Coral sex: How lab reproduction could restore wild reefs
Coral sex in the lab
Coral reefs are so enormous they’re visible from space. But watching them spawn is surprisingly tricky. They only do it on a handful of nights each year and the exact date and time is determined by environmental factors that scientists are still working to fully understand.
Climate change is causing reefs with known spawning patterns to shift their timing too,making these events less frequent and predictable. This makes it difficult for different colonies to synchronize spawning, reducing their chances of successful fertilization in the wild.
The CORALIUM Laboratory of the National Autonomous University of Mexico is part of aCaribbean-wide networkof dedicated coral spawning experts. Scientists here collect coral sperm and eggs from multiple Caribbean reefs in order to fertilize them in the lab.
The team waits for the full moon to signal when corals are likely to spawn. Coral sperm and eggs are collected with floating nets and plastic containers, and divers take extreme care to avoid damaging the reef. The millions of sperm and eggs collected are rushed back to the lab where they’re cleaned and monitored all night as they undergo assisted fertilization to begin life as free-swimming larvae. These larvae are very sensitive to water quality, temperature, and pathogens, so they need constant care.
Eventually, the larvae settle on hard surfaces where they change into polyps – the initial building blocks of a coral colony. In the ocean, these surfaces are often dead coral skeletons. In the lab, they areseeding units– 3-D shapes designed to resemble coral rubble that can float on ocean currents before resting on reefs.
Each juvenile produced this way carries a unique mix of genes that they will pass on to a new generation of corals. The resulting population has a stronger gene pool that can help it withstand new diseases and other threats. This long-term strategy also ensures sexual reproduction can continue on restored reefs, which would not be possible for a population composed of identical clones.
Restoring Caribbean reefs
The Caribbean may have lost as much as80% of its coral cover since the mid-1970s. The colonies that remain are now relatively isolated, reducing the chances of them being able to crossbreed. But in the controlled conditions of the lab, fertilization rates of over 80% are common and larval survival is high. That means thousands of juvenile corals are reared until they’re ready for the reef after just a few weeks of incubation.
But with late night dives by experts, specialized materials for collecting spawn and a lab where fertilization is carefully controlled, this work is often too expensive for smaller restoration projects. So scientists here have developed low-cost methods for lab spawning and are training teams from across the Caribbean to do it.
I took their course in 2016, and one year later, found myself setting up a new spawning site in Akumal, one hour south of the CORALIUM lab near Cancun. Coral spawning had never been observed here, but I trained volunteers from a local dive center on how to spot the signs. On our fifth consecutive night dive, we saw the synchronized spawning of multiple colonies of Elkorn corals.
We set up a hotel room as a temporary lab with sterilized plastic larvae tanks and filtered seawater and produced thousands of coral babies for restoration sites. In 2018, we built a beachside coral spawning laboratory on a shoestring budget. Positioned under a tree, the breeze block structure has mosquito netting walls that allow the cool sea breeze to keep the tanks at a constant 28-29°C.
The lab was just about up and running in time for that year’s lunar eclipse. We hadn’t anticipated a mass spawn of so many colonies, so the lab inauguration was a chaos of color-coded collection cups from different sites and parent colonies.
Running a coral spawning site has been the most rewarding experience of my career so far. It is everything that research should be: cutting edge, dynamic, and challenging. It’s what I signed up for when I became a marine scientist.
This article is republished fromThe ConversationbyJenny Mallon, PhD Candidate in Coral Reef Biogeochemistry,University of Glasgowunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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