Our ocean holds secrets: the strangest alien forms, reminiscent of spaceships. These gelatinous creatures are luminous, spreading waves of colour through their unpigmented body. They are the ctenophores, or comb jellies, and are our latest discovery of the magical organisms that lurk under our hulls.
Anatomy of a Comb Jellyfish
They are small (a few millimeters to several centimeters) and nearly totally transparent, which makes them relatively inconspicuous in day time, but at night, when you shine a strobe on them they glow. They occur in marine habitat both inshore and offshore, and from near the surface to the deep ocean. They are not uncommon, yet we know little about them.
The Ctenophore does not look like a traditional jellyfish since it does not have a bell and trailing tentacles. Instead it has translucent and highly expandable lobes and ladder-like structures – the combs. It swims by the synchronous beating of eight comb rows that are made of thousands of fused cilia, and through the flapping motion of the lobes. Ctenophores are strikingly beautiful, with shimmering waves of rainbow colours produced by the diffraction of light passing through the cilia as they flutter like eyelashes. They are also bioluminescent, glowing blue in the dark.
Another distinguishing feature is that the comb jellies lack stinging cells and have developed other strategies such as sticky tentacles and oral lobes to capture prey, much like spider webs. They won’t hurt you but they are carnivorous. You can see their digestive canals glowing in the centre. They prey on zoo plankton: copepods (tiny crustaceans), invertebrates, larvae and fish eggs. And they fall prey themselves to a variety of creatures seeking easily digested gelatinous morsels, including other jellies, fishes and sea turtles.
One of many kinds
There are apparently over a hundred different species of Ctenophores. The scientists at Jellywatch confirmed the identification of the ones we observed as the Ctenophore Bolinopsis. These aggregated in Sealers Cove, a large bay open to the ocean at Wilsons Promontory, on a full moon night. They were drifting with the tide past our anchored boat. We would have seen maybe 40 to 60 of them around us, but there could well have been hundreds in the bay. The next day we moved to Little Waterloo Bay and were ready for another light show, but none were there. It might have been a blessing, as although these creatures are very beautiful, there are fears they might become a pest, like their cousins the Mnemiopsis which invaded the Black Sea and have spread into the Mediterranean sea.
Like Spaceships in the Cosmos
The photos we took on the first night show how bizarre and fascinating these “alien spaceships” are. To us they look like spaceships in the Milky Way. On one hand we are excited to have seen these spectacular comb jellies, but on the other we wonder whether they are another sign of ecological trouble ahead.
Take a look at this gallery; isn’t nature astounding? All photos were taken with the Olympus TG4 waterproof camera, from the bottom step of the sugar scoops on our boat. I was precariously kneeling head down, bottom up, with a torch in one hand and the camera in the other, and my arm in the water up to my elbow! No diving in the very chilly water that night, but pleasing results nevertheless. All but the last photo in the gallery were taken at night.