MORPHOLOGICAL AND PHYSIOLOGICAL EFFECTS IN PROBOSCIA ALATA (BACILLARIOPHYCEAE) GROWN UNDER DIFFERENT LIGHT AND CO 2 CONDITIONS OF THE MODERN SOUTHERN OCEAN 1

• Published in: Journal of Phycology
• Main Authors: Hoogstraten, Astrid, Timmermans, Klaas R., de Baar, Hein J. W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Southern Ocean
• Online Access: http://dx.doi.org/10.1111/j.1529-8817.2012.01148.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1529-8817.2012.01148.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1529-8817.2012.01148.x

The combined effects of different light and aqueous CO 2 conditions were assessed for the Southern Ocean diatom Proboscia alata (Brightwell) Sundström in laboratory experiments. Selected culture conditions (light and CO 2(aq) ) were representative for the natural ranges in the modern Southern Ocean. Light conditions were 40 (low) and 240 (high) μmol photons · m −2 · s −1 . The three CO 2(aq) conditions ranged from 8 to 34 μmol · kg −1 CO 2(aq) (equivalent to a pCO 2 from 137 to 598 μatm, respectively). Clear morphological changes were induced by these different CO 2(aq) conditions. Cells in low [CO 2(aq) ] formed spirals, while many cells in high [CO 2(aq) ] disintegrated. Cell size and volume were significantly affected by the different CO 2(aq) concentrations. Increasing CO 2(aq) concentrations led to an increase in particulate organic carbon concentrations per cell in the high light cultures, with exactly the opposite happening in the low light cultures. However, other parameters measured were not influenced by the range of CO 2(aq) treatments. This included growth rates, chlorophyll a concentration and photosynthetic yield (F V /F M ). Different light treatments had a large effect on nutrient uptake. High light conditions caused an increased nutrient uptake rate compared to cells grown in low light conditions. Light and CO 2 conditions co‐determined in various ways the response of P. alata to changing environmental conditions. Overall P. alata appeared to be well adapted to the natural variability in light availability and CO 2(aq) concentration of the modern Southern Ocean. Nevertheless, our results showed that P. alata is susceptible to future changes in inorganic carbon concentrations in the Southern Ocean.