Ocean acidification at the 9th International Carbon Dioxide Conference (ICDC9)

Ocean acidification will be included in Theme 3 of the 9th International Carbon Dioxide Conference (ICDC9; www.icdc9.org), Beijing, China, 3-7 June 2013. The deadline for abstract submission is 1st February 2013.

PhD project: Vulnerability of marine invertebrates living along latitudinal and depth gradients to complex global environmental changes

FACULTY OF SCIENCE AND TECHNOLOGY
SCHOOL OF MARINE SCIENCE AND ENGINEERING

Marine Institute Funded PhD Research Studentship

Supervisors:
Dr Piero Calosi, Plymouth University
Professor Paul Shaw, University of Aberystwyth
Dr William Cheung, University of British Columbia

Project Description
As a result of on-going rapid global changes (warming, acidification, de-oxygenation) some areas of our oceans are becoming inhospitable for some marine organisms. In addition as marine animals are in general adapted to the conditions they live in, different populations and species living along environmental gradients may possess different levels of vulnerability to future environmental changes. Despite its paramount importance however, the physiological, ecological and genetic mechanisms which will define taxa vulnerability to complex environmental changes are still poorly understood for marine organisms. As a consequence, our capacity to predict ability of taxa to retain their range edges of distribution and size of their latitudinal range of geographical extension in the face of the global change is limited. We propose a challenging multidisciplinary PhD project which aims to explore the evolutionary macrophysiology of marine organisms within the context of global change. This PhD project will mainly be based at Plymouth University although the candidate will be expected to work for substantial periods of time both at the Population Genetics and Genomics Laboratory of Professor Shaw and at the Changing Ocean Research Unit of Dr Cheung, as well as at sea to participate to collection trips and scientific cruises. Ultimately the physiological, ecological and genetic data collected will be used to build statistical models, and also to parameterise Dr Cheung’s existing Dynamic Bioclimate Envelope Model.

Natural intrusions of hypoxic, low pH water into nearshore marine environments on the California coast

A decade-long time series recorded in Central California demonstrates that a shallow, near-shore environment (17 m depth) is regularly inundated with pulses of cold, hypoxic and low-pH water. During these episodes, oxygen can drop to physiologically stressful levels, and pH can reach values that potentially result in dissolution of calcium carbonate. Pulses of the greatest intensity arose at the onset of the spring upwelling season, and fluctuations were strongly semidiurnal and diurnal. Arrival of cold, hypoxic water on the inner shelf appears to be driven by tidal-frequency internal waves pushing deep, upwelled water into nearshore habitats. We found no relationship between the timing of low-oxygen events and the diel solar cycle. These observations are consistent with the interpretation that hypoxic water is advected shoreward from the deep, offshore environment where water masses experience a general decline of temperature, oxygen and pH with depth. Analysis of the durations of exposure to low oxygen concentrations establishes a framework for assessing the ecological relevance of these events, but physiological tolerance limits to such hypoxic events are not well documented for most near-shore organisms expected to be impacted.

Decadal changes in the aragonite and calcite saturation state of the Pacific Ocean

Based on measurements from the WOCE/JGOFS global CO₂ survey, the CLIVAR/CO₂ Repeat Hydrography Program and the Canadian Line P survey, we have observed an average decrease of 0.34% yr⁻¹ in the saturation state of surface seawater in the Pacific Ocean with respect to aragonite and calcite. The upward migrations of the aragonite and calcite saturation horizons, averaging about 1 to 2 m yr⁻¹, are the direct result of the uptake of anthropogenic CO₂ by the oceans and regional changes in circulation and biogeochemical processes. The shoaling of the saturation horizon is regionally variable, with more rapid shoaling in the South Pacific where there is a larger uptake of anthropogenic CO₂. In some locations, particularly in the North Pacific Subtropical Gyre and in the California Current, the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon. If CO₂ emissions continue as projected over the rest of this century, the resulting changes in the marine carbonate system would mean that many coral reef systems in the Pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole, and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival.

No stimulation of nitrogen fixation by non-filamentous diazotrophs under elevated CO2 in the South Pacific

Nitrogen fixation by diazotrophic cyanobacteria is a critical source of new nitrogen to the oligotrophic surface ocean. Research to date indicates that some diazotroph groups may increase nitrogen fixation under elevated pCO₂. To test this in natural mixed plankton communities, four manipulation experiments were carried out during two voyages in the South Pacific (30-35^oS). High CO₂ treatments, produced using 750ppmv CO₂ to adjust pH to 0.2 below ambient, and “Greenhouse” treatments (0.2 below ambient pH and ambient temperature +3°C), were compared with Controls in trace metal-clean deckboard incubations in triplicate. No significant change was observed in nitrogen fixation in either the high CO₂ or Greenhouse treatments over five day incubations. qPCR measurements and optical microscopy determined that the diazotroph community was dominated by Group A unicellular cyanobacteria (UCYN-A), which may account for the difference in response of nitrogen fixation under elevated CO₂ to that reported previously for Trichodesmium. This may reflect physiological differences, in that the greater cell surface area:volume of UCYN-A and its lack of metabolic pathways involved in carbon fixation may confer no benefit under elevated CO₂. However, multiple environmental controls may also be a factor, with the low dissolved iron concentrations in oligotrophic surface waters limiting the response to elevated CO₂. If nitrogen fixation by UCYN-A is not stimulated by elevated pCO₂, then future increases in CO₂ and warming may alter the regional distribution and dominance of the different diazotroph groups, with implications for dissolved iron availability and new nitrogen supply in oligotrophic regions.