Archive for October, 2017

Impact of climate change variables on nutrient cycling by marine microorganisms in the Southern California Bight and Ross Sea, Antarctica

Ocean environments are being impacted by climate warming, elevated carbon dioxide (CO2) levels, and shifting nutrient sources and sinks. It is essential to quantify the sensitivity of microorganisms to these effects of global change because they form the base of the marine food web and are an integral component of nutrient cycling on the planet. Their role in photosynthesis, nutrient uptake, and transfer of organic matter into higher trophic levels or to the deep ocean via the biological pump render microorganisms key in ecosystem structure and function and in regulating the global climate. The goal of this dissertation research was to determine how changing environmental conditions impact microbial communities and the rates at which they take up nutrients. Research for this dissertation took place in the Southern California Bight and in the Ross Sea, Antarctica, where fully factorial designs were used to investigate the response of microorganisms to multiple global change parameters. Nutrient uptake rates were measured using 13C and 15N stable isotopes for carbon and nitrogen substrates and 33P radioisotopes for phosphorus substrates. In the Southern California Bight, a microbial assemblage was collected and incubated in an ‘ecostat’ continuous culture system, where elevated temperature, CO2, and the dominant nitrogen substrate (nitrate or urea) in the diluent were manipulated. During this experiment uptake rates of dissolved inorganic carbon (DIC), nitrate (NO3-), and urea were determined for two microbial size classes (0.7-5.0 μm and >5.0 μm). Urea uptake rates were greater than NO3-, and uptake rates of urea and DIC for both size fractions increased at elevated temperature, while uptake rates of NO3- by smaller microorganisms increased when CO2 levels were high. In the Ross Sea, the impact of elevated temperature, CO2, and iron addition on DIC and NO3- uptake rates by two size classes (0.7-5.0 μm and >5.0 μm ) of a late-season microbial community were investigated using a semi-continuous and continuous ‘ecostat’ culturing approach. Temperature impacted the microbial community the most, significantly increasing NO3- and DIC uptake rates by larger microorganisms. The effects of iron addition were more apparent when temperature was also elevated, and CO2 did not impact rates. Bioassay experiments were also conducted in the Ross Sea to determine how increasing and decreasing the N:P supply ratio in combination with other parameters (temperature and iron) impact uptake rates of DIC, NO3-, and amino acids. Results from these experiments show that changes to the dissolved N:P supply ratio have the potential to alter nutrient uptake rates over short time scales, but that temperature elevation and iron addition have a larger impact. Additional experiments were completed on diatoms (Fragilariopsis cylindrus and Pseudo-nitzschia subcurvata) and Phaeocystis antarctica, three important phytoplankton species collected from the Ross Sea, to assess how temperature elevation and iron addition impact uptake rates of a number of inorganic and organic carbon, nitrogen, and phosphorus substrates. These culture studies generally show that when temperature is increased, diatoms are able to take up nutrients more rapidly than Phaeocystis antarctica.
Results from this dissertation show that nutrient cycles and phytoplankton communities in the Southern California Bight and the Ross Sea, Antarctica will likely be different in the future. Although all variables tested were found to exert some influence on microbial nutrient cycling, temperature elevation generally had the largest effect, increasing biomass and uptake rates, structuring the composition of the microbial community, and altering stoichiometry. This research did not include top down effects and it is limited spatially and temporally, however, it demonstrates the importance of studying different nutrient substrates and looking at multiple interactive stressors to gain a more comprehensive view of potential change.

Continue reading ‘Impact of climate change variables on nutrient cycling by marine microorganisms in the Southern California Bight and Ross Sea, Antarctica’

BBC article on ocean acidification report accurate but brief

Analysis of “More acidic oceans ‘will affect all sea life'”
Published in , by on

Three scientists analyzed the article and estimate its overall scientific credibility to be ‘high’.

A majority of reviewers tagged the article as: .



This BBC article describes an as-yet-unreleased report on ocean acidification from a major collaborative scientific project called BIOACID. The report will summarize the state of research on the impacts of ocean acidification—the changing pH and chemistry of seawater due to rising atmospheric carbon dioxide—on marine life.

Scientists who reviewed the article found that it was generally accurate in its description of the forthcoming report’s overall conclusions that ocean acidification poses an important threat to marine ecosystems. However, the BIOACID report will cover a broad and complex field of research, very little of which is explained in this short article.

Continue reading ‘BBC article on ocean acidification report accurate but brief’

Pair study effect of acidity, warm water on Dungeness crab

Juvenile Dungeness crabs are about to become lab rats for Aaron Galloway and Julie Schram of the Oregon Institute of Marine Biology in Charleston.

And with a lot of work and a little luck, the two researchers might be able to help the crab fishery — if needed — in the face of warming water and increasing acidity in the ocean.

