Coral sexual reproduction as a restoration method
The larval propagation program uses coral sexual reproduction as a restoration method which allows us to work with numerous coral species and morphologies. This method increases the genetic diversity of corals on reefs and potentially scales up the number of corals we can outplant.
Genetic diversity on coral reefs is important because it increases the chances of there being corals better capable of coping with the altered conditions on modern Caribbean reefs. Although Bonaire’s coral reefs still feature significant populations of coral species, the healthy colonies may be too far apart to reproduce successfully through sexual reproduction, limiting the formation of new genetic strains. For this reason, assisting the sexual reproduction of ecologically important coral species through the larval propagation method is critical to aid the recovery of the degraded populations.
The technique aims to increase the success and efficiency of each early phase of the coral life cycle. From the gamete’s initial fertilization to the larval settlement on the reef, to produce thousands of new genetically diverse corals every year.
After monitoring a coral species over time to learn more about its spawning habits, we narrow down the best time to carefully collect coral reproductive cells, or gametes. Using collection nets placed above the spawning colonies, divers collect gametes in collection tubes and bring them to our on-land lab facility.
Our team mixes gametes of genetically different coral colonies of the same species to assist the cross-fertilization. Recently fertilized eggs start developing into embryos and are carefully monitored as they develop.
The developing embryos are either kept in the lab or transferred back to the ocean in special rearing pools, called Coral Rearing In Situ Basins (CRIBs) designed by our partner SECORE International. These floating CRIBs support the larva development by allowing seawater to flow through the enclosure while keeping the larva contained as they grow.
After few days, depending on the coral species, the larvae eventually start scouting the bottom for a home to settle on, but they are picky! In the CRIBs, we place thousands of substrates called Seeding Units (SUs), carefully designed by SECORE International for easy outplanting and to provide the larvae with the most attractive place where to settle on.
Once the larvae have successfully settled and firmly attached onto the Seeding Units, we outplant them to degraded reef areas. Now they must face the reef life on their own, however we monitor their health over time till the day they might be ready to spawn too…
The next step: integrating propagation techniques
Fragmentation allows us to outplant bigger colonies and quickly restore reefs with corals that will reach maturity and begin spawning in just a couple of years. However, through larval propagation we can select or randomly mix gametes, producing always genetically unique individuals.
Since we witness our outplanted corals spawning every year, we can select specific strains that have performed well to be used for larval propagation. In the same way corals produced through larval propagation can enter the fragmentation process, and if well performing, get propagated in large numbers.