Laboratory observations of larval behavior and metamorphosis in the Mediterranean solitary coral Balanophyllia europaea (Scleractinia, Dendrophylliidae)

In sessile marine organisms, the potential for larval dispersal affects the degree of genetic differentiation among populations as well as the spatial distribution of adults. We describe larval behavior and metamorphosis in a laboratory population of Balanophyllia europaea (Risso, 1826), a zooxanthellate solitary coral common to rocky coasts in the Mediterranean Sea. When released by adult polyps, the planulae are zooxanthellate and large; their major diameter is about 2 mm. Planulae have neutral buoyancy, with a swimming and pelagic behavior. Larval longevity averages 10 d, with a maximum of 53 d. The average period between the time of release and metamorphosis is 7 d, with a maximum of 42 d. These two periods differ because some larvae died before metamorphosis. Almost half of the larvae that metamorphosed settled as far away from the parental polyp as possible. Thus, the dispersal potential of B. europaea larvae appears greater than that of its congener, Balanophyllia elegans Verrill, 1864, which is azooxanthellate. We suggest that the relatively high dispersal potential of larvae of B. europaea is enabled through symbiosis with zooxanthellae.