Coral spawning on St. Thomas

[Dr. Barbara Kojis]

Spawning of Montastrea annularis? (colonies were small and likely annularis but I couldn't say for certain) was observed on a wonderful night dive on Flat Cay reef south of St. Thomas, U.S. Virgin Islands on Wednesday, September 20, 2000.  The dive commenced at 19:45 hrs and spawning was first observed from a single colony of M. annularis? at approximately 20:00 hrs.  Spawning was subsequently observed to occur in approximately 8 other colonies over the next 45 minutes.  Our dive ended at 21:00.  

The Ruby Brittle Star (Ophioderma rubicundum) was also observed preparing to spawn (numerous indiviuals congregating on high points through the reef) and one individual was observed releasing gametes.

The Banded-arm Brittle Star (O. appressum) was also present on high points on the reef.  However, numbers were much lower and this species did not congregate.  No actual spawning was observed though the behavior suggested that this species was preparing to do so.

Red spawning products were visible in the water column in Botany Bay on the north side of St. Thomas the next morning indicating that spawning had likely occurred throughout the Virgin Islands.

The date of spawning coincides with that observed on Bonaire.  We did not dive the night before or after so do not know if spawning occurred on these nights as well.

Barbara Kojis
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