Brittle Star’s
Sensitivity to Light and Their Rate of Movement

Our interest in brittle stars began
after the completion of our collection tanks. Most groups had a
collection of brittle stars in their tanks. As we observed them we
noticed they were always found under rocks. After further research we
discovered they were highly sensitive to light and therefore always
seeking shelter to avoid light. We then decided to use them in our
experiment. In the field, we began to notice different patterns of
movement among two species of brittle stars; Ophiocoma echinata
and Ophioderma appressum, more commonly known as the Blunt
Spined Brittle Star and the Banded Arm Brittle Star respectively. We
used both species to determine if light would play a factor in the
brittle stars rate of movement. The rate of speed of both species was
calculated by measuring the amount of time it took to hide from the
light and the distance they moved in that time. We first measured the
rate without adding artificial light to use as a control. Then we
began trials using a flashlight to compare the rates. After, to
further our research, we used colored filters on the flashlight to
change the intensity of light available to the brittle stars. Unlike
the previous experiment, only Ophiocoma echinata was used to
monitor the effects of light filtration. We hypothesized that the
brittle stars will avoid light by moving faster towards a shadow or
some place to hide. When there is a continuous and more intense
source of light present, they will move faster to escape the light.

This was the set up used to calculate
the brittle stars rate of movement.