Coral Farming in Okinawa

By Rick Allen

30 November 2023, Onna Village, Japan

Waves picked up as the small, open-deck boat throttled toward the dive site.  Beyond the sapphire bay, deep water churned and the current grew visibly stronger. Above me, gray clouds had already swallowed the last of the day’s sunlight. I felt a momentary shiver in the cold breeze just before someone tapped my shoulder.

“It’s good you’re diving today,” the divemaster said in clear, but halted English. “I think the storm will make it too difficult to go out tomorrow.”

Diving is possible year-round in most of Japan, but high winds and large swells are more common in winter months. Fortunately I had arrived between the end of typhoon season and ahead of a rainy week in late November. Despite the weather – or perhaps because of it – conditions felt similar to misty winter mornings along the California coast. I was right at home. 

As the boat bounced along, shuddering through wave peaks and valleys, I stared out over the water and imagined the coral farm below.

Recently outplanted "seedlings" in front of corals outplanted three to six months prior.

Coral farming is a type of active coral restoration. Active restoration techniques involve making a direct impact on a chosen site by adding, removing, or altering the makeup of a reef. This might involve removing invasive species, adding structures for corals to grow on, or applying topical creams to diseased or at-risk corals.

Passive restoration primarily deals with removing anthropogenic factors and letting nature heal itself at its natural speed. We see passive restoration in action through the creation of marine preserves and national parks. However, with current global CO2 levels and other pollutants adding to the speed of climate change, not only is it impossible to completely remove all anthropogenic factors, but even if they were totally removed, the rising rate of global warming is such that the natural recovery of weakened reefs is too slow to outpace permanent damage.

Imagine you’re adrift in a row boat that’s taking on water. You desperately need to make it back to shore before it sinks. You can continue paddling, hoping the current pushes you back to land before it’s too late. Or you could bail water out as you go, limiting the weight of incoming water and delaying the point of no return. You’d probably choose the later. This is the difference between passive and active restoration.

It paints a bleak picture of the state of our global coral reefs, but there’s still plenty of hope remaining. 

One point the locals in Onna Village wanted to make known, is that the reefs in Okinawa are growing. This is partly due to the island’s slightly cooler subtropical climate (aided by deep, cold water brought in by typhoons) and the active coral restoration efforts of a community in harmony with their environment.

In true Japanese fashion, there’s even a kawaii style mascot named, "Sunna" - a coral fairy who encourages protection of the reefs.

My wife and I were there to take part in an active restoration technique, commonly called micro-fragmenting, which encourages coral reproduction by speeding up its natural division process. 

Small fragments, referred to as “seeds,” are harvested from healthy reefs and then kept in shallow water tanks at surface facilities. Once the fragments achieve a certain size, they’re ready for outplanting back into the bay. At Onna, newly outplanted corals are first installed onto a raised platform. After a few months of growth, larger fragments are placed in holes drilled into the seabed nearby.

Below is a comparison of newly outplanted corals versus corals that have continued growing in the bay for three to six months.

0-3 months after outplanting.

3-6 months after outplanting.

A month before arriving, we had signed up for a coral restoration class with Okinawa Lagoon Diving over email exchanges. The staff graciously accommodated our needs, allowing our daughters to join the 45-minute educational presentation and coral seeding experience. For a nominal fee, a divemaster was provided so that we could take turns diving and watching our children. Ocean-themed coloring pages and a Finding Nemo snow globe kept our three-year-old engaged while her younger sister - just six months old - snuggled close to Mom during the lecture.

As expected, there were some minor communication barriers during the presentation, but an accompanying slideshow and willingness amongst everyone to learn and teach smoothed over any unclear lesson points.

I’m a seasoned kelp forest diver, but I have limited experience with tropical coral reefs. The presentation was simple enough for coral novices, like me, yet it still provided deeper learning about the biology and lifecycle of corals. It was fascinating to learn that coral larvae in the planula stage can freely swim by means of cilia (hair-like appendages) before settling into a final location. A magnified view of a coral polyp reveals the continued use of cilia to agitate water near the coral's surface, drawing in nutrients. Through photosynthesis, symbiotic algae living inside the coral, called zooxanthellae, provide further compounds needed for the production of calcium carbonate. Calcium carbonate is the framework of all coral colonies. Over thousands of years, this process continues its cycle, developing stony surfaces into the habitats we know as coral reefs. 

Sexual reproduction in most corals occurs once every year during a mass spawning event, where a blizzard of coral eggs and sperm can be seen in the water column. Once egg and sperm join together in an embryo, they develop into a planula and begin searching for their forever home.

