Effects of Underwater Brightness on Japanese Spiny Lobster Behaviour during nighttime Scotophase

Abstract

Using an automatic sensing instrument developed for observing the behaviour of crawling creatures, the authors investigated the influence of different underwater light intensities on the behaviour of Japanese spiny lobster, Panulirus japonicus, under light and dark alternating cycles of 24 hours. When the downward irradiance during light period was 3.3×10²lx and that during the dark period was more than 5.2×10^-3lx, the spiny lobster's behaviour during the dark period were largely disturbed: locomotor frequency was less than 1/4 in comparison with that under 0lx conditions in the dark period. Such a response was continuously maintained during the experimental period of 31 days. The locomotor frequency did not decrease at all when the downward irradiance during the dark period was less than 2.3×10^-5lx. On the other hand, there was hardly any difference in locomotor frequency during the dark period when the downward irradiance during the light period was of 3.5×10^-2lx and 3.3×10²lx.
In consequence, it was understood that Japanese spiny lobster locomotive behavior was considerably suppressed whenever underwater brightness increased even slightly during the nighttime.