Marine microphytobenthic assemblage shift along a natural shallow-water CO<inf>2</inf>gradient subjected to multiple environmental stressors
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© 2015 by the authors; licensee MDPI, Basel, Switzerland. Predicting the effects of anthropogenic CO2emissions on coastal ecosystems requires an understanding of the responses of algae, since these are a vital functional component of shallow-water habitats. We investigated microphytobenthic assemblages on rock and sandy habitats along a shallow subtidal pCO2gradient near volcanic seeps in the Mediterranean Sea. Field studies of natural pCO2gradients help us understand the likely effects of ocean acidification because entire communities are subjected to a realistic suite of environmental stressors such as over-fishing and coastal pollution. Temperature, total alkalinity, salinity, light levels and sediment properties were similar at our study sites. On sand and on rock, benthic diatom abundance and the photosynthetic standing crop of biofilms increased significantly with increasing pCO2. There were also marked shifts in diatom community composition as pCO2levels increased. Cyanobacterial abundance was only elevated at extremely high levels of pCO2(>1400 μatm). This is the first demonstration of the tolerance of natural marine benthic microalgae assemblages to elevated CO2in an ecosystem subjected to multiple environmental stressors. Our observations indicate that Mediterranean coastal systems will alter as pCO2levels continue to rise, with increased photosynthetic standing crop and taxonomic shifts in microalgal assemblages.
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