The aquarium building of Palmer Station is where our project spends many hours a day running taste test experiments on the sea stars, checking on bucket experiments as Anne described last week and as you will read about in later entries, conducting feeding experiments on fish. It is also where we sort specimens collected on dives. Sometimes, particularly unique or pretty specimens are set aside for long term observations and admiration in what we call the tourist tanks.
We have two special aquaria lined up against the big garage door of the aquarium building. The tourist tanks as we call them, are so named because when cruise ships drop anchor in Arthur Harbor and send passengers ashore for a station tour, the garage door is rolled up so folks can see the show of science at work inside. Front and center stage and more interesting to watch than any of us at work in there, is this pair of plexi-sided aquaria. We keep the tanks stocked so visitors (and non-diving Palmerites) have the opportunity to get close up to some of the critters that live in the waters around station.
The station is no longer hosting cruise ship visits, so we have stopped stocking the larger tank. This tank is 6 ft x 2 ft x 2 ft. and not too long ago it featured small bottom dwelling fish, feathery or leafy algae that provided cover, food and aesthetic appeal and various snails and their one shelled cousin limpets would cruise around on the plexiglass cleaning it of filmy scum that grows in home aquaria tanks too. Currently one of the particularly prominent features of this tank are the large, multi-armed sun stars. These are closely related to the common 5 armed sea star we use in our taste testing experiments. (often called star fish, even though they are not fish) Like all sea stars and their cousins, the number of body parts is based on pentamerous symmetry. That means the number of body parts are in a multiple of 5. (Think of the 6-sided stop sign. It is a hexagon and thus has hexamerous symmetry- if you allow me a Webster-moment!)
Our sun stars, might have 20, 25, 30 arms- as long as it is divisible by 5. Feel free to count the arms in the second image on the right! I should say though, that we do see 4, 6 even 8 armed examples of the standard 5 armed star. This is a result of an injury to an arm or arms. Sea stars have the ability to regenerate or regrow parts that have been damaged and sometimes that leads to unusual patterns. The scientific name for the sun star is Labidaster annulatus. I think the second name- annulatus refers to the ring or halo formed by those many arms being reminiscent of the sun’s halo of rays. They may appear to be wearing a halo but they are no angels! They are predatory and with all those arms are most efficient at snatching critters swimming by or crawling atop slow moving victims. They are one reason we have stopped stocking that tank.
Another hungry predator in the big tank are large pycnogonids or sea spiders. As the common name implies, they are related to arachnids which include spiders, mites, scorpions, ticks. They are also equally related to another aquatic critter - the prehistoric looking horseshoe crabs that wash up on warm coastal beaches. Pycnogonids are found crawling around their long spidery legs in all oceans of the world. There are several hundred species of them and a few of those down here get quite large as you can see in the photo. They are carnivorous and prey on soft bodies animals like sponges and anemones. If you wonder why my hand is gloved to show off our ‘pyc’ its because the water is cold! Pycnogonids pose not threat to people by biting or stinging. In fact most feed by sticking a tube (proboscis) into their victim and sucking out the goodies. Ick…
The smaller tank has relatively kinder and gentler residents. There are several anemones, which are sort of like a sessile (bottom dweller that lives attached) upside down jellyfish. Like jellyfish, they have special cells that can sting and immobilize their prey. Those stinging cells (nematocysts) are associated with their crown of tentacles. Nemes as I call them for short, wave those tentacles in the water column to feed on small critters swimming or floating by and some can even capture fish. Can you see the three lined up waving at the camera in 4th image?
To the left of the trio of nemes is the tail end of what appears to be a cockroach! Well it is a crustacean (animals that have an outer skeleton and go crunch when stepped on). It is a distant relative to roaches and is a member in a category called isopod. But most isopods are about the size of a fingernail. This monster is commonly called the Antarctic giant isopod. Like its land look alike, it too is more active at night and was not very cooperative during my tank photo session. It is an omnivore, eating anything and everything – even its own young in some cases!
Also in the small tourist tank are distant cousins of the sea stars called urchins. Urchins and sea stars (plus several other forms) are all grouped together under a category called Echinodermata. “Echino” means spiny and “derma” means skin (eg dermatology). So these guys all have spiny skin. Yes, even stars have special structures that make their skin rough and bumpy but not as noticeably as the spines of urchins. You can find two different types of urchins in our tank. One is sort of the standard pincushion type urchin. The other has fewer thicker spines and is called a pencil urchin. And yes, like sea stars, urchins have pentamerous symmetry. The pencil urchin is over by the giant isopod.
Perhaps our favorite critters to watch are the beautiful and I think charismatic nudibranchs. A common name is sea slug which is dreadful public relations for such a stylish group of organisms. Nudibranchs are a molluscs, a sea shell without a shell. The first half of the name “nudi” means naked. These are the naked molluscs. What they lack in a shell, they make up with a stunningly colorful and elaborate wardrobe. Some are dressed with frills, others with short elegant tentacle-like structures called cerata. They glide with poise across the plexiglass, as if a high-fashion model on a runway. The trendy hues for the Antarctic this season are charcoal grays, mauvy-peach, soft mocha brown, and of course winter white.
I see 5 nudibranchs in the small tank aerial image at right. Can you find them all??