Seasonal and annual variability in the phytoplankton community of the Raunefjord, west coast of Norway from 2001–2006

ABSTRACT

Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes.

SUBJECT EDITOR:

• Audrey J. Geffen

KEYWORDS:

• Norway
• phytoplankton community
• Raunefjord
• seasonal and inter-annual changes
• succession
• time series

Acknowledgements

We would like to thank Tomas Sørlie and Mette Hordnes for assistance during sampling, and Bergen Municipality for providing nutrients data. We also thank the reviewers for valuable suggestions and comments to earlier versions of the manuscript.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported by the European Research Council through the Advanced Grant project No. 250254 'MINOS' and University of Bergen, Norway.