Toxic effects of phenanthrene intensify with an increase of temperature for the populations of a free-living nematode

[Display omitted] •Phenanthrene negatively affects population development of Diplolaimelloides delyi.•Phenanthrene concentrations over 10 µg ml−1 are lethal to D. delyi.•Increases in temperature enhances the toxic effect of phenanthrene.•D. delyi development time reduces with warming.•D. delyi sex ratio measurements are less affected by phenanthrene than temperature. Phenanthrene is one of the most common Polycyclic Aromatic Hydrocarbons (PAHs) in the marine environment. It has high lipoafinity and environmental persistence and tends to accumulate in benthic ecosystems. Exposure to phenanthrene can have severe impacts on a wide range of marine organisms, from nematodes to fish. These effects can be exacerbated with concurrent warming associated with climate change. In this study we investigated the response of free-living nematode populations of the species Diplolaimelloides delyi following exposure to different phenanthrene concentrations under normal and increased temperature conditions (from 25 °C up to 35 °C). Phenanthrene was toxic to D. delyi, causing a decrease in population growth (at concentrations ≥1 μg ml−1) and negatively affecting their development times and reproduction (at concentrations ≥2.5 μg ml−1). The observed effects intensified with increasing temperature, leading to further reduced development and population growth rate, arrested reproduction, and even mortality in 100% of the populations exposed to phenanthrene concentrations over 5 μg ml−1 at the highest temperature used (30 °C). Thermal-induced toxicity effects on marine populations can be significant, and current climate change and warming may have substantial implications for marine food webs and ecosystem functioning.