Factors influencing the vertical distribution of copepods in a tropical oligotrophic estuary, South China sea

Abstract

The distribution of copepods in relation to spatial and temporal variation is well understood, but less is known about the importance of various environmental factors and how these might concurrently influence the distribution of copepods in a river and it's estuary. However, investigations focusing on vertical dynamics of copepods coupled with various environmental factors are totally lacking particularly in an oligotrophic river. To address this deficit, triplicate monthly copepods samples were collected concurrent with various environmental parameters and in two layers (30 cm below the surface and 30 cm above the bottom) at two locations (estuary and upstream) of the Kuantan River, Malaysia. The results of this study affirm that the Kuantan River and it's estuary are oligotrophic. A total of 32 species of copepods under seven families were observed in this study. Total copepods were higher at the estuary compared to the upstream zone. Temperature, salinity and phytoplankton density were the most important factors affecting the density of copepods. Calanoid and cyclopoid copepods were positively influenced by the salinity, while they were negatively influenced by the water temperature. Harpacticoid copepods were observed largely in water near bottom, in which they were strongly and positively influenced by the phytoplankton density without any spatial effect. Other environmental factors minimally affected the density of copepods. Collecting similar data at other environments both nationally and internationally might facilitate future efforts of monitoring and managing aquatic systems.