jellyfish

Moon Jelly

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Young moon jellyfish at the London Aquarium.

The moon jelly, or Aurelia Aurita, is one of the most widely distributed jellyfish in the world, ranging from equatorial tropics, to more northerly seas around Europe and in the Atlantic. On my ‘Marine Biologist Day’ at the London Aquarium, I saw a tank of young moon jellies being raised until they were ready to go on display in one of the larger Kreisel Tanks. Jellies of the Aurelia genus are very distinctive from other jellyfish, by their large disc shaped bodies, which are roughly 10 – 20 cm in diameter. Unfortunately, it is virtually impossible to identify individual species in the genus without the use of genetic sampling. Like many other species, moon jellies are capable of free swimming, although they often move with the currents which makes them seem as though they are drifting with the current. In reality, most jellyfish swim by undulating their bodies, and one of the only free drifting jellyfish, is not really a jellyfish at all. The Portuguese Man O War is in fact a colony of four separate organisms, working symbiotically as a single siphonophore.

Moon jellies and other jellyfish have no internal systems, such as the nervous, endocrine, respiratory or excretory systems. The transfer of chemicals, oxygen and nutrients throughout the body, as well as the removal of waste products, are dealt with by diffusion, simply allowing the substances to move throughout the thin cell walls of the body, rendering the need for the latter three systems void. Nobody quite understands how the jellyfish is capable of operating without any kind of nervous system, however it is known that jellyfish can detect the direction of current, and respond to it.

Moon jellies normally feed on a diet of plankton, larvae, fish eggs and small molluscs, which they catch with their trailing tentacles and then pull into their stomach. The tentacles contain cnidoblasts, small exploding cells, that deliver the venom to the prey when they burst. Moon jellies are mainly predated by Leatherback Turtles, Sunfish, and various tiny parasites.

I only saw these moon jellies in passing at the London Aquarium, but I find these animals strangely beautiful and alien, and their lack of brain fascinates me. I hope that I will get more chances to interact with Moon Jellyfish in the future.

London Aquarium Non-Display Tanks

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A juvenile Thornback Ray in a tank in the London Aquarium tanks.

On my ‘Marine Biologist for a Day’ trip at London Aquarium, one of the first things that the staff showed me were the tanks where all of the animals not on display are kept, including the juveniles, like the Thornback Ray above. Any animal that was not out in the aquarium for the people to see, are kept in smaller tanks around the back of the site. Animals that are stressed, ill, too aggressive or just to young to be with the other animals are brought here until they are ready to be seen.

Every year the aquarium receives dozens of donations of tropical fish and aquatic reptiles, sent in from pet owners who have found they can no longer take care of the animals themselves. Red-Ear Terrapins are one example of animals that the aquarium is offered on a regular basis, and they are now at the stage that they cannot take on any more. This is also where breeding of the animals takes place, with new seahorses and jellyfish being born here, as well as Fire Eels, rays and corals.Some of the corals the aquarium grows for their tanks.

The corals from the aquarium are grown to be used in tank exhibits around the tropical reef sections of the aquarium. Again, most of the coral that the aquarium owns is donated by tank owners who no longer have use for their tanks. There is a common misconception that most of the coral is taken from people trying to smuggle it in and out of the country as ornamental pieces. In fact, there is very little of this occurring, since protection of reefs is so strong that the profit is normally not worth the potential punishment for the smugglers. Some of the corals that are kept in this part of the aquarium are Hammer Coral, which is a hard coral found in Indonesia and Australia, and Mushroom Coral, which originates in the Indian Ocean.Seahorses kept for breeding.Jellyfish kept in the iconic circular tanks.

These jellyfish are called Japanese Sea Nettles, and they are small juveniles kept here until they grow large enough for the exhibit. Jellyfish are always kept in these strange circular tanks, because they require currents to move them around, and in a normal square or oblong tank, the movement of the water will push them into the corners, causing them to get stuck and potentially damaging or killing the jellyfish. Luckily, the jellyfish seem quite beautiful spiralling in their round tanks.

The starfish and crabs that live in the rockpool section are kept on a rotation, since having people touch them can cause them quite a bit of stress. To prevent this from becoming unhealthy, every 2-3 hours the rockpool in changed, moving in new animals through the use of a bucket of cold water. There are about six tanks, meaning a full rotation lasts around 2 days, more than enough time for the starfish to recover. I was allowed to change the animals part way through the day, and had to remove the starfish from the tank by gently stroking their sides, until they let go of the rocks they held on to. Despite harassment from an over animated crab, I changed around the starfish without any trouble.

It was very interesting to see all of the processes that went behind running the aquarium, which I had only every seen from one side of the exhibits. Getting to help was one of the best experiences of my life.