Like many ocean lovers, I already understood that coral polyps are animals. However, this peculiar free swimming trait made me guilty of looking at them with a higher degree of anthropomorphism. The ability to sense their surroundings and choose where to ground themselves hinted at an intelligence I didn’t expect to encounter. Imagine a tree seedling drifting in the wind and directing itself to take root in rich soil rather than dry itself out on barren asphalt. I was amazed.

After the lecture was over, our three-year-old helped personalize the small cement stakes we would soon be mounting coral fragments to. I continued chatting with our presenter, Hiroaki Yamamoto - a Reef Check scientist - while my wife kitted up for her dives. It’d be her first time diving since getting pregnant with our second child. She beamed with excitement. I’d take my turn in the water after beach combing with the kids.  

Following a short drive down the street, we arrived at the above ground coral nursery. It resembled a long greenhouse with a saltwater tank stretching down the center. Fragmented corals in various stages of growth were neatly arranged on wire grates inside the tank. A staff member guided us in attaching coral fragments to our cement stakes. Once fastened, it was time for us to get wet.


Inside the coral nursery at Onna Village.

Back on the boat, cold whitewater sprayed a group of wobbling tourists who would be snorkeling above the reef in a few minutes. They laughed with delight, happily in the thrill of exploring someplace new. Their voices, a mix of European accents, carried on enthusiastically. One of them saw me in dive gear and struck up conversation. 

“So, you’re actually going down and planting the coral yourself?” he asked. “That’s incredible!” 

I should mention that Okinawa Lagoon Diving also allows non-divers to take part in the educational program and snorkel while staff divers install the non-diving guests’ personalized coral fragments.

Our own coral seedling, freshly outplanted.

The European relayed his desire to get certified and see more of the underwater world. I told him about some of the other countries I’ve dove at and the kelp forests back home, encouraging him to take lessons soon. Also next to me, stood a Taiwanese reporter bundled up in street clothes. The faux fur of her winter coat flapped wildly in the breeze. She was doing a story on the group of snorkelers. I didn’t catch the occasion, but she and I had a great chat about Taiwan’s Taroko National Park which I had recently visited.

I bring up these small interactions because they’re one of my favorite facets of dive travel. A packed dive boat can easily become a micro example of people with dissimilar backgrounds coming together through shared interests. On that day, our common ground was helping save coral reefs – something which impacts billions of people on this planet we call home. Imagine that sort of global teamwork scaled up for an even larger initiative.

The diving on Okinawa is fantastic. Brightly colored parrotfish flitted about with other tropical fish in the nooks and crannies of various corals. I was glad to see juvenile fish populating the coral farm in the safe, shallow water of the bay. The active restoration work was well into ensuring a thriving reef in Onna Village. During our fun dives, a large sea turtle joined me near the outer drop off and my wife had seen a whitetip shark. Both were signs that a healthy ecosystem was present.

There are three types of reef systems: fringing, barrier, and atoll. Okinawa has a fringing reef that extends from the shore out to a dramatic drop-off.

Dive sites feature a wonderful mix of rock formations similar to those found along the western coast of North America and the lush reefs of tropical islands.

Continuing the circle of life, a yellow-brown sunset wrasse turns a few outplanted corals into a light snack.

Despite the seemingly idyllic scenery, there’s still much work to be done. Mitigating climate change is an ongoing effort. In the example I gave of a sinking rowboat, that rowboat is still far from shore. Even the reef in Onna is still susceptible to change. An acknowledged weak area is the fact that most of the farmed coral - worldwide, not just in Onna – is often of a singular species. Underwater, monoculture is prone to the same issues facing commercial agriculture on land. Greater biodiversity is needed to prevent total collapse in the event of a species-specific outbreak. Continued research and experimentation is needed to evolve restoration practices. Young scientists with new perspectives and financial donors wanting to make a difference in the world are still needed.

The author stretches out over a massive table coral.

Joanna Tang glides over a section of the coral farm designed with posts rather than raised frames.

“Papa, can I come back and plant corals when I’m older?” my three-year-old asked as we walked back to our hotel.

Yes. 

Absolutely, yes.

The number of worldwide coral restoration programs is growing. Consider taking part in one while planning your next dive travel excursion. If you’re interested in learning more and would like to experience coral farming in Okinawa firsthand, you can reach out to Okinawa Lagoon Diving via email at: info@lagoon-diving.com.

A special thanks to the team at Okinawa Lagoon Diving for capturing great photos of us during the dives!  www.lagoon-diving.com

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