Germination Capability of Resting Cysts of Alexandrium spp.(Dinophyceae)Enclosed in the Fecal Pellets of Macrobenthic Organisms

Abstract

Abstract: A high abundance of Alexandrium spp. resting cysts occur in the fecal pellets of macrobenthic organisms in Hiroshima Bay. However, whether cysts enclosed within fecal pellets of macrobenthic organisms are able to germinate remains unclear. Therefore, cysts enclosed in fecal pellets were incubated for 29 days under two light intensities, sufficient light intensity for germination and near bottom light intensity at 24 m depth in Kure Bay, 50μmol photons/m2/s and 0.28μmol photons/m2/s, respectively. Subsequently, the germination frequency of cysts and the number of remaining cysts in the wells of microplates in each culture condition were compared. It was found that at 0.28μmol photons/m2/s the cysts remaining enclosed in the fecal pellets were mostly unable to germinate. For cysts extracted from the fecal pellets, 27% of the total cysts were not able to germinate at a light intensity of 50μmol photons/m2/s, and 75% at 0.28μmol photons/m2/s. Accordingly, at sites of similar depth to Kure Bay, it is suggested that resting cysts which are ingested and excreted in fecal pellets by macrobenthic organisms largely lose the ability to germinate.