Shade-seeking behaviour under polarized light by the brittlestar Ophioderma Brevispinum (Echinodermata: Ophiuroidea)

The effect of polarized light on the shade-seeking behaviour of the ophiuroid Ophioderma brevispinum was investigated at the Keys Marine Laboratory, Long Key, Florida, USA. Animals were collected and placed in a partially shaded arena. When the arena was illuminated with unpolarized light, the number of animals settling under the shaded portion of the arena was not significantly different from random (N=30, P>0.3). When the arena was illuminated with linearly polarized light, the number of animals settling in the shaded portion of the arena was approximately double what would be expected in a random distribution (N=30, P<0.001). The results are further evidence that O. brevispinum is sensitive to polarized light and are consistent with the hypothesis that polarized light may be used by the animals as an indicator of harmful levels of solar ultraviolet radiation.