For the first time, researchers have successfully bred and raised a rare and threatened Caribbean coral species in the lab.
Researchers plan to 'out-plant' these lab-grown juveniles in the wild which could help populations become more resilient to climate change.
The Caribbean Pillar Coral Dendrogyra cylindrus is rare and understudied, and small juveniles of this species have never been seen in over 30 years of surveys in the Caribbean.
Pillar Corals form a unique 'smoke stack' shape like no other coral species, and they display unusual mating behaviour compared to most spawning coral species.
Most spawning corals are hermaphrodites that release large bundles of eggs and sperm. Pillar corals, which only spawn on a few specific nights of the year, build colonies that are either all-male or all-female.
The males first release sperm into the seawater, shortly followed by the females releasing their individual eggs. This makes collection and breeding research extremely difficult.
"Now that we've successfully reared juvenile Pillar Corals in the lab, not only can we study them in more detail to find out what factors could be threatening their survival in the wild, but it also means that we can try to out-plant a small number back to the reef," said lead author Kristen Marhaver from the Caribbean Research and Management of Biodiversity (CARMABI) Foundation.
"We don't know if this will work and it is certainly not a cure-all for the reef.
"But especially in such a rare coral species, a tiny boost of a few new individuals could make a big difference in their genetic diversity, allowing their populations to adapt and become more resilient to the changing environment in the oceans," said Marhaver, who began this work while she was a postdoctoral researcher at the University of California at Merced.
After studying the sunset times and lunar cycles taken from other spawning observations, the research team timed their egg and sperm collection around the most likely annual spawning times - exactly three nights after the August full moon and around 100 minutes after sunset.
At depths of 6-7 metres on a Curacaoan coral reef with a large population of Pillar Corals, the team arranged nets and funnels over the female colonies to automatically collect eggs, and used syringes near the male colonies to manually collect sperm from spawn clouds as they appeared.
The team then attempted to fertilise the eggs by mixing the collected eggs and sperm underwater and on shore.
In the lab, the team carefully adjusted several factors related to fertilisation times and seawater type and nurtured the eggs to develop into larvae.
They managed to successfully grow the embryos to the swimming larvae stage and settled them onto ceramic tripods in water tanks. The settled juveniles then survived for over seven months.
