The sexual behaviour of Antarctic krill has been captured on underwater video for the first time. The video footage gives scientists new insights into the crustaceans’ brief and frenzied mating ritual and provides the first evidence that mating can take place near the sea floor at depths of 400–700m.

‘Previously scientists thought that krill mate and lay eggs in the surface waters, between zero and 200 metres,’ says Australian Antarctic Division krill biologist, Dr So Kawaguchi.

‘But this video footage shows that mating can take place near the sea floor, reinforcing the importance of the ocean bottom as habitat for krill.’

The video footage was captured at 507m depth and shows three krill — two males and a female — engaged in about five seconds of rapid spinning followed by six seconds of swimming in larger circles with the males pushing against the female.

By breaking the ritual down frame by frame, Dr Kawaguchi and his colleagues were able to define five mating phases: ‘chase’, ‘probe’, ‘embrace’, ‘flex ’and ‘push’.

During the embrace and/or flex phases the male krill seems to transfer sperm packets to the female, but further study is needed to precisely define the activities occurring in each phase.

Dr Kawaguchi says that while it is possible that mating was induced by the camera light, recent developments in underwater imaging systems has resulted in an expanding body of evidence for the existence of populations of krill near the sea floor, including females carrying developing eggs.

‘This research challenges the assumption that most krill live within the top 200 metres of the ocean and suggests that deeper layers are significant habitat for krill. Our observations will have considerable implications for understanding the Antarctic marine ecosystem and for the management of the krill fishery,’ Dr Kawaguchi says.

In collaboration with Dr Kawaguchi, arts-based researcher, Dr Lisa Roberts, has produced an animation of the mating sequence. Dr Roberts digitally traced each video frame and combined these tracings with drawings traced from illustrations of krill anatomy. 

The research and animations were published in the Journal of Plankton Research in February.

View the video footage, animation and research paper.

WENDY PYPER

Corporate Communications, Australian Antarctic Division