In general, amphibians often lose weight
when their artificial lighting, such as street lamps, are too bright to find
food, which leads to a decrease in population. (Fig.1)
Fig.1. Light in wetlands
can suppress diel vertical migration of zooplankton and influence foraging
behavior of amphibians.
Many aquatic invertebrates migrate up
and down in wetlands during the course of a night and day. This “diel vertical migration” presumably results
from a need to avoid predation during lighted conditions so many zooplankton
forage near water surfaces only during dark conditions. (Moore et al)
Disruption of diel vertical migration by
artificial lighting may have significant detrimental effects on ecosystem
health. Moore et al. conclude that “vertical
migration of lake grazers may contribute to enhanced concentrations of algae in
both urban lakes and coastal waters. This condition, in turn, often results in
deterioration of water quality”
Fig.2. Two tadpoles of
the same age and kept in 12:12 L:D lighting. (A) was kept in the equivalent of
very dark night (10–4 lux) in
the dark phase, while (B) was exposed to artificially bright illumination in
the dark phase and is not yet metamorphosing.
Amphibians are highly sensitive to light
and can perceive increases in illumination that are impossible for humans to
detect (Hailman and Jaeger). A rapid increase in illumination causes a
temporary reduction in visual acuity, from which the recovery time may be
minutes to hours. In this manner, a simple flash of headlights can arrest
activity of a frog for hours. Frogs in an experimental enclosure ceased mating
activity during night football games when lights from a nearby stadium
increased sky glow.
interferes with the production of the hormone melatonin, which is involved in
regulating many important functions, including sexual development,
thermoregulation, adaptation of eyes to the dark, and skin coloration. Current
research shows that artificial lighting slows larval amphibian development in
the laboratory. (Fig.2)
According to a report published by the
American Medical Association, artificial lighting should try to reduce the
amount of amphibian ecosystem disruption by adjusting the artificial lighting
at night, especially streetlights, below 3000K.
2. Moore, M. V., S.
J. Kohler, and M. S. Cheers. Artificial light at night in freshwater habitats
and its potential ecological effects. Ecological consequences of artificial
night lighting. Island Press, Washington, D.C.
3. Hailman, J. P.,
and J. G. Jaeger. A model of phototaxis and its evaluation with anuran
Jae Ho Lee, Ph.D
* Next week’s topic: Light and Human Body Summary I
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