Photo of samples in dark room
Dishes of samples
Using the microscope in the lab
radiation is high energy and can be damaging to tissue. We are familiar with its effects like sunburn and skin cancer. The sun can be equally damaging to aquatic organisms. Studying this is a major ecological concern these days as the ambient amount of UV-R has increased with damage to the protective ozone layer. This may have great effects on many lake ecosystems as they are exposed to higher levels of radiation.
There are several lines of defense against UV-R
damage. A behavior defense is
migrating down in the water column where UV-B (280-320
nm) is rapidly attenuated. Another is the development of photoprotective
pigments, which absorb the radiation before damage to DNA. Lastly, there
is a DNA repair mechanism known as photorepair in which enzyme changes
conformation upon being struck by a PAR photon and fixes the error along
the chromosome.
A series of experiments were conducted using the
phototron; an apparatus that
simultaneously irradiates samples with PAR and UV-B at
different levels, and others at only UV-B. This way we can compare differences
between tolerence and photorepair and remove the behavioral component.
We have developed a new characterization of UV sensitivity based on the
LT value following a 12h irridation versus dose. This is an innovation
that incorporates the effects of time and exposure levels.
Studies on Lepomis (sunfish) and Chaoborus (Phantom
Midge) paired these animals together as zooplanktivorous larvae of similar
size and pigmentation. Lepomis showed low tolerance to UV, but a marked
photorepair system. Chaoborus exhibited less photorepair capability, but
a tolerance that increased with age. These findings lead to some interesting
ecological questions that need further study. Could sunfish populations
be drastically altered by a slight increase in UV-B, and could increased
sensitivity at early stages induce mortality before complete development?
As important parts of the food web, these changes could severely alter
the function of many bodies of water.
