Engineered Holobionts

Our lab is focused on ecological intervention projects to enhance coral genetic diversity and standing stocks of key reef-building species in the Virgin Islands. To approach these goals, we implement selective breeding of corals using in vitro fertilization and captive settlement of the larvae. We first identify donor colonies with desirable characteristics (i.e. bleaching or disease resistance) and then carefully prepare for coral spawning, which only occurs a few nights per year. Utilizing SCUBA, our student dive teams collect gametes from donor colonies and transport them back to the lab to initiate fertilization between selected colonies. Under controlled laboratory conditions, we can fertilize and produce millions to billions of coral embryos with new genetic diversity in a matter of days.

Through this facilitated sexual reproduction, we can settle and rear tens- to hundreds of thousands of coral larvae each spawning cycle. The larvae begin aposymbiotically, meaning they have not yet acquired their necessary Symbiodiniaceae (zooxanthellae) symbionts. This provides us the unique opportunity to manipulatively engineer this association, by inoculating coral larvae with different species and populations of Symbiodiniaceae. Our primary objective is to produce holobionts (coral and symbiont) with enhanced characteristics. The engineered holobionts are then reared under a range of conditions and challenged with thermal stress and disease transmission experiments to evaluate and identify specific holobiont combinations as candidates for ecological intervention efforts.

 Assisted Evolution

As the generation times of Symbiodiniaceae are much faster than long-lived corals, the chance for desirable mutations is much greater. By manipulating this in the laboratory through a series of culturing rounds at elevated temperatures (called “ratchet experiments”), we can select for mutated genotypes that demonstrate increased thermal-tolerance. It is important to note that caution must be taken, because similar to the performance of D. trenchi in the Caribbean, there are potential trade-offs and other performance variables (i.e. carbon translocation) that must be evaluated simultaneously with thermal-tolerance. However, once we’ve isolated and screened “enhanced” symbiont genotypes, as compared to the wild-type, we can create clonal cultures for inoculation into aposymbiotic coral embryos to further enhance the rearing of engineered holobionts. These “assisted” corals then serve as prime candidates for propagation and outplanting in coral restoration efforts. 

 Manipulative Rearing

Aquarists have known for decades that there are ways to optimize, and even accelerate coral growth. However, caution must be taken to ensure there are no unintended consequences or undesirable tradeoffs that would render them less optimal when outplanted to the reef. For example, seawater parameter manipulations may lead to an increase in linear extension, but result in lower skeletal densities, leading to brittle skeletons that are more susceptible to damage by storms and wave energy.

Our lab is experimenting with artificially optimizing growth rates by manipulating seawater alkalinity, temperature cycling, photoperiod, and water velocity. Accelerating growth from embryo to juvenile stages is critical for scaling land-based nursery propagation for large scale coral restoration efforts.