MESA Archives: Aleutian Islands Deep Water Corals Cruise, July 27, 2004
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Observations by Scott C. France, University of Louisiana at Lafayette
Location: North of Atka Island.
Coral team researcher Les Watling, of the University of Maine,
removes a type of coral known as a sea pen from the starboard
"biobox" of the remotely controlled collecting vehicle Jason II on
the deck of the R/V Roger Revelle. The coral was plucked from the Aleutian
seafloor. The coral is commonly called a sea pen because,
underwater, it looks like an old-fashioned quill pen. Researchers
roamed undersea "forests" of such sea pens in the last couple of
days. The researchers keep detailed notes on where the collected
specimens are placed in the ROV's various collection boxes, so that
specimens can be rapidly retrieved upon being hauled aboard. Photo by Sonya Senkowsky.
Today's Jason II dive largely followed a muddy ridge, with relatively little
change in depth. Until the end of the dive, we did not encounter any steep
topography, walls, ledges or even outcrops of rocks and boulders -- and
therefore, saw few of the corals and related organisms we are searching for.
Most of the gorgonian sea fans and sponges we are looking for require exposed
hard bottoms to which they can attach themselves. The communities we encountered
today were soft bottom types.
At the deeper end of the dive (2900 meters) the soft bottom was hummocky due
to invertebrates burrowing through the mud. We saw thousands of spoon worms
-- or at least, we saw their "spoons," which are tongue-like proboscises
that extend from the burrow while the rest of the body remains buried. The
proboscis can extend more than 100 times the length of the body, and is used
to gather food particles from the surface of the bottom.
We did see one species of octocoral frequently in this area, a sea pen
(Pennatulacean) called Umbellula. Sea pens are corals specialized
for living on soft bottoms by anchoring themselves into the sediment with a
bulbous, inflatable base. Umbellula has a thin stalk standing almost
a meter above the bottom, with a pinwheel arrangement of large polyps -- the
tentacle-bearing feeding structures of corals -- at the top. They form
beautiful and graceful colonies. Several of the colonies had a pair of red
amphipods, small, shrimplike crustaceans, grasping the stalk. We collected
one colony that had a sea anemone attached to the stalk. This is a common
observation in the deep sea: many invertebrates that capture their food
from the water column climb up onto whatever structures they can find in
order to get into faster moving currents. We also saw polychaete worms
swimming up from the bottom as the ROV approached.
In a shipboard lab, late Tuesday evening Scott France points at an Umbellula
coral specimen, which appears to have a sea anemone attached to the stalk.
This is an example of associations between corals and other organisms, which use
the corals to get above the seafloor. Behind France are blue-capped falcon tubes
used to store tissues in ethanol for genetic analysis. Photo by Sonya Senkowsky.
Further along the transect, the muddy bottom became smoother and the
community changed to one dominated by two different species of sea pens: one
tall, thin one we referred to as a "whip sea-pen," and a shorter, fleshier
species. Many of the "whip sea-pens" had a brittle star wrapped around
them, with the star's arms drifting with the current. We collected a couple
of colonies with and without brittle stars to determine if the stars were
feeding on the sea pens, or simply using them to get up off the bottom. We
also saw the occasional sea cucumber and sea urchin, and numerous burrowing
Tuesday night on a shipboard wet lab, coral team researcher
Scott France holds a pycnogonid sea spider found on a curlicue-style
deepsea whip coral, Radicipes. One of the goals of the coral
expedition is to determine the role of deepwater corals as fish and
crab habitat. France and colleagues stayed up through the night to
preserve and log specimens for later study. Photo by Sonya Senkowsky.
Just before the ROV was to leave bottom, we encountered a small ledge that
was inhabited by many sponges, crab and hydrozoans (delicate "bushes" of
microscopic sea anemone-like animals). We also found one of our first
gorgonian corals of the day, a curly-cue whip coral in the family
Chrysogorgiidae. We collected a specimen that had a palm-sized sea spider
on the stalk, and a chunk of rock from the ledge that had a large sponge on it.
The ROV was recovered at about 11:30 p.m., and that is when my work really
began. I am interested in determining the geographic range the coral
species inhabit. Are the corals we see in the Aleutians the same as those
in the Gulf of Alaska or the deep sea around Hawaii and elsewhere in the
Pacific (or Atlantic), or are these species unique to this area? To answer
this question, I look at the DNA sequences of the corals. The DNA analysis
is done back in my lab at the University of Louisiana at Lafayette. Here on
the ship, I collect fragments of branches and tissue from which I extract the DNA.
Our collections yesterday resulted in nine sea pens, one curly-cue coral,
and several sponges. My colleague Gordon Hendler was very excited about the
several brittle stars we collected. It took us about six hours to complete
preserving and processing the samples. After a few hours sleep, we'll be
ready for -- and excited about -- the next dive!