EFFECTS OF UNDERWATER BRIGHTNESS ON JAPAN ESE SPINY LOBSTER BEHAVIOR DURING NIGHTTIME SCOTOPHASE

Using an automatic sensing instrument developed for observing the beha viour of crawling creatures, the authors investigated the influence of different underwater light intensities on the behaviour of Japanese s piny lobster, Panulirus japonicus, under light and dark alternating cy cles of 24 hours. When the downward irradiance during light period was 3.3 x 10(2) lx and that during the dark period was more than 5.2 x 10 (-3) lx, the spiny lobster's behaviour during the dark period were lar gely disturbed: locomotor frequency was less than 1/4 in comparison wi th that under 0 lx 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 irradia nce during the dark period was less than 2.3 x 10(-5) lx. On the other hand, there was hardly any difference in locomotor frequency during t he dark period when the downward irradiance during the light period wa s of 3.5 x 10(-2) lx and 3.3 x 10(2) lx. In consequence, it was unders tood that Japanese spiny lobster locomotive behavior was considerably suppressed whenever underwater brightness increased even slightly duri ng the nighttime.