their foraging responses to acute seawater acidification

Local adaptation can cause predator populations to vary in traits and their effects on prey, but few studies have tested whether divergent predator populations respond differently to acute environmental stressors. We tested how Nucella dogwhelks from 3 populations with natural exposure to distinct environmental regimes in the California Current System altered consumption of mussel prey (Mytilus californianus) in ambient (pH 8.0, 429 µatm partial pressure of CO2 [pCO2]) and acidified (pH 7.6, 1032 µatm pCO2) seawater. Overall, experimental acidification increased the variation in consumption time observed among populations. We found reduced consumption time for the population that experienced more frequent exposure to low pH conditions in nature but not for populations with less prior exposure. Exposure to acidification also altered the individual components of consumption time—search time and handling time—depending on source population. These results indicate that impaired predator performance is not a universal response to acidification, that predation responses to acute acidification can be population specific, and that individual population responses may relate to prior exposure. Our study highlights how population-specific responses to climate change can lead to differences in ecological effects that may restructure prey communities at local scales.

Continue reading ‘Predator populations differ in their foraging responses to acute seawater acidification’

Epiphytes provide micro-scale refuge from ocean acidification

Highlights

• OA induced bleaching and reduced metabolism in non-epiphytized coralline.

• Epiphytized corallines were less susceptible to the detrimental effects of OA.

• Epiphytized corallines had thicker diffusive boundary layer than non-epiphytized.

• Non-calcifying epiphytes provide small scale refuge from OA.

• Epiphytic refugia may protect corallines under future OA conditions.

Abstract

Coralline algae, a major calcifying component of coastal shallow water communities, have been shown to be one of the more vulnerable taxonomic groups to ocean acidification (OA). Under OA, the interaction between corallines and epiphytes was previously described as both positive and negative. We hypothesized that the photosynthetic activity and the complex structure of non-calcifying epiphytic algae that grow on corallines ameliorate the chemical microenvironmental conditions around them, providing protection from OA. Using mesocosm and microsensor experiments, we showed that the widespread coralline Ellisolandia elongata is less susceptible to the detrimental effects of OA when covered with non-calcifying epiphytic algae, and its diffusive boundary layer is thicker than when not covered by epiphytes. By modifying the microenvironmental carbonate chemistry, epiphytes, facilitated by OA, create micro-scale shield (and refuge) with more basic conditions that may allow the persistence of corallines associated with them during acidified conditions. Such ecological refugia could also assist corallines under near-future anthropogenic OA conditions.

Continue reading ‘Epiphytes provide micro-scale refuge from ocean acidification’

Amelioration of ocean acidification and warming effects through physiological buffering of a macroalgae

Concurrent anthropogenic global climate change and ocean acidification are expected to have a negative impact on calcifying marine organisms. While knowledge of biological responses of organisms to oceanic stress has emerged from single‐species experiments, these do not capture ecologically relevant scenarios where the potential for multi‐organism physiological interactions is assessed. Marine algae provide an interesting case study, as their photosynthetic activity elevates pH in the surrounding microenvironment, potentially buffering more acidic conditions for associated epiphytes. We present findings that indicate increased tolerance of an important epiphytic foraminifera, Marginopora vertebralis , to the effects of increased temperature (±3°C) and p CO2 (~1,000 µatm) when associated with its common algal host, Laurencia intricata . Specimens of M. vertebralis were incubated for 15 days in flow‐through aquaria simulating current and end‐of‐century temperature and pH conditions. Physiological measures of growth (change in wet weight), calcification (measured change in total alkalinity in closed bottles), photochemical efficiency (Fv/Fm ), total chlorophyll, photosynthesis (oxygen flux), and respiration were determined. When incubated in isolation, M. vertebralis exhibited reduced growth in end‐of‐century projections of ocean acidification conditions, while calcification rates were lowest in the high‐temperature, low‐pH treatment. Interestingly, association with L. intricata ameliorated these stress effects with the growth and calcification rates of M. vertebralis being similar to those observed in ambient conditions. Total chlorophyll levels in M. vertebralis decreased when in association with L. intricata , while maximum photochemical efficiency increased in ambient conditions. Net production estimates remained similar between M. vertebralis in isolation and in association with L. intricata , although both production and respiration rates of M. vertebralis were significantly higher when associated with L. intricata . These results indicate that the association with L. intricata increases the resilience of M. vertebralis to climate change stress, providing one of the first examples of physiological buffering by a marine alga that can ameliorate the negative effects of changing ocean conditions.

