Death by suffocation
SWIMMING SLOWLY over the reef investigating the nooks, crannies, sandy spits and rocky bottom, my eyes were drawn to a starfish with beautiful, mesmerising filaments that waved about in the current. I had never seen one like it.
I couldn’t identify the starfish but its colouring was unusual, bright orange and red with whitish blotches. As I looked more closely, it seemed as if the filaments were catching prey.
I watched in fascination as a tiny shrimp became entangled in a sticky frond and was then wrapped up by several other fronds before being reeled down towards the “skin” of the starfish.
Here, in some Alien-like process, the shrimp was absorbed, tail first, into the skin. Freakishly, its large eyes were the last part to be absorbed.
Was this some unusual type of feeding pattern I had not heard of before? I knew that starfish can be voracious predators that feed in several different ways.
The mouth is centrally placed beneath it, where it is protected, and the digestive system covers not only the mouth but also part of the arms.
A starfish will catch its prey, very often a crustacean, wrapping its powerful arms around it to break the shell.
It will then push its stomach out of its body and eat the contents, partially digesting it before the stomach is drawn back into the body.
In this way, it can consume prey much larger than its mouth.
All this activity takes place beneath the body, however, and not on top or through the skin. Watching this strange behaviour made me very curious, and keen to find out what was going on.
I asked the dive-guides. None of them knew for sure what was happening, but they all agreed that it seemed a very different way for starfish to eat.
OVER THE NEXT FEW DAYS of diving in Anilao in the Philippines I kept my eye out for more starfish. Spotting lots of bright blue Linckia, I examined them to see if they too fed this way, but they didn’t.
Eventually I found another starfish similar to the first, covered in the white fronds. This time I had a macro lens on, so I settled in to watch in the hope of capturing an example of this behaviour.
Sure enough, after a few minutes a tiny shrimp, carried by the slight current, swam into the path of the starfish.
Very quickly the fronds seemed to reach out and catch the shrimp, quickly rolling it up as if it was a body being rolled into a carpet for Mafia-type disposal.
Retracting the fronds, the shrimp was slowly pulled back towards the body, where a globule of skin seemed to envelope it.
It was quite distressing to see the shrimp’s eyes looking at me as it gradually disappeared.
Finally the eyes too were enveloped, and I could only think that the shrimp was being suffocated to death.
ONCE BACK in the UK reviewing my images, I decided to do some more research. I contacted several marine biologists, but none of them had seen the behaviour before, or could offer any type of explanation.
After weeks of research, I finally stumbled on something that amazed me. It seemed it was not the starfish itself that was feeding, but a type of benthic Ctenophora that was living communally with it.
Ctenophora are comb jellyfish and these examples, called Platyctenida, are the only benthic, or bottom-dwelling, sedentary comb jellyfish group in the range.
Normally comb jellies are seen in the water column around the world, pulsating and trailing long tentacles behind them. They are named for their unique feature of plates of giant fused cilia, known as combs, which run in eight rows up and down their bodies.
Sometimes these combs generate a psychedelic display of rainbow colours, when reflected light is scattered in different directions by the moving cilia.
These ancient animals are thought to have roamed the oceans for at least 500 million years. With sizes up to 15cm, Ctenophora have flattened, oval bodies and look very much like nudibranchs or flatworms. In fact they are often mistaken for such animals, as all but one species of Platyctenida lack the profusion of tentacles I had witnessed.
Some have no visible tentacles, only pores along the back, and most have only two tentacles, with branching side tentacles.
Being cryptically coloured, they are normally fairly well camouflaged, blending in well on the rocks, algae and soft coral on which they usually live.
They use their mouth as a muscular foot to move onto subjects and cling to them, living symbiotically with their host.
Thought to be asexual, they can self-fertilise, so populations can grow quite fast.
I was surprised by this, because they seem to have been discovered only around 1999, and are rarely reported. Perhaps this is because they are so often mistaken for flatworms.
Another theory is that they are very fragile because they don’t have to endure rough coastal waters. Many are so fragile that they cannot be collected for scientific research.
They are also food for more than 150 marine species.
SOME BUT NOT ALL comb jellies sting, but benthic Ctenophora, instead of releasing venom when their nematocysts fire on touch, release a sticky glue instead.
One species does use venom by recycling nematocysts from hydrozoans it eats. I was quite pleased not to be accidentally touched by a tentacle while I was photographing them, just in case this was a stinging type.
This starfish I had seen had been almost completely covered in the brightly coloured comb jellies, which were almost flat, so it was little wonder that I had mistaken them for starfish-skin.
Looking at other images of starfish I had taken on the same trip, I discovered one showing two starfish shrimp on the top of a starfish, with a side-branching comb jelly also on it!
Perhaps they are a lot more common than thought – it’s just that we don’t “see” them!
From now on, I’ll keep a close look-out for starfish and see if they are carrying their deadly hitch-hikers.