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Ultraviolet radiation and natural sunscreens in Antarctic krill

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Newman, Stuart James 2000 , 'Ultraviolet radiation and natural sunscreens in Antarctic krill', PhD thesis, University of Tasmania.

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Abstract

This thesis examines the adaptations of Antarctic krill (Euphausia superba Dana) to
ultraviolet radiation in terms of susceptibility, behavioural avoidance and the
presence/utility of UV-absorbing mycosporine-like amino acids (MAAs).
In order to test the susceptibility of krill to UVB (280-320 nm) radiation, groups of
animals in laboratory tanks were irradiated with various light treatments in order to
determine lethal dose and effect on generalised activity. It was found that krill were
killed within 3 days (8 hours of irradiation per day) by levels of UVB radiation
equivalent to that at 5-15 m depth in the Southern Ocean in Spring. UV A (320-400
nm) was found to have no more effect on mortality and activity than visible light
(PAR, 400-700 nm) only. This showed that krill are remarkably susceptible to low
levels of UVB radiation, and are therefore at risk given their photic zone habitat.
The behaviour of krill in response to gradients of visible light (photosynthetically
active radiation, PAR), ultraviolet-A (UVA) and ultraviolet-B (UVB) was examined.
It was found that krill swim away from high intensities of UV A and PAR, moving to
areas of low intensity, but that they appear insensitive to high levels of UVB
radiation. In a vertical tank, irradiance from above with UV A, but not UVB or PAR,
was found to cause krill to significantly increase their depth. I conclude that krill can
detect UVA but not UVB. Although detection of UVA may indirectly signal the
presence of invisible UVB radiation, the fact that the spring ozone hole allows more
UVB radiation through relative to UV A radiation, means that this response may not
be sufficient to alert krill to initiate behaviour to avoid harmful radiation.
The source, location and function of UV -absorbing MAAs were examined. Krill
were fed algae irradiated under different UV conditions, with the different MAAs
produced serving as a biological marker. In addition to MAA analysis of UV-killed
krill, it was found that krill acquire MAAs from dietary algae, and not by de novo
synthesis. Analysis of different krill tissues showed that some MAAs are selectively
accumulated in certain body parts - highest concentrations were measured in eye
tissues, and asterina-330 was found only in the eyes. This concentration of UV
absorbing compounds in the eyes may aid in protection from UVB radiation, or may
filter out UV A which can disrupt crustacean vision.
An analysis of MAAs in krill caught during a large-scale biological survey revealed
that concentration of MAAs was not directly correlated with the abundance of
sympatric algae in the upper 100m suggesting, along with experimental data, that
MAAs can be retained in tissues for long periods. This work also found that
concentrations of MAAs decline as krill become larger, which may mean that
susceptibility to UV changes with time. Variation of MAA concentrations along the
survey also suggests that susceptibility also varies geographically, and is most likely
influenced by abundance of phytoplankton.
Krill fed on high-MAA diets did not appear to survive high UVB radiation any
longer than those fed on low-MAA diets, although starved krill survived for a
significantly shorter time than either. However, a diet high in MAAs seemed to
reduce the detrimental effects of UVB radiation on activity. Further statistical
analyses suggested a relationship between mortality and MAA concentration
independent of feeding, specifically, survival time increased as concentrations of
total MAAs and mycosporine-glycine:valine increased.
It thus appears that Antarctic krill are equipped with a range of strategies to
counteract the effects of ultraviolet radiation that penetrates to significant depths (20
m and deeper) in Antarctic waters during spring. It is equivocal whether krill have
been impacted by UVB radiation in the past, due to a lack of data on krill populations
from periods before the onset of ozone depletion. However, it is likely that other
environmental factors are of more immediate concern in terms of the observed
variation in krill stocks.

Item Type: Thesis - PhD
Authors/Creators:Newman, Stuart James
Keywords: Zooplankton, Ultraviolet radiation, Krill, Krill, Antarctic krill, Antarctic krill
Copyright Holders: The Author
Copyright Information:

Copyright 2000 the author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

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