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Role of the meiobenthos in Antarctic ecosystems

Antarctica phase III (1993-1997)

Role of the meiobenthos in Antarctic ecosystems

Promotor

Professor Magda Vincx
Universiteit Gent
Instituut voor Dierkunde
Mariene Biologie
K.L. Ledeganckstraat, 35
B-9000 GENT
Phone: +32 (0)9 264 52 10
Fax: +32 (0)9 264 53 44
E-mail: magda.vincx@rug.ac.be

Topics

The relative importance of the meiofauna (size in the range of 38-1000 µm) in the Antarctic benthic community has been assessed by a combined field ecology and experimental approach. This was done in two contrasting conditions, e.g. the deep sea and low sub-tidal, where as to the depth of the water column the benthic characteristics were, respectively, indirectly or directly related to primary production.

Deep-sea samples were collected at Kapp Norvegia and Halley Bay (Weddell Sea) during the EPOS-leg 3 campaign (austral summer 1989) on board the R/V Polarstern at depths between 200 and 2000 m. Samples for the ecological experimental approach of the meiofauna in the low sub-tidal were taken at Signy Island at a water depth of 10 m, opposite the British Signy base. This was done fortnightly during 18 months in 1991/92 and during the summer of 1994. A set of environmental variables (oxygen, pore-water nutrients, particulate and dissolved organic matter, sediment texture, chloroplastic pigments, bacteria and diatoms) were concurrently monitored.

Despite the apparent harshness of the Antarctic environment the meiofauna thrived with high productive stocks, sometimes much higher than their temperate and tropical relatives. Numbers and biomass were more or less seasonal and inter-annual varying (in the case of the sub-tidal meiofauna). Correlation with environmental factors revealed that depth, sediment texture, oxygen availability, variations in organic matter flux to the sediment surface, and hence food, governed the meiobenthic distribution patterns. Towards this, minimum nematode production constituted 2 % of primary production in the pelagial and 11 % of the downward flux of organic matter to the sea-bed.

The energetic position of the meiofauna and their share in the remineralization processes and hence, re-introduction of regenerated nutrients and organic carbon through the sediment/water interface back into the water column, was inferred from flux measurements of nutrients, oxygen and organic matter. Grazing experiments with radio-labelled isotopes, used to quantify the carbon transfer between microbiota and their meiobenthic grazers (mainly epistratum and non-selective deposit-feeders), showed a clearance rate of 5.1·10-4·h-1. Yet, about 10 % of the annual benthic carbon production was grazed down by nematodes. Nutrient and oxygen fluxes were measured from concentration changes in incubation chambers and vertical profiles in the sediment core. The results evidenced an efflux of ammonia and phosphate to the water column and an uptake of nitrate and silicate by the sediments.

Respiratory activity was measured by a combined method of individual nematode and bulk sediment oxygen uptake. With an individual respiration of 0.89-2.77 nl O2·ind-1·h-1 (Q10 = 2) the nematode community contributed to a substantial proportion of benthic remineralization processes (13-42 % of the total benthic carbon demand was due to nematode respiration).

Secondary production by the nematode community at Factory Cove was among the highest in the world (P varying between 2.2 and 72.4 gC·m-2·y-1), and accounted for 9.4 % of total benthic production, 4.1 % of phytoplankton production and 11.9 % of microphytobenthic production.

From the flux measurements and production estimates it was suggested that, by using the substantial episodic food supply (both from water column and in situ production) very efficiently, the meiofauna might play a potentially important role in the energy transfer through the differing benthic components and from the sediment back into the water column.

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