Coral frags survive better on certain substrates


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A new study of transplanted coral frags has shown that survival rates differ according to the species, and to the substrate to which the frag has been attached.

Helen Yap of the University of the Philippines' Marine Science Institute studied two species of the hard coral Porites over several months, and has just published her study in the journal Marine Pollution Bulletin.

She produced frags from Porites cylindrica and P. rus, which both occur sympatrically on shallow reef flats, and attached them to three different types of substrate: live P. cylindrica colonies; dead P. cylindrica colonies and expoxy coated metal grids which were raised over the sand floor.

Once attached, the frags were then spread evenly over a sampling area and monitored over time. The rise in water temperature caused by El Nino in 1998 allowed Yap to monitor the effects of water temperature upon survival when attached to different substrates.

P. cylindrica appeared much more sensitive to raised temperatures than P. rus, and immediately started to show signs of tissue necrosis and bleaching, followed by algal overgrowth and then death.

P. rus frags were much more hardy and a few even showed signs of recovery towards the end of the study.

Yap says that the survival of rus over cylindrica could be linked to either their zooxanthellae or to the coral itself, or both.

Frags attached to metal grids had a survival rate of 35%, while those attached to live cylindrica colonies had a survival rate of around 22%. The worse survival rate was when corals were attached to dead coral chunks, with a rate of just 6%.

For more details see: Yap HT. (2004) - Differential survival of coral transplants on various substrates under elevated water temperatures. Mar Pollut Bull. 2004 Aug;49(4):306-12.