Continue reading ‘Amelioration of ocean acidification and warming effects through physiological buffering of a macroalgae’

Alkaline guts contribute to immunity during exposure to acidified seawater in the sea urchin larva

Larval stages of members of the Abulacraria superphylum including echinoderms and hemichordates have highly alkaline midguts. To date, the reason for the evolution of such extreme pH conditions in the gut of these organisms remains unknown. Here, we test the hypothesis that, analogous to the acidic stomachs of vertebrates, these alkaline conditions may represent a first defensive barrier to protect from environmental pathogens. pH-optimum curves for five different species of marine bacteria demonstrated a rapid decrease in proliferation rates by 50–60% between pH 8.5 and 9.5. Using the marine bacterium Vibrio diazotrophicus, which elicits a coordinated immune response in the larvae of the sea urchin Strongylocentrotus purpuratus, we studied the physiological responses of the midgut pH regulatory machinery to this pathogen. Gastroscopic microelectrode measurements demonstrate a stimulation of midgut alkalization upon infection with V. diazotrophicus accompanied by an upregulation of acid–base transporter transcripts of the midgut. Pharmacological inhibition of midgut alkalization resulted in an increased mortality rate of larvae during Vibrio infection. Reductions in seawater pH resembling ocean acidification conditions lead to moderate reductions in midgut alkalization. However, these reductions in midgut pH do not affect the immune response or resilience of sea urchin larvae to a Vibrio infection under ocean acidification conditions. Our study addressed the evolutionary benefits of the alkaline midgut of Ambulacraria larval stages. The data indicate that alkaline conditions in the gut may serve as a first defensive barrier against environmental pathogens and that this mechanism can compensate for changes in seawater pH.

Continue reading ‘Alkaline guts contribute to immunity during exposure to acidified seawater in the sea urchin larva’

The ability of fragmented kelp forests to mitigate ocean acidification and the effects of seasonal upwelling on kelp-purple sea urchin interactions

Bull kelp (Nereocystis leutkeana) forests along the coast for northern California have decreased dramatically as a result of a ‘perfect storm’ of multiple environmental stressors. The disappearance of a predatory sea star and subsequent increase in purple sea urchins (Strongylocentrotus purpuratus) and the recurrence of marine heat waves have caused these once diverse ecosystems to be rapidly converted into relative species-depauperate urchin barrens. By examining the interactive effects of both a rapidly changing abiotic environment and the increase in urchin grazing pressure that is affecting this vital ecosystem, we can better understand its ultimate fate and make better-informed decisions to manage and protect it. As once large and persistent kelp forests are converted into fragmented landscapes of small kelp patches, kelp’s ability to take up dissolved inorganic carbon and reduce nearby acidity and increase both dissolved oxygen and bio-available calcium carbonate may be reduced, preventing it from serving as an environmental stress-free ‘oasis’ of reduced environmental stresses for local marine organisms and affecting ecosystem dynamics. In my first chapter, I examined whether small, fragmented kelp patches are able to retain their ability to alter local seawater chemistry to the same extent a large persistent kelp forests that have been studied previously. I found that in the canopies of small kelp patches, multiple parameters of carbonate chemistry fluctuated more than in the kelp benthos and in adjacent urchin barrens, consistent with metabolic activity by the kelp. Further, kelp fragments increased pH and aragonite saturation and decreased pCO2 during the day to a similar degree as large, intact kelp forests. These results suggest that small kelp patches could mitigate OA stress during the day and serve as spatial and temporal refugia for canopy-dwelling organisms. I also found that the benthic environment in kelp forests and adjacent urchin barrens is subject to unbuffered decreases in temperature, dissolved oxygen and pH. Thus, in chapter two, I assessed how current-day and future-predicted fluctuations in the duration and magnitude of these upwelling-associated stressors would impact the grazing, growth, and survivorship of purple urchins from kelp forest and urchin barren habitats. With upwelling predicted to increase in both intensity and duration with global climate change, understanding whether urchins from different habitats are differentially affected by upwelling-related stressors will give insight into how current and future stressors may be able to help ‘tip the scales’ and convert the increasing number of urchin barrens back into healthy productive kelp forests. I found condition-dependent susceptibility in urchins to increased magnitude and duration upwelling-related stressors. Grazing and gonadal development in kelp forest urchins was most negatively affected by distant future upwelling conditions, whereas in urchin barren urchins, grazing and survival were sensitive to exposure to upwelling in general, and also to increase in magnitudes of acidity, hypoxia, and temperature across both upwelling and non-upwelling events in the future. These results have important implications for population dynamics of urchins and their interactions with bull kelp, which could strongly affect ecosystem dynamics and transitions between kelp forests and urchin barrens. Taken together, the two chapters my thesis provide valuable insight into the potential resilience of bull kelp, a critical foundation species in northeastern Pacific coastal habitats, in the face of a rapidly changing multi-stressor environment.

