26 December 2007Gifts from the deep seaPolarstern ANT–XXIV–2
Poseidon has been kind to us at Christmas — perhaps we were good this year! Polarstern has been sampling on the steep slope where the Antarctic continent drops down to the abyss at about 70° S, 3° W. Night trawls near the surface caught few animals and we had little hope for the deep trawls. So we were astonished to get big catches from the Agassiz trawl and the Epibenthic Sledge in nearly 2,200 m depth. At the same place, we sampled the sediment and water; the SYSTCO project studies how production in the sunlit layers is coupled with life on the dark seafloor.
The Agassiz trawl produced a great variety of ice fish, brittlestars, flower-like crinoids and some sponges. The bright red shrimps Nematocarcinus longirostris were abundant, with a total weight of about 4 kg. These crustaceans migrate towards the surface at night, a factor in the flux from deeper ocean layers. The crew were hopeful of a meal, until the biochemists demanded the shrimps for analysis!
Polychaete taxonomist Brigitte Ebbe from the Senckenberg Institute found a carnivorous polynoid, Laetmonice producta. The 90 mm long worm in the photo had beautiful scales about 10 mm in diameter. While escaping, this cunning polychaete flicks off its scales like fluorescent frisbees as a decoy to distract attackers. There was great excitement when Michael Schrödl and Enrico Schwabe from Munich University spotted an aplacophoran mollusc — it was twice the size of any they had seen before and may be a new species of the genus Neomania. This strange shell-less mollusc eats cnidarians — and looks like a Vanillekipferl cookie!
We found a flat leaf-shaped crustacean 80 mm long, the isopod Ceratoserolis trilobitoides, aptly named for its resemblance to an ancient trilobite. The fossil record of hard-shelled animals like isopods and bryozoans helps to reconstruct the story of repeated radiations of species from the Antarctic seafloor, during the various glacial cycles since the time of Gondwana.
A target species for our DNA barcoding, we grabbed a specimen of the pycnogonid Collossendeis megalonix. Compared with other oceans, pycnogonids (sea spiders) are extraordinarily varied in Antarctic waters — there are over 250 known species. Their dispersal is limited; males carry the eggs, which hatch where the adults live. Why then have so many species evolved here? The Census of Antarctic Marine Life logo shown above has a pycnogonid as a reminder of one of our central questions: is the Antarctic a hotbed of speciation in some groups? Research on the molecular biology, taxonomy and phylogeny of pycnogonids will answer such questions about how our present biodiversity has evolved.
Victoria Wadley |
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