Journal of the Marine Biological Association of the UK

Research Article

Heart rate as a measure of stress in Antarctic krill, Euphausia superba

D.A.  Ritz a1c1, L.  Cromer a1, K.M.  Swadling a1, S.  Nicol a2 and J.  Osborn a3
a1 School of Zoology, University of Tasmania, PO Box 252-5, GPO Hobart, Tasmania, 7001 Australia
a2 Australian Antarctic Division, Channel Hwy, Kingston, Tasmania, 7050 Australia
a3 School of Geography and Environmental Studies, University of Tasmania, PO Box 252-76, GPO Hobart, Tasmania, 7001 Australia


Antarctic krill, Euphausia superba, normally live in social aggregations (schools) but rarely aggregate in laboratory tanks. In order to study the effect of stress on solitary living we tethered krill to wooden skewers and measured heart rate both when they were held isolated from conspecifics and when they were held at normal schooling distances ([similar]1 body length). Heart rate did not differ significantly with sex or body size. However, intermoult krill had a significantly lower heart rate than postmoult animals. When two individuals were held at schooling distance, with one slightly higher in the water column than the other, the heart rate of the higher individual slowed significantly (106–98 beats min−1), while that of the lower individual remained the same. We interpret these results to mean that krill living solitarily are stressed but will respond to neighbouring individuals by decreasing their metabolic rate and saving energy.

(Received July 5 2002)
(Accepted October 4 2002)

c1 e-mail: