Effects of crude oil and gas condensate spill on coastal benthic microbial populations

Marine sediments are ecologically-important environments that act as a long-term depository for different contaminants from natural and anthropogenic sources. We investigated the response of crude-oil and gas-condensate spills on benthic microbial populations in the oligotrophic southeastern Mediterranean Sea using costume-design benthocosms. Additions of crude oil and gas condensate significantly changed the sediment’s chemical properties, with 2-fold elevated levels of total organic carbon (TOC) and up to ∼ 6-fold higher concentration of total polycyclic aromatic hydrocarbons (∑PAHs) relative to unamended sediments. Naphthalene and benzo(a)pyrene were the dominant species comprising the PAHs in both the crude-oil and gas-condensate treatments (29–43% and 26–35%, respectively). Porewater PO 4 3+ drastically declined throughout the experiment, whereas NO 2 − + NO 3 − decreased ∼100 days post hydrocarbons addition and then increased in the remaining ∼100 days till the conclusion of the experiment. This temporal variability in NO 2 − + NO 3 − hints that hydrocarbon pollution may affect the interplay between benthic denitrification and N 2 fixation, thus affecting nutrient limitation for benthic heterotrophic bacteria and phytoplankton. Moreover, our results show that crude oil and gas-condensate usually lead to a decline in benthic autotrophic microbial biomass (50–80%), while heterotrophic bacterial abundances remained unchanged, and bacterial production rapidly increased (maximal 1,600%, crude-oil > gas-cindensate). These effects were prolonged and lasted several months post hydrocarbons addition, highlighting the sediments as a repository for oil contaminants. Amplicon sequencing of the 16S rRNA gene revealed hydrocarbonoclastic bacteria including Methylophaga , Ponticaulis and Alcanivorax genera post crude-oil addition and Actinobacterota 67–14 lineage following gas-condensate amendments. Our results may enable applying a better science-based environmental policy for the benthic marine environment.