Posts Tagged 'North Atlantic'

Seasonal variability of the carbonate system and coccolithophore Emiliania huxleyi at a Scottish Coastal Observatory monitoring site

Highlights

• There is a “knowledge gap” on carbonate chemistry in inshore waters.
• Stonehaven coastal carbonate system shows a strong variability at short-time and year-to-year scales.
• Occurrence of E. huxleyi morphotypes shows a repeated seasonal pattern.
E. huxleyi in situ calcification seems not to be affected by carbonate chemistry.
• Seasonality in E. huxleyi morphotypes should be considered when interpreting sporadic cruises data.

Abstract

Lack of information about carbonate chemistry in inshore waters is a ‘knowledge gap’ in assessing the impacts of changing carbonate chemistry on the marine environment. Assessing the response of calcifying phytoplankton to this changing carbonate chemistry requires a greater understanding of temporal variation. This study provides a description of the variability of carbonate parameters at a monitoring site in the eastern coast of Scotland. Four-years of monthly data were analysed to assess the diversity, abundance and morphometrics of coccolithophores in relation to carbonate chemistry and environmental variables. The seasonality in carbonate parameters reflected the seasonal cycle in phytoplankton activity, with higher total alkalinity concentrations and pH and lower dissolved inorganic carbon concentrations during the growing season. The dominant coccolithophore at the site was Emiliania huxleyi which showed a clear seasonal pattern, being more abundant in mid-summer when warmer and nutrient-depleted conditions restricted the annual diatom bloom. This study revealed the presence of three morphotypes of E. huxleyi, type A, type A overcalcified (type AO) and type B, which were seasonally distributed throughout the year. The less calcified form was mainly observed in spring while heavily calcified morphotypes overlapped during summer. Autumn and winter months were dominated by the most calcified form (type AO). These results indicate that the seasonal pattern of E. huxleyi morphotypes was not related to the carbonate concentration at the site. This study reflects the strong interannual variability in carbonate chemistry and the complexity associated with coccolithophore calcification, and highlights the need of long-term data to understand the potential impact of ocean acidification on calcifying phytoplankton.

Continue reading ‘Seasonal variability of the carbonate system and coccolithophore Emiliania huxleyi at a Scottish Coastal Observatory monitoring site’

Interaction between elevated CO2 and phytoplankton-derived organic matter under solar radiation on bacterial metabolism from coastal waters

Microcosm experiments to assess bacterioplankton response to phytoplankton-derived organic matter obtained under current and future-ocean CO2 levels were performed. Surface seawater enriched with inorganic nutrients was bubbled for 8 days with air (current CO2 scenario) or with a 1000 ppm CO2–air mixture (future CO2 scenario) under solar radiation. The organic matter produced under the current and future CO2 scenarios was subsequently used as inoculum. Triplicate 12 L flasks filled with 1.2 µm-filtered natural seawater enriched with the organic matter inocula were incubated in the dark for 8 days under CO2 conditions simulating current and future CO2 scenarios to study the bacterial response. The acidification of the media increased bacterial respiration at the beginning of the experiment while the addition of the organic matter produced under future levels of CO2 was related to changes in bacterial production and abundance. The balance between both, respiration and production, made that the bacteria grown under future CO2 levels with an addition of non-acidified matter showed the best growth efficiency at the end of the incubation. However cells grown under future scenarios with high CO2 levels and acidified organic matter additions did not perform differently than those grown under present CO2 conditions, independently of the addition of acidified or non-acidified organic matter. This study demonstrates that the increase in atmospheric CO2 concentrations can affect bacterioplankton directly by changes in the respiration rate and indirectly by changes on the organic matter with concomitant effects on bacterial production and abundance.

Continue reading ‘Interaction between elevated CO2 and phytoplankton-derived organic matter under solar radiation on bacterial metabolism from coastal waters’

Taking the metabolic pulse of the world’s coral reefs

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems.

Continue reading ‘Taking the metabolic pulse of the world’s coral reefs’

Increased fitness of a key appendicularian zooplankton species under warmer, acidified seawater conditions

Ocean warming and acidification (OA) may alter the fitness of species in marine pelagic ecosystems through community effects or direct physiological impacts. We used the zooplanktonic appendicularian, Oikopleura dioica, to assess temperature and pH effects at mesocosm and microcosm scales. In mesocosms, both OA and warming positively impacted O. dioica abundance over successive generations. In microcosms, the positive impact of OA, was observed to result from increased fecundity. In contrast, increased pH, observed for example during phytoplankton blooms, reduced fecundity. Oocyte fertility and juvenile development were equivalent under all pH conditions, indicating that the positive effect of lower pH on O. dioica abundance was principally due to increased egg number. This effect was influenced by food quantity and quality, supporting possible improved digestion and assimilation at lowered pH. Higher temperature resulted in more rapid growth, faster maturation and earlier reproduction. Thus, increased temperature and reduced pH had significant positive impacts on O. dioica fitness through increased fecundity and shortened generation time, suggesting that predicted future ocean conditions may favour this zooplankton species.

