MEPS 308:101-116 (2006)  -  doi:10.3354/meps308101

Arctic zooplankton do not perform diel vertical migration (DVM) during periods of midnight sun

Katarzyna Blachowiak-Samolyk1,*, Slawek Kwasniewski1, Katherine Richardson2, Katarzyna Dmoch1, Edmond Hansen3, Haakon Hop3, Stig Falk-Petersen3, Lone Thybo Mouritsen2

1Institute of Oceanology, Polish Academy of Sciences, Powstancow Warszawy Street 55, 81-712 Sopot, Poland
2University of Aarhus, Department of Marine Ecology, University of Aarhus, Finlandsgade 14, 8200 Aarhus, Denmark
3Norwegian Polar Institute, 9296 Tromsø, Norway

ABSTRACT: Diel vertical distribution patterns of dominant zooplankton taxa were studied during a period of midnight sun (May 1999) in the Marginal Ice Zone (MIZ) of the Barents Sea along 2 transects across the ice edge. Eight stations were sampled every 6 h over 24 h at 5 depth intervals. Our study confirmed that copepod nauplii (most probably Calanus hyperboreus and C. glacialis) together with Pseudocalanus spp. preferred the surface water layer. The herbivores C. finmarchicus, C. glacialis, and C. hyperboreus concentrated in the upper 50 m depth interval, whereas the omnivores Metridia longa and Microcalanus spp. were generally found in deeper waters. As a result of vertical distribution patterns of the numerically abundant taxa, a bulk of zooplankton was concentrated within the 0–50 m layer. Vertical distribution patterns of all examined taxa/groups varied in time as a result of habitat changes (with respect to water mass distribution and sea depth) as well as random patchiness. Based on our data and on a comprehensive literature survey on Arctic zooplankton diel vertical migration (DVM), we postulate that common zooplankton taxa in the MIZ of the Barents Sea do not perform DVM under the midnight sun. Arctic C. glacialis in May 1999 occupied deeper layers at stations with more ice cover and less melt water. This distribution pattern was probably related to the species’ reproduction. At the same time, Atlantic C. finmarchicus was concentrated further away from the ice edge and chlorophyll a maximum, and presumably had not begun its seasonal reproduction.

KEY WORDS: Zooplankton · Calanus · Diel vertical migration (DVM) · Marginal Ice Zone · Barents Sea

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