Posts Tagged 'North Atlantic'

Effects of reduced pH on health biomarkers of the seagrass Cymodocea nodosa

Ocean acidification is a growing problem that may affect many marine organisms in the future. Within 100 years the pH of the ocean is predicted to decrease to 7.8, from the current ocean pH of around 8.1. Using phenolic acid levels as a stress indicator as well as respiration and chlorophyll content as a measure of health, the effect of lowering pH was tested on the seagrass, Cymodocea nodosa, in a controlled environment. Plant samples, water, and soil were taken from the Bay of Cádiz, Spain, and placed in aquaria in a temperature-controlled room. One control group was left untreated with a pH of approximately 8.1, while experimental groups maintained pH levels of 7.8 and 7.5. Using High Performance Liquid Chromatography (HPLC), concentration of the phenol rosmarinic acid was quantified in the plants. Average concentration for the control group was 1.7 μg g-1, while it was 2.9 μg g-1 for pH group 7.8, and 10.1g g-1 for pH group 7.5. To evaluate the overall health of C. nodosa within the three groups, chlorophyll concentration and photosynthesis/respiration rates were determined. A one-tailed ANOVA test was conducted using the chlorophyll concentrations of the three groups. With an F-value of 1.360 and a p-value of 0.287, the differences between the groups were not statistically significant. Although the raw data shows a slight decrease in chlorophyll content between the control group and the pH group 7.5, these discrepancies might have been larger or smaller due to sampling or experimental error. Additionally, the average values with their respective standard deviations were calculated for the respiration rates and oxygen production of each group. A one-tailed ANOVA was also used to determine the relationship between rosmarinic acid content and pH levels between the groups, with an F-value of 5.1423 and a p-value of 0.050.

Continue reading ‘Effects of reduced pH on health biomarkers of the seagrass Cymodocea nodosa’

Dynamics of benthic metabolism, O2, and pCO2 in a temperate seagrass meadow

Seagrass meadows play an important role in “blue carbon” sequestration and storage, but their dynamic metabolism is not fully understood. In a dense Zostera marina meadow, we measured benthic O2 fluxes by aquatic eddy covariance, water column concentrations of O2, and partial pressures of CO2 (pCO2) over 21 full days during peak growing season in April and June. Seagrass metabolism, derived from the O2 flux, varied markedly between the 2 months as biomass accumulated and water temperature increased from 16°C to 28°C, triggering a twofold increase in respiration and a trophic shift of the seagrass meadow from being a carbon sink to a carbon source. Seagrass metabolism was the major driver of diurnal fluctuations in water column O2 concentration and pCO2, ranging from 173 to 377 μmol L−1 and 193 to 859 ppmv, respectively. This 4.5‐fold variation in pCO2 was observed despite buffering by the carbonate system. Hysteresis in diurnal water column pCO2 vs. O2 concentration was attributed to storage of O2 and CO2 in seagrass tissue, air–water exchange of O2 and CO2, and CO2 storage in surface sediment. There was a ~ 1:1 mol‐to‐mol stoichiometric relationship between diurnal fluctuations in concentrations of O2 and dissolved inorganic carbon. Our measurements showed no stimulation of photosynthesis at high CO2 and low O2 concentrations, even though CO2 reached levels used in IPCC ocean acidification scenarios. This field study does not support the notion that seagrass meadows may be “winners” in future oceans with elevated CO2 concentrations and more frequent temperature extremes.

Continue reading ‘Dynamics of benthic metabolism, O2, and pCO2 in a temperate seagrass meadow’

Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring

Coral calcification is expected to decline as atmospheric carbon dioxide concentration increases. We assessed the potential of Porites astreoides, Siderastrea siderea and Porites porites to survive and calcify under acidified conditions in a 2-year field transplant experiment around low pH, low aragonite saturation (Ωarag) submarine springs. Slow-growing S. siderea had the highest post-transplantation survival and showed increases in concentrations of Symbiodiniaceae, chlorophyll a and protein at the low Ωarag site. Nubbins of P. astreoides had 20% lower survival and higher chlorophyll a concentration at the low Ωarag site. Only 33% of P. porites nubbins survived at low Ωarag and their linear extension and calcification rates were reduced. The density of skeletons deposited after transplantation at the low Ωarag spring was 15–30% lower for all species. These results suggest that corals with slow calcification rates and high Symbiodiniaceae, chlorophyll a and protein concentrations may be less susceptible to ocean acidification, albeit with reduced skeletal density. We postulate that corals in the springs are responding to greater energy demands for overcoming larger differences in carbonate chemistry between the calcifying medium and the external environment. The differential mortality, growth rates and physiological changes may impact future coral species assemblages and the reef framework robustness.

