한국 남해 연안역의 동일 수괴내에서 나타난 적조 원인종 Gymnodinium impudicum의 일주수직이동

Abstract

This study originally aimed to explore diel vertical migration of chain forming species as a major mechanism of blooms around Naro-do where outbreaks of C. polykrikoides have been frequently found since 1982. For a consistent sampling in an identical water mass, we introduced a chemical tracer sulfur hexafluoride (SF6) into a water mass and investigated the vertical distribution of phytoplankton by tracking the core of SF6-labeled water mass during 25 hours from 19:00 14 August to 20:00 15 August 2005. We expected to meet patches bloomed by C. polykrikoides, but relative abundance of the species to entire phytoplankton community was very low ( < 1 %), which was not enough to recognize the existence of the diel cycle pattern. Diatoms mostly dominated the phytoplankton community with the range of 73.4~94.5 %, while dinoflagellates occupied 3.6~23.8 % of entire community. Diatoms were mostly comprised of Skeletonema costatum with occupation percentage of 49.8~69.2 % to entire community, while dinoflagellates were dominated by Gymnodinium impudicum with the range of 0.7~18.1 %. Vertical distributions of G. impudicum explained clearly the diel cycle pattern with high density by day and low density at night in the surface waters, and vice versa in the bottom waters. A weak upward migration of the species from the bottom was likely to begin after 05:00 before sunrise, and population of the species concentrated into the surface waters at 11:00 on 15 August. After 16:00, the population was likely to start to migrate downwards, and they reached to depth (16 m) around 19:00. The vertical migration pattern of G. impudicum resembles the migration of C. polykrikoides representing a &apos;nutrient-retrieval&apos; strategy. Chain length of the species showed temporal pattern which percentage of 3 or 4 cells a chain gradually increased from 22 to 57 % as the species migrated upwards, in contrast, percentage of 1 cell or 2 cells a chain was high between 47 and 85 % as it migrated downwards