Viv Johnson and colleagues recently published their paper, Temperate and tropical brown macroalgae thrive, despite decalcification, along natural CO2 gradients, in Global Change Biology 2012 18(9).
Their work relates to our work with seagrasses and is more evidence that in order to understand the true impacts of climate change and ocean acidification we need to examine species interactions in nature. Their underwater volcanic vents sites are excellent “natural experiments” for understanding future ecosystem changes.
Summary: Here, we compare ecological shifts in subtidal rocky shore systems along CO2 gradients created by volcanic seeps in the Mediterranean and Papua New Guinea, focussing on abundant macroalgae and grazing sea urchins. In both the temperate and tropical systems the abundances of grazing sea urchins declined dramatically along CO2 gradients. Temperate and tropical species of the calcifying macroalgal genus Padina (Dictyoaceae, Phaeophyta) showed reductions in CaCO3 content with CO2 enrichment. In contrast to other studies of calcified macroalgae, however, we observed an increase in the abundance of Padina spp. in acidified conditions. Reduced sea urchin grazing pressure and significant increases in photosynthetic rates may explain the unexpected success of decalcified Padina spp. at elevated levels of CO2.