Bacteria growth, enzyme activities and TEP during KOSMOS 2011 mesocosm experiment in the Raunefjord

Marine bacteria are the main consumers of freshly produced organic matter. Many enzymatic processes involved in the bacterial digestion of organic compounds were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years but the consequences for microbial physiology, organic matter cycling and marine biogeochemistry are still unresolved. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging initially from ca. 280 to 3000 µatm and sampled every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During the first phytoplankton bloom, 5-10% more transparent exopolymer particles were formed in the high pCO2 mesocosms. Simultaneously, the efficiency of the protein-degrading enzyme leucine aminopeptidase increased with decreasing pH resulting in up to three times higher values in the highest pCO2/lowest pH mesocosm compared to the controls. In general, total and cell-specific aminopeptidase activities were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported up to 28% higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean.

Enzyme activities of digestive and metabolic enzymes of Calanus finmarchicus from Maria S. Merian cruise MSM26 in spring 2013

The present study aimed to contribute to the knowledge on the intraspecific variations of enzyme activities in populations of Calanus finmarchicus from different longitudes across the North Atlantic Ocean and their relation to changing environmental conditions. C. finmarchicus was sampled across the North Atlantic in basins with decreasing temperature regimes from east to west (Iceland Basin, Irminger Basin and Labrador Basin) in late March/early April 2013. Potential maximum enzyme activities of digestive (proteinases and lipases/esterases) and metabolic (citrate synthase) enzymes of copepods from all sampling stations were analysed and thermal profiles (5-50°C) of enzyme activities were determined. In order to investigate its acclimation potential, C. finmarchicus were acclimated to 4°C and 15°C for two weeks and thermal profiles of enzyme activities were compared afterwards.