We’ve been growing Acropora tenuis in their millions for over 20 years now and have been roaming Indonesian reefs for over 25 years. So we can say we’ve seen our fair share of tenuis, but there are some colonies that have a special place in our memory. A bit like an old friend, we always enjoy paying them a visit, to see how they’re doing.
We met for the first time over 10 years ago. I remember seeing this white 4-5 meter high, huge coral mass in the distance. I swam right to it, slowly realizing it was an Acropora, then a few seconds later that it actually was an Acropora tenuis. I couldn’t believe it as I didn’t expect this species there. It’s a bit too deep for Acropora tenuis, around 14-18 m (40-55′) when they usually favor shallow water above 10 m (30′).
The size of it was not like anything I’d seen before, as it was huge. We rarely accounter colonies bigger than a meter (3′) wide, but this colony is just a monster and we’ve seen nothing like it before. An Acropora tenuis 3-4 meters (9-12′) long by 3-4 m (9-12′) high is astonishing. It’s growing in layers above layers like a staircase that follows the underwater slope.
The coloration of that particular colony is not amazing like many Acropora tenuis we see now and are used to. But nevertheless, it does show a few characteristics of a small potential under blue light. Considering the depth it was found, and the potential of deep water corals growing in reduced light, when brought up to more vivid lights, it could actually be quite interesting. The inside of the corallites are fluorescent yellow and the tentacles are bright purple. That’s a good sign to us that it has potential.
Large coral colonies, especially Acropora, are an excellent sign of reef health. The fact that this colony is surviving the different coral bleaching, Drupella or crown of thorn starfish events, pollution, overfishing, and didn’t get entangled in a discarded fishing net is just a miracle. The depth is probably what is saving it, keeping cooler and darker during warming events, and out of the reach of many fishermen.
This colony is at the entrance of a small canyon, at the tip of a small peninsula. In the sweet spot where the deep, cool underwater flow comes right in front of it and then splits into both directions along the reef walls. It goes in one direction on one side of the colony and the other on the opposite side, which is quite remarkable. This particular spot is quite tricky to dive, and we usually wait for slack or nip tides to get down there. Otherwise, we are in for a rough ride and a long swim!
That very particular underwater current is actually the exact reason why that particular colony could grow that big. That current brings cooler, deeper water onto the reef, but also sucks rich surface water down the reef slope. This current is packed with the necessary phytoplankton food, necessary for species of like Acropora tenuis. All these small layers of coral filter the down current, and have allowed it to grow humongous.
It takes special conditions to produce special corals and this is the perfect example. That colony deserves its own name, just like the giant redwoods in California.