Meiofauna responses to an experimental oil spill in a Louisiana salt marsh

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Abstract
To determine the potential impact of an oil spill on Louisiana salt marsh meiofauna, 21/m2 South Louisiana crude oil was applied to 4 randomly assigned experimental plots in a Spartina alterniflora marsh. Four unoiled plots served as controls. All plots were sampled 1-3 h before and on days 2, 5, 10, 20, 30, 60, 95 and 144 following oil application. Meiofauna were sorted to major taxon, and copepods identified to species. These meiofauna were highly tolerant of hydrocarbon stress as no oil-induced mortality was identified in any taxon even though > 13,000 .mu.g oil/g dry sediment was applied. Densities of several taxa did respond positively to oil application. Nematodes were significantly more numerous in oiled plots on days 5 and 20; copepods on days 30 and 60. The increase in copepod numbers was due largely to a significant increase in Enhydrosoma woodini which reached densities of 180/10 cm2 in oiled plots. Copepods displayed only slight changes in community structure and no successional sequence was identified. Numbers of species were reduced on days 5-10 as certain rare species were not encountered in oiled plots. Density increases most likely occurred because of increases in microbial production by oil-degrading bacteria, or because of oil-induced inhibition of predation. A long-term effect may have been present: copepod densities were significantly lower in oiled plots after 144 days.