Influence on the vertical distribution and germination of Alexandrium spp. cysts by macrobenthic organisms [Perinereis nuntia (Polychaeta) and Theora fragilis (Mollusca)]
2006
Tsujino, M.(National Research Inst. of Fisheries and Environment of Inland Sea, Hatsukaichi, Hiroshima (Japan))
Influence on the vertical distribution and germination of the resting cysts of Alexandrium spp. by two macrobenthos, Perinereis nuntia (Polychaeta) and Theora fragilis (Mollusca), was experimentally examined in culture sediments containing a high density of cysts. The present results indicated that P. nuntia and T. fragilis transferred vertically the cysts in the surface sediments due to ingestion, excretion and movement. However, the cyst densities in the surface sediments decreased more than expected from the vertical transfer to the deeper layers throughout the experimental periods. The accumulative number of vegetative cells of Alexandrium spp. that germinated from the culture sediments with P. nuntia and T. fragilis were lower as compared with those from the control sediments without any macrobenthos. It was considered that germination was suppressed by enclosing cysts in the fecal pellets and digestion of cysts, as well as the vertical transfer of cysts to the deeper layers. Therefore, it was suggested that the surface deposit feeders such as P. nuntia and T. fragilis have a significant role in decreasing the abundance of Alexandrium cysts in the surface sediments and suppressing the germination of them by the digestion, movement and enclosing in the fecal pellets.
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