Reproductive biology of three congeneric sea cucumber species, Holothuria atra, H. impatiens and H. edulis, at Heron Reef, Great Barrier Reef

Abstract

Three Holothuria species at Heron Reef showed considerable variation in reproductive seasonality, magnitude of gonad index, egg size and numbers, and frequency of asexual reproduction by transverse binary fission. H. atra from the shallow lagoon spawned biannually (in summer and winter), females produced a large number of small ova, and asexual reproduction was frequent. H. impatiens from the reef flat spawned annually in late spring or summer, with females producing a small number of large ova; signs of asexual reproduction were never observed. H. edulis from the deep lagoon showed no annual reproductive pattern, produced an intermediate size and number of eggs, and reproduced asexually moderately frequently. Preliminary results indicated that reproductive maturation and magnitude of gonad index might vary between sites for H. atra. There was little temporal overlap in spawning by the three species at the sites sampled, and this may be a factor in the maintenance of their genetic isolation.