有害渦鞭毛藻類の分布域と導入

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New records of phytoplankton, especially harmful species, in many marine areas have been reported worldwide, and in many of these were often supposed to be due to the artificial transfer of organisms via ship ballast waters and from finfish and shellfish cultures. The presence of motile cells and cysts of phytoplankton in ballast water strongly supports the hypothesis of artificial introduction. However, recent introduction is difficult to demonstrate based only on their morphological comparisons of phytoplankton species such as diatoms, dinoflagellates and raphidophytes, because previous distributions of almost all these organisms have not been elucidated, even in well-investigated harmful species that can cause damage to fisheries activities. On the other hand, DNA sequence data, which can differentiate populations in the species, have becn accumulated for some harmful dinoflagellates and the recent transfers identified by these methods have been discussed. In the present paper, we summarize the present status of knowledge concerning the distribution and introduction of the harmful dinoflagellates, Alexandrium spp., Gymnodinium catenatum, Heterocapsa circularisquama and Cochlodinium polykrikoides, based mainly on the phylogenetic studies to detect intraspecific relationships and the presence of resting cysts. 1. In Alexandrium spp., especially the A. iamarense species complex, molecular data based on LSU rDNA sequences have been well examined and this has clarified the presences of intraspecific clades or "ribotypes", each of which represents a population distributed in different sea areas and thereby the recent introductions were able to be detected. 2. Recent introduction of G. catenatum is discussed based on the presencc or absence of its resting cysts in the core samples of marine sediments, but rDNA sequences were unable to reveal their intraspecific relationships. 3. Occurrences of H. circularisquama have reported only from western Japanese coasts, and the presence of this species in Hong Kong prior to the reports of these Japanese occurrences suggests that the Japanese population is likely to be introduced from the tropical or subtropical Asian waters. 4. Distribution of C. polykrikoides appears to be expanding and ribotypes of this species can be distinguished by LSU rDNA sequences, but the original distribution of each ribotype is now under investigation.
2007-02-26

有害渦鞭毛藻類の分布域と導入

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