Continue reading ‘Species-specific calcification response of Caribbean corals after 2-year transplantation to a low aragonite saturation submarine spring’

Spatiotemporal variability in seawater carbonate chemistry at two contrasting reef locations in Bocas del Toro, Panama

There is a growing concern for how coral reefs may fare in a high-CO2 world. The majority of laboratory and mesocosm experiments have revealed negative effects on the growth and calcification of reef builders exposed to elevated CO2 conditions. However, coral reefs are highly dynamic systems and the interplay between different biogeochemical and physical processes on reefs results in large variability of seawater carbonate chemistry on different functional scales. This can create localized seawater conditions that can either enhance or alleviate the effects of ocean acidification (OA). Consequently, in order to predict how coral reef ecosystems may respond to OA in the future, it is necessary to first establish a baseline of natural carbonate chemistry conditions. This includes characterizing the range and variability of carbonate chemistry and the physical and biogeochemical controls across a broad range of environments over both space and time. Here, we have characterized the spatial and temporal physiochemical variability of two contrasting coral reef locations in Bocas del Toro, Panama that differed in their benthic community composition, reef morphology, and exposure to open ocean conditions, using a combination of research approaches including stationary autonomous sensors and spatial surveys during the month of November 2015. Mean and diurnal temporal variability in both physical and chemical seawater parameters were remarkably similar between sites and sampling depths, although, the magnitude of spatial variability was quite different between the sites. Spatial gradients in physiochemical parameters at Punta Caracol reflected the cumulative modification from terrestrial runoff and benthic metabolism. Based on graphical vector analysis of salinity normalized TA-DIC data, reef metabolism was dominated by organic carbon cycling over inorganic carbon cycling at both sites, where the outer reef reflected net heterotrophy likely owing to remineralization of organic matter from terrestrial inputs. Altogether, the results of this study highlight the strong influence of terrigenous runoff on reef metabolism and seawater chemistry conditions and demonstrate the importance of considering external inputs of alkalinity in reefs when interpreting TA-DIC data in systems with large freshwater inputs. Predicting future changes to coral reef ecosystems requires an understanding of the natural complexity of these systems in which various physical, ecological and biogeochemical drivers interact creating large variability in seawater chemistry over space and time.

Continue reading ‘Spatiotemporal variability in seawater carbonate chemistry at two contrasting reef locations in Bocas del Toro, Panama’

Local drivers of the seasonal carbonate cycle across four contrasting coastal systems

Highlights

• This dataset illustrates how local carbonate chemistry can vary widely along short lengths of coastline due to local drivers, particularly bedrock geology.

• Results highlight which season is most/least favourable for calcifying species and how this relates to their lifecycle.

• The dataset identified a number of key issues when addressing indicators of ecosystem vulnerability (calcium in omega calculations and SIR-).

• Results illustrate that we must understand both regional and local conditions in order to estimate future ocean acidification conditions and potential impacts on local ecosystems and shellfish aquaculture.

Abstract

Four contrasting coastal systems in Ireland, each with shellfish production activities, were studied to provide a first evaluation of the spatial and seasonal influences on the local carbonate system. The study sites included; (1) a coastal system with sandstone bedrock and minimal freshwater sources, (2) an estuarine system with a catchment limestone bedrock, (3) an estuarine system with a catchment granite bedrock, and (4) a karst groundwater-fed estuary. The type of bedrock was the dominant control on regional carbonate chemistry, where the calcium carbonate catchment bedrock was a strong source of both dissolved inorganic carbon and total alkalinity input in the two limestone regions, which are supersaturated with respect to atmospheric CO2 throughout the year. Primary production played an important role in the non-limestone regions, where both systems were CO2-undersaturated during productive months. Minimum aragonite saturation () was observed at all sites during winter when productivity is lowest; surface winter is 2 in the inner estuary. The substrate-to-inhibitor ratio (SIR), an alternative indicator of ecosystem vulnerability to acidification, was positively correlated to in all systems, however with more variability in the two limestone regions. Results highlight challenges of assessing local ecosystem vulnerability to future acidification and the importance of understanding the local spatio-temporal biogeochemistry.

