Temporal dynamics of invertebrate community assembly in Lake Victoria since the Late Pleistocene based on chitinous remains

Preserved assemblages of invertebrate remains in lacustrine sediment reveal temporal variations of community composition and environmental conditions. However, records for large tropical lakes are scarce. Lake Victoria, the largest tropical lake, has a dynamic history of changes in water level, biogeochemistry, and fish community composition over the past ~17,000 cal yr BP. In order to quantify changes in the invertebrate assemblage of Lake Victoria from the Late Pleistocene throughout the Holocene, we examined chitinous remains of Cladocera and larval dipterans (Chironomidae and Chaoboridae) from a sediment core (37 m water depth) dated from ~13,700 cal yr BP to present. We identified four major phases in the invertebrate assemblage throughout this period of lake history. First, Chironomidae and Chaoboridae appeared at low abundances during the earliest stages of the lake inundation in the late Pleistocene, at a time when Cladocera were notably absent. Second, chaoborids and chironomids increased in abundance during the Mid Holocene, which coincided with high diatom production towards the end of the Holocene African Humid Period. Third, starting ~4,700 cal yr BP, Alona, a predominantly littoral cladoceran genus, consistently appeared in the invertebrate assemblage alongside changes in mixing regimes and persisted throughout the Late Holocene to present. Fourth, the arrival of both Chydorus and Bosmina longirostris marked the establishment of an abundant cladoceran assemblage at ~1,350 cal yr BP. The assemblage then gradually shifted toward the increasing dominance of B. longirostris, a planktonic cladoceran. This study provides the first multi-millennial record of sedimentary invertebrate assemblages in Lake Victoria, and elucidates some of the temporal development of these communities throughout most of the modern ecosystem's dynamic history. Overall, we provide novel insights into the temporal dynamics of invertebrate community assembly in relation to climatic and environmental variability in tropical lakes.