Archive for April, 2016

Antarctic crustacean grazer assemblages exhibit resistance following exposure to decreased pH

Anthropogenic atmospheric CO2 concentrations are increasing rapidly, resulting in declining seawater pH (ocean acidification). The majority of ocean acidification research to date has focused on the effects of decreased pH in single-species experiments. To assess how decreased pH may influence natural macroalgal-grazer assemblages, we conducted a mesocosm experiment with the common, chemically defended Antarctic brown macroalga Desmarestia menziesii and natural densities of its associated grazer assemblage, predominantly amphipods. Grazer assemblages were collected from the immediate vicinity of Palmer Station (64°46′S, 64°03′W) in March 2013. Assemblages were exposed for 30 days to three levels of pH representing present-day mean summer ambient conditions (pH 8.0), predicted near-future conditions (2100, pH 7.7), and distant-future conditions (pH 7.3). A significant difference was observed in the composition of mesograzer assemblages in the lowest pH treatment (pH 7.3). The differences between assemblages exposed to pH 7.3 and those maintained in the other two treatments were driven primarily by decreases in the abundance of the amphipod Metaleptamphopus pectinatus with decreasing pH, reduced copepod abundance at pH 7.7, and elevated ostracod abundance at pH 7.7. Generally, the assemblages maintained at pH 7.7 were not significantly different from those at ambient pH, demonstrating resistance to short-term decreased pH. The relatively high prevalence of generalist amphipods may have contributed to a net stabilizing effect on the assemblages exposed to decreased pH. Overall, our results suggest that crustacean grazer assemblages associated with D. menziesii, the dominant brown macroalgal species of the western Antarctic Peninsula, may be resistant to short-term near-future decreases in seawater pH.

Continue reading ‘Antarctic crustacean grazer assemblages exhibit resistance following exposure to decreased pH’

Long-term effects of altered pH and temperature on the feeding energetics of the Antarctic sea urchin, Sterechinus neumayeri

This study investigated the effects of long-term incubation to near-future combined warming (+2 °C) and ocean acidification (−0.3 and −0.5 pH units) stressors, relative to current conditions (−0.3 °C and pH 8.0), on the energetics of food processing in the Antarctic sea urchin, Sterechinus neumayeri. After an extended incubation of 40 months, energy absorbed, energy lost through respiration and lost as waste were monitored through two feeding cycles. Growth parameters (mass of somatic and gonad tissues and the CHN content of gonad) were also measured. There were no significant effects of combined ocean acidification (OA) and temperature stressors on the growth of somatic or reproductive tissue. Despite more food being consumed in the low temperature control, once food processing and maintenance costs were subtracted, there were no significant effects of treatment on the scope for growth. The biggest significant differences were between amounts of food consumed during the two feeding cycles. More food was consumed by the low temperature (0 °C) control animals, indicating a potential effect of the changed conditions on digestive efficiency. Also, in November, more food was consumed, with a higher absorption efficiency, which resulted in a higher scope for growth in November than September and may reflect increased energetic needs associated with a switch to summer physiology. The effect of endogenous seasonal cycles and environmental variability on organism capacity is discussed.

Continue reading ‘Long-term effects of altered pH and temperature on the feeding energetics of the Antarctic sea urchin, Sterechinus neumayeri’

Warming and acidification-mediated resilience to bacterial infection determine mortality of early Ostrea edulis life stages

The combined effects of temperature and seawater acidification were investigated across larval stages of the European flat oyster Ostrea edulis, from veliger sizes released by gravid individuals to spat. Simultaneous experiments were also conducted to investigate the potential effects of reduced pH levels on bacterial growth that could provide a more comprehensive understanding of the effects of seawater acidification on larval mortality. Larvae (veliger, umbonate, and pediveliger) and spat were exposed to 4 temperatures (18, 22, 26, and 30°C) and 4 pH treatments (7.83-7.92 [ambient], low-reduced, medium-reduced, and high-reduced), and the 4 pH treatments were also used in bacterial experiments. Results showed increased larval mortalities at 30°C (by ca. 49 and 44% in veliger and umbonate stages, respectively), although there was also a bottleneck in pediveligers from 22 to 30°C and no effects on spat. In contrast, the survival of veligers increased with pH reductions by ca. 26%, and was marginally increased in pediveligers despite high mortality at this stage. No shell malformations were observed at any larval stage or in spat, and growth patterns tended to mirror those of survival. This coincided with lower bacterial growth, particularly of Vibrio spp., in the 2 lowest pH treatments, suggesting that seawater acidification may help to prevent bacterial pathogenicity in O. edulis larvae. Compared to available information on the vulnerability of other commercial bivalves to ocean acidification, our results suggest that O. edulis could be a more resilient species; however, further research is needed to investigate the potential effects on gravid females and sperm.

