Carbonate system parameters of an algal-dominated reef along West Maui

Constraining coral reef metabolism and carbon chemistry dynamics are fundamental for understanding and predicting reef vulnerability to rising coastal CO2 concentrations and decreasing seawater pH. However, few studies exist along reefs occupying densely inhabited shorelines with known input from land-based sources of pollution. The shallow coral reefs off Kahekili, West Maui, are exposed to nutrient-enriched, low-pH submarine groundwater discharge (SGD) and are particularly vulnerable to the compounding stressors from land-based sources of pollution and lower seawater pH. To constrain the carbonate chemistry system, nutrients and carbonate chemistry were measured along the Kahekili reef flat every 4 h over a 6-d sampling period in March 2016. Abiotic process – primarily SGD fluxes – controlled the carbonate chemistry adjacent to the primary SGD vent site, with nutrient-laden freshwater decreasing pH levels and favoring undersaturated aragonite saturation (Ωarag) conditions. In contrast, diurnal variability in the carbonate chemistry at other sites along the reef flat was driven by reef community metabolism. Superimposed on the diurnal signal was a transition during the second sampling period to a surplus of total alkalinity (TA) and dissolved inorganic carbon (DIC) compared to ocean end-member TA and DIC measurements. A shift from net community production and calcification to net respiration and carbonate dissolution was identified. This transition occurred during a period of increased SGD-driven nutrient loading, lower wave height, and reduced current speeds. This detailed study of carbon chemistry dynamics highlights the need to incorporate local effects of nearshore oceanographic processes into predictions of coral reef vulnerability and resilience.

Continue reading ‘Carbonate system parameters of an algal-dominated reef along West Maui’

Functional spatial contextualisation of the effects of multiple stressors in marine bivalves

Many recent studies have revealed that the majority of environmental stressors experienced by marine organisms (ocean acidification, global warming, hypoxia etc.) occur at the same time and place, and that their interaction may complexly affect a number of ecological processes. Here, we experimentally investigated the effects of pH and hypoxia on the functional and behavioural traits of the mussel Mytilus galloprovincialis, we then simulated the potential effects on growth and reproduction dynamics trough a Dynamic Energy Budget (DEB) model under a multiple stressor scenario. Our simulations showed that hypercapnia had a remarkable effect by reducing the maximal habitat size and reproductive output differentially as a function of the trophic conditions, where modelling was spatially contextualized. This study showed the major threat represented by the hypercapnia and hypoxia phenomena for the growth, reproduction and fitness of mussels under the current climate change context, and that a mechanistic approach based on DEB modelling can illustrate complex and site-specific effects of environmental change, producing that kind of information useful for management purposes, at larger temporal and spatial scales.

Continue reading ‘Functional spatial contextualisation of the effects of multiple stressors in marine bivalves’

Pteropods counter mechanical damage and dissolution through extensive shell repair

The dissolution of the delicate shells of sea butterflies, or pteropods, has epitomised discussions regarding ecosystem vulnerability to ocean acidification over the last decade. However, a recent demonstration that the organic coating of the shell, the periostracum, is effective in inhibiting dissolution suggests that pteropod shells may not be as susceptible to ocean acidification as previously thought. Here we use micro-CT technology to show how, despite losing the entire thickness of the original shell in localised areas, specimens of polar species Limacina helicina maintain shell integrity by thickening the inner shell wall. One specimen collected within Fram Strait with a history of mechanical and dissolution damage generated four times the thickness of the original shell in repair material. The ability of pteropods to repair and maintain their shells, despite progressive loss, demonstrates a further resilience of these organisms to ocean acidification but at a likely metabolic cost.

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Interactive effects of temperature, CO2 and nitrogen source on a coastal California diatom assemblage

Diatoms are often considered to be a single functional group, yet there is a great deal of morphological, genetic and ecological diversity within the class. How these differences will translate into species-specific responses to rapid changes in the ocean environment resulting from climate change and eutrophication is currently poorly understood. We investigated the response of a natural diatom-dominated assemblage in coastal California waters to interactions between the variables nitrogen source (nitrate and urea), temperature (19 and 23°C) and CO2 (380 and 800 ppm) in a factorial experimental matrix using continuous culture (ecostat) methods. The community included diatoms of the cosmopolitan genera Pseudo-nitzschia and Chaetoceros, as well as Leptocylindrus and Cylindrotheca. Our results demonstrate strong interactive effects of these variables on community composition; notably, nitrogen source alone and nitrogen and CO2 together had a much greater influence on diatom community structure at 23°C compared with 19°C. In addition, warming and acidification interactions significantly increased cellular quotas of the neurotoxin domoic acid produced by Pseudo-nitzschia multiseries. In general, the effects observed for the factors tested differed significantly between the various diatom genera in this assemblage, suggesting potentially divergent responses of some of these ecologically and biogeochemically important phytoplankton taxa to interactions between global-scale and local-scale anthropogenic stressors in a changing ocean.

