Host niche partitioning and coexistence in <i>Amoebophrya</i> and <i>Parvilucifera</i> parasitoids infecting dinoflagellates

Although much attention has been paid to defining the ecological niches of phytoplankton, those of marine parasites and/or parasitoids remain unclear. In this study, we aimed to define the ecological niches of <i>Amoebophrya</i> and <i>Parvilucifera</i> parasitoids infecting dinoflagellates. By performing high-frequency (i.e. daily) time series monitoring over 411 days at a temperate coastal site in Jinhae Bay located on the southern coast of the Korean Peninsula, we isolated infected dinoflagellates and performed the outlying mean index analysis, a multivariate technique that identifies realized niches in field data. Our findings revealed distinct niche properties: <i>Amoebophrya</i> spp. (i.e. Syndiniales clades II-C2, -C3, and -C4) exhibited high marginality, while <i>Parvilucifera</i> spp. exhibited moderate marginality. These findings suggest that the latter species occupy more typical environmental conditions. Despite their shared realized niches, the parasitoids exhibited varying levels of niche overlap and used host niche partitioning to reduce competition and coexist. These findings enhance our understanding of the distribution and dynamics of marine parasitoids in the field.