Soft coral colonies of the family Nephtheidae are among the most beautiful corals on the reef. Lacking a rigid external skeleton like the hard corals, nephtheid corals maintain their rigidity by the matrix of calcite spicules, called sclerites, in their tissues.
These spicules are obvious in the Dendronephthya sp. coral above at Basilisk Harbour, Papua New Guinea. Soft corals can radically alter their size and shape depending on the prevailing conditions. When not feeding the polyps may retract and the fleshy stems contract, giving the coral 'trees' a wilted appearance. Also unlike the hard corals, soft corals also lack the symbiotic algae
(zooxanthellae) in their tissues and consequently they are dependant on planktonic food taken directly from the surrounding water.
Extract from Reef and Rainforest by Michael McCoy, CSIRO Publishing.
Photo Credit: Michael McCoy