Habitat of the deep-sea anemone, Cribrinopsis japonica, with shrimp: Does Cribrinopsis japonica establish a symbiotic relationship with shrimp?

We recently found Cribrinopsis japonica Tsutsui & Tsuruwaka, 2014 (Shinkai-hakutou-ginchaku in Japanese name) at the depth between 384 and 800 m in Toyama Bay, Sea of Japan. Since then, C. japonica has been reared under atmospheric pressure in the laboratory for seven years. C. japonica may use a fluorescent protein carried in its tentacles to lure shrimp (Tsutsui et al., 2016^*1). However, the ecology of C. japonica in the deep-sea is hardly known. To elucidate the unknown ecology, we coupled one of the first long-term in situ studies of deep-sea organisms with complementary laboratory experiments. Our exploration of deep-sea benthos revealed that C. japonica inhabits the deepest areas of the sea floor at 1,960 m. Moreover, 80% of C. japonica in the deep-sea stayed together with the deep-sea shrimp. In the laboratory environment, when we added the same shrimp species which was observed in situ to the rearing tank with C. japonica, C. japonica stayed closer with the shrimp without attacking using the tentacles. It is rare to observe different animals together at one place or space since there are very few animals in the ocean floor at > 1,000 m depth in the Sea of Japan (Motokawa & Kajihara, 2017^*2). In such depopulated environment, it is conceivable that C. japonica and the shrimp may receive benefit mutually or one side by establishing a ‘symbiotic relationship.’ We will elucidate their relationship in more details by studying the possible ‘symbiosis’ in the laboratory.