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Marine Ecology Progress Series

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MEPS 366:99-110 (2008)  -  DOI:

Influence of individual state on swimming capacity and behaviour of Antarctic krill Euphausia superba

Magnus L. Johnson1,*, Geraint A. Tarling2

1Centre for Environmental and Marine Sciences, University of Hull, Filey Rd., Scarborough YO11 3AZ, UK
2British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Rd., Cambridge CB3 0ET, UK

ABSTRACT: Swarms of Antarctic krill are frequently biased towards certain body sizes, sexes, maturities and physiological states. However, the mechanisms causing such biases remain unclear, with some speculating on differential responses to chemical or visual cues. This study examines the influence of individual state on swimming behaviour and performance, which, in turn, may cause biases in swarm composition. The frequency and strength of pleopod beats as well as the overall swimming capacity of Antarctic krill Euphausia superba were measured using a tethering technique. Individual state was considered in terms of body size, sex, maturity, moult stage and stomach fullness. Significant differences in the rate and strength of pleopod strokes as well as in the overall swimming capacity were found between individuals in different states. Body size had one of the strongest influences, with beat rate decreasing and beat strength increasing with increasing size. The sex and maturity of an individual altered this pattern, with adult females having faster but weaker pleopod beats than males of equivalent size. The difference in swimming style of females may impose a different lifestyle to that of males. Moult stage also had a significant influence on swimming, with moulting/post-moult individuals having significantly lower swimming capacities, making them unlikely to keep pace with intermoult counterparts. Both the rate and the strength of the pleopod beat were significantly lower in satiated compared to unsatiated individuals, which may contribute to the dispersion of swarms during feeding.

KEY WORDS: Sex-dependent · Moult · Maturity · Swarm · Satiation · Pleopods · Antarctic · Southern Ocean

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Cite this article as: Johnson ML, Tarling GA (2008) Influence of individual state on swimming capacity and behaviour of Antarctic krill Euphausia superba. Mar Ecol Prog Ser 366:99-110.

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