Nematode rapid adaptative response to the massive Deepwater Horizon oil spill

The Gulf ecosystem health was of great concern after the explosion of the Deepwater Horizon oil platform (April 2010). After the spill, a large volume of oil trapped in the deep-sea plumes was transported offshore and to deep-water sediments, causing detrimental effects on the benthic fauna. In this study, the variability in nematode standing stock, structural and functional diversity has been investigated. Nematodes were collected in October 2010 from stations characterized by different levels of impact and along the sediment vertical profile. Immediately after the oil spill, nematode abundances rapidly increased moving towards impacted stations and reaching unusual abundances for the deep-sea. Despite the sediment toxicity, impacted stations showed dense populations of small-sized nematodes concentrated in the surface sediment, whereas no-impact stations displayed more even vertical distributions and more stable size spectra. High turnover across horizontal and vertical gradients demonstrated substantial species replacement linked to contamination. Impacted stations were dominated by opportunistic and tolerant species, while sensitive taxa were restricted to no-impact stations. Functional traits provided additional resolution: impacted stations exhibited a marked dominance of juveniles, indicating rapid population turnover and resilience to hydrocarbon contamination. In contrast, no-impact stations were characterized by a higher proportion of adults and k-strategist nematodes, reflecting more stable communities. Bacterivorous/deposit-feeding nematodes dominated the impacted stations, compared to a more diversified trophic community in no-impact stations. The combined use of standing stock, taxonomic, and functional descriptors offered a powerful framework for assessing deep-sea oil spill magnitude and impacts, highlighting the nematodes as reliable bioindicators of oil pollution.