Posts Tagged 'laboratory'

Calcifying algae maintain settlement cues to larval abalone following algal exposure to extreme ocean acidification

Ocean acidification (OA) increasingly threatens marine systems, and is especially harmful to calcifying organisms. One important question is whether OA will alter species interactions. Crustose coralline algae (CCA) provide space and chemical cues for larval settlement. CCA have shown strongly negative responses to OA in previous studies, including disruption of settlement cues to corals. In California, CCA provide cues for seven species of harvested, threatened, and endangered abalone. We exposed four common CCA genera and a crustose calcifying red algae, Peyssonnelia (collectively CCRA) from California to three pCO2 levels ranging from 419-2,013 µatm for four months. We then evaluated abalone (Haliotis rufescens) settlement under ambient conditions among the CCRA and non-algal controls that had been previously exposed to the pCO2 treatments. Abalone settlement and metamorphosis increased from 11% in the absence of CCRA to 45-69% when CCRA were present, with minor variation among CCRA genera. Though all CCRA genera reduced growth during exposure to increased pCO2, abalone settlement was unaffected by prior CCRA exposure to increased pCO2. Thus, we find no impacts of OA exposure history on CCRA provision of settlement cues. Additionally, there appears to be functional redundancy in genera of CCRA providing cues to abalone, which may further buffer OA effects.

Continue reading ‘Calcifying algae maintain settlement cues to larval abalone following algal exposure to extreme ocean acidification’

Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi

A series of semi-continuous incubation experiments were conducted with the coccolithophore Emiliania huxleyi strain NIWA1108 (Southern Ocean isolate) to examine the effects of five environmental drivers (nitrate concentration, phosphate concentration, irradiance, temperature and pCO2) on both the physiological rates and elemental composition. Here, we report the alteration of the elemental composition of E. huxleyi in response to the changes in these environmental drivers. A series of dose response curves for the cellular elemental composition of E. huxleyi were fitted for each of the five drivers across an environmentally-representative gradient. The importance of each driver in regulating the elemental composition of E. huxleyi was ranked using a semi-quantitative approach. The percentage variation in elemental composition arising from the change in each driver between present day and model-projected conditions for the year 2100 were calculated. Temperature was the most important driver controlling both cellular particulate organic and inorganic carbon content, whereas nutrient concentrations were the most important regulator of cellular particulate nitrogen and phosphorus of E. huxleyi. In contrast, elevated pCO2 had the greatest influence on cellular particulate inorganic carbon to organic carbon ratio, resulting in a decrease in the ratio. Our results indicate that the different environmental drivers each play specific roles in regulating the cellular elemental composition of E. huxleyi with wide-reaching implications for coccolithophore biogeochemistry, as a consequence of the regulation of E. huxleyi physiological processes.

Continue reading ‘Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi’

The effects of pH and pCO2 on photosynthesis and respiration in the diatom Thalassiosira weissflogii

The response of marine phytoplankton to the ongoing increase in atmospheric pCO2 reflects the consequences of both increased CO2 concentration and decreased pH in surface seawater. In the model diatom Thalassiosira weissflogii, we explored the effects of varying pCO2 and pH, independently and in concert, on photosynthesis and respiration by incubating samples in water enriched in H218O. In long-term experiments (~6-h) at saturating light intensity, we observed no effects of pH or pCO2 on growth rate, photosynthesis or respiration. This absence of a measurable response reflects the very small change in energy used by the carbon concentrating mechanism (CCM) compared to the energy used in carbon fixation. In short-term experiments (~3 min), we also observed no effects of pCO2 or pH, even under limiting light intensity. We surmise that in T. weissflogii, it is the photosynthetic production of NADPH and ATP, rather than the CO2-saturation of Rubisco that controls the rate of photosynthesis at low irradiance. In short-term experiments, we observed a slightly higher respiration rate at low pH at the onset of the dark period, possibly reflecting the energy used for exporting H+ and maintaining pH homeostasis. Based on what is known of the biochemistry of marine phytoplankton, our results are likely generalizable to other diatoms and a number of other eukaryotic species. The direct effects of ocean acidification on growth, photosynthesis and respiration in these organisms should be small over the range of atmospheric pCO2 predicted for the twenty-first century.

Continue reading ‘The effects of pH and pCO2 on photosynthesis and respiration in the diatom Thalassiosira weissflogii’

Effects of diel-cycling hypoxia and acidification on juvenile weakfish Cynoscion regalis growth, survival, and activity