Continue reading ‘Warming and acidification-mediated resilience to bacterial infection determine mortality of early Ostrea edulis life stages’

The sensitivity of the early benthic juvenile stage of the European lobster Homarus gammarus (L.) to elevated pCO2 and temperature

The early benthic juvenile stage of many marine invertebrates is a key step in the transition from the planktonic larval stages to the benthic adult stage. It is characterised by high mortality, in part, due to sensitivities to abiotic factors. The impacts of elevated pCO2 and temperature on the physiology and life history of these sensitive life stages are, however, poorly understood. Consequently, the aim of the present study was to investigate the vulnerability of survival, growth, metabolic rate, feeding rate, organic content, and carapace mineralisation of the early benthic juvenile stage of the European lobster Homarus gammarus (L.) to predicted levels of elevated pCO2 [ocean acidification (OA) and carbon capture and storage (CCS) scenarios] and elevated temperature [ocean warming (OW)]. Early benthic juvenile H. gammarus exhibited increased mortality under both OA and CCS conditions at both experimental temperatures, and these mortalities were due to moult death syndrome. There were OA-related reductions in metabolism, food acquisition, and carapace mineral content, while CCS-exposed lobsters exhibited severe shell dissolution. We suggest that disruption of metabolic and calcium homoeostasis is associated with, and possible the cause of, the increased incidence of moult-related mortalities in juvenile lobsters. We conclude that early benthic juvenile lobsters are sensitive, in terms of physiology and life history traits, to both OA and CCS, with OW sometimes mitigating and at other times increasing sensitivities.

Continue reading ‘The sensitivity of the early benthic juvenile stage of the European lobster Homarus gammarus (L.) to elevated pCO2 and temperature’

Lecture: “Climate change and its evil twin, ocean acidification”, Saint Joseph’s College, 26 April 2016

Date & time: 26 April 2016, 4-6 p.m.

Location: Viola George Auditorium, St Joseph’s College, 278 Whites Bridge Road, Standish, ME 04084

Dr. Paul Andrew Mayewski, PhD, director and professor of the Climate Change Institute, and Dr. Mark Green, PhD, professor of natural sciences at Saint Joseph’s College, present “Climate change and its evil twin, ocean acidification”. The two expert professors will discuss the importance of climate change and its implications on Maine’s marine ecosystem—and beyond. Each will present on their area of specialty, after which the floor will be open for questions and discussion.

This public event is free to attend. Light refreshments will be served. For more information, contact Jean Maginnis, senior director of Development, at jmaginnis(at) or 207-730-0694.

Further information.

Dan Haifley, Our Ocean Backyard: fight against acidification includes curbing organic pollution

A group of scientists convened by west coast state governments unveiled a plan earlier this month that proposes a series of initiatives to combat the effects of the changing chemistry of west coast waters. One of those proposals is an effort to further curb the amount of land-based organic pollution that flows to the sea.

Last August, I wrote about the underwater river that crosses the Pacific’s intermediate depths for a period of 20 to 50 years, bringing nutrient-laden water to the west coast. Having picked up organic material along the way, what arrives is lower in oxygen content than when its journey began north of Japan, with the potential to change the matrix of marine life over a period of time.

Scientists are now looking at the threat posed from the opposite direction — from land. The California Ocean Protection Council and the Ocean Science Trust have identified lower oxygen levels, known as hypoxia, and ocean acidification as priorities for research and action. Ocean acidification, evidenced by a minute lowering of the pH level of ocean waters, is a result of the absorption of excess carbon from the atmosphere.

