Temperate and tropical brown macroalgae thrive, despite decalcification, along natural CO2 gradients

• Published in: Global Change Biology
• Main Authors: Johnson, VR, Russell, BD, Fabricius, KE, Brownlee, C, Hall-Spencer, JM
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: calcification; ocean acidification; photosynthesis; temperate and tropical coastal ecosystems; Ocean acidification
• Online Access: http://hdl.handle.net/10026.1/1320; https://doi.org/10.1111/j.1365-2486.2012.02716.x

<jats:title>Abstract</jats:title><jats:p>Predicting the impacts of ocean acidification on coastal ecosystems requires an understanding of the effects on macroalgae and their grazers, as these underpin the ecology of rocky shores. Whilst calcified coralline algae (Rhodophyta) appear to be especially vulnerable to ocean acidification, there is a lack of information concerning calcified brown algae (Phaeophyta), which are not obligate calcifiers but are still important producers of calcium carbonate and organic matter in shallow coastal waters. Here, we compare ecological shifts in subtidal rocky shore systems along <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub> 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 <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub> gradients. Temperate and tropical species of the calcifying macroalgal genus <jats:italic>Padina</jats:italic> (Dictyoaceae, Phaeophyta) showed reductions in Ca<jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>3</jats:sub> content with <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub> enrichment. In contrast to other studies of calcified macroalgae, however, we observed an increase in the abundance of <jats:italic>Padina</jats:italic> spp. in acidified conditions. Reduced sea urchin grazing pressure and significant increases in photosynthetic rates may explain the unexpected success of decalcified <jats:italic>Padina</jats:italic> spp. at elevated levels of <jats:styled-content style="fixed-case">CO</jats:styled-content><jats:sub>2</jats:sub>. This is the first ...