| Summary: | The effects of hydrocarbons in marine sediments on Antarctic meiofaunal communities (nematodes and copepods) were investigated in a five year field experiment at Casey Station, East Antarctica. The effects of four different types of hydrocarbons were examined: clean mineral lube oil, used mineral lube oil, synthetic lube oil marketed as being rapidly biodegradable, and diesel fuel (Special Antarctic Blend). Sediments were sieved to remove macrofauna and then treated with one of the oils, then deployed in trays on the seabed (12–18 m) under sea ice, along with control, uncontaminated sediment. Samples of the meiofaunal communities were collected at one, two and five years and nematodes identified to genus and copepods to family. There were significant differences between meiofaunal communities in hydrocarbon-treated sediment compared to controls, but each hydrocarbon type had quite different effects. Effects persisted to five years and communities showed no signs of recovery or becoming more similar to controls. Nematodes were more sensitive to hydrocarbons than copepods, showing very distinct community differences between different treatments which persisted over the five years. In contrast, copepod communities showed less distinct, more variable changes, which decreased in severity over five years. Nematode abundance initially decreased in hydrocarbon treatments in comparison to controls, except for the biodegradable oil treatment, and this persisted also over five years. In contrast, copepod abundance initially increased in hydrocarbon treatments compared to controls, and then declined, and by five years abundances were lower in hydrocarbon treatments than in controls. Whilst structural community, abundance and diversity differences for nematodes and copepods remained after 5 years, the nematode functional parameters based on feeding types and maturity characteristics showed a substantial degree of recovery after 5 years, suggesting some functional recovery of the nematode community. This experiment demonstrates that different hydrocarbons can have very different effects on sediment meiofauna and that despite strong patterns of community effects it was very difficult to characterize effects on different taxa. The effects of oils in sediments are also likely to persist for periods greater than five years and could take decades to recover.
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