Hall-Spencer, JM

Rodolfo-Metalpa, R

English

Hall-Spencer, Jason

Plymouth Electronic Archive and Research Library

22 JMBA Global Marine EnvironmentThe global oceans currently absorb over 25 milliontons of CO2 every day. This has caused surface waters tobecome 30% more acidic since wide-spread burning offossil fuels began. As well as lowering pH, increased CO2levels are altering surface water chemistry, causing adecline in carbonate ions, an increase in bicarbonate ionsand lowering calcium carbonate saturation states. Fallingcalcite and aragonite levels are a concern since these arethe building-blocks of shells for a range of marineorganisms from tiny coccolithophores to giant coral reefs.Research into the marine environmental effects ofincreased oceanic CO2 levels is mainly being carried outusing short-term-shock experiments whereby pH or CO2levels are manipulated in aquaria and enclosures overshort timescales.Plymouth researchers teamed-up with scientists fromlabs in France, the UK, Israel and Italy to document thefirst ecosystem-wide responses to long-term changes inocean pH. The effects were studied on marinecommunities around underwater volcanic vents off Ischiaisland (Figure 1), where carbon dioxide bubbles-up like aJacuzzi (Figure 2). Gas analyses showed that the ventsreleased millions of litres of CO2 per day (Figure 3)causing seawater acidification but the gas was at ambienttemperature and lacked poisonous sulphur compoundswhich typify most volcanic vents. Impacts on marine lifeincluded 30% reductions in biodiversity in areas whereaverage pH had dropped by 0.4 units compared withareas at normal seawater pH (8.2).Natural CO2 vents can provide insights into whichspecies are tolerant of long-term high CO2 levels and canbe used to test predictions based on modelling andlaboratory work, such as what levels of CO2 exposurerestrict the ability of marine organisms to build shells(Figure 3). Although lush stands of seagrasses thrived atincreased CO2 levels (Figure 4), major groups such ascorals, sea urchins and bivalves were removed from theecosystem and replaced by algae such as Sargassum sp.and Caulerpa spp. In brief, the research showed:• major ecological tipping points along a gradient ofincreasing CO2 levels• acidification dissolved the shells of calcified speciessuch as corals, sea urchins and snails, which wereabsent in areas with a pH less than 7.4ECOLOGICAL EFFECTSOF VOLCANIC CO2 VENTSFIGURE 1: Anton Dohrn’s summer house on Ischia island, now part of StazioneZoologica Naples, the oldest marine biology institute in the world.FIGURE 2: Carbon dioxide vents in shallow waters at 0-10 m depth off Ischia Island, Bay of Naples.JMBA Global Marine Environment 23• high CO2 favoured the production of seagrass andremoved its calcareous epiphytes• the amount of calcified algae, which bind coral reefstogether in the tropics, fell from more than 60 per centcover outside the vent areas to zero within these areas• invasive alien species, which cause damage toecosystems worldwide, may thrive at high CO2 levelsThis study demonstrates, for the first time, whathappens to marine ecosystems when key groups ofspecies are killed due to rising CO2 levels. We are nowundergoing the fastest rate of ocean acidification the Earthhas seen for at least the past 20 million years so this studyadds urgency to the international policy drive to reduceCO2 emissions.Riccardo Rodolfo-Metalpa and Jason Hall-SpencerMarine Institute, University of Plymouth, PL4 8AA.FURTHER READINGHall-Spencer JM, Rodolfo-Metalpa R,  Martin S, Ransome E, Fine M,Turner SM, Rowley S, Tedesco D & Buia M-C. (2008) Volcanic carbondioxide vents reveal ecosystem effects of ocean acidification. Nature454, 96–99.FIGURE 3: SCUBA diver collecting volcanic gasses for analysesFIGURE 5: Posidonia oceanica seagrass meadow a) growing in acidified waterwith few calcified epiphytes such as b) the bryozoan Electra posidoniae, c) growing in normal seawater with abundant calcified epiphytes such as d) coralline algae.FIGURE 4: Dramaticdissolution of intertidallimpet (Patella caerulea)living near CO2 vents

ECOLOGICAL EFFECTS OF VOLCANIC CO2 VENTS

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