Washington: Scientists have for the first time successfully raised laboratory-bred colonies of a critically endangered Caribbean coral species to their reproductive age, a step towards sustainable restoration of degraded reefs.

An estimated 80% of all Caribbean corals have disappeared over the last four decades and repopulating degraded reefs has since become a management priority throughout the Caribbean region, researchers said. The elkhorn coral was one of the species whose decline was so severe that it was one of the first coral species to be listed as threatened under the US Endangered Species act in 2006, and as critically endangered under The International Union for Conservation of Nature (IUCN) Red List of Threatened species in 2008.

Due to its large size and branching shape, elkhorn corals created vast forests in shallow reef waters that protect shores from incoming storms and provide a critical habitat for a myriad of other reef organisms, including ecologically and economically important fish species. “In 2011, offspring of the critically endangered elkhorn coral (Acropora palmata) were reared from gametes collected in the field and were outplanted to a reef one year later," said Valerie Chamberland, coral reef ecologist at the US-based non-profit SECORE International.

“In four years, these branching corals have grown to a size of a soccer ball and reproduced, simultaneously with their natural population, in September 2015," said Chamberland, who also works for Carmabi Marine Research Station in Curacao. “This event marks the first ever successful rearing of a threatened Caribbean coral species to its reproductive age," she said.

Since 2010, SECORE, Carmabi, and partners from aquariums around the world started a project aimed at developing techniques to rear larger numbers of elkhorn coral offspring so they could eventually be outplanted to degraded reefs throughout the Caribbean.

“SECORE developed a technique whereby male and female gametes are caught in the wild and fertilised in the laboratory to raise larger numbers of genetically unique corals," said Dirk Petersen, coral reef expert and director of SECORE. Elkhorn corals reproduce only once or twice a year, generally a few days after the full moon in August.

During those nights, Acropora colonies synchronously release their gametes into the water column. The researchers collected a small proportion of these gametes by gently placing special nets around spawning colonies to collect the floating gamete bundles. They then produced coral embryos by in vitro fertilisation, mixing sperm and eggs in the laboratory.

Coral embryos develop into swimming larvae within days and eventually settle onto specifically designed substrates. After a short nursery period, researchers outplanted the substrates with the newly settled corals to the reef.

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