The organizing effects of elevated CO2 on competition among estuarine primary producers
In: Scientific Reports (Nature Publishing Group). Nature Publishing Group: London. ISSN 2045-2322; e-ISSN 2045-2322, more
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| Abstract |
Fossil fuel combustion, eutrophication, and upwelling introduce excess CO2 into coastal zones. The extent to which marine autotrophs may benefit from elevated CO2 will be a function of their carbon limitation and, among other factors, competition with other primary producers. Here, we report on experiments performed with North Atlantic species of Ulva and Gracilaria grown in situ or exposed to ambient (similar to 400 mu atm) and elevated pCO(2) (similar to 2500 mu atm) and/or subjected to competition with each other and/or with natural plankton assemblages. Elevated pCO(2) significantly increased the growth rates of Gracilaria and Ulva and yielded significant declines in tissue delta C-13, suggesting that increased growth was associated with increased CO2 use relative to HCO3-. Gracilaria growth was unaffected by competition with plankton or Ulva, while Ulva experienced significantly reduced growth when competing with Gracilaria or plankton. Dinoflagellates experienced significantly increased growth when exposed to elevated pCO(2) but significantly slower growth when competing with Gracilaria. Elevated carbon-tonitrogen ratios among macroalgae suggested that competition for nitrogen also shaped interactions among autotrophs, particularly Ulva. While some estuarine autotrophs benefit from elevated pCO(2), the benefit can change when direct competition with other primary producers is considered with Gracilaria outcompeting Ulva and dinoflagellates outcompeting diatoms under elevated pCO(2). |
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