Global resemblance, local divergence? – A comparison of meiobenthic invertebrate communities dwelling in ancient lakes Malawi, Ohrid and Baikal

Ancient lakes are known as biodiversity hotspots and provide unique opportunities to study diversity patterns. We compared the distribution and community characteristics of the meiofauna in the littoral (soft-substrate and hard substrates) and profundal (soft-substrate) of three ancient lakes situated in three different continents: Lake Baikal (Asia), Lake Ohrid (Europe), and Lake Malawi (Africa). We expected that, for microscopic creatures like meiofauna, community structure would be more influenced by local habitat features than by spatial distances between lakes. This was found for the deep profundal, a unique system not showing differences in meiofaunal abundance (about 500,000 ind. per m²) and biomass (about 100 mg dry weight per m²) across the lakes. But littoral communities differed across lakes in abundance (up to 7,000,000 ind. per m²) and biomass (on average 400 mg dry weight per m²).

The community structure was found to change significantly across the lakes and habitats, with distinct differences between profundal and littoral communities. Chironomids, copepods, and tardigrades were typical representatives of littoral communities, while nematodes dominated the profundal communities with >80 % of the individuals. Rotifers made up more than 50 % of the littoral hard substrate communities, while ostracods were more dominant in Lake Baikal. Abundance-biomass regressions of nematodes indicated significantly different trophic transfer efficiency and carrying capacity between profundal and littoral habitats, but no differences across the lakes. Nevertheless, this first comparative study of meiofauna in three ancient lakes revealed the need for more thorough investigations for a better understanding of these systems.