基金This work was supported by the Natural National Science Foundation of China （Nos. 41306127 and 41276156）, the Innovation Program of Shanghai Municipal Education Commission （No.13YZ091）, the Ph.D Programs Foundation of Ministry of Education of China （No. 20133104120001） and Shanghai Universities First-class Disciplines Project （Fisheries A）.
基金Supported by the National Key Technology R＆D Program （No. 2013BAD 13B06） and the Guangdong Provincial Program of Science and Technology （No. 2014A020217011）, while the survey cruises were funded by the State Oceanic Administration （No. GAS1-02-SCS-YSW）. The first author was also supported by a Special Fund for Youth Training from the South China Sea Fisheries Research Institute 6 ACKNOWLEDGEMENT We are grateful to Dr. CHEN Yong for his help to complete the manuscript. We thank CHEN Sen, LI Jie, YAN Lei and YANG Bingzhong for their assistance in sample and data collection, and WANG Lianggen and LI Zengguang for their help in preparing figures. We thank to two anonymous reviewers for their comments and suggestions on the manuscript.