Continue reading ‘Dan Haifley, Our Ocean Backyard: fight against acidification includes curbing organic pollution’

Combined effects of short-term exposure to elevated CO2 and decreased O2 on the physiology and energy budget of the thick shell mussel Mytilus coruscus

Hypoxia and ocean acidification are two consequences of anthropogenic activities. These global trends occur on top of natural variability. In environments such as estuarine areas, short-term acute pH and O2 fluctuations are occurring simultaneously. The present study tested the combined effects of short-term seawater acidification and hypoxia on the physiology and energy budget of the thick shell mussel Mytilus coruscus. Mussels were exposed for 72 h to six combined treatments with three pH levels (8.1, 7.7 and 7.3) and two dissolved oxygen (DO) levels (2 mg L−1, 6 mg L−1). Clearance rate (CR), food absorption efficiency (AE), respiration rate (RR), ammonium excretion rate (ER), O:N ratio and scope for growth (SFG) were significantly reduced, and faecal organic dry weight ratio (E) was significantly increased at low DO. Low pH did not lead to a reduced SFG. Interactive effects of pH and DO were observed for CR, E and RR. Principal component analysis (PCA) revealed positive relationships among most physiological indicators, especially between SFG and CR under normal DO conditions. These results demonstrate that Mytilus coruscus was sensitive to short-term (72 h) exposure to decreased O2 especially if combined with decreased pH levels. In conclusion, the short-term oxygen and pH variation significantly induced physiological changes of mussels with some interactive effects.

Continue reading ‘Combined effects of short-term exposure to elevated CO2 and decreased O2 on the physiology and energy budget of the thick shell mussel Mytilus coruscus’

Environmental factors influencing phytoplankton productivity in the context of climate change

Anthropogenic activities are increasing CO2 in the atmosphere and in the ocean, raising global temperatures and lowering the oceanic pH. Since phytoplankton perform nearly half of the global carbon fixation via photosynthesis, and control the biological sequestration of CO2 in the ocean, their response to increasing CO2/decreasing pH is a key to the effect of “ocean acidification” on marine ecosystems. Previous work on this question has shown contradictory results, possibly as a consequence of separate and opposite effects of environmental parameters on photosynthesis and respiration. The primary goal of this thesis was therefore to disentangle these effects, and determine how they translate into changes in productivity. To do so, I conducted a combination of laboratory experiments with model organisms, and field research on natural phytoplankton communities.

Effects of pH and pCO2 changes on photosynthesis and respiration were investigated with the diatom Thalassiosira weissflogii, using H218O as a tracer. The effects at saturating light were examined in long term incubations (several hours) using an isotope ratio mass spectrometer. To expand the matrix of conditions, short term experiments were also performed, under different light intensities, with a membrane inlet mass spectrometer (MIMS). The MIMS allowed real time measurements of photosynthesis and respiration. Under all light conditions, no effects of either pH or pCO 2 were found on photosynthesis or respiration, despite an acclimation of the carbon concentrating mechanism (CCM) with pCO2, measured via the activity of carbonic anhydrase, one of the CCM enzyme. Calculations using Rubisco selectivity and half-saturation constant, predicted that, under nutrient replete conditions, a doubling of CO2 would result in less than ∼3% change on photosynthesis in T. weissflogii, and at most ∼8.5% in other diatoms. These results are due to the energetic efficiency of the CCM in diatoms and would vary for other groups of phytoplankton with different CCM.

During a field campaign near the Western Antarctic Peninsula (WAP), we analyzed some of the metabolic characteristics of the natural community responsible δfor the high productivity of the region, despite cold temperatures. Three different techniques were used to measure productivity: 1) 14C incubations, measuring fixation of CO2 into the biomass during the dark reactions of photosynthesis, 2) H218O incubations, measuring the splitting of water during the light reaction of photosynthesis and 3) in situ measurements of O2 /Ar and triple oxygen isotope, which allowed derivation of time-integrated ratios of Net/Gross production. The spring bloom represented more than half of the production of the growing season (spring-summer). During this event, the net-to-gross production ratios were ∼60%, among the highest ever reported. This study showed that these high ratios were partly due to low daylight respiration and low heterotrophic respiration. Additional laboratory experiments with the polar diatom Fragilariopsis cyclindrus, demonstrated an important level of cyclic electron flow (CEF) in this organism. CEF is an alternative pathway that allow the cell to produce energy from light, in the form of adenosine triphosphate (ATP), independently of mitochondrial respiration. As such, it could also contribute to the high productivity in the field.

