Effects of Ocean Acidification on Physiological Characteristics of Coccolithophores

Abstract:

Ocean acidification caused by increasing amounts of carbon dioxide has a great impact on marine organisms, especially calcified coccolithophores. However, culture experiments examining the response of coccolithophores to elevated CO2 pa have mostly been based on investigations of a single strain and have yielded differences and even contradictory results from experiments between and even within species. Here, four strains of the coccolithophores, which contained naked and calcifying strains, were investigated simultaneously for the first time. Four carbon dioxide concentration gradients (400 µatm, 750 µatm, 1000 µatm, and 2000 µatm) were set up to systematically study the effects of ocean acidification on growth, photosynthesis, nitrogen source absorption, element composition and calcification efficiency of four coccolithophore species by batch aeration culture. The results did not show a uniform response from the different strains to elevated CO2 concentrations up to 2000 µatm, and the naked strain Emiliania huxleyi (N-E) was seriously suppressed, which was in sharp contrast to the positive response of the other three algae to the different levels. On the other hand, photosynthetic parameters Fv/Fm, Y(II) and pigment show overall downward trend for all four strains, and calcification efficiency of C-E and C-G decrease 35.4% and 68.9% respectively, on the seventh day. In addition, the four coccolithophore strains of particulate organic nitrogen production show an increasing trend and the resulting POC/PON and PIC/POC declin. We determined that the responses of coccolithophores to ocean acidification are specific, and this variation may cause changes to biodiversity and other ecosystem processes in the ocean of the future.