25 November 2004

Kathy’s update for November 25, with apologies for my tardiness!

Having just returned from New Harbor, we had a load of samples to process and we wasted no time at getting back at the field work. So my update got farther and farther behind. Since November 25th was spent dealing with sample after sample, and I thought that pretty boring, I thought instead I would show you some of the neat animals the divers have been bringing into the aquarium.

Here is the Crary lab’s aquarium, which always attracts visitors. They are amazed at what a variety of life the cold Southern Ocean harbors. Many of the animals are long-lived and slow growing, able to wait out the long Antarctic winter with little to eat.

Parborlasia corrugatus is a ribbon worm. Some can get as long as 2 metres! You can see its mouth from which it can shoot out a harpoon-like proboscis. Ribbon worms knot around each other when they find food worth eating. They are voracious predators and scavengers. When hunting, they glide on a trail of acidic slime.
The scallop, Adamussium colbecki, was really abundant at New Harbor but is rare around McMurdo. This is a youngster sitting atop an adult. You can see its hairy tentacles and beady eyes that ring the edge of the mantle and sense the passing world.

This beautiful nudibranch, called Tritoniella belli, is a snail without a shell. The white spiral is its egg mass.
The yellow ball inside the scallop shell that Glyptonotus is walking past is also a snail. It’s called Marseniopsis mollis. Marseniopsis has a shell but it is inside its body. Marseniopsis gathers a chemical from its food that makes it distasteful. The yellow colour is probably a good advertisement for that.

Sea spiders suck juices from soft corals with their proboscis. On the underside view of the sea spider, you can see the legs that it uses to carry the eggs and then the hatched young. The males take over this chore and once in awhile we find one covered in youngsters.
Glyptonotus antarcticus looks like a prehistoric trilobite wandering slowly over the bottom, looking for food. It scavenges and preys on worms, clams, snails, and crustaceans. The females brood their young in a pouch under their thorax.

Astrotoma agassizii, a brittle star, climbs up on sponges and extends its arms into the water, catching small animals and phytoplankton that drift by. Using growth rings, the oldest has been aged at 91 years!
The sea urchin, Sterechinus neumayeri eats algae and other small organisms on the surface of the seabed. For protection, it camouflages itself with whatever is nearby. Passing by a sea anemone, the anemone will capture the camouflage instead of the sea urchin underneath. This urchin is carrying around a dead sea spider.

Perknaster fuscus antarcticus is a sponge predator and harbors chemicals that make it unpalatable to most predators.
Odontaster validus is the commonest starfish wherever we dive on this coast. It is voracious and is quick to arrive at a new food suppy, carpeting it in a sea of interlocking red arms. Odontaster validus particularly liked our food-laced dishes of sediment, requiring us to construct fences around all our colonization dishes. The fences slowed down the stars but eventually they climbed up and over.

Here are two stars to show the range in size of some of the stars here. The big one, Acodontaster conspicuus, is a sponge predator, which is kept in check by Odontaster validus. The small star is Odontaster meridionalis. It also preys on sponges. Here is a closeup of the tube feet of Acodontaster. Stars walk with their tube feet and also use them to pry apart clams by persistently pulling on the shells until the clam tires and opens.
Trematomus bernacchii has antifreezes in its blood to prevent it from freezing in the -1.8°C seawater. We see Trematomus wherever we dive, looking for worms and crustaceans that we might stir up with our fins.

This Dissostichus mawsoni is about 30 years old. Seals dive deep to catch these. Dissostichus mawsoni are now being fished in the Southern Ocean and sold under the name “Chilean sea bass”. Although the fishery is regulated, many are being caught illegally.
If you would like to know more about the marine life of McMurdo Sound, check out The Underwater Field Guide to Ross Island and McMurdo Sound, Antarctica at http://scilib.ucsd.edu/sio/nsf/fguide/index.html

Lets see the next day!