Posts Tagged 'growth'

Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore Emiliania huxleyi under future ocean climate change conditions

Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on growth rate, particulate organic (POC) and inorganic (PIC) carbon quotas of the cosmopolitan coccolithophore Emiliania huxleyi. Population growth rate increased with increasing temperature (16 to 20 °C) and light intensities (60 to 240 μmol photons m−2  s−1), but decreased with elevated pCO2 concentrations (370 to 960 μatm) and reduced availability of nitrate (24.3 to 7.8 μmol L−1) and phosphate (1.5 to 0.5 μmol L−1). POC quotas were predominantly enhanced by combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected growth, photosynthetic carbon fixation and calcification of E. huxleyi, and imply that plastic responses to progressive ocean acidification, warming and decreasing availability of nitrate and phosphate reduce population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

Continue reading ‘Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore Emiliania huxleyi under future ocean climate change conditions’

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’

Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa

Global warming and ocean acidification influence marine calcifying organisms, particularly those with external shells. Among these, mussels may compensate for environmental changes by phenotypic plasticity, but this may entail trade-offs between shell deposition, growth and reproduction. We assessed main and interactive effects of pH and temperature on four mussel species on the west coast of South Africa (33°48′ S, 18°27′ E) in October 2012 by comparing shell dissolution, shell growth, shell breaking force and condition index of two native species, the ribbed mussel Aulacomya atra and the black mussel Choromytilus meridionalis, and two aliens, the Mediterranean mussel Mytilus galloprovincialis and the bisexual mussel Semimytilus algosus. Live mussels and dead shells were exposed for 42 days to seawater of pH 7.5 or 8.0, at 14 °C or 20 °C. Low pH, high temperature and their combination increased shell dissolution of the two aliens but their growth rates and condition indices remained unchanged. Aulacomya atra also experienced greater shell dissolution at a low pH and high temperature, but grew faster in low-pH treatments. For C. meridionalis, shell dissolution was unaffected by pH or temperature; it also grew faster in low-pH treatments, but had a lower condition index in the higher temperature treatment. Shell strength was not determined by thickness alone. In most respects, all four species proved to be robust to short-term reduction of pH and elevation of temperature, but the native species compensated for greater shell dissolution at low pH by increasing growth rate, whereas the aliens did not, so their invasive success cannot be ascribed to benefits accruing from climate change.

Continue reading ‘Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa’

Unique genomic and phenotypic responses to extreme and variable pH conditions in purple urchin larvae

Environmental variation experienced by a species across space and time can promote the maintenance of genetic diversity that may be adaptive in future global change conditions. Selection experiments have shown that purple sea urchin, Strongylocentrotus purpuratus, populations have adaptive genetic variation for surviving pH conditions at the “edge” (pH 7.5) of conditions experienced in nature. However, little is known about whether populations have genetic variation for surviving low-pH events beyond those currently experienced in nature or how variation in pH conditions affects organismal and genetic responses. Here, we quantified survival, growth, and allele frequency shifts in experimentally selected developing purple sea urchin larvae in static and variable conditions at three pH levels: pH 8.1 (control), pH 7.5 (edge-of-range), and pH 7.0 (extreme). Variable treatments recovered body size relative to static treatments, but resulted in higher mortality, suggesting a potential tradeoff between survival and growth under pH stress. However, within each pH level, allele frequency changes were overlapping between static and variable conditions, suggesting a shared genetic basis underlying survival to mean pH regardless of variability. In contrast, genetic responses to pH 7.5 (edge) versus pH 7.0 (extreme) conditions were distinct, indicating a unique genetic basis of survival. In addition, loci under selection were more likely to be in exonic regions than regulatory, indicating that selection targeted protein-coding variation. Loci under selection in variable pH 7.5 conditions, more similar to conditions periodically experienced in nature, performed functions related to lipid biosynthesis and metabolism, while loci under selection in static pH 7.0 conditions performed functions related to transmembrane and mitochondrial processes. While these results are promising in that purple sea urchin populations possess genetic variation for surviving extreme pH conditions not currently experienced in nature, they caution that increased acidification does not result in a linear response but elicits unique physiological stresses and survival mechanisms.

