Villefranche sur Mer: multistressors experiment March 2012

The effect of ocean warming and acidification was investigated on a natural plankton assemblage from an oligotrophic area, the bay of Villefranche (NW Mediterranean Sea). The assemblage was sampled in March 2012 and exposed to the following four treatments for 12 days: control ( 360 µatm, 14°C), elevated pCO2 ( 610 µatm, 14°C), elevated temperature ( 410 µatm, 17°C), and elevated pCO2 and temperature ( 690 µatm, 17°C). Nutrients were already depleted at the beginning of the experiment and the concentrations of chlorophyll a (chl a), heterotrophic prokaryotes and viruses decreased, under all treatments, throughout the experiment. There were no statistically significant effects of ocean warming and acidification, whether in isolation or combined, on the concentrations of nutrients, particulate organic matter, chl a and most of the photosynthetic pigments. Furthermore, 13C labelling showed that the carbon transfer rates from 13C-sodium bicarbonate into particulate organic carbon were not affected by seawater warming nor acidification. Rates of gross primary production followed the general decreasing trend of chl a concentrations and were significantly higher under elevated temperature, an effect exacerbated when combined to elevated pCO2 level. In contrast to the other algal groups, the picophytoplankton population (cyanobacteria, mostly Synechococcus) increased throughout the experiment and was more abundant in the warmer treatment though to a lesser extent when combined to high pCO2 level. These results suggest that under nutrient-depleted conditions in the Mediterranean Sea, ocean acidification has a very limited impact on the plankton community and that small species will benefit from warming with a potential decrease of the export and energy transfer to higher trophic levels.

Sample characteristics and pigment concentration of arctic snow and permafrost algal strains

Ten algal strains from snow and permafrost substrates were tested for their ability to produce secondary carotenoids and ?-tocopherol in response to high light and decreased nitrogen levels. The Culture Collection of Cryophilic Algae at Fraunhofer IBMT in Potsdam served as the bioresource for this study. Eight of the strains belong to the Chlorophyceae and two strains are affiliated to the Trebouxiophyceae. While under low light, all 10 strains produced the normal spectrum of primary pigments known to be present in Chlorophyta, only the eight chlorophyceaen strains were able to synthesize secondary carotenoids under stress conditions, namely canthaxanthin, echinenone and astaxanthin; seven of them were also able to synthesize minor amounts of adonixanthin and an unidentified hydroxyechinenone. The two trebouxiophyceaen species of Raphidonema exhibited an unusually high pool of primary xanthophyll cycle pigments, possibly serving as a buffering reservoir against excessive irradiation. They also proved to be good alpha-tocopherol producers, which might also support the deactivation of reactive oxygen species. This study showed that some strains might be interesting novel candidates for biotechnological applications. Cold-adapted, snow and permafrost algae might serve as valuable production strains still exhibiting acceptable growth rates during the cold season in temperate regions.

Hydrochemistry, phytoplankton pigment concentration and phytoplankton abundance in water samples obtained in the Kuroshio Extension Front in October 2009

This data was collected during a cruise to the Kuroshio Extension Front in October 2009. Several chemical and biological parameters were measured: dissolved nutrients, picophytoplankton (by flow cytometry), microphytoplankton (by light microscopy) and phytoplankton pigments (HPLC).