There’s something strange under the waters around Koh Tao, in fact, there is a whole alien world just waiting to be discovered. We are not talking about just the wonder and beauty of the coral reefs, but of the extraordinary creatures living out deeper in the sands. Out away from the reefs there is an incredible diversity of soft-bottomed ecosystems consisting of sand, sea grass, macro-algae, and mud; collectively known as the ‘muck.’
Coral reefs are sometimes called the rainforests of the sea, as they are the two most biodiverse ecosystems on our planet. In both ecosystems, life thrives and diversifies because essentially everything needed to survive is in abundance (food, shelter, water, etc) and the evolutionary arms race involving predator vs. prey along with the need to impress a potential mate become the dominate factors controlling evolution. The ‘muck’ areas however are more analogues to the deserts of the terrestrial landscape - in that life is hard. There is little shelter and few places to make a permanent home, forcing animals to either invest a lot of time and energy in digging, or to be able to blend in well with the background. What makes these places interesting to visit is not the abundance of life, but how specialized and well adapted the organisms living here are.
This year we have been spending more and more time out ‘in the muck’ as we complete surveys for seahorses, Opisthobranchs (sea slugs), and other rare organisms. This time out away from the reefs has really paid off in terms of adding new species to the checklists for our personal observations, and for the Thai Gulf. Here is our top ten list of the coolest things we have seen in ‘the muck’ this year:
10. Mantis Shrimp
The Mantis shrimp is actually quite common, but it still deserves mention in this list as it is arguably one of the most amazing animals on the planet. One of the first things that sets mantis shrimp apart from other shrimps is that they are predators — feeding on fish, clams, and other crustaceans. Generally they are ambush predators that come in two main groups, those that ‘spear’ their prey, and those that knock out their prey. The mantis shrimp has evolved one of the strongest and fastest punches in the world, so strong that they can easily break through clam shells or aquarium glass, and so fast that it actually generates a wave of energy so intense that it vaporizes the water in front of the moving arm and produces light. If that wasn’t enough, they also have the most well developed eyesight in the animal kingdom; and are able to see in the full visible spectrum of light, plus UV, infrared, and polarized light. This is the true bad ass of the invertebrate world.
9. Synaptid Sea Cucumbers
The synaptid sea cucumber doesn’t have any really interesting adaptations like the mantis shrimp (that we know of), but it made the list because. . .well, what the hell. A 3-meter long sea cucumber that looks like a snake is pretty cool, and it is also home to shrimp who ride around on it and have adapted their color to blend in with the sea cucumber. We think that’s pretty cool, and its something that we enjoy observing on our dives. Plus occasionally we can watch a student’s eyes go big with fear when the think they are looking at a huge sea snake.
Lionfish are a very rare sight for the reefs of Koh Tao, and in fact when a lionfish showed up at Chumphon pinnacle a few years back many in the dive community thought it had surely been released there from somewhere else (and some called for its removal). But those of us who dive in the muck are more familiar with these beautiful creatures. They are still quite rare, but on one dive in Chalok Last year we managed to spot about 6 of them. Despite their ornate beauty, they are a voracious predator with lighting fast jaws and poisonous spines. Always a pleasure to see and photograph.
If there was ever a shining example of being well adapted to your environment, the cuttlefish is it. Not only have they evolved amazing eyesight, but the can also change the color and texture of their skin instantly, both to blend in with their surrounds and for communication. That’s right, communication. This mollusk will use rapidly changing skin colors and patterns to warn rivals, attract mates, coordinate hunting, and confuse prey. Smaller males have also been known to disguise themselves as females so they can infiltrate the breeding harem of a larger male and mate with his females. Although they hunt in the coral reefs, often we find them sleeping in the deep muck areas during the day.
This one made the list because it is a well camouflaged ambush predator with poisonous spines on its back, and also it is just so ugly that it’s hard to stop staring. Scorpionfish and closely related stonefishes do their best to look like a harmless rock or bit of algae, and when prey comes by they open their huge mouth, increasing its volume by 400-500% and suck the prey right in. It all happens faster than the human brain can perceive, but there are some really high speed videos on youtube you can watch to actually see it happen. We have about 6 species of stonefish and scorpion fish on Koh Tao, but you have to look closely as they blend in to the rock or sand almost seamlessly.
5. Headshield slug (Philinopsis pilsbryi)
Head shield slugs are part of an order called cephalaspedia, and are related to nudibranchs. They are carnivores, but spend most of their time buried under the sand, so finding them is a real special occasion. This species in particular always catches our eye as it is relatively fast (for a slug), and has a striking pattern covering its body.
4. Anemone fish embryos
Anemone fish are actually quite abundant in the sands around Koh Tao, in fact every anemone has a family of them. This family unit starts out when females lay eggs on a rock or object brought near to the anemone by the male. After the eggs are laid, the male fertilizes them, and over the course of about two weeks they develop under near constant care and protection the parents before hatching. Often when we come across the developing embryos we can see all their little eyes peering out from the transparent eggs (did I just hear you say ‘awwww’?). It is hard not to be moved by such a site, and to end up spending the rest of the dive contemplating the circle of life. At least until you happen across our next animal.
3. Sea Apples
For my fellow American readers, these are not related to road apples. In fact, sea apples are related to sea cucumbers, except that they have tube feet specialized to grab plankton from the water column and bring it into the mouth. Generally they will be buried almost completely, with just the dendritic filter feeding feet above the sand. As the feet become covered in plankton and detritus they are pulled into the mouth, scraped clean, and then re-extended. This process causes a lava-lamp like state of hypnosis in divers, and I for one find it hard to leave them. We know of only two sightings of these creatures around Koh Tao, both from our team and both from this year.
2. Janolus savinkini Nudibranch
One of the main reasons that we do muck dives is to find nudibranchs, and with 64 recorded species for the island we could have filled this whole list with amazing nudibranch species we love. Sea slugs are some of the most brightly colored and dramatically patterned invertebrates in the marine world. They are toxic, sometimes photosynthetic and can even be cannibalistic, all the more reason to find them fascinating. This species was only described as a species as recently as 2012, and when our team found 2 baseball sized individuals of these incredibly ornate and alien looking nudibranchs back in April, it was sure to make the list. This species is thought to have been seen less than 5 times on Koh Tao and was a pleasant addition to our ever growing list of species found in the muck. A rare one to find, this is a classic Koh Tao nudi that is at the top of any marine animal ‘must see’ list for the region.
1. A pregnant male seahorse – Hippocampus spinosissimus
The animal that brought us to start doing regular muck surveys, seahorses are of course one of our favorite fishes to find. Not only are they one of the most unique looking fishes in the sea, but they also have some of the most interesting behaviors and reproductive strategies. In fact all of the normal reproductive strategies practiced by animals are reversed in seahorses, with females showing off themselves and being promiscuous and males doing all the offspring rearing. Not often in the animal kingdom have females evolved to force the males to take care of the eggs while they continue on with life as usual, and finding a pregnant male gives you quite a bit of human analogies to contemplate on for the rest of the day.
We hope you enjoyed our list of things to find ‘in the muck, of course there is a lot more amazing life down there than we can talk about here. If you are interested to find out more than please check out some of the other articles at the bottom of this page or learn more about marine invertebrates at our learning resources section.