Mushroom Coral

An example of a mushroom coral at the Natural History Museum.

This unusual coral is a Ctenactis Echinata, a species of mushroom coral, so named due to their similarity to the cap of a mushroom and I saw it at the Secret Cities of the Sea exhibition. Most mushroom corals are free-living rather than colonial and sit by themselves in crevasses and on the edge of kelp forests. Many mushroom corals also looked bleached due to a lack of zooxanthelles, symbiotic algae, in their bodies which is unusual for a coral and as such many people mistake them for dead. Luckily, unlike the coral reefs we are used too, bleaching in many species of mushroom coral is perfectly healthy.

The specimen above is particularly round in shape, ctenactis echinata normally being more of an oval pattern around 20-30cm long and roughly half that in width. Like most mushroom coral, this coral has a single mouth opening on the top of its body, through which polyps will emerge at night in order to feed. The edged plates that make up the radius of the coral are sharply edged with tiny teeth, that can badly cut attackers although, other than specialised coral eaters, this species doesn’t have much to fear except from attacks by other coral. This species does not appear bleached, instead having a dark brown colour while alive, that makes it look similar to the rocks it nestles amongst.

The Ctenactis Echinata can both reproduce with the use of spawning, in which all corals simultaneously release eggs and sperm into water, or by sprouting off smaller versions of itself to create genetically identical clone corals. Asexual reproduction like this is often done when the current coral is to badly injured to continue living for long, and such a measure is required to ensure the corals genes continue to exist. Fortunately for the coral, its genetics do not seem under threat, being rated as one of the least concerning species in terms of its rarity. This is perhaps due both to its enormous distribution, across most of the Pacific from China to the Red Sea to Australia, and the lengths to which it will go in order to survive.

It is almost impossible to go diving in the Pacific ocean without coming across on of these corals or one of its mushroom coral cousins. If I am able to pursue diving in those areas I’m sure I will see it.

Sea Fan

A preserved sea fan on display at the museum.

In the Secret Cities of the Sea exhibition at the Natural History Museum in London, which I discovered while listening to an Inside Science program, there were various displays about the inhabitants of the reefs. One such example was this stunningly preserved sea fan. The sea fan is a type of coral that grows out of the continental shelves at the edge of tropical and subtropical reefs. They build out into large fan-like structures that help them to catch plankton and other tiny organisms that are brought up from the deep waters of the Twilight Zone by strong currents. These same currents are what feed the reef and keep a large supply of nutrients available to the creatures that live there, and the sea fan is simply seating itself closer to the source.

Like other corals, often contain zooxanthellae, tiny algae that are allows to grow inside and around the coral giving them protection in return for photosynthesising for the coral. This symbiotic relationship is essential for keeping reefs alive, since most reefs are fairly near the surface. These algae are also what give the coral its colour, which is why coral bleaching occurs when a reef is sick, since the stress of illness makes the coral jettison its cargo of zooxanthellae. With changes in acidity and temperature in coral reefs across the globe (mainly due to what humans are doing to the ocean) more and more reefs are beginning to bleach and turn white, which will eventually kill them. Some sea fans, that live deeper down in the shelf wall do not have zooxanthellae, since it is no longer beneficial due to the lack of light, and so they must rely entirely on capturing enough plankton to eat.

Many species live in the winding mazes that sea fans create, jutting out of the shelf walls, including starfish, kinds of pipefish, and colonies of bryozoan, which are actually several zooids living together. Bargibant’s Pygmy Seahorse and Denise’s Pygmy Seahorse are two species of the tiny pygmy seahorse that live especially on sea fans and their relatives. They are perfectly camouflaged to the coral, coloured and with bumps and knobs in lighter colours over them. Large groups of these seahorses can be found over a sea fan, where they eat the plankton that filter through from the deeps. The Bargibant’s Seahorse will likely never leave the coral that they were born on, leading to large families of seahorses living in the same place for generations.

These sea fans are extremely interesting, now being looked into by the medical industry for the chemicals they produce, and I am glad that I saw them here at the museum.

London Aquarium Non-Display Tanks

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.