'Neither here nor there'? Meiofauna as an effective tool to evaluate the impacts of the 2019 mysterious oil spill in a Northeast Brazil coral reef.

During the last half of 2019, the Northeast coast of Brazil suffered from an extensive oil spill of unknown origin, and marine organisms in those areas were subjected to significant impacts. In situations like this, the contaminant effects can persist for varying periods. Oil contaminants, such as polycyclic aromatic hydrocarbons (PAHs), generally reduce taxa's abundance and diversity in benthic communities in areas with greater exposure to chemical components. Meiofaunal organisms are excellent indicators of impacts caused by oil spills due to their holobenthic strategy, short life cycle, high taxonomic diversity, and the use of various microhabitats. Thus, we aim to evaluate the impact of the 2019 oil spill by comparing the meiofauna of a strongly impacted coral reef area (Cupe Reef) and an unaffected reef area (Serrambi Reef). The latter considered a control area in our study. Since pre-impact data was unavailable for the Cupe Reef, an in situ limited experiment was run to simulate a small local and immediate impact of oil on the control reef. We used synthetic grass mats as an artificial substrate unit (ASU) to colonize meiofauna. Our results suggest that the tar-like oil that hit the Brazilian coast in late 2019 affected the coral reef meiofauna community. We show that its effect was still evident a few years after the oil spill. The use of ASU as a standardized substrate for colonization and a sampling design that controls for within-reef spatial variability (pools) enabled us to determine impacts at different taxonomic resolutions. The measured impact is equivalent to that caused by a metropolitan region with more than four million inhabitants and with a discharge of several heavily polluted rivers in nearby reefs. Furthermore, our results largely agree with the literature suggesting a higher sensitivity of Copepoda compared to Nematoda, the main taxa of meiofauna.