Nobuyuki Nakano

Suctorians of the genus Ephelota are stalked ciliates and ectocommensals of marine invertebrates and plants. Ephelota gigantea has long been known as a major nuisance to the cultured seaweed industries in the coastal area of northeastern Japan. However, little is known about its life history, so in situ growth experiments were performed in the vicinity of wakame (Undaria pinnatifida) long-line culture in Iwate Prefecture, and the development of swarmers was investigated in the laboratory. The stalk elongated first, followed by enlargement of body length and body width, with body width increasing linearly with time. Over 5–6 days, E. gigantea increased 4–5-fold by external budding. Such an experiment was carried out for the first time for E. gigantea and possibly for any Ephelota species. The information obtained is important not only in understanding the life history of this species but also for understanding the interactions with host organisms.

Wakame seaweed is an important aquatic resource in Iwate Prefecture. However, a suctorianEphelota gigantea sometimes causes great damage to wakame culture. Since little is known about the biological characteristics of E. gigantea, its detailed morphology and temporal change of biological characteristics during the 2010 culture season were investigated. Scanning electron microscope observations showed that E. gigantea had different striation patterns on the stalk; there was a swell made of cement by which the stalk was attached to wakame firmly; and the buds had cilia arranged in concentric circles about a ring in the center of the ventral side. A suctorian parasite was found to infect E. gigantea, and the infection seemed to have decreased drastically the attached density of E. gigantea on wakame. Cell size of parasite-infected E. gigantea individuals was larger than that of uninfected individuals, probably because larger E. gigantea has larger surface area for attachment of the parasite. Cyst formation or conjugating individuals were not observed.