Environmental
biochemistry
UV photobiology
of Antarctic marine organisms
Walter C Dunlap
Environmental Biochemistry
Marine Bioproducts Project
One of the primary issues
of global climatic change is the
environmental implications of
increasing levels of solar
ultraviolet radiation caused by
declining levels of stratospheric
ozone resulting from destructive
photoreactions of anthopogenic
pollutants (mainly
chlorofluorocarbons) in the upper
atmosphere [1].
| Although this problem is
of global concern [2],
including the low-latitude
tropics where UV levels are
normally high [3],
the most dramatic change occurs
over Antarctica during the annual
springtime formation of the
"ozone hole" when
vertically integrated, ozone
concentrations are typically
depleted to less than 40% of
normal seasonal levels [4-6]
(Fig 1) causing significant
enhancement in the short,
higher-energy, and biologically
more injurious, wavelengths of
UV-B radiation (Fig. 2).
Early
predictions gave that ozone depletion
over the Antarctic region could cause
catastrophic destruction of marine
phytoplankton placing the food-chain of
the Antarctic and Southern Ocean
ecosystems at risk [7, 8]. |
|
 |
Fig.1
Differences in atmospheric ozone
concentrations recorded from
radiotelemetry of balloon-borne
ozonesonde measurements during
high (22 October) and low (18
October) ozone periods; data are
from Palmer Station, Antarctica,
1994.
|
 |
Fig.
2
Surface UV radiation levels at
sea level measured by
spectroradiometry during high (22
October) and low (18 October)
ozone periods; data are from
Palmer Station, Antarctica, 1994.
|
A 6-12% minimum loss in primary
production was estimated under a
well-developed ozone hole [8].
Yet long-term measurements have shown
that ozone depletion may account for only
=<3.8% loss in daily primary
production (=<0.2% loss in
annually-averaged, total primary
production) [9, 10].
This departure from previous predictions
is largely due to the biochemical
capacity of primary producers to adapt to
changing levels of environmental UV
radiation.
This
adaptational response may in part be due
to the activation of biomolecular repair
and photoprotective mechanisms [11,
12], including the elaboration
of UV-absorbing compounds [13].
| Research diver
at Palmer research station. |
|
Our work has
demonstrated that phytoplankton,
particularly diatoms, can rapidly adjust
to increasing levels of UV by producing
UV-absorbing, mycosporine-like amino
acids (MAAs) [13-16] [see
Photobiochemistry of coral
symbiosis].
However, individual species have
different inherent adaptive abilities
which can cause a nutrient-limited shift
in the floristic composition of the
plankton community [9, 11, 17].
The
effects of this restructuring on dietary
selection and nutrition at the next
trophic level (e.g., salps, tunicates,
copepods, fish larvae and krill) are yet
poorly understood [18].
Collaborative
field research was conducted at Palmer
Station (U.S. National Science
Foundation) during the 1991/2 Austral
summer with Dr Deneb Karentz (University
of California at San Francisco) on the
NSF-funded project, "Physiological
ecology of UV-absorbing compounds in
Antarctic organisms".
|
|
Palmer research station. |
Further collaborative
field research was undertaken in years
1993-1994 with Professor Osmund
Holm-Hansen (Scripps Institution of
Oceanography) on the NSF project,
"Effects of ozone-related increases
in UV-B fluences on photosynthesis,
photoadaptation and viability of
phytoplankton in Antarctic waters".
The NSF proposal
"UVR damage to planktonic
procaryotic and eucaryotic organisms in
Antarctic waters; mechanisms of damage
and cellular responses" was
submitted in 1997 by Professor
Holm-Hansen for research continuation.
While this proposal was unsuccessful to
secure competative funding with NSF Polar
Programs in 1997, we hope for success in
the future.
One aspect
of continuing research is being conducted
by Mr Stuart Newman, PhD candidate at the
University of Tasmania under the
supervision of Associate Professor David
Ritz (Department of Zoology) and Drs
Stephen Nicol and Harvey Marchant of the
Australian Antarctic Division with
co-supervision provided by W Dunlap.
| Researchers
in a zodiac near Palmer research station. |
|
The
occurrence of UV-absorbing MAAs has
previously been reported in Euphausia
superba (Antarctic krill) [13,
15]. However, the source and
putative function of these UV-absorbing
compounds have not been demonstrated in
zooplankton or free-swimming nekton,
although trophic acquisition of
phytoplankton MAAs is likely [19].
This study
is designed to determine the trophic
accumulation and clearance rates of
dietary phytoplankton MAAs by E.
superba, to determine if the
UV-protective function of MAAs in krill
is environmentally relevent, and to test
the hypothesis that herbivorous
zooplankton and nekton (krill) are
trophically "co-adapted" via
the phytoplankton food-chain to changing
levels of UV exposure.
 Antarctic
images
References
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