Physiological and morphological colour change in Antarctic krill, Euphausia superba: a field study in the Lazarev Sea

Author:

Auerswald Lutz1,Freier Ulrich2,Lopata Andreas34,Meyer Bettina2

Affiliation:

1. Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Rogge Bay 8012, Cape Town, South Africa

2. Scientific Division Biological Oceanography, Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven,Germany

3. Division of Immunology, IIDMM-Institute, University of Cape Town, 7925 Observatory, Cape Town, South Africa

4. School of Applied Sciences, Allergy Research Group, RMIT University,Melbourne, VIC 3083, Australia

Abstract

SUMMARY Antarctic krill, Euphausia superba, is very susceptible to harmful solar radiation because of its unique genetic setup. Exposure occurs in spring to autumn during vertical diel migration and during occasional daytime surface-swarming. We have investigated colour change in Antarctic krill, Euphausia superba, during summer and winter in the Lazarev Sea in response to ultraviolet radiation (UVR) and photosynthetically active radiation (PAR). Short-term physiological colour change and long-term(seasonal) morphological colour change are present. Both are facilitated by a single type of monochromatic red chromatophore, i.e. erythrophores, of 20–450 μm diameter. Superficial erythrophores cover large dorsal areas, especially above vital organs (brain, sinus glands), additional`profound' erythrophores cover internal organs (heart, gut, nerve cords). Short-term change in light regime causes rapid physiological colour change along dense bundles of microtubules: pigment disperses into chromorhizae upon exposure to PAR and UVA and to a lesser extent to UVB. Darkness leads to aggregation of pigment in the centre and hence blanching. There is no circadian rhythm in the dispersal state of erythrophores present in winter. Physiological colour change in adult krill is two to three times more rapid in summer than in winter. Furthermore, seasonal changes in light regime also result in a profound morphological colour change: in summer animals, abdominal astaxanthin concentration is 450% and erythrophore count is 250–480%higher than in winter krill. We conclude from our results, that pigmentation of E. superba serves in the protection from harmful solar radiation and is adapted to the varying diel and seasonal light conditions.

Publisher

The Company of Biologists

Subject

Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics

Reference54 articles.

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2. Auerswald, L. and Gäde, G. (2005). The West Coast rock lobster, Jasus lalandii, as a valuable source for chitin and astaxanthin. Afr. J. Mar. Sci.27,257-264.

3. Babak, E. (1913). Über den Einfluss des Lichtes auf die Vermehrung der Hautchromatophoren. Arch. Ges. Physiol.149,462-470.

4. Ban, S., Ohi, N., Leong, S. C. Y., Takahashi, K. T., Riser, C. W. and Taguchi, S. (2007). Effect of ultraviolet radiation on survival of krill larvae and copepods in Antarctic Ocean. Polar Biol.30,1295-1302.

5. Boyle, R. T. and McNamara, J. C. (2005). Association of kinesin and myosin with pigment granules in crustacean chromatophores. Pigment Cell Res.19, 68-75.

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