Deep-sea anemone (Cnidaria: Actiniaria) exhibits a positive behavioural response to blue light

The photobiology of sea anemones in shallow waters has been studied extensively in recent decades, while that of deep-dwelling species remains unclear. There is evidence that many deep-sea organisms are sensitive to blue light, and it may hold for sea anemones as well. The present study tested the hypothesis that the sea anemone Cribrinopsis japonica, caught at the depth of 800 m, is photosensitive to blue light, focusing on whether this anemone (1) showed behavioural responses to blue light, (2) possessed colour sensitivity, and (3) detected diminished intensity of light. When exposed to blue and red light separately, the anemone was behaviourally more sensitive to blue light than red light. The initiated behaviour was positive and immediate, and consisted of an increase in the area covered by tentacles and contraction of the column, which is considered as preparatory feeding behaviour. The anemone’s sensitivity to diminished intensity of light within the peak wavelength of bioluminescence opens up the possibility that the deep-sea anemone senses the presence of bioluminescent organisms.