During summertime, dissolved oxygen (DO) and pH/pCO2 cycle daily in shallow estuarine waters used by young fishes as nursery habitat. Laboratory experiments on juvenile weakfish Cynoscion regalis examined individual and interactive impacts of present-day levels of diel-cycling hypoxia and acidification on growth and activity. Fish were exposed to 3 DO treatments (extreme cycling DO, 1-11 mg O2 l-1; moderate cycling DO, 3-9 mg O2 l-1; and constant normoxia, 7.5 mg O2 l-1) and 3 pH treatments (extreme cycling pH, 6.8-8.1; moderate cycling pH, 7.2-7.8; and constant pH, 7.5) for 20 d in a 3 × 3 factorial design. Growth was not impacted by moderate diel cycles of DO and acidification with mean daily lows of 3.0-3.3 mg O2 l-1 and mean daily highs of 7.8-9.5 mg O2 l-1 (mean daily low pH 7.03-7.47 and high pCO2 ~16000-5000 µatm). However, 100% mortality occurred within ~10 d at extreme diel-cycling hypoxia during which DO cycled between mean daily lows of 1.5-2.1 mg O2 l-1, mean daily low pH 6.99-7.44, and associated high pCO2 of ~16500-5500 µatm. We found no clear independent or interactive effect of pH/pCO2 on growth or survival despite pH being as low as 6.86 and pCO2 as high as ~20000 µatm. Furthermore, fish that survived as much as 10 d exposure to extreme and moderate diel cycles of DO and acidification experienced no residual negative impact on growth following return to normoxia and static pH. Our results suggest that juvenile weakfish have substantial tolerance of diel cycles of oxygenation and acidification encountered in shallow estuarine nursery habitat.

Continue reading ‘Effects of diel-cycling hypoxia and acidification on juvenile weakfish Cynoscion regalis growth, survival, and activity’

Phytoplankton community responses to iron and CO2 enrichment in different biogeochemical regions of the Southern Ocean

The ongoing rise in atmospheric CO2 concentration is causing rapid increases in seawater pCO2levels. However, little is known about the potential impacts of elevated CO2 availability on the phytoplankton assemblages in the Southern Ocean’s oceanic regions. Therefore, we conducted four incubation experiments using surface seawater collected from the subantarctic zone (SAZ) and the subpolar zone (SPZ) in the Australian sector of the Southern Ocean during the austral summer of 2011–2012. For incubations, FeCl3 solutions were added to reduce iron (Fe) limitation for phytoplankton growth. Ambient and high (~750 µatm) CO2 treatments were then prepared with and without addition of CO2-saturated seawater, respectively. Non-Fe-added (control) treatments were also prepared to assess the effects of Fe enrichment (overall, control, Fe-added, and Fe-and-CO2-added treatments). In the initial samples, the dominant phytoplankton taxa shifted with latitude from haptophytes to diatoms, likely reflecting silicate availability in the water. Under Fe-enriched conditions, increased CO2 level significantly reduced the accumulation of biomarker pigments in haptophytes in the SAZ and AZ, whereas a significant decrease in diatom markers was only detected in the SAZ. The CO2-related changes in phytoplankton community composition were greater in the SAZ, most likely due to the decrease in coccolithophore biomass. Our results suggest that an increase in CO2, if it coincides with Fe enrichment, could differentially affect the phytoplankton community composition in different geographical regions of the Southern Ocean, depending on the locally dominant taxa and environmental conditions.

Continue reading ‘Phytoplankton community responses to iron and CO2 enrichment in different biogeochemical regions of the Southern Ocean’

Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance

The Arctic Ocean is a region particularly prone to ongoing ocean acidification (OA) and climate-driven changes. The influence of these changes on Arctic phytoplankton assemblages, however, remains poorly understood. In order to understand how OA and enhanced irradiances (e.g., resulting from sea–ice retreat) will alter the species composition, primary production, and eco-physiology of Arctic phytoplankton, we conducted an incubation experiment with an assemblage from Baffin Bay (71°N, 68°W) under different carbonate chemistry and irradiance regimes. Seawater was collected from just below the deep Chl a maximum, and the resident phytoplankton were exposed to 380 and 1000 µatm pCO2 at both 15 and 35% incident irradiance. On-deck incubations, in which temperatures were 6 °C above in situ conditions, were monitored for phytoplankton growth, biomass stoichiometry, net primary production, photo-physiology, and taxonomic composition. During the 8-day experiment, taxonomic diversity decreased and the diatom Chaetoceros socialis became increasingly dominant irrespective of light or CO2 levels. We found no statistically significant effects from either higher CO2 or light on physiological properties of phytoplankton during the experiment. We did, however, observe an initial 2-day stress response in all treatments, and slight photo-physiological responses to higher CO2 and light during the first five days of the incubation. Our results thus indicate high resistance of Arctic phytoplankton to OA and enhanced irradiance levels, challenging the commonly predicted stimulatory effects of enhanced CO2 and light availability for primary production.

Continue reading ‘Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance’

Assessment of the environmental impacts of ocean acidification (OA) and carbon capture and storage (CCS) leaks using the amphipod Hyale youngi

This study aims to ascertain the effects of CO2 induced water acidification and leaks from Carbon Capture and Storage activities on the South American amphipod Hyale youngi. A 10-day acute toxicity test was performed using sediments from two sites located inside the Santos Estuarine System. They were subjected to five pH treatments (8.1, 7.6, 7.0, 6.5, and 6.0). Metals (Cd, Cu, Cr, Pb, Ni and Zn) and the metalloid As were analyzed to determine the influence of their acidification-related mobility on the amphipods mortality. The results showed that mortality becomes significant when compared to control in pH 6.5 in the Canal de Piaçaguerasediment (contaminated) and at pH 6.0 in Ilha das Palmas sediment (reference).

Continue reading ‘Assessment of the environmental impacts of ocean acidification (OA) and carbon capture and storage (CCS) leaks using the amphipod Hyale youngi’


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