16 January 2008

Small creatures from the seafloor sediments

Polarstern ANT–XXIV–2 — weekly report 7

In the last week, we have been breaking heavy ice towards the edge of the continental shelf of Antarctica, to make a corridor for the supply vessel Naja Arctica. An impressive storm with windswept snow at Force 9 interrupted the operations for two days. The analysis of our samples is keeping us occupied in the meantime.

Polarstern rams a channel in the ice off Neumayer station. Photo: B. Ebbe, Senckenberg Institute

The windswept landscape of Atka Bay during a during a storm. Photo: F. Pey, University of Bergen

A nematode from the meiofuna sample. Photo: NeMys

During the voyage, we have sampled animals from the seafloor sediments with a box corer and a multicorer. Between the sediment grains live the small but important creatures of the meiofauna. Nematodes (microscopic worms) are dominant in abundance and highly diverse with over 4,000 species worldwide; how many species live around Antarctica is unknown. In samples at 2,150 m depth on Maud Rise, Katja Guilini found the live nematodes that she needed for experiments with contrasting food availability. At present the nematodes are grazing for up to 12 days on a selection of 13C-labelled microbes and plant detritus. The results on food utilisation will show the trophic position of these species in the sediment community.

Delia Fontaine sorting trawl samples to find foraminiferans. Photo: D. Fontaine, University of Geneva

Last Saturday, we squeezed in an unscheduled trawl at 600 m depth over rocks. Delia Fontaine was happy to find some live foraminiferans among the catch. 'Forams' to their friends are tiny sculptured creatures, with over 4,000 species in the sediment and 50 species in the plankton worldwide; again, we do not know how many we will find in the Antarctic region. Although abundant, forams are often overlooked, being difficult to identify and to extract from the sediment. Scanning electron microscopy and examination of the size and shape (morphology) is important for their classification. Delia also uses molecular methods to extract their DNA. Fresh, cold specimens are essential for reliable results; this was not a problem while sorting for hours on the deck at -2.3° C!

The foram shell of calcium carbonate is vulnerable to the increasing acidity of the ocean. Among our collections, other at-risk groups with 'houses' of calcite and aragonite include the phytoplankton coccolithophorids and the zooplankton pteropods. The burning of fossil fuels has increased the production of greenhouse gases such as carbon dioxide; after dissolving in the ocean, they increase the acidity of the seawater. The ocean is changing due to the activities of humankind; the impact of ocean acidification on marine biodiversity is a big question.

Cibicides sp. a foraminiferan from the Polarstern voyage. Photo: D. Fontaine, University of Geneva

Antarctic foraminiferan Reophax nodulosus from the Polarstern voyage. Photo: D. Fontaine, University of Geneva

We have had a lively debate during the voyage about the capacity of the Southern Ocean to draw down carbon dioxide. The availability of dissolved iron in the seawater here is a limiting factor for plant growth and carbon dioxide utilisation. A recent lecture on Polarstern about the iron experiments during 2004-2006 showed that even in its most iron-enriched state, the ecosystem of the Southern Ocean could not quite keep pace with our current production of carbon dioxide, let alone the projection over the next decades. When even the huge Southern Ocean cannot incorporate the excesses of human activities, we concluded that there is an urgent need to reverse the trend in carbon emissions on our planet.

Victoria Wadley
Census of Antarctic Marine Life and Australian Antarctic Division