Mesozooplankton community development at elevated CO₂ concentrations: results from a mesocosm experiment in an Arctic fjord

• Main Authors: B. Niehoff, T. Schmithüsen, N. Knüppel, M. Daase, J. Czerny, T. Boxhammer
• Format: Article
• Language: English
• Published: Copernicus Publications 2013-03-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/10/1391/2013/bg-10-1391-2013.pdf

The increasing CO₂ concentration in the atmosphere caused by burning fossil fuels leads to increasing <i>p</i>CO₂ and decreasing pH in the world ocean. These changes may have severe consequences for marine biota, especially in cold-water ecosystems due to higher solubility of CO₂. However, studies on the response of mesozooplankton communities to elevated CO₂ are still lacking. In order to test whether abundance and taxonomic composition change with <i>p</i>CO₂, we have sampled nine mesocosms, which were deployed in Kongsfjorden, an Arctic fjord at Svalbard, and were adjusted to eight CO₂ concentrations, initially ranging from 185 μatm to 1420 μatm. Vertical net hauls were taken weekly over about one month with an Apstein net (55 μm mesh size) in all mesocosms and the surrounding fjord. In addition, sediment trap samples, taken every second day in the mesocosms, were analysed to account for losses due to vertical migration and mortality. The taxonomic analysis revealed that meroplanktonic larvae (Cirripedia, Polychaeta, Bivalvia, Gastropoda, and Decapoda) dominated in the mesocosms while copepods (<i>Calanus</i> spp., <i>Oithona similis</i>, <i>Acartia longiremis</i> and <i>Microsetella norvegica</i>) were found in lower abundances. In the fjord copepods prevailed for most of our study. With time, abundance and taxonomic composition developed similarly in all mesocosms and the <i>p</i>CO₂ had no significant effect on the overall community structure. Also, we did not find significant relationships between the <i>p</i>CO₂ level and the abundance of single taxa. Changes in heterogeneous communities are, however, difficult to detect, and the exposure to elevated <i>p</i>CO₂ was relatively short. We therefore suggest that future mesocosm experiments should be run for longer periods.