TITLE: PALMER LTER:  EFFECTS OF ULTRAVIOLET RADIATION ON THE BEHAVIOR OF KRILL LARVAE (EUPHAUSIA SUPERBA)
AUTHORS: L.B.Quetin, R.C.Smith, K.Patterson, R.M.Ross, C.Wyatt-Evens, H.Coe
DATE: 31 Aug - 4 Sep 1998
PLACE: SCAR VII International Biology Symposium in New Zealand 


Langdon B. Quetin1, Raymond C. Smith2, Karen Patterson2, Robin. M. Ross1,
Carol Wyatt-Evens1 and Holly Coe1
1Marine Science Institute, University of California, Santa Barbara, CA
93106 USA; 2Institute of Computational and Earth System Science, University
of California, Santa Barbara, CA 93106 USA


Krill in their first year of development (Age Class 0, AC0) feed on sea ice
biota in winter and early spring.  This coupling to the undersurface of sea
ice maintains AC0s in the surface waters when ultraviolet radiation (UV)
levels may be unnaturally high due to the seasonal development of the ozone
hole in the Antarctic.  The objectives of this study were to determine
whether UV has an effect on the swimming behavior and viability of AC0
krill during the austral spring, and to determine whether UV effects are
primarily due to UVA or UVB radiation.  During October 1993, AC0s were
maintained under three replicated light regimes in an outside aquarium at
Palmer Station, Antarctica.  Four experiments of 3 to 5 d duration were
conducted between October 16 and November 8.  Groups of krill were
maintained near the top of the aquarium in submerged Plexiglas boxes that
allowed only PAR (photosynthetically available radiation) (400-700 nm), PAR
and UVA, or PAR and UVA plus UVB to penetrate to the interior.  Two
observers monitored krill behavior in the different treatments at 3 h
intervals during daylight throughout the experiment.  Krill behavior was
categorized as swimming in the water column, swimming upright within 0.5 cm
of the bottom, swimming on the side on the bottom, and not swimming on the
bottom.  Cumulative dosages of UV, UVA and UVB were calculated for the
duration of the experiment.  With PAR only, krill remained swimming in the
water column or close to the bottom.  At the highest cumulative dosages of
UV, krill were found lying on the bottom, either dead or only feebly
kicking.  There was some recovery in the behavioral index over night.
Results showed that modifications in swimming behavior of AC0 krill and
decreases in viability due to physiological stress were the result of UVA
and not UVB radiation.  The behavioral response to UVA, swimming down in
the water column, serves as a direct protective mechanism against UV
damage.  Results are further discussed in relation to the life cycle of
krill and calculations of dosages important to biological systems.