Asexual reproduction, fragmentation, and skeletal morphology of a plexaurid gorgonian

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Abstract
The Caribbean gorgonian Plexaura A, a species of uncertain affinity, relies almost entirely on asexual reproduction for the formation of new colonies. At a site of the San Blas Islands, Panama, 94% of the colonies < 10 cm in height had apparently developed from fragments of larger colonies. These fragments were formed when branches broke off from Plexaura A colonies. In situ tests of the force required to break off branches indicate that downward directed forces of as low as 0.1 N induced failure of Plexaura A branches. In contrast, branches of equivalent diameter of the sympatric congenor P. homomalla (Esper) frequently remained unbroken at forces up to 19.6 N. Most fragments broke off the colony at points exhibiting a constriction in the axial skeleton. Constrictions in the branch axis of Plexaura A were not distributed uniformly on the colony. Branch points distant from the branch tip were more likely to have axis constrictions than those close to the tip. Fragments are believed to be produced by wave action during squalls and loose fragments were regularly found at the study site. The axis constrictions in Plexaura A may be an adaptation for enhanced asexual reproduction.

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