Galloway gave a presentation last week in Harbor for the Oregon Dungeness Crab Commission in which he outlined the research he and Scham, an ocean acidification expert, plan to conduct under an Oregon Sea Grant they were awarded this week.

Continue reading ‘Pair study effect of acidity, warm water on Dungeness crab’

Harpswell group hears warning about rising ocean acidity

HARPSWELL — For those paying attention to Maine’s shellfish industry, new predators who pose a threat to the shell-sporting species are hogging headlines.

But another risk to the state’s coastal industries is perched on the horizon, with ominous, lesser-known outcomes that could potentially affect lobster, too.

The waters are warming, and they’re also getting more acidic, Aaron Strong, a University of Maine scientist studying the gulf’s changing oceans, told the Harpswell Heritage Land Trust Oct. 17.

Continue reading ‘Harpswell group hears warning about rising ocean acidity’

Effects of ocean acidification and UV radiation on marine photosynthetic carbon fixation

The oceans absorb anthropogenically released CO2 at a rate of more than one million tons per hour, which causes a pH decrease of seawater and results in ocean acidification (OA). The effect of OA and absorption of CO2 via the biological carbon pump driven by marine photosynthesis has drawn increasing attentions. As a consequence, there are numerous studies on influences of OA on primary producers, and the effects on photosynthetic carbon fixation are still under debate. OA can promote the growth of diatoms at low PAR irradiances and inhibit it at high PAR. Besides, OA may influence metabolic pathways of phytoplankton, upregulating β-oxidation, and the tricarboxylic acid cycle, resulting in increased accumulation of toxic phenolic compounds. In parallel, phytoplankton cells in the upper mixed layer are affected by intense PAR and UV radiation (UVR). The calcareous layers of calcified algae, which have been shown to shield the organisms from UVR, are thinned due to OA, exposing the cells to increased UVR and further inhibiting the calcification. Therefore, effects of OA and UV on marine photosynthetic carbon fixation could be compounded. While the photosynthetic carbon fixation is controlled by other environmental stressors in addition to OA and UV, such as nutrients limitation and warming, combined effects of OA and UV have been less considered. In this review, we synthesize and analyze recent advances on effects of OA and UV and their combined effects, implying that future studies should pay special attentions to ecological and physiological effects of OA in the presence of solar UV irradiance to reflect more realistic implications. The ecophysiological effects of OA and/or UV and their mechanisms in complex environments should be further explored.

Continue reading ‘Effects of ocean acidification and UV radiation on marine photosynthetic carbon fixation’

Systems biology and the seagrass paradox: adaptation, acclimation, and survival of marine angiosperms in a changing ocean climate

Predicting adaptive fitness to any environment requires mechanistic understanding of environmental influence on metabolic networks that control energy assimilation, growth, and reproduction. Although the potential impacts of environment on gene products are myriad, important phenotypic responses are often regulated by a few key points in metabolic networks where externally supplied resources or physiological reaction substrates limit reaction kinetics. Environmental resources commonly limiting seagrass productivity, survival, and growth include light and CO2 availability that control carbon assimilation and sucrose formation. Phosphate availability can also be important in oligotrophic tropical environments, particularly in the presence of carbonate sediments. Temperature and macronutrient oversupply (eutrophication) can act as confounding stressors, particularly in temperate environments. Photoacclimation can be regulated by electron transport pathways residing in the chloroplast stroma, but stress responses are often manifest by the expression of generalized stress response proteins, both of which appear to be affected by temperature and CO2 availability. A systems approach is employed to explore (1) the responses of seagrasses to the combined impacts of environmental limiting factors that control fundamental physiological processes leading to whole-plant performance; (2) sediment diagenetic processes that facilitate nutrient remineralization, carbon sequestration, and toxin neutralization; (3) interactions with other organisms induced by trophic cascades; and (4) impacts of human-induced climate change that affect system dynamics at numerous points in the network.

Continue reading ‘Systems biology and the seagrass paradox: adaptation, acclimation, and survival of marine angiosperms in a changing ocean climate’

Ocean acidification does not impair predator recognition but increases juvenile growth in a temperate wrasse off CO2 seeps


  • CO2 effects on the ocellated wrasse predator cue recognition were assessed.
  • Behavioural and otolith analyses were performed on Symphodus ocellatus from CO2 seeps.
  • Predation risk perception by the ocellated wrasse juveniles was unaffected by CO2.
  • High CO2 levels enhanced the S. ocellatus post-settlement growth.


