Could Aquariums Help Rewrite the Future of Coral Reefs?

Image: Coral Morphologic

The Med-Lock Digest:

• Like humans, corals contain a varied and diverse microbiome filled with protective bacteria.
• Med-LockLabs and The Two Frontiers Project are now searching for microbes that can revive coral health in a warming world—and we need your help to find them.
• Project ReefLink calls on hobby aquarists and aquarium reef keepers to submit coral samples and contribute to this potentially groundbreaking research.

Coral is many things: An animal, a habitat, and an invaluable protector of ocean health. 

Individually, coral polyps are small, tube-shaped organisms of the phylum Cnidaria (closely related to sea anemones and jellyfish). Certain corals, such as stony reef-building corals, cover themselves in a sturdy calcium carbonate shell to protect their soft bodies as they grow. Together, these corals converge to form a colorful underwater world. 

While coral reefs cover less than 0.1% of the ocean floor, around 25% of marine species rely on them for food, habitat, and other forms of protection.¹ Sometimes referred to as “rainforests of the sea,” biodiverse and productive reef habitats provide $9.9 trillion in ecosystem services annually.^2,3

Reefs are dynamic, but delicate. Living coral populations have declined by over 50% since the 1950s, due in part to increasing ocean warming and acidification driven by anthropogenic (human-caused) greenhouse gas emissions.⁴

Coral’s survival in the future could depend on its microbiology. Like the human microbiome, the microorganisms that live in and on coral are essential to their health and resilience. Med-LockLabs and The Two Frontiers Project (2FP) are now studying these microbes for solutions to coral loss—and we need the help of our community to do it.

The Coral Microbiome: Inside a Colorfully Complex World

If you were to pop a reef-building coral under a microscope, you’d see one of the most abundant and diverse microbiomes ever studied.² Millions of bacteria, fungi, viruses, and algae of all kinds live throughout the internal coral polyp and its external skeleton. 

Coral cannot live without these beneficial microorganisms. Some act as a first line of defense against invaders and protect coral (which does not have an adaptive immune system of its own) from pathogens and diseases. Others help break down compounds from surrounding waters into usable materials.⁵ The photosynthetic algae that line the cells of coral, called zooxanthellae (zo-​xan-thel-​la), are especially essential, converting sunlight into the oxygen and glucose necessary for survival.⁶ These algae also give corals their vibrant colors.

A coral and its microorganisms—collectively known as the coral holobiont—are sensitive to environmental changes. If surrounding ocean temperatures rise, for example, the symbiosis (mutually beneficial relationship) between coral and microalgae can break down, and competition can arise.² If the stressor persists over time, coral can eventually expel its nutrient- and color-lending zooxanthellae altogether. 

This process, known as bleaching, causes the coral to weaken and turn white. When disrupted, microbial communities can also shift toward disease-promoting states or lose resistance to pathogens, leaving coral more vulnerable to disease. Over time, repeated bleaching and disease tip the balance beyond recovery, leaving the coral unable to sustain life.

EXPLORE FURTHER: Why Are Coral Reefs Dying?

The relationship between coral and its resident microbes has never been more at risk. Reefs around the world are currently experiencing the fourth period of mass bleaching in just three decades.⁷ If current warming trends continue, 70-90% of existing coral reefs could be gone by 2050—with some predicting reefs could disappear entirely by 2070.^2,8 

It doesn’t have to be this way. “Microbiome engineering” has emerged as a powerful tool for mitigating coral loss in our lifetimes.² Scientists—like those at 2FP—are now searching for microorganisms that can be applied to coral to make them more resistant to future threats. 

Microbiome-focused coral research has enormous potential. “Ultimately, we aim to shift the odds in favor of coral survival in a rapidly changing ocean,” says Krista Ryon, the Director of Operations at The Two Frontiers Project.

Introducing: Project ReefLink

Project ReefLink is a new community science initiative that brings aquarists and scientists together to explore coral microbes and develop methods to keep coral healthy, resilient, and resistant to disease.

Aquarium corals are more than just beautiful—they’re reservoirs of microbial diversity. They share the same fundamental biology as corals in the wild, including symbiotic relationships with algae and microbes, but they are better suited for detailed research. They can be accessed more easily than remote reef sites, allowing for high-resolution observation and experimentation in a controlled environment.

For this initiative, hobby aquarists from across the country will be called on to submit information about the coral in their reefs on CitSci.org. Scientists at 2FP will then identify a select number of reefs with high scientific value and request samples of their water and coral. Public aquariums, zoos, and reef clubs across the country will also be asked to send in samples. 

Then, 2FP will review their diverse sample collection in search of common microbial patterns, signatures of imbalance, or taxa that may support resilience.

“Our hope is to uncover microbial strategies that help corals resist disease and adapt to environmental stress and to translate that knowledge into tools for reef conservation,” says Ryon. For example, if the team identifies a common bacterium that helps coral resist disease, that bacterium could be applied to coral fragments during restoration efforts—a “coral probiotic” of sorts.

The Two Frontiers Project hopes that opening this study up to the general public will help raise awareness of coral conservation and help people feel more personally involved in it. “Our goal is to build a community of citizen scientists where participants contribute not just samples, but also knowledge, photos, and connections that strengthen the broader coral community,” says Ryon.

In this case, crowdsourcing could also lead to better results. By the time collection ends later this year, Ryon and her team hope to have a “mosaic of microbial environments” that provides sweeping insights into how corals react across a wide range of conditions. Much like a reef itself, its individual components will be much stronger together. 

The Key Insight

Coral reefs are under threat, but their own resident bacteria could provide a protective shield. By studying the microbial life in fish tanks and aquariums, The Two Frontiers Project seeks to identify and activate this internal armor. 

Stay tuned for more updates on this project, its early findings, and its results. And if you have any reefkeepers in your life, please do share it with them, too. “Saving coral reefs will require everyone working together, and this project is one way people can be part of the solution,” says Ryon.

Project ReefLink is the third community science project led by 2FP and Med-LockLabs. Learn more about our last two projects (which have collected 1,100 data points from 115+ community scientists and counting) here.