Abstract
Abstract. Phaeocystis globosa (Prymnesiophyceae) is an ecologically dominating phytoplankton species in many areas around the world. It plays an important role in both the global sulfur and carbon cycles, by the production of dimethylsulfide (DMS) and the drawdown of inorganic carbon. Phaeocystis globosa has a polymorphic life cycle and is considered to be a harmful algal bloom (HAB) forming species. All these aspects make this an interesting species to study the effects of increasing carbon dioxide (CO2) concentrations, due to anthropogenic carbon emissions. Here, the combined effects of three different dissolved carbon dioxide concentrations (CO2(aq)) (low: 4 μmol kg−1, intermediate: 6–10 μmol kg−1 and high CO2(aq): 21–24 μmol kg−1) and two different light intensities (low light, suboptimal: 80 μmol photons m−2 s−1 and high light, light saturated: 240 μmol photons m−2 s−1) are reported. The experiments demonstrated that the specific growth rate of P. globosa in the high light cultures decreased with increasing CO2(aq) from 1.4 to 1.1 d−1 in the low and high CO2 cultures, respectively. Concurrently, the photosynthetic efficiency (FV/FM) increased with increasing CO2(aq) from 0.56 to 0.66. The different light conditions affected photosynthetic efficiency and cellular chlorophyll a concentrations, both of which were lower in the high light cultures as compared to the low light cultures. These results suggest that in future inorganic carbon enriched oceans, P. globosa will become less competitive and feedback mechanisms to global change may decrease in strength.
Highlights
The genus of Phaeocystis (Prymnesiophyceae) has a global distribution and consists of several species, three of which are known to form large blooms of colonies (P. antarctica, P. pouchetii and P. globosa)
When the data of the high light and the low light cultures were separated, it was observed that the difference between AT(pred) and AT(meas) slightly decreased with increasing particulate organic carbon (POC) concentrations in the high light cultures, ranging between −0.4 and 23.0 μmol kg−1 (r2 = 0.31, n = 16)
The increasing atmospheric concentrations of carbon dioxide due to anthropogenic CO2 emissions lead to changes the inorganic carbon chemistry of seawater
Summary
The genus of Phaeocystis (Prymnesiophyceae) has a global distribution and consists of several species, three of which are known to form large blooms of colonies (P. antarctica, P. pouchetii and P. globosa). The large colonies on the other hand, which can reach a size of up to 3 cm in diameter and can contain thousands of cells in a polysaccharide matrix, are grazed upon by meso-zooplankton, and are not prone to viral infection (Schoemann et al, 2005; Whipple et al, 2005 and references therein). It is not exactly clear what causes colony formation in P. globosa. This irradiance threshold is strain dependent, since colony formation of other strains has been observed in light conditions between 10 and 20 μmol photons m−2 s−1
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