Coral Health and Genetics

A finger points to numbers on a clipboard — Coral restoration practitioners keep track of specific genotypes to ensure diversity on the reef. Photo: Scott Atwell/NOAA

Corals are complex animals. Just like humans and other animals, corals have immune systems to protect them from disease, but when those immune defenses don't work, corals can get sick. Understanding the different aspects of coral health is important to researchers working to restore coral reefs, while also accounting for threats such as climate change and poor water quality. The genetics of corals plays an important role in this research of understanding what's happening inside the coral's body. Researchers are working to understand the whole coral complex — the coral "holobiont" — which includes the coral animal, an algal partner (called "zooxanthellae") that provides food, as well as an entire microbial community. Similar to our gut health as humans, corals have a complex community hidden in their tissues made up of viruses, bacteria, fungi, and more! The population of this microscopic community changes in the face of environmental stressors like water quality changes and high temperatures. These communities can even differ between corals of the same species, depending on their location and other factors. Scientists are examining the role the coral holobiont plays in coral health and resilience to a changing ocean. Scientists can use genetic sequencing to look at which types of organisms make up this holobiont community and are looking to understand how this community plays a role in coral survival and success.

A man points to a large screen with trays of dark coral fragments and bleached coral fragments during a presentation — Genetics at work: Reef Renewal's Ken Nedimyer points to dark coral fragments that survived a summer heat wave, next to bleached counterparts that died. Photo by Scott Atwell/NOAA

Scientists are also working to understand which species and which genotypes of coral, paired with different strains of algal symbionts, will survive best in future scenarios. Scientists are experimenting with pairing corals with different types of zooxanthellae to see if these algal partners will stay with the corals as they are placed back onto the reef.

All of this research is especially important in restoration work as some coral and zooxanthellae individuals and some holobiont compositions may be more resilient to warmer temperatures or disease. Researchers can subject the corals to different environmental conditions and evaluate which ones are a little bit stronger. Research into the holobiont community also may have implications for diseases like stony coral tissue loss disease, which is hypothesized to be an imbalance of the holobiont caused by harmful bacteria.

clear glass tanks in a laboratory filled with water and fragments of corals — Corals in the NOAA/AOML and University of Miami/CIMAS Experimental Reef Lab, where they will be subjected to different stressors to determine performance and susceptibility. Photo: Joshua Prezant/University of Miami

tiny white dots float around branching corals and a cone-shaped net captures some of the material — Once a year, on cues from the lunar cycle and the water temperature, entire colonies of coral reefs simultaneously release their tiny eggs and sperm, called gametes, into the ocean. The phenomenon brings to mind an underwater blizzard with billions of colorful flakes cascading in white, yellow, red, and orange.

Strong genetic diversity is the underpinning of resilience and adaptation. New breakthroughs in scientific research help restoration organizations to increase coral survival and their success in restoration work.