Instead of using wild fish species for the investigation of PAHs pollution in the ECS, here we use

zooplankton for conducting such an investigation. Zooplankton species are lower trophic-level animals and typically move with ocean currents. To better understand how PAHs are distributed in zooplankton in the ECS, we investigated zooplankton PAHs concentrations in the ECS, with special emphasis on the effects of salinity (i.e., density) fronts. A total of 32 hydrographic stations along several transects on the ECS shelf were conducted by the R/V Ocean Researcher I from April 29 to May 10, 2009 ( Fig. 1). Temperature, salinity, and buy Lumacaftor density were recorded using a Seabird SBE 911 plus a conductivity–temperature–depth (CTD) profiler. Concentrations of nitrate were measured

according to Shih et al. (2013). The concentrations of chlorophyll-a (chl-a) in the surface layer (∼2 m) were determined according to Chen et al. (2013b). In brief, the chl-a samples were collected by filtering 500–2000 ml of seawater through a GF/F filter and stored at −20 °C until analysis. Chl-a on the GF/F filter was then extracted by acetone and determined according to standard procedures using a Turner Designs 10-AU-005 fluorometer by the non-acidification method ( Chen et al., 2013b). The abundance of zooplankton in the surface layer was determined by collecting zooplankton with a standard Dabrafenib cell line zooplankton net (200 μm) towing in the surface layer for about 10–20 min. Prior to the analysis of PAHs, a small number of zooplankton samples were filtered for calculating

the dry weight of zooplankton. The zooplankton sample was cleaned by separating it from possible micro-debris artifacts, as follows. The large visible non-zooplankton particles were picked out first and the rest of zooplankton samples with some seawater were stored at −20 °C until analysis ( Hung and Gong, 2010). Sucrase Towed zooplankton samples were defrosted and centrifuged (4000 rpm) at 4 °C for 15 min. The supernatant was discarded to remove micro-debris. As mentioned earlier, the zooplankton net was used to collect zooplankton in the surface layer. If some micro-debris were collected with zooplankton in our samples, these tiny micro-debris should be in the supernatant after high-speed centrifugation. Therefore, we believe that almost all the micro-debris was removed after this procedure. After centrifugation, zooplankton were freeze-dried and weighed. Procedures for sample extraction, preparation, and analysis for PAHs in zooplankton were adapted from previous studies ( Ko and Baker, 1995 and Ko and Baker, 2004). Four perdeuterated PAHs (naphthalene-d8, fluorine-d10, fluoranthene-d10, and perylene-d12) were added to each sample prior to extraction as surrogates to assess the overall procedural recovery.