Fish behavioural effects under Ocean Acidification (OA) rely on changes expected to occur in brain function, which can be reversed by gabazine, a GABA-A antagonist. Here, using standard two-channel choice flume, we assessed OA effects on the predator recognition ability of both gabazine-treated and -untreated Symphodus ocellatus post-settlers living off CO2 seeps in the Mediterranean Sea. To estimate the post-settlers background predation risk we evaluated the density of their predator in the wild and through otolith aging techniques we assessed their post-settlement growth. Results showed that: 1) post-settlers predator recognition was unaffected under OA; 2) post-settlers living in elevated CO2 were on average 15% bigger in size than those from ambient conditions. Our results support fish behavioural tolerance to OA, potentially mediated by pre-exposure to high-risk predation levels, and speculate that by increasing body size, juvenile fish might more efficiently avoid their predators.
Continue reading ‘Ocean acidification does not impair predator recognition but increases juvenile growth in a temperate wrasse off CO2 seeps’

Oyster reproduction is compromised by acidification experienced seasonally in coastal regions

Atmospheric carbon dioxide concentrations have been rising during the past century, leading to ocean acidification (OA). Coastal and estuarine habitats experience annual pH variability that vastly exceeds the magnitude of long-term projections in open ocean regions. Eastern oyster (Crassostrea virginica) reproduction season coincides with periods of low pH occurrence in estuaries, thus we investigated effects of moderate (pH 7.5, pCO2 2260 µatm) and severe OA (pH 7.1, pCO2 5584 µatm; and 6.7, pCO2 18480 µatm) on oyster gametogenesis, fertilization, and early larval development successes. Exposure at severe OA during gametogenesis caused disruption in oyster reproduction. Oogenesis appeared to be more sensitive compared to spermatogenesis. However, Eastern oyster reproduction was resilient to moderate OA projected for the near-future. In the context of projected climate change exacerbating seasonal acidification, OA of coastal habitats could represent a significant bottleneck for oyster reproduction which may have profound negative implications for coastal ecosystems reliant on this keystone species.

Continue reading ‘Oyster reproduction is compromised by acidification experienced seasonally in coastal regions’

Potential influence of ocean acidification on deep-sea Fe–Mn nodules: results from leaching experiments

With the continuous rise in CO2 emissions, the pH of seawater may decrease extensively in the coming centuries. Deep-sea environments are more vulnerable to decreasing pH since sediments in deep oceans below the carbonate compensation depth (CCD) are often completely devoid of carbonate particles. In order to assess the potential risk of heavy metal release from deep-sea deposits, the mobility of elements from ferromanganese (Fe–Mn) nodules and pelagic clays was examined by means of leaching experiments using phosphate buffer solutions ranging in pH from 7.1 to 8.6 (NBS scale). With decreasing pH, the results showed an enhanced leaching of elements such as Li, B, Mg, Si, Sc, Sr, Ba, Tl, and U, but a reduced leaching of V, Cu, Mo, Cd, and W. Elements in leachates originate mainly from exchangeable fractions, and tend to be affected by sorption–desorption processes. Concentrations of most elements did not exceed widely used international water quality criteria, indicating that changes in pH caused by future ocean acidification may not increase the risk of heavy metal release during deep-sea nodule mining operations.

Continue reading ‘Potential influence of ocean acidification on deep-sea Fe–Mn nodules: results from leaching experiments’

Spectrophotometric pH measurements from river to sea: calibration of mCP for 0 ≤ S ≤ 40 and 278.15 ≤ T ≤ 308.15 K


• Need for a spectrophotometric model using purified mCP across the estuarine salinity range is described.
• Estuarine pH data using unpurified mCP are corrected for impurity absorbances.
• A new model is presented to characterize behavior of purified mCP across the range of temperatures and salinities for temperate estuaries.
• New estuarine model corroborates models of purified mCP in pure water and seawater and bridges the salinity gap between them.


The indicator meta-cresol purple (mCP) has been widely used for spectrophotometric pH measurements in seawater and has been recently used in freshwater as well. Previous works have not, however, provided the comprehensive characterization of purified mCP (equilibrium and spectral behavior) required for pH measurements across the full ranges of temperature (T) and salinity (S) found in temperate estuaries. This work provides, for the first time, a comprehensive S– and T-dependent model for spectrophotometric pH measurements appropriate to freshwater, estuarine water, and seawater. Our model combines previous characterizations of the behavior of (a) purified mCP in pure water (S = 0), (b) purified mCP in seawater (20  S  40), and (c) unpurified mCP at 298.15 K and 0  S  40, herein corrected for the effects of impurities. Using the ratio (R) of mCP absorbances at 578 nm and 434 nm, the summary equations for calculations of pH on the total proton concentration scale for the conditions of 0  S  40 and 278.15  T  308.15 K are as follows:


where e1 =  0.007762 + 4.5174 10 5 T


This new model, appropriate for use with purified mCP, produces pH values that are within ± 0.004 of those obtained using previously published data and purified-mCP models for pure water and seawater.

Continue reading ‘Spectrophotometric pH measurements from river to sea: calibration of mCP for 0 ≤ S ≤ 40 and 278.15 ≤ T ≤ 308.15 K’

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Ocean acidification in the IPCC AR5 WG II

OUP book