High CO2 and silicate limitation synergistically increase the toxicity of Pseudo-nitzschia fraudulenta

Anthropogenic CO₂ is progressively acidifying the ocean, but the responses of harmful algal bloom species that produce toxins that can bioaccumulate remain virtually unknown. The neurotoxin domoic acid is produced by the globally-distributed diatom genus Pseudo-nitzschia. This toxin is responsible for amnesic shellfish poisoning, which can result in illness or death in humans and regularly causes mass mortalities of marine mammals and birds. Domoic acid production by Pseudo-nitzschia cells is known to be regulated by nutrient availability, but potential interactions with increasing seawater CO₂ concentrations are poorly understood. Here we present experiments measuring domoic acid production by acclimatized cultures of Pseudo-nitzschia fraudulenta that demonstrate a strong synergism between projected future CO₂ levels (765 ppm) and silicate-limited growth, which greatly increases cellular toxicity relative to growth under modern atmospheric (360 ppm) or pre-industrial (200 ppm) CO₂ conditions. Cellular Si:C ratios decrease with increasing CO₂, in a trend opposite to that seen for domoic acid production. The coastal California upwelling system where this species was isolated currently exhibits rapidly increasing levels of anthropogenic acidification, as well as widespread episodic silicate limitation of diatom growth. Our results suggest that the current ecosystem and human health impacts of toxic Pseudo-nitzschia blooms could be greatly exacerbated by future ocean acidification and ‘carbon fertilization’ of the coastal ocean.

Impacts of seawater acidification on mantle gene expression patterns of the Baltic Sea blue mussel: implications for shell formation and energy metabolism

Marine organisms have to cope with increasing CO₂ partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pCO₂ treatments (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 μatm) on mantle gene expression patterns in the blue mussel Mytilus edulis from the Baltic Sea. Based on the M. edulis mantle tissue transcriptome, the expression of several genes involved in metabolism, calcification and stress responses was assessed in the outer (marginal and pallial zone) and the inner mantle tissues (central zone) using quantitative real-time PCR. The expression of genes involved in energy and protein metabolism (F-ATPase, hexokinase and elongation factor alpha) was strongly affected by acclimation to moderately elevated CO₂ partial pressures. Expression of a chitinase, potentially important for the calcification process, was strongly depressed (maximum ninefold), correlating with a linear decrease in shell growth observed in the experimental animals. Interestingly, shell matrix protein candidate genes were less affected by CO₂ in both tissues. A compensatory process toward enhanced shell protection is indicated by a massive increase in the expression of tyrosinase, a gene involved in periostracum formation (maximum 220-fold). Using correlation matrices and a force-directed layout network graph, we were able to uncover possible underlying regulatory networks and the connections between different pathways, thereby providing a molecular basis of observed changes in animal physiology in response to ocean acidification.

Review of climate change impacts on marine fish and shellfish around the UK and Ireland

1. Recent and projected future changes in the temperature and chemistry of marine waters around the UK and Ireland are having, and will in the future have, effects on the phenology, productivity and distribution of marine fish and shellfish. However, the overall consequences are still hard to predict because behaviour, genetic adaptation, habitat dependency and the impacts of fishing on species, result in complex species’ responses that may be only partially explained by simple climate envelope predictions.
2. There is a broad body of evidence that climatic fluctuations are playing an important role in changing fish distributions and abundances, which is discernible against the background of trends in abundance due to fishing. During warm periods, southern species have tended to become more prominent and northern species less abundant. However, the changes in distribution are often more complicated than might be expected from a simple climate envelope approach, partly due to ocean circulation patterns which create invasion routes for southern water species into the North Sea from the south and from the north via the continental shelf west of Britain and Ireland.
3. The eventual population-scale impacts of ocean acidification on fish and shellfish are currently very difficult to predict. However, the scant evidence suggests that indirect food web effects arising from the enhanced sensitivity of calcifying planktonic organisms may be important, and the direct effect on fish sensory systems leading to subtle influences on behaviour with possible population-level implications are possible.
4. In British waters, the lesser sandeel (Ammodytes marinus) is identified as being at particular risk from climate change. Owing to its strict association with coarse sandy sediments it is unable to adapt its distribution to compensate for warming sea temperatures. Sandeels are a key link in the food web, linking primary and zooplankton production to top predators.

Ocean acidification is a product of our emissions, but there’s little will to change our ways

Rob Jackson, Ph.D., is the Nicholas Chair of Global Environmental Change at Duke University and a professor in the Biology Department. He is also a co-chair of the Carbon Cycle Science Working Group—a group of researchers who recommend carbon cycle priorities for the coming decades—as expressed in the document A U.S. Carbon Cycle Science Plan. It is only in the most recent 2011 version of the plan, Jackson notes, that researchers have recommended treating humans as central to the Earth’s carbon cycle, to address emissions issues from cities and industrial activities and to better study the impact of the carbon cycle on species and ecosystems—including oceans. Below, Jackson talks about ocean acidification, hypothetical fixes and the world’s serious emissions problem.

Ocean acidification: global warming’s evil twin

Recent studies have demonstrated that both the temperature increases and the increased concentrations of CO₂ in the oceans are causing significant changes in marine ecosystems. Many marine organisms are already affected by these anthropogenic stresses, including impacts due to coral bleaching and ocean acidification.

Dr. Richard A. Feely, a Senior Scientist at the NOAA Pacific Marine Environmental Laboratory in Seattle, will discuss the present and future implications of CO₂ levels on the health of our ocean ecosystems and related ocean-based economies.

Acidifying oceans and the future of molluscs: implications for food security? (audio)

Some of the threats posed by climate change can appear rather esoteric or abstract. One of these is ocean acidification – it is not immediately obvious why we should care. A recent paper by Sara Cooley and colleagues give a good example of why the threat of changing ocean chemistry matters.