Zooplankton species composition in Kongsfjorden (Calanus spp.)

A net for catching zooplankton.
Photo: Ann Kristin Balto / Norwegian Polar Institute

The Kongsfjorden pelagic ecosystem is influenced by both Atlantic and Arctic waters. The relative amount of the Atlantic Calanus finmarchicus and the Arctic Calanus glacialis varies from year to year. Calanus finmarchicus has been the dominant species the last decade, due to increased inflow of Atlantic water and hence increased temperature. Changes in zooplankton community will cascade to higher trophic levels, and might change the character of the pelagic ecosystem. Therefore, the composition of zooplankton community in Kongsfjorden might function as a climate indicator on a local scale.

What is being monitored?

Calanus species in Kongsfjorden

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The figure shows the proportion of the total Calanus abundance made up of the Atlantic species, Calanus finmarchicus, and the two Arctic species, Calanus glacialis and Calanus hyperboreus. The Arctic species (especially C. glacialis) dominate in Kongsfjorden in "cold" years when the influx of Atlantic water is low, as in 1999, 2000 and 2008. The density of C. finmarchicus rises in "warm" years with a larger inflow of warm, Atlantic water. Strong inflows of Atlantic water during the winter 2005-2006 have led to Kongsfjorden remaining ice-free in winter since then. The Atlantic, C. finmarchicus has dominated in Kongsfjorden the last decade, except for in 2008.

Status and trend

The Kongsfjorden pelagic ecosystem is influenced by influx of both Atlantic and Arctic waters, consequently the zooplankton community is composed of both Atlantic and Arctic species.  The amount of Atlantic water in the West Spitsbergen Current and hence the inflow into Kongsfjorden depends or larger scale climatic factors. Therefore, the composition of zooplankton community in Kongsfjorden might function as a climate indicator on a local scale. Copepods of the genus Calanus dominates the mesozooplankton community in Kongsfjorden, both in terms of abundance and biomass. The Calanus population exist of three species, the smaller Atlantic Calanus finmarchicus, the medium sized Arctic Calanus glacialis and the large Arctic Calanus hyperboreus. The relative abundance of C. finmarchicus and C. glacialis in Kongsfjorden depends on the inflow of Atlantic water. The larger C. hyperboreus, which is a deep water species, is only present in low numbers in Kongsfjorden and does not contribute much to the total abundance of Calanus.

Years with C. glacialis dominance are characterized by lower water temperatures whereas dominance of C. finmarchicus usually coincides with periods with increasing inflow of Atlantic water and hence increased water temperatures. The years with domination of the cold-water species, C. glacialis, were 1999, 2000 and 2008. The Atlantic C. finmarchicus was the predominating Calanus species in 1997, from 2001 to 2003 and in 2007 until today, except for 2008. 2004, 2006 and 2008 were characterized by the almost equal abundance of both Calanus species.

The trend is less pronounced when looking at the relative proportion of Atlantic and Arctic Calanus species in terms of biomass. The large Arctic species (C. glacialis and C. hyperboreus) will contribute more biomass than the smaller Atlantic species (C. finmarchicus) at the corresponding development stage. However, there is a large difference in biomass for the different development stages. An adult might have six times as much biomass as a young individual (copepodit stage 2-3). The total biomass is therefore not only dependent on the number of individuals, but also of the stage composition of the different species at the time of sampling.

Causal factors

Changes in the zooplankton community structure in Kongsfjorden can be associated with the advection of water masses from the adjacent shelf. There is a significant variability in the degree to which Atlantic water occupies Kongsfjorden. The large interannual variations in Calanus abundance and species composition observed in the time series data from Kongsfjorden seem to correlate to changes in hydrography, i.e. warm years favour different species than cold years.

Consequences

The variability in the abundance of C. glacialis and C. finmarchicus may have implications for the pelagic ecosystem in Kongsfjorden, since variable abundances of these species lead to a shift in the size structure and the amount of energy as lipids available for the next trophic level.

Planktivorous seabirds and fish tend to be size selective in search of prey. A decrease of the mean size of available prey through a shift in species composition of the zooplankton may have consequences for predators. For example, little auks have a strong preference for larger prey items and years with a dominance of the smaller C. finmarchicus inside the fjord may force the birds to fly longer distances to find suitable food (e.g. C. glacialis), thereby reducing survival and recruitment success.

About the monitoring

The composition of key zooplankton species in Svalbard waters is being monitored because it may be influenced by climate change and can lead to fundamental changes in the marine ecosystem.

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring