Each this website freeze-dried sample was mixed with anhydrous sodium sulfate, ground with mortar, and pestled to obtain a dry powder. The powdered mass was then extracted with dichloromethane using an ASE 200 extractor (Dionex, Salt Lake City, UT, USA). The extracted volume was reduced to ∼1.5 ml using a rotary evaporator and then fractionated through an alumina oxide column to remove polar interferences using 35 ml of petroleum ether. The extract was concentrated to ∼5 ml by rotary evaporation and transferred to a pre-combusted, glass test tube. The extract volume was further reduced to ∼1 ml using a purified nitrogen stream and sealed in an amber vial

for GC-MS analysis. The sample analysis was performed by a Varian 3800GC/Saturn 4000 ion trap mass spectrometer (Varian, Walnut Creek, CA, USA) operated in the ion-monitoring mode. Prior to the analysis, a mixture of perdeuterated PAHs, including phenanthrene-d10, benzo(a)anthracene-d10, benzo(a)pyrene-d12,

and benzo(g,h,i)perylene-d12, was added immediately to each extract as an internal standard. Each PAH was identified by its retention time relative to the internal standards and quantified by comparing the integrated CX-5461 supplier area of the molecular ion chromatogram to that of the internal standard ( Ko and Baker, 1995 and Ko and Baker, 2004). The detailed description about the PAH’s analysis can be found in Hung et al (2010). The concentrations of PAHs in zooplankton at 27 stations (excluding station 30 due to sample spilling) are expressed in two different units: ng g−1 (e.g., PAHs normalized by dry weight of zooplankton) and ng m−3 (e.g., PAH concentrations (ng g−1) normalized by zooplankton biomass in seawater (g m−3)). There

are at least four main water masses (Fig. 1, CDW: Changjiang Diluted Water, TCWW: Taiwan Current Warm Water, KW: the Kuroshio Water, YS: Yellow Sea Water) in the ECS in April based on temperature and salinity distributions (Fig. 1 and Fig. 2 and Table 1). CDW is a mixture of Changjiang River runoff and shelf water with low salinity and high nutrient concentrations (Gong et al., 2003 and Hung et al., 2013). YSW is mainly carried into the northern part of the ECS through the Chinese Coastal Current from the Yellow Sea (Ichikawa and Beardsley, 2002), showing moderate salinity, Thymidine kinase low temperature and low nutrient concentrations (Gong et al., 2003 and Chou et al., 2009). TCWW enters the ECS from the Taiwan Strait with high temperature and high salinity (Gong et al, 2003), but its salinity is lower than that of the KW. The KW flows northeast along the shelf with high temperature, high salinity and low nutrient concentrations (Gong et al., 2003 and Hung et al., 2009b). As a whole, the hydrographic setting in this survey in spring was similar to that reported for previous investigations (Gong et al., 2003 and Chou et al., 2009). Fig. 2 shows contour maps of surface salinity, NO3−, Chl-a and plankton biomass in the ECS.