Human activities such as pollution, overfishing, destructive forestry, and mining practices are posing a significant threat to coral reefs, some of the oldest and most diverse ecosystems on Earth. Climate change, another human-driven factor, is worsening the situation by causing ocean warming and acidification, potentially leading to the extinction of most corals within a few generations.
For the past 17 years, I have been part of a global science program called the Reef Recovery Initiative at the Smithsonian’s National Zoo and Conservation Biology Institute. The goal of this program is to save coral reefs using the science of cryopreservation.
Understanding Cryopreservation
Cryopreservation is an innovative approach that involves storing and cooling coral sperm and larvae, or germ cells, at extremely low temperatures and holding them in government biorepositories. These repositories serve as a crucial safeguard against coral extinction. If managed effectively, they can help mitigate threats to the Earth’s reefs on a global scale. These frozen assets can be used today, 10 years, or even 100 years from now to help reseed the oceans and restore living reefs.
The Cryopreservation Process
Cryopreservation is a process for freezing biological material while maintaining its viability. It involves introducing sugarlike substances, known as cryoprotectants, into cells to help prevent lethal ice formation during the freezing phase. If done correctly, the cells remain frozen and alive in liquid nitrogen, unchanged, for many years.
Currently, coral cryopreservation techniques primarily rely on freezing sperm and larvae. Since 2007, I have trained many colleagues in coral cryopreservation and worked with them to successfully preserve coral sperm. Today we have sperm from over 50 species of corals preserved in biorepositories worldwide.
Assisted Gene Flow
We have used this cryopreserved sperm to produce new coral across the Caribbean via a selective breeding process called assisted gene flow. The aim was to use cryopreserved sperm and interbreed corals that would not necessarily have encountered each other—a type of long-distance matchmaking.
Genetic diversity is maintained by combining as many different parents as possible to produce new sexually produced offspring. Since corals are cemented to the seabed, when population numbers in their area decline, new individuals can be introduced via cryopreservation. The hope is that these new genetic combinations might have an adaptation that will help coral survive changes in future warming oceans.
Scaling Up the Rescue
To collect coral material faster, we are developing a cryopreservation process for whole coral fragments, using a method called isochoric vitrification. This technique is still in development. However, if fully successful, it will preserve whole coral fragments without causing ice to form in their tissues, thus producing viable fragments after they’ve thawed that thrive and can be placed back out on the reef.
Securing the Future
Recent climate models estimate that if greenhouse gas emissions continue unabated, 95% or more of the world’s corals could die by the mid-2030s. This leaves precious little time to conserve the biodiversity and genetic diversity of reefs.
