The diversity and ecological roles of protists in marine plankton are still poorly known. In 2011, we made a substantial effort to isolate parasites into cultures during the course of blooms of the toxic microalga Alexandrium minutum (Dinophyceae) in two estuaries (the Penzé and the Rance, Brittany coast, north-west of France). In total, 99 parasitic strains were obtained. Screening of ribosomal internal transcribed spacer regions (including ITS1, 5.8S and ITS2) revealed the existence of two ribotypes. Small subunit and partial large subunit rRNA genes revealed that these two ribotypes belong to different species of the genus Parvilucifera. The first ribotype was tentatively affiliated to the species Parvilucifera infectans, whilst the second represents a new species, Parvilucifera rostrata sp. nov. The new species has several distinct morphological features in the general organization of its zoospore and in the shape and size of processes covering the sporangium. Both Parvilucifera species are generalist parasitoids with similar generation times, and this study thus raises the question of how two parasitoids exploiting similar ecological resources and infection strategies can coexist in the same ecosystem. Taxonomic relationships between Parvilucifera spp. and other closely related marine parasitoids, such as syndinians, are discussed.
Keywords: Alexandrium minutum; Parvilucifera; dinoflagellate; parasitoid; toxic blooms..
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