Subtle changes in community composition of marine fungi following the Orange County, California, oil spill

Oil spills represent a major disturbance for marine fungal communities, yet their response in coastal systems over time is uncharacterized. During the Orange County oil spill on October 1st, 2021, a pipeline leak released 93,484 L of crude oil in Huntington Beach, California, USA. We examined the effect of this disturbance on the richness and community composition of marine fungal communities over 2 months. Based on a qualitative shoreline survey, we collected surface seawater samples nearshore from very lightly or lightly oiled sites at 18, 34, 49, and 66 days after the spill and sequenced the ITS2 region. Unexpectedly, fungal richness remained similar across oiling degrees and time points. Furthermore, oil pollution had a limited effect on overall fungal community composition, with only marginal differences between oiling levels. Instead, changes occurred on a finer scale. Light oiling reduced the relative abundance of genera typical of coastal ecosystems, including Mycosphaerella, Papiliotrema and Rhodotorula. Moreover, indicators for light oiling included oil-tolerant and opportunistic species belonging to Aspergillus and Thermomyces, known for consuming oil-derived compounds. Despite these small shifts, fungal community composition in both oiling conditions did not become more similar over time. Collectively, our results indicate the oil spill had a subtle but persistent effect on marine fungal communities over two months, primarily by altering specific fungal taxa, rather than modifying overall composition and richness. Characterizing fungal responses to even limited oil exposure may be important for detecting, monitoring and understanding the ecological influence of oil contamination in coastal marine ecosystems.