Persistent natural acidification drives major distribution shifts in marine benthic ecosystems

7 páginas, 4 figuras.Ocean acidification is receiving increasing attention because of its potential to affect marine ecosystems. Rare CO2 vents offer a unique opportunity to investigate the response of benthic ecosystems to acidification. However, the benthic habitats investigated so far are mainly found at very shallow water (less than or equal to 5 m depth) and therefore are not representative of the broad range of continental shelf habitats. Here, we show that a decrease from pH 8.1 to 7.9 observed in a CO2 vent system at 40 m depth leads to a dramatic shift in highly diverse and structurally complex habitats. Forests of the kelp Laminaria rodriguezii usually found at larger depths (greater than 65 m) replace the otherwise dominant habitats (i.e. coralligenous outcrops and rhodolith beds), which are mainly characterized by calcifying organisms. Only the aragonite-calcifying algae are able to survive in acidified waters, while high-magnesium-calcite organisms are almost completely absent. Although a long-term survey of the venting area would be necessary to fully understand the effects of the variability of pH and other carbonate parameters over the structure and functioning of the investigated mesophotic habitats, our results suggest that in addition of significant changes at species level, moderate ocean acidification may entail major shifts in the distribution and dominance of key benthic ecosystems at regional scale, which could have broad ecological and socio-economic implications.Financial support was provided by Fundación Biodiversidad through the LIFE+ INDEMARES project, the EC within the VII Framework Programme through the MIDAS project (ref. GA no. 603418) and the Spanish Ministry of Economy and Competitivity through the SMART project (CGL2012-32194). Additional support was received from Catalan Government Grups de Recerca Consolidats grants (2009 SGR 361, 1174 and 1068). C.L. was funded by a Ramón y Cajal research contract (RyC-2011-08134). This is a contribution of INTRAMURAL-CSIC 065 project to E.B.Peer reviewe