Sexual reproduction in the Mediterranean solitary coral Balanophyllia europaea (Scleractinia, Dendrophylliidae)

Abstract

Balanophyllia europaea (Risso, 1826) is a common scleractinian coral living on subtidal rocky substrates in the Mediterranean Sea. The annual sexual reproductive cycle of this species is studied in specimens from an area near Leghorn (Tuscany, Italy). This study represents the first report of a reproductive cycle in a Mediterranean scleractinian coral. B. europaea is a simultaneous hermaphrodite and brooder. Polyp size at sexual maturity occurs at approximately 3 yr of age (6 to 10 mm maximum oral disc diameter). Observation of hermaphroditic polyps shows several significant differences in the distribution of spermaries and oocytes along the oral-aboral axis. Mean distance of spermaries from the oral pole is less than that of oocytes. Also, large mature spermaries tend to line up towards the mouth, while large mature oocytes tend to line up towards the polyp base. This differential gamete distribution could result in a barrier to self-fertilization, as it reduces encounters between gametes of the opposite sex produced by the same individual. Testes require 1 yr to reach maturity with a maximum spermary diameter of 500 μm. Oogenesis lasts 2 yr with a maximum oocyte diameter of 1400 μm. Fecundity varies significantly with polyp size. The rate of gonadal development increases significantly during January and February, fertilization takes place in March to June and planulation in August and September. Released larvae have a maximum diameter of 2000 μm. The annual cycle of photoperiod and water temperature appear to coincide with the reproductive cycle in B. europaea.