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>Seas: < 1 foot
>Winds 5 knots
>Temp -1.5 C ; w/ wind chill –2.9 C
>Location: Latitude 62 degrees 08.74’ S; Longitude 57 degrees 32.86 W

Above: When this glass sponge was pulled apart, several amphipods (relatives of sand fleas) were discovered living inside.
Below: Esperanza Station, at the very tip of the Antaractica, is an Argentine military and research base.
Click on image for larger view.

5 December 2004

Our work area continues to be the Bransfield Strait on the southern side of the South Shetland Islands. The seas are calm owing to the shelter provided by these snow and glacier covered peaks. This makes living and working aboard ship that much nicer. It is most distressing to watch your coffee cup careening towards the edge of the table as the ship lists to one side or another.

Today we turned our attention towards the "deep" benthos. The benthic samples were taken at depths as deep as 900 m. Sampling at these depths required an hour to deploy 2400 m of wire and an hour to bring the dredge to the surface. For our efforts we were rewarded with an abundance and variety of segmented worms (Phylum Annelida, Class Polychaeta) and brittle stars (Phylum Echinodermata, Class Ophiuroidea).

We are beginning to capture the planktotrophic larvae of nemerteans (Phylum Nemertea — ribbon worms) in our plankton tows. Biology 219 students will recall that this helmet-shaped larval form is restricted to the Class Heteronemertea. Also there is an abundance of larvae asteroid echinoderms (sea stars). Dr. Balser and I collected and examined several hundred starfish larvae (bipinnariae and brachioloariae) today to see if these larvae, like their relatives in the subtropical Atlantic, undergo asexual reproduction. If cloning by larvae exists in such a cold climate (e.g., seawater < 0° C), then the larval lifetime and dispersal potential will be significantly increased. An interesting idea, but we have yet to capture a cloning sea star larva.

In her copious free time Dr. Balser has been working feverishly on the three species of Cephalodiscus that we have collected. In addition to preparing samples of adults for an examination of their morphology, she has discovered that there are developing embryos within the tubes of two species. This provides an unusual opportunity to directly compare developmental processes of these taxa. Unlike some of their enteropneust (acorn worm) relatives that produce a feeding tornaria larva, development of pterobroanchs is direct and apparently occurs within the adult tubes. No one knows what happens to the juveniles after they leave (?) the tubes of their maternal parent.

The Salp Group has discovered that their species of interest performs a vertical migration each day. Salpa thompsoni stays deep during the day and migrates to the surface waters at night and retreats to the deep at dawn. Salps are pelagic members of the subphylum Urochordata (Phylum Chordata – that the phylum to which you belong). Like many holoplanktonic organisms (a member of the planktonic community their entire life) these animals live in a supportive medium (seawater) and have evolved in the absence of solid surfaces. Hence, these organisms are gelatinous, delicate, and can be easily damaged when collected with nets. To avoid damaging their specimens, this group of scientists collects their specimens in bottles while scuba diving. So, at midnight tonight six divers will enter the water (0.34° C) in search of Salpa thompsoni. Fear not, it will not be dark as dawn and dusk are growing closer together and we have now nearly lost the night.

For those enamored with charismatic vertebrate megafauna, we saw two Minke whales yesterday evening.

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