Hydromechanical adaptation in the solitary free-living coral Fungia scutaria

Abstract

THE scleractinian coral Fungia scutaria produces a dense, diskoid skeleton that is adapted for stability and abrasion resistance in turbulent water. Water motion rights skeletons at velocities lower than needed to disturb upright corals. Flow of water over the coral is controlled largely by passive hydro-mechanical adaptations. Previous reports^1–3 suggest that muscular activity is the main mechanism enabling free-living solitary corals to follow their peculiar way of life. Our work indicates that passive hydromechanical adaptations can be a more important factor in shallow turbulent waters. Several species of free-living corals are known to migrate, avoid burial, and right themselves by action of their polyp^1,2 or by symbiotic activity of sipunculid worms³. Most other Indo-Pacific solitary corals such as F. scutaria are inactive, yet remain upright in turbulent waters. Dead skeletons of F. scutaria are generally found with the oral surface upward, and seem to resist erosion far better than other corals. We overturned dead skeletons in one area; they were righted during the next period of heavy waves, suggesting unique hydraulic and structural properties of the skeleton.