13 April, 2000

Bahia Dive; Tunicates

Question 54: What do skuas eat?

Today I finally got to see the Bahia Paraiso underwater! In a 40-minute dive, Chuck and I swam a little over halfway along its length from the stern towards the bow. The propellers and hull are still in good shape, but the superstructure has been crushed and broken into large chunks of steel. The ship's deck faces down at about a 30-degree angle with the bottom.

The Bahia sits in around 60 feet of water. There is still very good light at that depth and the visibility was excellent (45 feet). Even the cavern formed by the deck leaning over the bottom is fairly well lit, and we had a clear view of everything. It is a breathtaking sight. As we descended, I could see the squared-off stern dropping away on my right. Swimming over the curve of the hull and "up" the side of the ship, I passed the window openings in the deck level from which passengers filmed a home video of the ship running aground in '89.

When we reached the bottom, we turned to our left and started working our way up the length of the ship. There are all sorts of algae growing on and under the wreck. There are long, flowing species of brown algae growing on the sides of the ship. Underneath and on the broken metal pieces there are dozens of smaller, branched and leafy red alga species. This is one of the best sites in the area for red algae. The algae sway back and forth with the surge of the waves, as do some of the metal pieces. They make the wreck look fuzzy and alive rather than like just a twisted pile of broken steel.

The underside of every piece of metal, including the huge expanse of deck, is covered with tunicates (ascidians). Tunicates are the group of invertebrate animals that are the closest relatives of vertebrates. Some live as individuals while other species are colonial. The adults are sedentary and attached permanently to the substrate. The juvenile larvae stage is free-swimming. We have found a total of around 25 species of tunicates on our dives. There are three species that are especially common on the Bahia. All three are solitary animals. We do not know the scientific genus and species for two of them. One is a clear, solid tunicate with an orange-colored disc inside; another is a round, light-orange, bumpy tunicate that is squishy and squirts water when squeezed; and the last, Cnemidocarpa varricosa, is a larger brown lumpy species that has obvious siphons and works as a traditional sea squirt.

Tunicates are soft-bodied filter-feeders; they suck in water through their oral siphon, then food parcticles are collected by cilia and mucus and digested in the stomach. Waste exits the intestine and is flushed out the atrial siphon with water. Tunicates have a primitive heart that circulates blood in two directions, although they do not have a closed circulatory system. The features that relate them closely to vertebrates are the notochord and the dorsal nerve cord.

We have also found many species of colonial ascidians, but none at the Bahia. A bright yellow-green one is found deep at Christine Island and Janus Island. Another colonial type we have found is a long mustard-colored, sausage-shaped ascidian, Dystaplia cylindrica. It inhabits soft bottom areas so we have not found any underwater, but storm conditions dislodge them and we find many of them at the surface. Today, we found the longest example yet of this species. It is 5.4 meters long and weighs 5.3 kg! Colonial tunicates are made of many individuals, called zooids, embedded in a common tissue layer.

Answer 53: Christine Muller-Schwarze spent three summers in Antarctica studying penguin behavior with her husband, Dietland. She arrived in October 1969 at McMurdo and flew by helicopter to Cape Crozier, site of the largest Adelie breeding colony in Antarctica. After two summers there, Christine and Dietland went to the Antarctic Peninsula to study other penguins and the relationships among penguin species and to make a census of penguin numbers. They surveyed 24 rookeries on the peninsula and 26 more on the Antarctic islands. An island near Palmer Station that had penguins but no name was named after Christine by US government mapmakers in honor of her work there.