A sulfur hexafluoride-based Lagrangian study on initiation and accumulation of the red tide Cochlodinium polykrikoides in southern coastal waters of Korea

Abstract

We report continuous in situ measurements of a population of the harmful algal bloom species Cochlodinium polykrikoides in a fixed volume of inshore waters near the island of Naro-do (34.47 degrees N and 127.55 degrees W), off the southern coast of Korea and where the earliest bloom of C polykrikoides occurs regularly. This Lagrangian experiment was carried out by injecting the inert chemical tracer sulfur hexafluoride (SF6) into a patch of seawater carrying C polykrikoides and tracking the SF6-labeled water mass for 4 d. Our results suggest that in situ growth of C polykrikoides within the SF6-labeled water accounts for only a fraction of the total cell increase. A probable mechanism we invoke here is that bloom initiation and much of the cell accumulation in inshore waters near Naro-do are due to the input of C. polykrikoides cells via lateral mixing of inshore waters with the alongshore current containing high C. polykrikoides cell density.