Assessing the effects of long-term ocean acidification at volcanic CO2 vents

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Objective: to determine the ecological effects of elevated CO2 levels in coastal habitats. In an 8 month training period at CNRS Roscoff and the MBA Plymouth the student will monitor variations in carbonate chemistry and biota of rockpool habitats. The student will be trained by a supervisory team that is world-leading in ecosystem based ocean acidification research using natural analogues. The student will then apply these skills to monitor spatial and temporal variability in pH (Total Scale) and seawater carbonate chemistry (DIC and total alkalinity) on coastal habitats off Pantelleria and Vulcano (Sicily) where gas vents are shallow (<10 m depth) and have shorelines with mean pCO2 levels of 380, 1000 and 2000 ppm, similar to those recently described in Nature by the PI off Ischia. These gas vent sites have been chosen carefully and are suited to test the following hypotheses; 1) near-future levels of ocean acidification (year 2100 scenarios) may enhance the growth and reproduction of sea grasses and certain invasive macroalgae in natural settings, 2) chronic hypercapnia can lead to an overall reduction in benthic biodiversity, including the loss of numerous calcified species, with negative effects on ecosystem function in intertidal and subtidal habitats, 3) transplant experiments, coupled with sampling along pCO2 gradients, confirm that some species can adapt to long-term acidification by altering skeletal mineralogy, 4) active metazoans (e.g. shrimp and fish) can withstand high levels of CO2 as adults but do not complete their life-histories at naturally acidified sites. This approach is innovative as ecosystem effects are difficult to assess using methods adopted by the BIOACID and EPOCA programmes, whereby CO2 levels are manipulated in aquaria and mesocosms over timescales of weeks-months. This studentship is designed to meet the UK OA Science Plan which states that 'Powerful insights may also be gained from studies of areas with natural CO2 enrichment'. The studentship addresses Aims 3.1, 3.3 and will also obtain data to improve our understanding of OA impacts for commercially important species. The lead supervisor is a PI within the EPOCA program and co-author of their 'Guide to Best Practices in Ocean Acidification Research' which will be the methodological basis of this studentship. Comparisons will be made of benthic biodiversity and biomass on replicate plots from 380 to mean 1000 and 2000 ppm CO2 using hand-held cores in sediments (e.g. for foraminifera) and 0.5 m2 quadrats on rock. Settlement plates will be deployed to investigate recruitment processes at different levels of pCO2 and transplant experiments (of coralline algae, mussels and oysters) will be used to determine the effects of long-term exposures to high CO2 levels on calcification, fecundity and growth. Photosynthesis (using PAM), reproduction and growth will be measured on seagrass (Posidonia) and macroalgae (Sargassum, Asparagopsis). The student will examine whether calcified algae, foraminifera and corals can adapt their mineralogy depending on the amounts of CO2 in the surrounding seawater under supervision in Bijma's BIOACID group using Atomic force- and Raman-microscopy to study the impact on the fine- and ultra-structure of calcified organisms that grew at high CO2. During field excursions in 2012 repeated visual counts will be used to assess the diversity, behavior and abundance of shrimps and fish recording the distribution of gravid females and fish nests in relation to CO2 monitoring zones, as juvenile stages can be the most vulnerable to OA effects. The range of hypotheses to be tested are not too ambitions for doctoral research, given our supervisory track-record, preliminary surveys of Vulcano and Pantelleria and our experience at Ischia.