Continue reading ‘Local drivers of the seasonal carbonate cycle across four contrasting coastal systems’

Characteristics of the carbonate system in a semiarid estuary that experiences summertime hypoxia

In oceanic environments, two sources of CO2 have been found to contribute to acidification of stratified water bodies, i.e., CO2 invasion due to anthropogenic atmospheric CO2 increase and respiration-produced CO2 from organic matter remineralization. Acidification caused by these CO2 sources has been observed frequently in numerous environments spanning from open continental shelves to enclosed estuaries. Here, we report observations on carbonate system dynamics in a relatively well-buffered lagoonal estuary, Corpus Christi Bay (CCB), in a semiarid subtropical region that is influenced by summertime hypoxia as well as strong evaporation and seagrass vegetation in the vicinity. While the relationship between dissolved oxygen (DO) and pH in the bottom waters of CCB was positive as in other coastal and estuarine environments prone to hypoxia, the slope was significantly less than in other systems. We attribute the high buffering capacity in CCB to the presence of abundant seagrass meadows adjacent to CCB and strong evaporation-produced density flow that delivers low CO2 waters to the bottom of CCB. Thus, despite the occurrence of hypoxia, neither bottom water carbonate saturation state with respect to aragonite (Ωarg) nor CO2 partial pressure (pCO2) reached critical levels, i.e., undersaturation (i.e., Ωarag1000 µatm), respectively.

Continue reading ‘Characteristics of the carbonate system in a semiarid estuary that experiences summertime hypoxia’

In vivo 31P-MRS of muscle bioenergetics in marine invertebrates: future ocean limits scallops’ performance

Object

Dynamic in vivo 31P-NMR spectroscopy in combination with Magnetic Resonance Imaging (MRI) was used to study muscle bioenergetics of boreal and Arctic scallops (Pecten maximus and Chlamys islandica) to test the hypothesis that future Ocean Warming and Acidification (OWA) will impair the performance of marine invertebrates.

Materials & methods

Experiments were conducted following the recommendations for studies of muscle bioenergetics in vertebrates. Animals were long-term incubated under different environmental conditions: controls at 0 °C for C. islandica and 15 °C for P. maximus under ambient PCO2 of 0.039 kPa, a warm exposure with +5 °C (5 °C and 20 °C, respectively) under ambient PCO2 (OW group), and a combined exposure to warmed acidified conditions (5 °C and 20 °C, 0.112 kPa PCO2, OWA group). Scallops were placed in a 4.7 T MR animal scanner and the energetic status of the adductor muscle was determined under resting conditions using in vivo 31P-NMR spectroscopy. The surplus oxidative flux (Qmax) was quantified by recording the recovery of arginine phosphate (PLA) directly after moderate swimming exercise of the scallops.

Results

Measurements led to reproducible results within each experimental group. Under projected future conditions resting PLA levels (PLArest) were reduced, indicating reduced energy reserves in warming exposed scallops per se. In comparison to vertebrate muscle tissue surplus Qmax of scallop muscle was about one order of magnitude lower. This can be explained by lower mitochondrial contents and capacities in invertebrate than vertebrate muscle tissue. Warm exposed scallops showed a slower recovery rate of PLA levels (kPLA) and a reduced surplus Qmax. Elevated PCO2 did not affected PLA recovery further.

Conclusion

Dynamic in vivo 31P-NMR spectroscopy revealed constrained residual aerobic power budgets in boreal and Arctic scallops under projected ocean warming and acidification indicating that scallops are susceptible to future climate change. The observed reduction in muscular PLArest of scallops coping with a warmer and acidified ocean may be linked to an enhanced energy demand and reduced oxygen partial pressures (PO2) in their body fluids. Delayed recovery from moderate swimming at elevated temperature is a result of reduced PLArest concentrations associated with a warm-induced reduction of a residual aerobic power budget.
Continue reading ‘In vivo 31P-MRS of muscle bioenergetics in marine invertebrates: future ocean limits scallops’ performance’


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