Antipredator Defenses in Soft Corals of the Genus Sarcophyton (Octocorallia; Alcyoniidae) from Coastal Waters of Central Vietnam

As sessile marine organisms, soft corals may use chemical or/and physical factors of defense against fish predators for their survival and growth. In Vietnam, corals of the speciose genus Sarcophyton are abundant on reefs. However, little is known about their defensive traits and strategies. In the study of feeding deterrence, experiments in the field and in an aquarium were conducted using only crude extract, only sclerites, and a mixture of both from Sarcophyton cinereum , S. glaucum , S. serenei , S. trocheliophorum and Sarcophyton sp. For all species, pellets containing a mixture of crude extract and sclerites were consumed by reef fishes from 0.8 to 14.6% (in the field, F) and from 0.3 to 13.3% (in aquarium, A); crude extract was consumed from 5.2 to 42.6% (F) and from 7.4 to 64.0% (A); and sclerites were consumed from 34.6 to 100% (F) and from 30 to 83.3% (A). The consumption of pellets containing S. serenei sclerites was significantly reduced both in the field assays with reef fishes and in the aquarium assays with the moon wrasse Thalassoma lunare ( P < 0.05), which showed sclerites as a dominant physical factor in the S. serenei feeding deterrence. Overall, in Sarcophyton soft corals, the effect of fish predation prevention was most pronounced in the combination of both chemical and physical defense factors, followed by the chemical and then the physical factor alone. Hence, both chemical and physical factors of defense against predation may contribute to the Sarcophyton abundance on reefs.