Ten years after: krill as indicator of changes in the macro-zooplankton communities of two Arctic fjords

Abstract

A macro-zooplankton study from 1996 was repeated in 2006 and focused on euphausiid species as indicators of advection and warming effects in Kongsfjorden, West Spitsbergen, Svalbard. The influence of warmer Atlantic water in Kongsfjorden was indicated by the findings of three additional euphausiid species of typically Atlantic origin, relative to the previous study 10 years ago. The predominant presence of Thysanoessa inermis in Hornsund suggested persisting cold conditions in this more southerly, but more Arctic influenced fjord. In this species, moult stage analysis showed that trophic effects can override temperature forcing. Histology and lipid analysis suggest that reproductive activity should be monitored as an indication of warming and possibly a shift in food web composition.

Primary producers and production in Hornsund and Kongsfjorden – comparison of two fjord systems

“…Grazing on microplankton in fjords increases from spring to summer, when the new generation of local herbivorous copepods grows (Kwaśniewski et al 2010) and large herbivores, such as krill, are advected from the shelf area (Buchholz et al 2010). …”

Growth and Moulting in Northern Krill (Meganyctiphanes norvegica Sars)

“…However, there are increasing numbers of reports from the west-Spitsbergen area to which M. norvegica seems to be regularly advected. In the Kongsfjord, there are even the first indications of reproductive processes in krill (Buchholz et al, 2010). These observations may be taken as a further indication of a warming effect or a change in food web composition which may be advantageous to Northern krill, enabling it to expand its distributional range northwards.…”

“…Accordingly, end sizes of up to 43 mm are reached. This probably reflects krill profiting from the enhanced plankton production through nutrient fertilisation from the land surrounding fjords (Buchholz et al, 2010).…”

“…This phase (D3 A B) has been found to comprise 22% of a moult cycle in an actively moulting population, meaning that if random moulting is going on in a population, 22% of the krill can be expected to be found in that phase (see above; Buchholz et al, 2006). Accordingly, comparison of the observed percentage against this number is an indicator of whether a population is active with regards moult and growth or whether it is in a quiescent state and spending proportionally larger amounts of time in, for instance, stages, C and D2 (Buchholz et al, 2010), so decreasing the proportion of moult active specimens.…”

“…The krill are presumably advected from the open Norwegian sea and may reflect its environmental condition rather than the fjord situation. Norwegian sea krill are believed to contain the northernmost self sustaining population of M. norvegica (Dalpadado et al, 2008;Buchholz et al, 2010).…”