Potential Threat of Microplastics to Zooplanktivores in the Surface Waters of the Southern Sea of Korea

The potential impact of microplastic to zooplanktivores was assessed by measuring a ratio of neustonic microplastics to zooplankton by abundance in the southern sea of Korea. Neustonic microplastics and zooplankton (0.33–2 mm) were collected using a 330-μm mesh Manta trawl in Geoje eastern Bay and Jinhae Bay before and after the rainy season in 2012 and 2013. The mean microplastic to zooplankton ratios were 0.086 (May) and 0.022 (July) in 2012, and 0.016 (June) and 0.004 (July) in 2013, indicating that zooplanktivores could be more likely to feed on microplastics than natural preys before the rainy season in 2012 and 2013. In particular, the relatively high ratio occurred in a semi-enclosed bay characterized by a shipyard and a beach resort in Geoje Bay, and at stations close to a wastewater treatment plant and an aquaculture facility in Jinhae Bay before the rainy season. Among dominant microplastics and zooplankton before the rainy season, meroplankton of macrobenthos could be confused with paint particles in Geoje Bay, 2012, whereas Styrofoam could be mistaken as immature copepods by predators in Jinhae Bay, 2013. These observations suggest that zooplanktivores could be more likely to feed on microplastics than natural preys around Geoje and Jinhae Bays before the rainy season.