Continue reading ‘The ability of fragmented kelp forests to mitigate ocean acidification and the effects of seasonal upwelling on kelp-purple sea urchin interactions’

External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease

Aims
Brown Ring Disease (BRD) is an infection of the Manila clam Ruditapes philippinarum due to the pathogen Vibrio tapetis . During BRD, clams are facing immunodepression and shell biomineralization alteration. In this paper, we studied the role of pH on the growth of the pathogen and formulated hypothesis on the establishment of BRD by V. tapetis .

Methods and Results
In this study, we monitored the evolution of pH during the growth of V. tapetis in a range of pH and temperatures. We also measured the pH of Manila clam hemolymph and extrapallial fluids during infection by V. tapetis . We highlighted that V. tapetis modulates the external pH during its growth, to a value of 7.70. During the development of BRD, V. tapetis also influences extrapallial fluids and hemolymph pH in vitro in the first hours of exposure and in vivo after 3 days of infection.

Conclusions
Our experiments have shown a close interaction between V. tapetis CECT4600, a pathogen of Manila clam that induces BRD, and the pH of different compartments of the animals during infection. These results indicate that that the bacterium, through a direct mechanism or as a consequence of physiological changes encountered in the animal during infection, is able to interfere with the pH of Manila clam fluids. This pH modification might promote the infection process or at least create an imbalance within the animal, that would favor its persistence. This last hypothesis should be tested in future experiment.

Significance and Impact of Study
This study is the first observation of pH modifications in the context of BRD and might orient future research on the fine mechanisms of pH modulation associated to BRD.

Continue reading ‘External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease’

High CO2 and warming affect microzooplankton food web dynamics in a Baltic Sea summer plankton community

Aquatic ecosystems face a multitude of environmental stressors, including warming and acidification. While warming is expected to have a pronounced effect on plankton communities, many components of the plankton seem fairly robust towards realistic end-of-century acidification conditions. However, interactions of the two stressors and the inclusion of further factors such as nutrient concentration and trophic interactions are expected to change this outcome. We investigated the effects of warming and high CO2 on a nutrient-deplete late summer plankton community from the Kiel Fjord, Baltic Sea, using a mesocosm setup crossing two temperatures with a gradient of CO2. Phytoplankton and microzooplankton (MZP) growth rates as well as biomass, taxonomic composition, and grazing rates of MZP were analysed. We observed effects of high CO2, warming, and their interactions on all measured parameters. The occurrence and direction of the effects were dependent on the phytoplankton or MZP community composition. In addition, the abundance of small-sized phytoplankton was identified as one of the most important factors in shaping the MZP community composition. Overall, our results indicate that an estuarine MZP community used to strong natural fluctuations in CO2 can still be affected by a moderate increase in CO2 if it occurs in combination with warming and during a nutrient-deplete post-bloom situation. This highlights the importance of including trophic interactions and seasonality aspects when assessing climate change effects on marine zooplankton communities.

