Posts Tagged 'algae'

Plasticity of adult coralline algae to prolonged increased temperature and pCO2 exposure but reduced survival in their first generation

Crustose coralline algae (CCA) are vital to coral reefs worldwide, providing structural integrity and inducing the settlement of important invertebrate larvae. CCA are known to be impacted by changes in their environment, both during early development and adulthood. However, long-term studies on either life history stage are lacking in the literature, therefore not allowing time to explore the acclimatory or potential adaptive responses of CCA to future global change scenarios. Here, we exposed a widely distributed, slow growing, species of CCA, Sporolithon cf. durum, to elevated temperature and pCO2 for five months and their first set of offspring (F1) for eleven weeks. Survival, reproductive output, and metabolic rate were measured in adult S. cf. durum, and survival and growth were measured in the F1 generation. Adult S. cf. durum experienced 0% mortality across treatments and reduced their O2 production after five months exposure to global stressors, indicating a possible expression of plasticity. In contrast, the combined stressors of elevated temperature and pCO2 resulted in 50% higher mortality and 61% lower growth on germlings. On the other hand, under the independent elevated pCO2 treatment, germling growth was higher than all other treatments. These results show the robustness and plasticity of S. cf. durum adults, indicating the potential for them to acclimate to increased temperature and pCO2. However, the germlings of this species are highly sensitive to global stressors and this could negatively impact this species in future oceans, and ultimately the structure and stability of coral reefs.

Continue reading ‘Plasticity of adult coralline algae to prolonged increased temperature and pCO2 exposure but reduced survival in their first generation’

Acclimation history modulates effect size of calcareous algae (Halimeda opuntia) to herbicide exposure under future climate scenarios

Highlights

•Calcifying algae were exposed to herbicide and future climate scenarios combined.

•Half of the algae were given long acclimation to future climate-change conditions.

•Experimental effects were exaggerated for algae that were not acclimated.

•Still, herbicide effects on acclimated algae stronger in future climate conditions

•Results show the need of climate-adjusted thresholds for water quality guidelines.

Abstract

Tropical marine habitat-builders such as calcifying green algae can be susceptible to climate change (warming and acidification). This study evaluated the cumulative effects of ocean warming (OW), ocean acidification (OA) and the herbicide diuron on the calcifying green algae Halimeda opuntia. We also assessed the influence of acclimation history to experimental climate change conditions on physiological responses. H. opuntia were exposed for 15 days to orthogonal combinations of three climate scenarios [ambient (28 °C, pCO2 = 378 ppm), 2050 (29 °C, pCO2 = 567 ppm) and 2100 (30 °C, pCO2 = 721 ppm)] and to six diuron concentrations (up to 29 μg L−1). Half of the H. opuntia had been acclimated for eight months to the climate scenarios in a mesocosm approach, while the remaining half were not pre-acclimated, as is current practice in most experiments. Climate effects on quantum yield (ΔF/Fm′), photosynthesis and calcification in future climate scenarios were significantly stronger (by −24, −46 and +26%, respectively) in non-acclimated algae, suggesting experimental bias may exaggerate effects in organisms not appropriately acclimated to future-climate conditions. Thus, full analysis was done on acclimated plants only. Interactive effects of future climate scenarios and diuron were observed for ΔF/Fm′, while the detrimental effects of climate and diuron on net photosynthesis and total antioxidant capacity (TAC) were additive. Calcification-related enzymes were negatively affected only by diuron, with inhibition of Ca-ATPase and upregulation of carbonic anhydrase. The combined and consistent physiological and biochemical evidence of negative impacts (across six indicators) of both herbicide and future-climate conditions on the health of H. opuntia highlights the need to address both climate change and water quality. Guideline values for contaminants may also need to be lowered considering ‘climate adjusted thresholds’. Importantly, this study highlights the value of applying substantial future climate acclimation periods in experimental studies to avoid exaggerated organism responses to OW and OA.

Continue reading ‘Acclimation history modulates effect size of calcareous algae (Halimeda opuntia) to herbicide exposure under future climate scenarios’

The influence of plastic pollution and ocean change on detrital decomposition

Highlights

•The combined effects of plastic pollution, ocean warming, and acidification on macrophyte decomposition were tested.

•High quantities of plastic slowed the decomposition of seagrass and kelp.

•Ocean warming increased the decomposition rates of seagrass and kelp.

•Ocean acidification did not significantly influence macrophyte decomposition.

•Reducing plastic pollution and CO2 emissions is likely the best approach for preserving detritus-based ecosystem processes.

