Responses of benthic meiofauna to long-term, low-level additions of No. 2 fuel oil

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Abstract
Three experiments were conducted to investigate the responses of benthic meiofauna to long-term, low-level additions of no. 2 fuel oil in large (13 m3), outdoor tanks (mesocosms) containing sediment and sea water from Narragansett Bay, Rhode Island, USA. In the 1st experiment, an average water column oil concentration of 190 ppb was maintained for 168 days followed by a 64 day period of no oil additions. During the 2nd experiment, an average oil concentration of 90 ppb was maintained for 122 days. A 386 day period of no oil additions (experiment III) followed experiment II. The abundances of metazoan meiofauna decreased during oil addition periods in experiments I and II with the oil more extensively affecting the meiofauna in the 1st experiment. In both experiments, ostracods and harpacticoid copepods were the most sensitive metazoan groups. In contrast, abundances of protozoan meiofauna (foraminiferans and ciliates) were higher in the oiled mesocosms. Abundances of most meiofaunal groups returned to levels similar to the controls within 2 to 7 mo. following the termination of oil additions. The abundances of kinorhynchs and halacarids remained depressed for more than 1 yr after the last oil addition, presumably due to residual oil in the sediments.