50 S. Afr. T. Antarkt. Nav., Deel 12, 1982
Cannibalism in Euphausia superba Dana
Cannibalistic behaviour was observed in captive Euphausia superba. The suggestion is made that such behaviour may be utilised under natural conditions to offset low food availability.
Die kannibaalse gedrag van Euphausia superba is in 'n laboratorium waargeneem. Daar word voorgestel dat hierdie gedrag in die natuur gebruik word ten tye van voedselskaarste.
The Antarctic krill, Euphausia superba Dana, is considered a selective herbivore (Barkley 1940, Marr 1962). However, it has been suggested that under certain conditions it may become carnivorous, consuming a variety of zooplankton, particularly copepods (Mauchline & Fisher 1969). To date, cannibalism has been observed only once as a method of food selection (McWhinnie er al. 1979).
During a recent cruise to the Southern Ocean, kri!J were maintained for some time in a large aquarium (Miller et al.
1983). Cannibalistic behaviour by captive animals was observed on two occasions. In each case, a relatively large, mature animal (body length ea. 45 mm) was seen to consume a smaller live juvenile (body length ea. 20 mm). Chitinous material and eye fragments were later found in the gut of the larger animals when sacrificed, suggesting that prey animals were actually ingested.
It was not possible to ascertain whether the observed behaviour was a result of captive conditions or not. Never- theless, krill have been shown to exhibit cannibalistic tenden- cies in their natural environment and it has been suggested that
South African Scientific Committee for Antarctic Research (SASCAR) 1982
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D.G.M. Miller Sea Fisheries Research Institute Cape Town
this would provide an alternative food resource during periods of low food availability (Pavlov 1971). For this reason, cannibalistic behaviour in E. superba may represent a response to the highly seasonal variation of Antarctic plankton abundance (Foxron 1962), thus providing nourishment during unproductive winter months.
Acknowledgements
The funding of the Sea Fisheries Research Institute and South African National Committee for Oceanographic Research is gratefully acknowledged.
References
BARKLEY. E. 1940. Nahrung und Filterapparat des Walkrebschens Euphausia superba Dana.
z.
Fisch. 65-156.FOXTON. P. 1962. Seasonal variation in the plankton of Antarctic waters. In: Biolog.ie Antarctique, eds. R. Carrick, M. Holdgate and J. Prevost. Hennan, Paris.
MARR, J.W.S. 1962. The natural histOry and geography of the Antarctic krill (Euphausia superba Dana). Discovery Rept.
32: 33-464.
MAUCHLJNE, J. & FISHER, L.R. 1969. The biology of euphausiids. Adv. mar. Bioi. 7: 454 p.
MCWHINNIE, M.A., DENYS, C., PARKIN, R. & PARKIN, K.
1979. Biological investigations of Euphausia superba•Dana. Am. J.
u.s.
14: 163-164.MILLER, D.G.M., HORSTMAN, D.A., WEHMEYER, H.G. &
KOSTER, S. '1983. Maintenance of living Euphausia superba in simple aquaria. S. Afr. J. Mar. Sci. 1: 65-69 (io press).
PAVLOV. V.Y. 1971. 0 kachestvennoi sostave pischi Euphausia superba Dana. Trudy. VNR/0. 86: 42-54.
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