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.
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