Abstract

Plastic pollution and ocean change have mostly been assessed separately, missing potential interactions that either enhance or reduce future impacts on ecosystem processes. Here, we used manipulative experiments with outdoor mesocosms to test hypotheses about the interactive effects of plastic pollution, ocean warming and acidification on macrophyte detrital decomposition. These experiments focused on detritus from kelp, Ecklonia radiata, and eelgrass, Zostera muelleri, and included crossed treatments of (i) no, low and high plastic pollution, (ii) current/future ocean temperatures, and (iii) ambient/future ocean partial pressure of carbon dioxide (pCO2). High levels of plastic pollution significantly reduced the decomposition rate of kelp and eelgrass by approximately 27% and 36% in comparison to controls respectively. Plastic pollution also significantly slowed the nitrogen liberation from seagrass and kelp detritus. Higher seawater temperatures significantly increased the decomposition rate of kelp and eelgrass by 12% and 5% over current conditions, respectively. Higher seawater temperatures were also found to reduce the nitrogen liberation in eelgrass. In contrast, ocean acidification did not significantly influence the rate of macrophyte decomposition or nutrient liberation. Overall, our results show how detrital processes might respond to increasing plastic pollution and ocean temperatures, which has implications for detrital-driven secondary productivity, nutrient dynamics and carbon cycling.

Continue reading ‘The influence of plastic pollution and ocean change on detrital decomposition’

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’

Ocean acidification induces carry-over effects on the larval settlement of the New Zealand abalone, Haliotis iris

Larval settlement is a key process in the lifecycle of benthic marine organisms; however, little is known on how it could change in reduced seawater pH and carbonate saturation states under future ocean acidification (OA). This is important, as settlement ensures species occur in optimal environments and, for commercially important species such as abalone, reduced settlement could decrease future population success. We investigated how OA could affect settlement success in the New Zealand abalone Haliotis iris by examining: (1) direct effects of seawater at ambient (pHT 8.05) and reduced pHT (7.65) at the time of settlement, (2) indirect effects of settlement substrates (crustose coralline algae, CCA) preconditioned at ambient and reduced pHT for 171 days, and (3) carry-over effects, by examining settlement in larvae reared to competency at ambient and reduced pHT (7.80). We found no effects of seawater pH or CCA incubation on larval settlement success. OA-induced carry-over effects were evident, with lower settlement in larvae reared at reduced pH. Understanding the mechanisms behind these responses is key to fully comprehend the extent to which OA will affect marine organisms and the industries that rely on them.

Continue reading ‘Ocean acidification induces carry-over effects on the larval settlement of the New Zealand abalone, Haliotis iris’

Spatial risk assessment of global change impacts on Swedish seagrass ecosystems

Improved knowledge on the risk in ecologically important habitats on a regional scale from multiple stressors is critical for managing functioning and resilient ecosystems. This risk assessment aimed to identify seagrass ecosystems in southern Sweden that will be exposed to a high degree of change from multiple global change stressors in mid- and end-of-century climate change conditions. Risk scores were calculated from the expected overlap of three stressors: sea surface temperature increases, ocean acidification and wind driven turbid conditions. Three high-risk regions were identified as areas likely to be exposed to a particularly high level of pressure from the global stressors by the end of the century. In these areas it can be expected that there will be a large degree of stressor change from the current conditions. Given the ecological importance of seagrass meadows for maintaining high biodiversity and a range of other ecosystem services, these risk zones should be given high priority for incorporation into management strategies, which can attempt to reduce controllable stressors in order to mitigate the consequences of some of the impending pressures and manage for maintained ecosystem resilience.

Continue reading ‘Spatial risk assessment of global change impacts on Swedish seagrass ecosystems’

Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata

Ulva fenestrata is an economically and ecologically important green algal species with a large potential in seaweed aquaculture due to its high productivity, wide environmental tolerance, as well as interesting functional and nutritional properties. Here, we performed a series of manipulative cultivation experiments in order to investigate the effects of irradiance (50, 100, and 160 μmol photons m−2 s−1), temperature (13 and 18 °C), nitrate (< 5, 150, and 500 μM), phosphate (< 1 and 50 μM), and pCO2 (200, 400, and 2500 ppm) on the relative growth rate and biochemical composition (fatty acid, protein, phenolic, ash, and biochar content) in indoor tank cultivation of Swedish U. fenestrata. High irradiance and low temperature were optimal for the growth of this northern hemisphere U. fenestrata strain, but addition of nutrients or changes in pCO2 levels were not necessary to increase growth. Low irradiance resulted in the highest fatty acid, protein, and phenolic content, while low temperature had a negative effect on the fatty acid content but a positive effect on the protein content. Addition of nutrients (especially nitrate) increased the fatty acid, protein, and phenolic content. High nitrate levels decreased the total ash content of the seaweeds. The char content of the seaweeds did not change in response to any of the manipulated factors, and the only significant effect of changes in pCO2 was a negative relationship with phenolic content. We conclude that the optimal cultivation conditions for Swedish U. fenestrata are dependent on the desired biomass traits (biomass yield or biochemical composition).

