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Krill ( Meganyctiphanes norvegica ) swim faster at night
Author(s) -
Klevjer Thor A.,
Kaartvedt Stein
Publication year - 2011
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2011.56.3.0765
Subject(s) - diel vertical migration , krill , nocturnal , daytime , crustacean , predation , euphausiacea , environmental science , oceanography , biology , antarctic krill , fishery , euphausia , ecology , atmospheric sciences , geology
Krill are key members in marine food webs, and measurement of swimming speed is vital to assess their bioenergetic budgets, feeding, and encounters with predators. We document a consistent and marked diel signal in swimming speed of krill in their natural habitat that is not related to diel vertical migration. The results were obtained using a bottom‐mounted, upward‐looking echo sounder at 150‐m depth in the Oslofjord, Norway, spanning 5 months from late autumn to spring at a temporal resolution of ~1–2 records s −1 . Swimming speed was assessed using acoustic target tracking of individual krill. At the start of the registration period, both daytime and nocturnal average swimming speeds of Meganyctiphanes norvegica were ~ 3.5 cm s −1 (~ 1 body lengths ([bl] s −1 ) in waters with oxygen concentrations of ~ 15–20% O 2 saturation. Following intrusion of more oxygenated water, nocturnal average swimming speeds increased to ~ 10 cm s −1 (~ 3 bl s −1 ), i.e., more than double that of daytime swimming speeds in the same period. We hypothesize that krill activity during the first period was limited by oxygen, and the enhanced swimming at night subsequent to the water renewal is due to increased feeding activity under lessened danger of predation in darkness.