Correlation between body length and habitat depth in endemic amphipods of Lake Baikal

Amphipods (Crustacea, Amphipoda) are among the most ancient and taxonomically diverse invertebrate groups in Lake Baikal, comprising over 350 morphological species and subspecies. This group of Baikal endemics has remarkably divergent morphological features and occupies various biotopes and depths of the lake (from shallow waters to the deepest zones). This study examines the relationship between maximum body length and habitat depth in Baikal amphipods. The analysis of the literature data has shown that most species have a body length that does not exceed 40 mm. Amphipod species are unevenly distributed by depth, with most of them inhabiting the littoral (0 – 20 m) and sublittoral (20 – 70 m) zones. We show that both dwarf forms of Baikal amphipods (body length < 5 mm) and giant forms (body length > 50 mm) occupy deep-water zones of Lake Baikal, but the dwarf forms mainly inhabit the littoral and sublittoral zones. Statistical analysis revealed a moderate positive correlation between amphipod body length and habitat depth. The removal of the parasitic genus Pachyschesis (Bazikalova, 1945) from the dataset led to an increase in the correlation strength.