Continue reading ‘High CO2 and warming affect microzooplankton food web dynamics in a Baltic Sea summer plankton community’

Model simulation of seasonal growth of Fucus vesiculosus in its benthic community

Numerical models are a suitable tool to quantify impacts of predicted climate change on complex ecosystems but are rarely used to study effects on benthic macroalgal communities. Fucus vesiculosus L. is a habitat‐forming macroalga in the Baltic Sea and alarming shifts from the perennial Fucus community to annual filamentous algae are reported. We developed a box model able to simulate the seasonal growth of the Baltic Fucus–grazer–epiphyte system. This required the implementation of two state variables for Fucus biomass in units of carbon (C) and nitrogen (N). Model equations describe relevant physiological and ecological processes, such as storage of C and N assimilates by Fucus, shading effects of epiphytes or grazing by herbivores on both Fucus and epiphytes, but with species‐specific rates and preferences. Parametrizations of the model equations and required initial conditions were based on measured parameters and process rates in the near‐natural Kiel Outdoor Benthocosm (KOB) experiments during the Biological Impacts of Ocean Acidification project. To validate the model, we compared simulation results with observations in the KOB experiment that lasted from April 2013 until March 2014 under ambient and climate‐change scenarios, that is, increased atmospheric temperature and partial pressure of carbon dioxide. The model reproduced the magnitude and seasonal cycles of Fucus growth and other processes in the KOBs over 1 yr under different scenarios. Now having established the Fucus model, it will be possible to better highlight the actual threat of climate change to the Fucus community in the shallow nearshore waters of the Baltic Sea.

Continue reading ‘Model simulation of seasonal growth of Fucus vesiculosus in its benthic community’

Cascading effects of climate change on plankton community structure

Plankton communities account for at least half of global primary production and play a key role in the global carbon cycle. Warming and acidification may alter the interaction chains in these communities from the bottom and top of the food web. Yet, the relative importance of these potentially complex interactions has not yet been quantified. Here, we examine the isolated and combined effects of warming, acidification, and reductions in phytoplankton and predator abundances in a series of factorial experiments. We find that warming directly impacts the top of the food web, but that the intermediate trophic groups are more strongly influenced by indirect effects mediated by altered top-down interactions. Direct manipulations of predator and phytoplankton abundance reveal similar strong top-down interactions following top predator decline. A meta-analysis of published experiments further supports the conclusion that warming has stronger direct impacts on the top and bottom of the food web rather than the intermediate trophic groups, with important differences between freshwater and marine plankton communities. Our results reveal that the trophic effect of warming cascading down from the top of the plankton food web is a powerful agent of global change.

Continue reading ‘Cascading effects of climate change on plankton community structure’

Symbiont community diversity is more variable in corals that respond poorly to stress

Coral reefs are declining globally as climate change and local water quality press environmental conditions beyond the physiological tolerances of holobionts—the collective of the host and its microbial symbionts. To assess the relationship between symbiont composition and holobiont stress tolerance, community diversity metrics were quantified for dinoflagellate endosymbionts (Family: Symbiodiniaceae) from eight Acropora millepora genets that thrived under or responded poorly to various stressors. These eight selected genets represent the upper and lower tails of the response distribution of 40 coral genets that were exposed to four stress treatments (and control conditions) in a 10‐day experiment. Specifically, four ‘best performer’ coral genets were analyzed at the end of the experiment because they survived high temperature, high pCO2, bacterial exposure, or combined stressors, whereas four ‘worst performer’ genets were characterized because they experienced substantial mortality under these stressors. At the end of the experiment, seven of eight coral genets mainly hosted Cladocopium symbionts, whereas the eighth genet was dominated by both Cladocopium and Durusdinium symbionts. Symbiodiniaceae alpha and beta diversity were higher in worst performing genets than in best performing genets. Symbiont communities in worst performers also differed more after stress exposure relative to their controls (based on normalized proportional differences in beta diversity), than did best performers. A generalized joint attribute model estimated the influence of host genet and treatment on Symbiodiniaceae community composition and identified strong associations among particular symbionts and host genet performance, as well as weaker associations with treatment. Although dominant symbiont physiology and function contribute to host performance, these findings emphasize the importance of symbiont community diversity and stochasticity as components of host performance. Our findings also suggest that symbiont community diversity metrics may function as indicators of resilience and have potential applications in diverse disciplines from climate change adaptation to agriculture and medicine.

Continue reading ‘Symbiont community diversity is more variable in corals that respond poorly to stress’


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Ocean acidification in the IPCC AR5 WG II

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