Jellyfish

Estimated abundance of large gelatinous zooplankton was higher in 2013 than in 2012. The center of distribution and highest abundance was located in the central to south-western part of the Barents Sea in 2013; a quite typical pattern consistent with observations from 2008 until present. During this period, occurrence of “jellyfish” has overlapped significantly with regions of low mesozooplankton biomass.

Calanus glaciale. Photo: Norsk Polarinstitutt

Samples were collected by PINRO in the Barents Sea during the 2011-2012 autumn bottom-trawl survey to estimate pre-winter euphausiid assemblages.   During 2012, further decrease in the abundance of euphausiids was recorded in some areas; at the same time their abundance increased in other areas.  However, euphausiid abundance generally remained above the long-term mean in all areas of the Barents Sea (Figure 4.3.7).

Calanus glaciale - nauplius stages N2 to N4. Photo: Norwegian Polar Institute

Horizontal distribution of mesozooplankton biomass in 2013 is shown in Figure 4.3.2. Patterns of distribution have been similar between years, even though the area of survey coverage may vary. Particularly low biomass was observed in central parts of the Barents Sea. In westernmost areas southeast of Bear Island, slightly higher zooplankton biomass was observed — somewhat similar to what was observed in 2009 and 2010. Another area with high mesozooplankton biomass was observed in the Russian sector of the Barents Sea, west of Novaja Zemlja and east of 25°E.

Marine plankton. Photo: Norwegian Polar Institute

During August and September of 2013 in the Norwegian sector of the Barents Sea, the average mesozooplankton biomass was clearly below the long-term average.  During 2008-2012 in this region, estimates of average biomass were relatively stable and slightly above 6.0 g dry weight m-2, although the 2012 Norwegian data was less certain than in previous years. In 2013, highest mesozooplankton biomass in the Norwegian sector was observed north-east of Svalbard and in Atlantic Water masses in the south-west — where transport of zooplankton from the Norwegian Sea into central and western parts of the Barents Sea occurs.

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