Bioconcentration and lethal effects of gas-condensate and crude oil on nearshore copepod assemblages

To assess the toxicity of petroleum pollutants on copepod assemblages, we conducted microcosm experiments simulating slick scenarios at five different concentrations (0, 50, 250, 500, 100 ppm) of gas-condensate and crude oil. We collected natural zooplankton from a coastal station (32°51'07.1 N 34°59'26.2 E) on July 18, 2021 (“gas-condensate experiment”) and July 27, 2021 (“crude oil experiment”) by two horizontal Bongo net tows (200 and 65 µm mesh size; 300 µm mesh size), and surface seawater (sieved through a 50 µm mesh). The seawater was enriched with the collected zooplankton (65 µm - 2 mm size fraction) and incubated in 10 L polycarbonate container microcosms for 48 hours. After incubation, a subsample of 5 L was taken from each experimental microcosm using a hand pump. Each sample was sieved through a 50 µm mesh, rinsed with 0.2 μm filtered seawater, and concentrated in 200 ml in a glass beaker. The samples were examined under the stereomicroscope (SZX16, Olympus, Japan) and the number of dead (not swimming and/or not moving) and live individuals (swimming and/or moving after being gently touched with tweezers) of calanoid and cyclopoid copepods were counted for estimating survival. e data included the counts of the dead and live individuals (copepods, including calanoid and cyclopoid copepods). Survival (%) was estimated for each treatment as the live/dead ratio at the end of each incubation (48h).