To follow-up on the field findings, diel cycle experiments were performed on the psychrophilic diatom Proboscia alata. This organism (obtained from A. Marchetti) was isolated in the WAP. Measurements of total protein, particulate organic carbon and nitrogen were taken throughout the day. They revealed a synthesis of proteins in the morning, likely from recycling of other cellular molecules (i.e. lipids and ribosomes), and an increase of the biomass around midday. Carbon fixation was assessed using time course incubations of 20, 40 or 60 min, and net and gross photosynthesis were determined using H218O incubations. A comparison of 14C time course and H218O revealed a shift between the morning and afternoon from low to high respiration and recycling. These results provide new insights into the mechanisms used by this psychrophilic organism for energy balance and carbon storage during a diel cycle.

Continue reading ‘Environmental factors influencing phytoplankton productivity in the context of climate change’

Influence of ocean acidification on the organic complexation of iron and copper in Northwest European shelf seas; a combined observational and model study

The pH of aqueous solutions is known to impact the chemical speciation of trace metals. In this study we conducted titrations of coastal seawaters with iron and copper at pH 7.91, 7.37 and 6.99 (expressed on the total pH scale). Changes in the concentration of iron and copper that complexed with the added ligands 1-nitroso-2-napthol and salicylaldoxime respectively were determined by adsorptive cathodic stripping voltammetry – competitive ligand equilibrium (AdCSV-CLE). Interpretation of the results, assuming complexation by a low concentration of discrete ligands, showed that conditional stability constants for iron complexes increased relative to inorganic iron complexation as pH decreased by approximately 1 log unit per pH unit, whilst those for copper did not change. No trend was observed for concentrations of iron and copper complexing ligands over the pH range examined. We also interpreted our titration data by describing chemical binding and polyelectrolytic effects using non-ideal competitive adsorption in Donnan-like gels (NICA-Donnan model) in a proof of concept study. The NICA-Donnan approach allows for the development of a set of model parameters that are independent of ionic strength and pH, and thus calculation of metal speciation can be undertaken at ambient sample pH or the pH of a future, more acidic ocean. There is currently a lack of basic NICA-Donnan parameters applicable to marine dissolved organic matter (DOM) so we assumed that the measured marine dissolved organic carbon could be characterized as terrestrial fulvic acids. Generic NICA-Donnan parameters were applied within the framework of the software program visual MINTEQ and the metal –added ligand concentrations [MeAL] calculated for the AdCSV-CLE conditions. For copper, calculated [MeAL] using the NICA-Donnan model for DOM were consistent with measured [MeAL], but for iron an inert fraction with kinetically inhibited dissolution was required in addition to the NICA-Donnan model in order to approximate the trends observed in measured [MeAL]. We calculated iron and copper speciation in Northwest European shelf water samples at ambient alkalinity and projected increased pCO2 concentrations as a demonstration of the potential of the approach.

Continue reading ‘Influence of ocean acidification on the organic complexation of iron and copper in Northwest European shelf seas; a combined observational and model study’

Ocean acidification weakens the immune response of blood clam through hampering the NF-kappa β and toll-like receptor pathways

The impact of pCO2 driven ocean acidification on marine bivalve immunity remains poorly understood. To date, this impact has only been investigated in a few bivalve species and the underlying molecular mechanism remains unknown. In the present study, the effects of the realistic future ocean pCO2 levels (pH at 8.1, 7.8, and 7.4) on the total number of haemocyte cells (THC), phagocytosis status, blood cell types composition, and expression levels of twelve genes from the NF-kappa β signaling and toll-like receptor pathways of a typical bottom burrowing bivalve, blood clam (Tegillarca granosa), were investigated. The results obtained showed that while both THC number and phagocytosis frequency were significantly reduced, the percentage of red and basophil granulocytes were significantly decreased and increased, respectively, upon exposure to elevated pCO2. In addition, exposure to pCO2 acidified seawater generally led to a significant down-regulation in the inducer and key response genes of NF-kappa β signaling and toll-like receptor pathways. The results of the present study revealed that ocean acidification may hamper immune responses of the bivalve T. granosa which subsequently render individuals more susceptible to pathogens attacks such as those from virus and bacteria.

Continue reading ‘Ocean acidification weakens the immune response of blood clam through hampering the NF-kappa β and toll-like receptor pathways’

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Ocean acidification in the IPCC AR5 WG II

OUP book