Surface water samples were collected using a Neuston net (JMA Neuston net, RIGO Co. Ltd, Tokyo, Japan) (mesh size 350μm), fitted with a collection bucket at the end (RIGO Co. Ltd, Tokyo, Japan) (mesh size 315μm). The net was half submerged and towed alongside the designated vessel at approximately 1~2 knots for a total time of 30 minutes, providing that the submerged portion of the net opening was constant without showing signs of clogging. All neuston samples were placed in aluminium zip lock bags and stored in a cool box for transport.