Continue reading ‘Unique genomic and phenotypic responses to extreme and variable pH conditions in purple urchin larvae’

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’

Responses of oysters to a changing climate in southeast Australia

Securing economically and ecologically significant oyster species, as our oceans warm and acidify from climate change, is a priority. Native oysters along the southeast coast of Australia will be particularly vulnerable to ocean change due the strengthening of the East Australian Current. Oysters form complex aggregations and reef structures which provide ecosystem services and habitat for several species in coastal and estuarine areas. The Sydney rock oyster Saccostrea glomerata and flat oyster Ostrea angasi are two native species with overlapping distribution in the state of New South Wales (NSW). Currently, both species are commercially cultivated and restoration projects are in progress in southern states. The overall aim of this thesis was to determine the impact of climate change stressors (warming and acidification) on these species to support their persistence and oyster reef restoration as anthropogenic actions modify our oceans. To detect effects of stressors in the capacity of energy gain through feeding, a laboratory experiment was done to evaluate responses of S. glomerata. Oysters responded to stressors by increasing standard metabolic rates (SMR), clearance, ingestion and absorption rates. Such responses suggest that climate change will alter feeding and metabolism of S. glomerata. To predict species responses to changing climate, experiments need to approximate conditions relevant to the region and species natural habitat. It was also investigated the impact of elevated temperature and pCO2 on O. angasi using outdoor flow through mesocosms in Sydney Harbour, NSW. Elevated temperature caused high mortality and decreased the condition of oysters. Elevated pCO2 increased SMR almost four-fold and lowered the extracellular pH. Based on these responses, Ostrea angasi will be living near the limits of its thermal tolerance as climate change worsen by 2050. The potential pathways oysters will use to cope and acclimate to climate change may “climate proof” aquaculture species and ensure reef restoration efforts. An experimental study was done where both species, O. angasi and S. glomerata, were given a mild dose of thermal stress in the laboratory (“stress inoculation”) and then transferred and exposed to warm seawater at Lake Macquarie, NSW for seven months. Shell growth, condition index, lipid content and survival of O. angasi and condition of S. glomerata were all significantly reduced by warming. Overall, in this thesis, S. glomerata were more resilient in their response to elevated pCO2 and temperature. Ostrea angasi had the greatest vulnerability to warming, which may be ameliorated by elevated pCO2. If we are to secure the great benefits oysters bring to coastal ecosystems, we need realistic experiments to predict their responses to climate change stressors. This thesis findings reinforce that project managers need to consider the current and future climate change in sustaining oyster reef restoration.

Continue reading ‘Responses of oysters to a changing climate in southeast Australia’

Transgenerational plasticity and acclimation of tropical sea urchins to ocean warming and acidification

Anthropogenic CO2 emissions are causing the oceans to simultaneously warm and become increasingly acidic, with rates of change that are putting evolutionary pressure on many marine organisms. As a result, both short-term responses and the ability of organisms to acclimate to rapid environmental change through phenotypic plasticity are expected to play a considerable role in persistence of many species under future ocean change. Evidence is accumulating that non-genetic inheritance and transgenerational plasticity (TGP) may be important mechanisms which may facilitate acclimation to ocean warming and acidification. This thesis tests the overarching hypothesis that TGP and parental acclimation to predicted ocean warming and acidification conditions promote greater resilience in offspring using two tropical sea urchins, Tripneustes gratilla and Echinometra sp. A, as model organisms.

Continue reading ‘Transgenerational plasticity and acclimation of tropical sea urchins to ocean warming and acidification’

The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii) (update)

The high-latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50 S in the Southern Ocean and north of 40 N in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) found at these high latitudes, which dominate the biogenic sediments recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We apply it for the first time to evaluate the relationship between seawater pH, δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured across a range of carbon dioxide partial pressure (pCO2) and pH values. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejía et al., 2013). δ11B shows a relatively well defined negative trend with increasing pH, completely distinct from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high-latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.

Continue reading ‘The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii) (update)’


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