Ecological distribution, population structure and reproduction of a coral Oulangia stockesiana miltoni in Mutsu Bay
Moritaka Nishihira and Mitsuru Yajima
Biological Institute, Faculty of Science, Tohoku University, Sendai 980-8578, Japan
Distribution, population structure and reproductive cycle of a solitary sessile coral Oulangia stokesiana miltoni were studied on concrete blocks at Asamushi marina in Mutsu Bay, northern Japan. Corals were distributed from just below low water mark to the depth of 5 m, where the sediment became mud. Densities ranged from 0 to 7.48 per 100 cm2 and were higher on horizontal surfaces (where sediment was more accumulated) than on inclined surfaces. On the vertical surfaces, corals were not observed. Corals did not make dense aggregations, showing average distances between individuals of 2.2 to 5.8 cm. Longer diameter of calice ranged from 1 to 9 mm with an average of 4.72 mm. Population structure was unimodal. Monthly histological studies for those corals of ＞ 7.5 mm diameter revealed that this species is dioecious and exhibits an annual reproductive cycle with a spawning season in June to July when sea water temperature gradually increasing (around 15℃). Gametogenesis took 10 to 11 months.
