A Comparative Study of Sexual Reproduction in Three Species of Panamanian Zoanthids (Coelenterata: Anthozoa)

Colonies of Zoanthus sociatus, Z. solanderi, and Palythoa caribaeorum were sampled at 1–2 month intervals between December 1974 and April 1976 to determine their reproductive condition. Z. sociatus and P. caribaeorum exhibited seasonal patterns. Z. sociatus underwent gametogenesis from December 1974 through June 1975, and December 1975 through March 1976; P. caribaeorum underwent gametogenesis from December 1974 through June 1975.

All three species appear to be broadcast spawners with external fertilization. Maximum oocyte sizes varied between 250 and 450 μm. Comparisons of fecundity and reproductive effort indicate that Z. sociatus had the highest number of oocytes per unit dry weight and per unit substrate area. P. caribaeorum had the highest reproductive effort in terms of oocyte volume per unit dry weight and per unit substrate area; this zoanthid produced the largest oocytes, Z. solanderi had the lowest fecundity and reproductive effort.

All three species are hermaphroditic: Z. solanderi (10 of 15 fertile colonies), Z. sociatus (4 of 24), and P. caribaeorum (4 of 23). We could not distinguish between zoanthids having independent male, female, and hermaphroditic colonies or sequential hermaphroditic patterns.

Zoanthid spawning may have been correlated with seasonal variation in environmental parameters. Near the end of the dry season a combination of long aerial exposures and high reef fiat temperatures may have synchronized zoanthid spawning in April 1976. Partial mortality of Z. sociatus on the reef fiat was also correlated with extreme exposures.