The aim of the study was to compare cyanobacterial and algal assemblages occurring in ornithocoprophilous habitats formed under the influence of two seabird colonies (mixed colony of piscivorous Uria lomvia and Rissa tridactyla and planktivorous Alle alle) nesting on the southwest side of Hornsund (Spitsbergen). Various influences of the bird colonies (e.g. surface trophy, treading) lead to the formation of ornithogenic habitats with quantitatively and qualitatively diverse cyanobacterial and algal assemblages. Only 6 species common to both habitats were identified, but due to their different proportions the similarity ended there. Cyanobacterial and algal assemblages of both ornithogenic habitats also react rather differently to the intensity of the bird colonies' influence. The assemblages located directly beneath piscivorous bird nests were characterized by a larger number of species, which decreased the farther from the colony it was. Cyanobacterial and algal assemblages located directly next to planktivorous bird nests were species poor, but species richness increased at locations farther from their direct influence. The obtained results confirmed that bird colonies characterized by different diet and behavior influenced the formation of two separate, quantitatively and qualitatively different cyanobacterial and algal assemblages. Species such as Eucapsis sp., Gleocapsopsis sp., Gloeothece sp., Woronichinia sp., Hematococcus sp. were characteristic for algae and cyanobacteria assemblages in the vicinity of piscivorous bird colonies, whereas Aphanocapsa sp., Gloeothece sp., Komvophoron minutum, Pseudanabaena sp., Gloeocystis sp. 2 occurred in the vicinity of planktivorous bird colonies.
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