The effect of chronic and acute low pH on the intracellular DMSP production and epithelial cell morphology of red coralline algae

The release of dimethylsulphoniopropionate (DMSP) by marine algae has major impacts on the global sulphur cycle and may influence local climate through the formation of dimethylsulphide (DMS). However, the effect of global change on DMSP/DMS (DMS(P)) production by algae is not well understood. This study examined the effect of low pH on DMS(P) production and epithelial cell morphology of the free-living red coralline alga Lithothamnion glaciale. Three pH treatments were used in the 80-day experiment: (1) current pH level (8.18, control), (2) low, chronic pH representing a 2100 ocean acidification (OA) scenario (7.70) and (3) low, acute pH (7.75, with a 3-day spike to 6.47), representing acute variable conditions that might be associated with leaks from carbon capture and storage infrastructure, at CO₂ vent sites or in areas of upwelling. DMS(P) production was not significantly enhanced under low, stable pH conditions, indicating that red coralline algae may have some resilience to OA. However, intracellular and water column DMS(P) concentrations were significantly higher than the control when pH was acutely spiked. Cracks were observed between the cell walls of the algal skeleton in both low pH treatments. It is proposed that this structural change may cause membrane damage that allows DMS(P) to leak from the cells into the water column, with subsequent implications for the cycling of DMS(P) in coralline algae habitats.

Arctic study of ocean acidification impacts

As the UK approaches summer with high hopes of good weather, a team of adventurous scientists will be setting sail for far chillier climes. Thirty researchers from eight laboratories will leave the UK on 1st June 2012 to study the effect of ocean acidification on the Norwegian, Barents and Greenland Seas.

They will travel as far north as polar ice will allow, collecting seawater samples from both the open water and gaps in the sea-ice. This study is the largest ever to examine the effects of altering carbon dioxide (CO2) levels in “real world” seawater samples directly after they are collected at sea.

Polar seas are expected to be especially sensitive to the effects of ocean acidification, since more CO2 dissolves in cold water, making Arctic waters a valuable natural example of how the marine environment will respond to a high CO2 world. Also, the chemical sensitivity of surface seawater in the Arctic means that it will become corrosive to calcium carbonate before anywhere else in the world. This could pose a serious problem for marine plankton and other organisms that use calcium carbonate for theirshells or skeletons.

During the expedition, the scientists will study the impact of the changing chemistry on marine organisms and ecosystems, the cycling of carbon and nutrients in the sea and how the sea interacts with the atmosphere to influence climate.

Two approaches will be used in this study. Firstly, the researchers will look at how ecosystems vary between areas where the chemistry of seawater is naturally more acidic or alkaline. By contrasting the observations over a range of different conditions, insights researchers will discover how acidification may affect organisms living in their natural environment, where natural selection and adaptation have had time to play out.

The second approach is experimental, using tanks of natural seawater collected from the upper ocean and brought into controlled conditions on deck. This natural seawater will be subjected to various levels of CO2 that are likely to occur in the future. The expedition, aboard the RRS James Clark Ross, will end on 4th July in Reykjavik, Iceland and members of the team will be blogging about their progress at http://www.arcticoacruise.org/?cat=1.

Dr Ray Leakey, Arctic Research Theme Leader at the Scottish Association for Marine Science (SAMS) and the leader of the current expedition says, “Few studies have investigated the effects of ocean acidification on the marine food web of the remote Arctic seas, and most have focused on laboratory cultures or natural communities from a limited number of relatively accessible coastal locations. By contrast our expedition will be by ship in both ice-covered and ice-free oceanic waters far from land. This will allow us to undertake the most comprehensive study to date of the ways in which the plants and animals living in the surface waters of the Arctic ocean respond to acidification.”

Dr Toby Tyrrell from the National Oceanography Centre and coordinator of the Sea Surface consortium added, “Following our cruise last year to the northwest European shelf (for more information please see Notes to Editors), this second cruise will visit the more remote Arctic Ocean which may well be more seriously affected by ocean acidification. The data collected will improve our understanding of future impacts, providing important information about the consequences of continuing to burn fossil fuels in enormous quantities (atmospheric CO2 is already 40% above its preindustrial level, and still climbing). Our final cruise, in 6 months time, will visit the other polar ocean, the Southern Ocean.”

The global ocean has absorbed about a third of the total CO2 produced by human activities in the past 200 years. This uptake of CO2 has greatly slowed the rate of human-driven climate change. It is also responsible for major changes to ocean chemistry, known as ocean acidification, with potentially serious implications for marine life.

The research is part of the UK Ocean Acidification Research Programme (UKOA), funded by the Natural Environment Research Council (NERC), the Department of Environment, Food and Rural Affairs (Defra) and the Department of Energy and Climate Change (DECC).

Gene transcripts encoding hypoxia-inducible factor (HIF) exhibit tissue- and muscle fiber type-dependent responses to hypoxia and hypercapnic hypoxia in the Atlantic blue crab, Callinectes sapidus

Hypoxia inducible factor (HIF) is a transcription factor that under low environmental oxygen regulates the expression of suites of genes involved in metabolism, angiogenesis, erythropoiesis, immune function, and growth. Here, we isolated and sequenced partial cDNAs encoding hif-α and arnt/hif-β from the Atlantic blue crab, Callinectes sapidus, an estuarine species that frequently encounters concurrent hypoxia (low O2) and hypercapnia (elevated CO2). We then examined the effects of acute exposure (1 hr) to hypoxia (H) and hypercapnic hypoxia (HH) on relative transcript abundance for hif-α and arnt/hif-β in different tissues (glycolytic muscle, oxidative muscle, hepatopancreas, gill, and gonads) using quantitative real-time RT-PCR. Our results indicate that hif-α and arnt/hif-β mRNAs were constitutively present under well-aerated normoxia (N) conditions in all tissues examined. Further, H and HH exposure resulted in both tissue-specific and muscle fiber type-specific effects on relative hif-α transcript abundance. In the gill and glycolytic muscle, relative hif-α mRNA levels were significantly lower under H and HH, compared to N, while no change (or a slight increase) was detected in oxidative muscle, hepatopancreas and gonadal tissues. H and HH did not affect relative transcript abundance for arnt/hif-β in any tissue or muscle fiber type. Thus, in crustaceans the HIF response to H and HH appears to involve changes in hif transcript abundance, with variation in hif-α and arnt/hif-β transcriptional dynamics occurring in both a tissue- and muscle fiber type-dependent manner.