Ice disturbance is possibly the major structuring element of polar nearshore biological cornrnunities. Effects range from encapsulation by ice forming on rock substrata to gouging and trampling by bergs. Some 15 to 20% of the world's oceans are affected by this phenomenon, yet measurements of the extent of biological destruction from iceberg irnpacts and subsequent community recovery are very rare. Comrnunities can be held at early successional Stages. or even completely destroyed by scouring. and these effects occur from the intertidal to depths around 500 m in Antarctica. The wide scales of disturbance intensity are thought to add to the overail high levels of Antarctic benthic biological diversity. which has recently been shown to be similar to tropical areas. Data here indicate >99.5 % removal of all macrofauna and >90% removal of most meiofauna by iceberg impact on a soft-sediment habitat at Signy Island. Antarctica. Species return was via locomotion. advection or larval recolonisation, and al13 mechanisms worked on different timescales. Locomotion caused groups to return ~rithin 10 d of a n impact. Storms with wind speeds around 100 km h-' induced water movements intense enough to advect meiofauna to the 9 m depth site. However, it was only dunng the strongest storm which occurred during the study (maximum wind speed 148 km h-I) that water movements were powerful enough to redistribute small macrofauna such as the bivalve Mysella charcoti.

A series of 10 samples from sediment in and adjacent to a shallow coastal iceberg scour at Signy Island, Antarctica, were taken by hand coring from 17 December 1993 until 23 August 1994. Scouring by the iceberg led to more than a 95% decrease in meiofaunal abundance and to a certain degree of reduction in diversity. Nematodes were always the most dominant group of meiofauna. The return of major meiofauna groups to control levels was accomplished in 30 days, although a decrease in abundance on the 50th day made interpretation dicult. The pioneering meiofaunal colonisers were copepods and ostracods, followed by nematodes. Microlaimus sp.1 was dominant among the nematodes throughout the whole period. Epistratum feeders and non-selective deposit feeders were highly dominant over selective deposit feeders and predators/ omnivores. The Maturity Index, a measure for stress within nematode communities, was relatively low at all times and in controls, which indicates that r-strategists prevail in this community. In spite of the catastrophic destruction, nematode community structure was not aected by the iceberg impact, and there was no evidence of succession during recovery. This suggests that the nematode community in the shallow subtidal coast at Signy Island is well adapted to ice disturbance.

Nothing is known about the structure of free-living manne nematode coinmunities in the high Antarctic. Our attempt at surveying this n~unerically most abundant meiobenthic taxon along the continental shelf and slope (200 to 2000 m) furmshed information on generic, trophic and age composition in 2 regions in the Weddell Sea (Kapp Norvegia, 6 stations, 71-72"S, 12-13" W; Halley Bay, 11 stations, 74-75"S, 25-29" W). A total of 7300 nematode identifications to generic level were analyzed by means of a variety of statistical techniques. The spatial structure indicated the existence of 4 major nematode genus associations colonizing the upper slope, downslope, Halley shelf and a muted habitat consisting of shelf break and Kapp Norvegia shelf. Dominated by genera like Sabatiena, Molgolaimus, A4icrolalmus, Monhystera, Daptonema, Leptolaimus, Acantholaimus and Dichromadora, these habitats often contained distinct associations of less abundant genera. The trophically diverse communities exhibited an equal shanng of epistrate, nonselective and selective deposit feeders, with a slight dominance of the flrst feedlng category. Each feeding guild was considered in light of the correlations with microbial food and fresh versus decomposing organic matter, leading to the conclusion that the applied classification does not adequately explain the trophic status of the deep-water communities. Globalscale compaiisons with literature data indicated the broad geographical distnbution of predominant nematode taxa and a lack of Antarctic endermsm. Only a weak separation of the entire nematode communities on a geographical basis was suggested by multivariate techniques. Although ocean-wide comparison was hampered by limited comparable literature data, diversity indices scored high and surpassed the Arctic bathyal assemblage The major agents behind the observed patterns involved sediment grain size and food content, operating over different scales. Depth per se had no major effect. Underlying mechanisms included water-column productivity, hydrodynamics, iceberg activity and macrofaunal presence.

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