Ocean acidification (OA) is the decrease in ocean pH due to increasing atmospheric pC02• It is predicted that by the year 2100, the pC02 will rise from ca 385 uatm today to 750 uatrn, with a corresponding decrease in surface ocean pH from 8.1 to 7.8. pH was monitored at five stations around a coastal CO2 vent site in Ischia, Italy and the utility of such areas discussed. An ecological survey of benthic macroalgae revealed a substantial community shift at lower pH toward reduced species richness and diversity. The chlorophytes became more dominant at lower pH, with cover increasing from 45-55% at pH 8.16-7.84, to 67-90% at pH 7.48-7.11. Heavily calcified species disappeared at pH 7.48-7.11, but their total cover did not change significantly between pH 8.16-7.80, suggesting some resilience over this century. At lower pH, the DMSP content in macroalgae from Ischia increased in the chlorophytes while in rhodophytes and phaeophytes it decreased. The dark-adapted algal photophysiology suggested a significant benefit when pH was 7.84-7.80, which was lost at pH 7.48-7.11. Two species of common chlorophyte macroalgae VIva lactuca and VIva clathrata, were incubated under pC02 conditions ranging from 432 to 1514 uatrn, In both species, the results indicated that by the year 2100 there could be a large decrease by 50-58% in DMS production, a reduction in chlororespiration, and increased reproductive output in these species. I conclude that increasing pC02 does not directly fertilise photosynthesis or somatic growth in the Ulvales but, reduces chlororespiration, possibly due to carbon-concentrating mechanism down-regulation. This may be the cause of the large reduction in DMS production seen and may lead to a reallocation of resources towards reproductive output. This may increase the prevalence of chlorophyte macroalgae in the future with major repercussions for coastal ecosystems.
Kerrison P. D., 2012. The effect of ocean acidification on the ecology and physiology of marine macroalgae. PhD thesis, University of Essex. Thesis (restricted access).