Growth characteristics of Ephelota gigantea: a pest to seaweed culture along the northeastern coast of Japan

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.