Continue reading ‘Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata’

Impacts of ocean acidification on intertidal macroalgae and algivore preference

Ocean acidification, a facet of global climate change, has the potential to induce changes in marine macroalgae that modify their existing interactions with algivorous invertebrates. In this study, I examined the effects of elevated carbon dioxide (pCO2) on several species of intertidal macroalgae (Phaeophyta, Rhodophyta) and evaluated the present-day and predicted future preferences of algivores (Pugettia producta and Tegula funebralis) by assessing grazing rates on untreated algal tissue and on algae exposed to high-pCO2 seawater. Both red and brown algae grew faster in elevated pCO2 than in ambient seawater, and algae in intermediate pCO2 generated more new growth overall than those in highly elevated pCO2. The effect of pCO2 on the carbon and nitrogen contents of algae depended on species identity, and C:N ratios decreased slightly with increasing pCO2 for four of the five species studied. Total phenolic content in each alga was unaffected by pCO2 treatment, although similar (distinct) levels between untreated species became distinct (similar) when those same species were compared after highpCO2 treatment. Algivores demonstrated contrasting responses to changes in their food sources; P. producta, a specialist crab grazer, did not modify its preference for the brown alga Egregia menziesii when offered high-pCO2 treated individuals, but the generalist snail T. funebralis adjusted its feeding behavior to choose algae with low phenolic contents, which created different patterns of preference for untreated and pCO2-treated algae. C:N ratios of algae did not appear to be a strong driver of preference for either grazer in feeding experiments. These results indicate that algae may be well-equipped to benefit from moderate increases in seawater pCO2, but they exhibit species-specific rates of growth and phenolic production, which in turn affect their appeal to a generalist algivore. Intertidal algal communities will therefore face altered patterns of predation under future ocean acidification conditions as generalist algivores adjust to new variation in algal palatability.

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Global warming offsets the ecophysiological stress of ocean acidification on temperate crustose coralline algae

Highlights

•The ecological risk of climate change on temperate CCA has been assessed by mesocosm.

•Future change in carbonate chemistry has led to ecophysiological change of CCA.

•Oxygenic photosynthesis and growth decreased under acidified seawater.

•Negative metabolic changes in ocean acidification were offset by elevated temperature.

Abstract

Dramatic increases in the release of anthropogenic CO2 and global temperatures have resulted in alterations to seawater carbonate chemistry and metabolisms of marine organisms. There has been recent interest in the effects of these stressors on crustose coralline algae (CCA) because photosynthesis and calcification are influenced by all components of carbonate chemistry. To examine this, a mesocosm experiment was conducted to evaluate photosynthesis, calcification and growth in the temperate CCA Chamberlainium sp. under acidification (doubled CO2), warming (+5 °C), and greenhouse (doubled CO2 and +5 °C) conditions compared to present-day conditions. After 47 days of acclimation to these conditions, productivity was lowest under acidification, although photochemical properties were improved, while respiration was highest under warming. Likewise, growth was lowest under acidification, but this negative response was offset by elevated temperature under greenhouse. Together, these results suggest that warming offsets the negative effects of acidification by creating more suitable conditions for photosynthesis and growth.

Continue reading ‘Global warming offsets the ecophysiological stress of ocean acidification on temperate crustose coralline algae’

How does the sexual reproduction of marine life respond to ocean acidification?

Recent research indicates that synchronicity of sexual reproduction in coral spawning events is breaking down, leading to aging populations and decreased recruitment success. In this perspective, we develop a hypothesis that this phenomenon could be caused by ongoing ocean acidification (OA). We hypothesize, that the underlying physiological machinery could be the carbon concentrating mechanism (CCM). The endosymbiotic zooxanthellae of corals could use this mechanism to sense calm water motion states in a comparable way to that known from macroalgae. In macroalgae, it is well-established that dissolved inorganic carbon (DIC) acts as the trigger for signaling low water motion. Hence, evolutionarily developed signals of low water motion, suited for gamete-release, may be misleading in the future, potentially favoring opportunistic species in a broad range of marine organisms.

Continue reading ‘How does the sexual reproduction of marine life respond to ocean acidification?’

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Ocean acidification in the IPCC AR5 WG II

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