Planting Coral One Piece at a Time — Notes from Under the Sea at Koh Talu

1 day ago

4 min read

Six months underwater with the foundation team, thumb-sized coral fragments, and the reefs off Ao Muk and Ao Tian

Before We Dive

The sea off Koh Talu is usually at its calmest in the early morning. That's when the Siam Marine Rehabilitation Foundation team starts loading air tanks onto the raft. The work we're about to describe took more than six months, and almost all of it happened underwater.

We had restored coral before, using PVC pipe frames. With that method, we tied coral branches onto the frames on land, then dove down to set the frames on the reef.

Early PVC pipe coral nursery frames at Koh Talu

PVC frame with coral branches underwater

In 2019, we went to learn a new technique at Koh Racha Yai and came back with a different challenge: this time, every step had to be done underwater, from choosing the fragments to fixing them in place. The team joked that we dove so much we nearly grew gills.

A few days later, Reef Management Co., Ltd. sent a staff member to stay on Koh Talu as our mentor and work closely alongside us.

Foundation team briefing with the Reef Management mentor

Starting From One

The first lesson was learning to tell living coral from dead. We don't cut coral from anywhere for this work. We collect small fragments, about the size of a thumb, that have already broken off and are lying on the seabed.

Thumb-sized coral fragment collected from the seabed

These fragments come from many places. Some break off in wind and waves, some because the surface they grew on wasn't stable, and quite a few because of people: anchors dropped onto the reef, boats scraping past, or visitors who step on them by accident.

Whatever the cause, a coral fragment rolling around on the sand has little chance of surviving. Fixing it to solid ground gives it a chance to keep going.

Neighbours With Stingers

But saving one fragment must not harm the corals already living there. Corals really do compete for space, reaching out tentacles armed with stinging cells (nematocysts) to damage their neighbours' tissue.

Brain coral surrounded by neighbouring corals

So we choose each attachment spot with enough distance, so the new fragment doesn't bother anyone, and isn't bullied to death by the established residents before it can settle in.

Nails, Ties, and Epoxy

Every dive day starts with collecting fragments from the seabed. Most of what we find around Koh Talu is petal coral (Pavona sp.), Montipora (Montipora sp.), and boulder coral (Porites sp.). How we attach each piece depends on its shape.

Branching corals

We hammer a 3-inch concrete nail into a dead coral base, place the fragment against the nail, and secure it with a plastic cable tie. The key is that the living part must touch the base, because from here the coral will grow down over it and anchor itself, instead of rolling around on the seabed.

Concrete nails and cable ties holding coral on a dead coral base

Boulder and plate corals

These are less common. For them we use an epoxy putty the team calls "Maha-ud". It comes in two parts, A and B. We take the whole pack underwater, then unwrap and knead the two parts together right there. It looks a lot like someone kneading bread dough in the middle of the sea.

It's great practice for buoyancy and focus. You have to knead until the putty is completely mixed, while finding a spot to hover where you won't touch any coral around you. New team members often get this job first, so they can watch the seniors work at the same time.

Before pressing the putty down, we scrub the dead coral surface with a wire brush to remove turf algae, sponges, zoanthids and mushroom corals. We pinch off a piece of putty slightly smaller than the fragment, press it onto the base, then press the coral onto the putty. If the kneading was done well, in 12 hours the putty sets as hard as cement.

Wedging into natural crevices

The simplest method is to find a gap or crevice that fits the fragment and wedge it in. But finding the right gap takes a long time underwater, and it only works for branching corals, so we don't use it often.

Branching coral successfully attached to its base

A Raft at Sea

Koh Talu Island Resort let us set up a work station on the island and gave us a raft to use as a station at sea. Every morning we loaded our gear onto the raft and dove from there.

The raft used as a work station at sea off Koh Talu

Diver entering the water from the raft to plant coral

On days when the raft was busy or broken, we had a special trip instead: load the tanks and all the equipment onto a cart, haul it from our lodgings to the beach, gear up, and walk straight into the sea. After the dive, we walked back out and hauled the cart home.

Small but Significant

Over six months, the foundation team lived and breathed coral. Our target was more than twenty thousand fragments off Ao Muk and Ao Tian. Compared with the PVC frame work we'd done before, that number may not sound like much. But each piece needed a deeper level of understanding, and every one had to be trackable.

Small work, but it means a lot.

We want to thank everyone on the team, those who dropped by to help and those who stayed until the end. We hope this is a small way of giving back to the reef on our doorstep, the one we have gathered from and relied on for so long. And we look forward to seeing how the corals we saved will grow in the years to come.

If you come diving at Koh Talu, ask our Dive Center team about the coral plots off Ao Muk and Ao Tian. And if you haven't read it yet, here's another story from the same sea: The Mother Sea Turtle and Her Foster-Mothers