Continue reading ‘Increased fitness of a key appendicularian zooplankton species under warmer, acidified seawater conditions’

Community composition in mangrove ponds with pulsed hypoxic and acidified conditions

The potential resilience of biological communities to accelerating rates of global change has received considerable attention. We suggest that some shallow aquatic ecosystems, where temperature, dissolved oxygen (DO), and pH can exhibit extreme variation on short timescales of hours or days, provide an opportunity to develop a mechanistic understanding of species persistence and community assembly under harsh environmental conditions. Extreme diel swings in DO and pH have been observed in eutrophic temperate ecosystems, and here, we describe a similar phenomenon consistently occurring across tropical sites that included relatively remote atolls on the Meso-American barrier reefs in Belize and oligotrophic coastal lagoons in Panama. In particular, we documented large daily swings in temperature, DO, and pH within shallow ponds of Caribbean mangrove forests. Water in seven of 13 ponds went hypoxic (<2 mg/L DO) during the multiday sampling period, and pH dipped nightly to low levels, falling below 7.0 in some ponds. Minimum pH and minimum DO were correlated, and showed a similar relationship in Belize and Panama, suggesting a common mechanism produced diel cycles. Remarkably, most ponds exhibited high abundance of macroalgae, macroinvertebrates, and fish, despite potentially stressful abiotic conditions. Although fish diversity was negatively correlated with pH range, our overall results from the ponds suggest that many species are sufficiently resistant such that a functionally complex community can persist in the midst of pulsed stressful conditions. We propose that the mangrove ponds could serve as a model ecosystem for investigating resistance and resilience of coastal marine communities to global change factors such as climate change, hypoxia, and ocean acidification.

Continue reading ‘Community composition in mangrove ponds with pulsed hypoxic and acidified conditions’

Short-term spatial and temporal carbonate chemistry variability in two contrasting seagrass meadows: implications for pH buffering capacities

It has been hypothesized that highly productive coastal ecosystems, such as seagrass meadows, could lead to the establishment of ocean acidification (OA) refugia, or areas of elevated pH and aragonite saturation state (Ωa) compared to source seawater. However, seagrass ecosystems experience extreme variability in carbonate chemistry across short temporal and small spatial scales, which could impact the pH buffering capacity of these potential refugia. Herein, short-term (hourly to diel) and small-scale (across 0.01–0.14 km2) spatiotemporal carbonate chemistry variability was assessed within two seagrass meadows in order to determine their short-term potential to elevate seawater pH relative to source seawater. Two locations at similar latitudes were chosen in order to compare systems dominated by coarse calcium carbonate (Bailey’s Bay, Bermuda) and muddy silicate (Mission Bay, CA, USA) sediments. In both systems, spatial variability of pH across the seagrass meadow at any given time was often greater than diel variability (e.g., the average range over 24 h) at any one site, with greater spatial variability occurring at low tide in Mission Bay. Mission Bay (spatial ΔpH = 0.08 ± 0.08; diel ΔpH = 0.12 ± 0.01; mean ± SD) had a greater average range in both temporal and spatial seawater chemistry than Bailey’s Bay (spatial ΔpH = 0.02 ± 0.01; diel ΔpH = 0.03 ± 0.00; mean ± SD). These differences were most likely due to a combination of slower currents, a larger tidal range, and more favorable weather conditions for photosynthesis (e.g., sunny with no rain) in Mission Bay. In both systems, there was a substantial amount of time (usually at night) when seawater pH within the seagrass beds was lower relative to the source seawater. Future studies aimed at assessing the potential of seagrass ecosystems to act as OA refugia for marine organisms need to account for the small-scale, high-frequency carbonate chemistry variability in both space and time, as this variability will impact where and when OA will be buffered or intensified.

Continue reading ‘Short-term spatial and temporal carbonate chemistry variability in two contrasting seagrass meadows: implications for pH buffering capacities’

Linking genotype to phenotype in a changing ocean: inferring the genomic architecture of a blue mussel stress response with genome-wide association

A key component to understanding the evolutionary response to a changing climate is linking underlying genetic variation to phenotypic variation in stress response. Here we use a genome-wide association approach (GWAS) to understand the genetic architecture of calcification rates under simulated climate stress. We take advantage of the genomic gradient across the blue mussel hybrid zone (Mytilus edulis and Mytilus trossulus) in the Gulf of Maine (GOM) to link genetic variation with variance in calcification rates in response to simulated climate change. Falling calcium carbonate saturation states are predicted to negatively impact many marine organisms that build calcium carbonate shells – like blue mussels. We sampled wild mussels and measured net calcification phenotypes after exposing mussels to a “climate change” common garden, where we raised temperature 3°C, decreased pH by 0.2 units, and limited food supply by filtering out planktonic particles > 5 μm, compared to ambient GOM conditions in the summer. This climate change exposure greatly increased phenotypic variation in net calcification rates compared to ambient conditions. We then used regression models to link the phenotypic variation with over 170,000 single nucleotide polymorphism loci (SNPs) generated by genotype by sequencing to identify genomic locations associated with calcification phenotype, and estimate heritability and architecture of the trait. We identified at least one of potentially 2-10 genomic regions responsible for 30% of the phenotypic variation in calcification rates that are potential targets of natural selection by climate change. Our simulations suggest a power of 13.7% with our study’s average effective sample size of 118 individuals and rare alleles, but a power of > 90% when effective sample size is 900.

Continue reading ‘Linking genotype to phenotype in a changing ocean: inferring the genomic architecture of a blue mussel stress response with genome-wide association’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book