By: Arin
The northern waters of the Pacific and Atlantic are opaque from above, a dusty turquoise with not much visible in open water. But in the late summer near the coast you can sometimes see comb jellies floating near the surface; orbs with tentacles and 8 ribbed sections lined in cilia, or tiny combs, that sometimes flash colors. I find it amazing that evolution produced these strange rainbow-making little creatures, and that something so intensely fragile and odd has outlived the dinosaurs.
I was on the docks in Svalbard harbor in late July when I noticed red strings in the water that turned out to be the tentacles of passing arctic comb jellies. Closer inspection in the shadows of the boats revealed transparent orbs with stripes of feathery cilia running down in different colored lights. The stripes ran down gold, then the next wave was blue, then red, then lime green. They changed every second, and with the direction you saw them from.
There were dozens of them below the boats, floating in the arctic water and drifting their tentacles about for prey. Unlike jellyfish, comb jellies do not have stinging tentacles, only sticky ones that they can reel up when they catch something. In my haste to get a picture I dropped my lens cap into the harbor and it sank down into the arctic mud after 8 years of use. Oh well. It gave its life for science.
I've seen comb jellies before in Alaska but I always thought they were bioluminescent jellyfish. Bioluminesence is incredibly common after all, with some 75% of all marine creatures thought to produce their own light through either bacterial mutualism or chemical reaction, and many comb jellies do produce their own light, but the colors I saw were something else. As I searched for more information about them I found that they were incredible creatures who were nothing like I expected.
First of all, comb jellies are not jellyfish (they're in a unique phyla all their own, Ctenophora, while jellyfish share the phylum Cnidaria with sea anemones, corals, sea pens, and other species) but they share many of the same features. And if it was not bioluminescence, why did the arctic comb jelly have beads of lights that clearly changed color and winked in and out?
These jellies actually refracted sunlight along their numerous cilia, small hair-like projections that help them move (often seen in the movement of one-cell organisms like bacteria. In fact comb jellies are the largest organisms to employ cilia for movement). The cilia refract sunlight like a raindrop and produce the same effect: a rainbow. Near the surface of the water, lines of feathery cilia catch this light and form iridescence, sending lines of color down their gelatinous bodies like lights on a runway. While incredible to watch, this light show doesn't seem to serve the same purposes that bioluminescence does (mainly communication, defense, and hunting in the light-less world of the deep ocean), as it only works in the tiny layer of the ocean that sees sunlight, and comb jellies use their cilia constantly, light or no light. The rainbow effect seems to just be a fun extra feature of the necessary movement of its cilia.
So comb jellies actually produce light in two ways: bioluminescence, which can only be seen at night or in deep water, and the rainbow movement of the cilia, which can only be seen in the daytime. Current research has not discovered an exact purpose for either trait in comb jellies.
A few days after finding the arctic comb jelly, I was at a cabin out in the Svalbard archipelago waiting for the weather to clear up enough for us to look for birds. The midnight sun kept the sky light with swirling clouds past 2 in the morning, when we decided to fire up the sauna. Traditional Scandinavian saunas require a few minutes in extremely hot cedar rooms followed by mad dashes into the arctic ocean and back again to cool off. So at 3 in the morning I was shrieking in the arctic ocean under a white sky when I saw little pink blobs floating along and winking rainbow light. This was my second experience with comb jellies in as many days.
The sea strawberries drifted about the shallow water, with faint lights flickering along their facets. It was amazing how such a creature could function. All comb jellies lack lungs (obviously), a stomach or intestines, and they use the most simplistic nervous system known, a tiny net of nerves that suffices as a rudimentary brain, which allows them to sense when they are touched, keep upright, and detect light. They are often hermaphroditic (they produce both sperm and eggs), their entire body can be 95% water, and they're carnivorous. They've also been around for some 500 million years, with comb jelly fossils being found in the Burgess shale fossil site from the end of the Cambrian explosion. Not bad for a sticky blob that swims with tiny rainbow feathers.
This sea strawberry (Beroe cucumis) is red because the color red can't be seen in dark water and is less taxing to produce than black as a camouflage pigment, suggesting this species spends most of its time in deep water where it can't be seen. Probably due to behavior like this, only about 150 species of comb jelly have been described, compared to 4,000 species of jellyfish. They can be found all over the world, and many more species have yet to be discovered.
I tended to see comb jellies in the late summer when jellyfish and comb jellies alike would bob close to the coasts. While they cannot sting, they do melt apart when removed from the ocean, so should be observed carefully, and kept in the water. If you explore the tide pools along the coastal oceans you might see some clear blobs floating along in the current, sometimes only visible by the rainbow of lights flashing colors on their tiny oars as they weather the eras, as though unconcerned with the happenings of the world.