Unveiling copepod diversity and faunal patterns in Middle Siberia: insights from Tiksi settlement vicinity

The study addresses an uneven and incomplete understanding of copepod fauna in Middle Siberia, particularly in its northeastern region. While the microcrustacean composition in the Lena River Delta is well documented, the Tiksi settlement vicinity, nearby the Lena Delta, remains unexplored. This research focuses on characterizing copepod crustaceans in Tiksi's waters. The collected data enriches the microcrustacean distribution database in Arctic and Subarctic regions worldwide and facilitates an analysis of copepod faunal variation in northeastern Eurasia. A total of 64 copepod species were discovered near Tiksi, with 19 being newly identified for the region. Brackish water reservoirs and lakes demonstrated the greatest diversity within the fauna. The structure of copepod species complexes was consistent among water bodies of the same hydrological type. In brackish lagoons, bays, and lakes, species complexes exhibited intricate, multilevel functional and trophic structures. In contrast, rivers and streams displayed simplified complex structures. Around 20% of the examined fauna displayed East Asian-North American ranges, suggesting a connection to the ancient land of Beringia. Similarity among local Copepoda orders' faunas is linked to crustaceans' dispersal ability, with increasing similarity from Harpacticoida to Calanoida and Cyclopoida. Two distinct groups of regions with comparable faunas are recognized in northeastern Eurasia: European-Siberian, divided into European and Siberian branches, and Far Eastern. The potential existence of transitional zones between these groups is also discussed.