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Diversity of coccoid algae in shallow lakes during winter

Abstract Very little is known about the distribution and diversity of freshwater unicellular coccoid algae, primarily because of the simple morphology and small size of these organisms, which make reliable identification extremely difficult. In this study, we examined the diversity of autosporic coccoid algae from under ice in the shallow lakes of Arrowwood National Wildlife Refuge, North Dakota. Coccoid algae were isolated from phytoplankton samples collected during three consecutive winters (1994–1997) at four sites in three lakes. Seventy-five isolates were examined by high-performance liquid chromatography analysis of photosynthetic pigments, specific polymerase chain reaction (PCR) primers, and PCR-restriction fragment length polymorphism of the 18S rDNA. Thirteen 18S rDNA types of coccoid Trebouxiophyceae, three types of coccoid Chlorophyceae and one type of coccoid eustigmatophyte were detected. One of the green algae was tentatively identified as Mychonastes homosphaera; the other green algae are probably undescribed species. These results indicate a much higher level of diversity in coccoid green algae than has been reported in regional floras.