Continue reading ‘Interactive effects of temperature, CO2 and nitrogen source on a coastal California diatom assemblage’

Seasonal variation in aragonite saturation in surface waters of Puget Sound – a pilot study

A pilot study of sampling, using monthly marine flights over spatially distributed stations, was conducted with the aim to characterize the carbonate system in Puget Sound over a full year-long period. Surface waters of Puget Sound were found to be under-saturated with respect to aragonite during October–March, and super-saturated during April–September. Highest pCO2 and lowest pH occurred during the corrosive October–March period. Lowest pCO2 and highest pH occurred during the super-saturated April–September period. The monthly variations in pCO2 , pH, and aragonite saturation state closely followed the variations in monthly average chlorophyll a. Super-saturated conditions during April–September are likely strongly influenced by photosynthetic uptake of CO2 during the phytoplankton growing season. The relationship between phytoplankton production, the carbonate system, and aragonite saturation state suggests that long-term trends in eutrophication processes may contribute to trends in ocean acidification in Puget Sound.

Continue reading ‘Seasonal variation in aragonite saturation in surface waters of Puget Sound – a pilot study’

Autonomous optofluidic chemical analyzers for marine applications: insights from the submersible autonomous moored instruments (SAMI) for pH and pCO2

The commercial availability of inexpensive fiber optics and small volume pumps in the early 1990’s provided the components necessary for the successful development of low power, low reagent consumption, autonomous optofluidic analyzers for marine applications. It was evident that to achieve calibration-free performance, reagent-based sensors would require frequent renewal of the reagent by pumping the reagent from an impermeable, inert reservoir to the sensing interface. Pumping also enabled measurement of a spectral blank further enhancing accuracy and stability. The first instrument that was developed based on this strategy, the Submersible Autonomous Moored Instrument for CO2 (SAMI-CO2), uses a pH indicator for measurement of the partial pressure of CO2 (pCO2). Because the pH indicator gives an optical response, the instrument requires an optofluidic design where the indicator is pumped into a gas permeable membrane and then to an optical cell for analysis. The pH indicator is periodically flushed from the optical cell by using a valve to switch from the pH indicator to a blank solution. Because of the small volume and low power light source, over 8,500 measurements can be obtained with a ~500 mL reagent bag and 8 alkaline D-cell battery pack. The primary drawback is that the design is more complex compared to the single-ended electrode or optode that is envisioned as the ideal sensor. The SAMI technology has subsequently been used for the successful development of autonomous pH and total alkalinity analyzers. In this manuscript, we will discuss the pros and cons of the SAMI pCO2 and pH optofluidic technology and highlight some past data sets and applications for studying the carbon cycle in aquatic ecosystems.

Continue reading ‘Autonomous optofluidic chemical analyzers for marine applications: insights from the submersible autonomous moored instruments (SAMI) for pH and pCO2’

Combined effects of ocean acidification and nutrient levels on the photosynthetic performance of Thalassiosira (Conticribra) weissflogii (Bacillariophyta)

The purpose of this study was to investigate the effects of ocean acidification and nutrient level on the growth and photosynthetic performance of the diatom Thalassiosira (Conticribra) weissflogii. Cells were exposed to varying levels of CO2 [current CO2 (LC), 400 μatm; high CO2 (HC), 1000 μatm] and nutrients, with NO3 and PO43− concentrations enriched, respectively, at 50 μmol l−1 and 5 μmol l−1 [high nutrient (HN)], 20 μmol l−1 and 2 μmol l−1 [mid-level nutrient (MN)] and 10 μmol l−1 and 1 μmol l−1 [low nutrient (LN)]. After acclimatization for over 20 generations, no significant differences in growth rates were observed between LC and HC cultures under both HN and LN conditions; whereas, HC significantly reduced the growth rate under MN conditions. Lower nutrient loading significantly inhibited the growth rates of both LC and HC cultures; whereas, HC (but not LC) significantly decreased chlorophyll a and carotenoid contents in LN treatments. HC conditions significantly increased maximum relative electron transport rates (rETRmax) and saturating light intensity (Ik) of HN cultures, with rETRmax showing a positive relationship with growth rates stimulated by nutrient enrichments. The maximum (Fv/Fm) and effective quantum yield (Yield) were all inhibited under LN conditions, with the greatest reduction in Yield observed under LC conditions, corresponding to the highest nonphotochemical quenching, lowest light use efficiency (α) and lowest rETRmax. Based on these results, ocean acidification and nutrient availability may influence photosynthetic performance in T. weissflogii individually or interactively, with the future growth of marine diatoms mediated by these codependent environmental drivers.

Continue reading ‘Combined effects of ocean acidification and nutrient levels on the photosynthetic performance of Thalassiosira (Conticribra) weissflogii (Bacillariophyta)’


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Ocean acidification in the IPCC AR5 WG II

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