World’s first successful lab breeding of corals to repopulate reefs

Curaçao offers NEW hope for coral reefs

Photo: Paul Selvaggio

Photo: Paul Selvaggio

Global change and local threats such as pollution, overfishing and coastal development are real threats to coral reefs on Curaçao and other Caribbean islands. Researchers from SECORE International and Carmabi have developed a unique method to breed and propagate threatened coral species to aid their recovery. The team is leading worldwide education on coral spawning and reef management through sexual coral propagation.

Scientists estimate coral reefs provide a home for millions of species and these ecosystems are therefore often called the ‘tropical rainforests of the sea’ for their astounding richness of life. Due to the structural complexity they create, corals are one of the most productive ecosystems on Earth. They provide important goods and services to mankind as they support fisheries, protect our coasts, are a source of compounds that can be used in pharmaceutics, and they generate important revenue via recreation and tourism.

At their brightest and most vibrant, coral reefs are among the noisiest environments on the planet and a healthy reef can be heard by sea creatures from several miles away. Fish larvae use sound to find their way to reefs. Shrimp make a loud popping sound to ward off predators. Caribbean spiny lobsters produce rasp sounds to escape octopus attacks. Most marine invertebrates clap, rasp or pop sounds, while other creatures react to vibrations, like corals do. The different sounds are an integral part of the reef ecosystem.

‘Curaçao harbors some of the healthiest reefs in the Caribbean.’

Corals are formed by small colonial animals that together form coral colonies that can reach the size of car. They derive nutritional resources and energy from a symbiotic relationship with an endosymbiotic algae, the zooxanthellae. Coral reefs are formed over the course of thousands of years as limestone skeletons constructed by corals accumulate and form a structural base for living corals. ‘Curaçao harbors some of the healthiest reefs in the Caribbean,’ says coral reef ecologist Valerie Chamberland, ‘These healthy reefs are mainly located at the east side of the island along the coast of the uninhabited area where very little human disturbance occurs. At other sites along the Curaçaoan coast, coral reefs have been heavily impacted by human activities and are completely degraded’. ‘And then, she says, there is also everything in between healthy and degraded, with populations that grow in places you would not expect them to, and sometimes composed of surprising assemblages of species’ which makes Curaçao a very interesting place for coral reef ecologists to carry-out research.

Photo : Benjamin Mueller

Photo : Benjamin Mueller

Valerie Chamberland, is a Canadian PhD candidate who has been conducting research in Curacao for over five years and has lately seen her experimental research come to full fruition: Chamberland and other researchers of SECORE International (USA, Germany), the University of Amsterdam (Netherlands) and the Carmabi Marine Research Station (Curaçao) have for the first time successfully raised laboratory-bred colonies of the Elkhorn coral, a critically endangered Caribbean coral species, to sexual maturity. This is a first ever for the Caribbean. 

Coral offspring are raised in a laboratory setting and then reintroduced into the wild to aid the recovery of threatened populations.

The method Chamberland and her colleagues use differs substantially from the one generally used by reef restoration groups. These groups generally use the ‘coral gardening’ approach, whereby small fragments are harvested from coral colonies on the reef. The fragments are then grown in special nurseries to larger sizes before they are returned to the reef. This can be defined as cloning; the fragments harbor the same genes as the donor colonies and are therefore copies of their parents. ‘This makes them vulnerable to environmental change,’ says Chamberland. ‘If one is susceptible to a disease or other environmental stressors, they likely all are because they are all made up of identical genes’. SECORE developed a technique whereby male and female gametes are caught in the wild and fertilized in the laboratory to raise larger numbers of genetically unique corals. ‘This allows for new genetic combinations,’ explains Chamberland, ‘and hopefully stronger coral populations that will be able to withstand the conditions on present day reefs.’ These coral offspring are raised in a laboratory setting and then reintroduced in the wild to aid the recovery of threatened populations.

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. ‘In contrast to Indo-Pacific where hundreds of coral species are found, there are only 68 coral species in the Caribbean, and the loss of just one can have major devastating effects on the ecosystem,’ says Chamberland. 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 U.S. Endangered Species act in 2006, and as critically endangered under the IUCN Red List of Threatened species in 2008. Due to its large size and branching shape, healthy Elkhorn coral populations historically 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 the Caribbean 95 percent of Elkhorn have died, explains Chamberland, ‘No other species resembles the Elkhorn coral morphologically, and therefore the shallow reefs remained denuded of corals in many areas in the Caribbean.’

In 2011, SECORE raised offspring of the endangered elkhorn coral (Acropora palmata) from gametes collected in the field on Curaçao. The Elkhorn coral reproduces during mass spawning events a few nights after the August full moon, during which colonies simultaneously release sperm and eggs. The gametes float their way up to the surface where they eventually concentrate and fertilization occurs. ‘It’s incredible, really, and still amazes me too, how corals have adjusted their internal clocks to all spawn at the exact same moment’. The resulting embryos drift for hours before they develop into a coral larvae that can actively swim towards the reef and attach onto the reef framework.  ‘Although they are extremely small and appear as helpless little creatures, coral larvae know where to find the reef from the open ocean because they can sense vibrations and react to sounds. They can also detect light levels and select for an appropriate depth where to settle’, explains Chamberland.

‘We have become very successful at providing each species with tailored conditions for them to develop properly.’

Photo: Skylar Snowden

Photo: Skylar Snowden

During coral spawning, the SECORE/Carmabi team collects large numbers of gametes by gently placing special nets around spawning colonies to catch the floating gametes. After collection, the researchers produce coral embryos via in vitro fertilization by mixing sperm and eggs from all different parents in the laboratory. This critical step takes place at the Curaçao Sea Aquarium, one of SECORE and Carmabi’s most important local partners. Once they are fertilized, the embryos develop into swimming larvae within days and eventually settle onto specifically designed artificial substrates. Chamberland shows the aquaria where offspring of different species are growing on artificial substrates. ‘Each single species has very specific requirements when it comes to the environment in which they are raised, and in the past years we have learned what they like, and also what they don’t! We have become very successful at providing each species with tailored conditions for them to develop properly in our laboratory and settle on especially designed artificial substrates’. 

One year after the coral spawning in 2011, the tiny artificially bred Elkhorn corals were outplanted to a reef. Within the following three years, these branching corals had grown to the size of a small soccer ball and reproduced, simultaneously with their natural population in September 2015. This event marks the first ever successful rearing of a threatened Caribbean coral species to its reproductive age. ‘So now we know it takes four years for Elkhorn to reproduce’ says Chamberland. ‘This means that these artificially-bred corals can quickly contribute to the natural pool of gametes during the annual mass-spawning of Elkhorn corals and thereby increase the genetic diversity of these threatened populations’. 

This coming spawning season will be very busy for the SECORE/Carmabi team as they have big plans.  ‘We plan on upscaling our production to several thousands of artificial substrates with corals to rehabilitate coral populations on larger sections of reefs’ says Valerie Chamberland. She also stresses that she and her team can’t perform miracles. ‘Our techniques can only support natural recovery, we don’t get around to protect coral reefs and to apply additional management tools to reduce overfishing, pollution and other threats to coral reefs.’ The researchers hope to raise public awareness of the uniqueness and importance of the reefs surrounding the island. ‘Our future depends on it, really,’ says Chamberland. ‘But many people in Curaçao are not aware of their treasures beneath the surface and what they can do to help protect them. We hope that more people will come visit Carmabi to learn about the coral reefs and the important roles they play.’ Carmabi has recently opened a Marine Education Center where locals and tourists of all ages are welcome to visit to learn more about coral reefs.