Ocean acidification effects on benthic Mediterranean organisms along a natural CO2 gradient

Increasing anthropogenic CO2 is predicted to be a major driver of environmental change during the current century in both terrestrial and marine ecosystems (Edenhofer et al., 2011). Climate change is a threat to marine biota because increased atmospheric CO2 is causing ocean warming, acidification, hypercapnia, decreased carbonate saturation and hypoxia (Cao et al., 2007) leading to more corrosive conditions for calcifying organisms and making it more difficult for them to build and maintain their carbonate skeletons (Raven et al., 2005).

Most studies to date investigating how elevated CO2 conditions will impact the function of marine organisms have been single-species laboratory experiments that last a year at most (Martin and Gattuso, 2009). Such experiments provide important information on species’ responses to increased pCO2 but fail to account for the effects of long-term exposure, ignoring full organism acclimatization. They are also unrepresentative of natural ecosystems since, for example, they remove the effects of species interactionsproviding little or no information on processes leading to ecosystem adaptation, such as altered reproduction, competition, food webs and disease susceptibility or genetic adaptation (Barry et al., 2010). There is, therefore, great need for empirical data documenting the long-term effects of ocean acidification on marine ecosystems acclimatized to high pCO2 as found, for example, around submarine CO2 vents. Vent systems are not perfect predictors of future ocean ecology owing to temporal variability in pH, spatial proximity of populations unaffected by acidification and multiple environmental parameters which may co-vary, making it difficult to resolve the influence of Ωarag on calcification from that of other factors (Hall-Spencer et al., 2008). However, such vents acidify seawater on sufficiently large spatial and temporal scales to integrate ecosystem processes such as production, competition and predation.

Here we assess the effect of increasing levels of CO2 on the abundance of the scleractinian solitary zooxanthellate coral Balanophyllia europaea (Anthozoa), the tube-forming gastropod Vermetus triqueter (Gastropoda), the brown alga Padina pavonica (Phaeophyceae) which deposits calcium carbonate as aragonite needles extracellularly on the surface of fan-shaped thalli (Okazaki et al., 1986), the green alga Acetabularia acetabulum (Ulvophyceae) whose outer surfaces of the cell wall and intercellular spaces are calcified with aragonite crystals (Kingsley et al., 2003), and the brown foliose macroalga Lobophora variegata (Phaeophyceae).

Prada F., Caroselli E., Zaccanti F., Capaccioni B., Falini G., Levy O., Dubinsky Z. & Goffredo S., 2013. Ocean acidification effects on benthic Mediterranean organisms along a natural CO2 gradient. In Lang M. A. & Sayer M. D. J. (Eds.), Proceedings of the Joint International Scientific Diving Symposium, p. 231-234. Article.

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