Comparative analysis of meiobenthic diversity across habitats in ancient lakes

Wilden B. <em>Comparative analysis of meiobenthic diversity across habitats in ancient lakes</em>. Bielefeld: Universität Bielefeld; 2025.

Freshwater ecosystems, including rivers, lakes, wetlands, and streams, serve as critical biodiversity reservoirs, supporting a diverse array of ecological functions and community structures. Lake ecosystems, in particular, exhibit a high degree of species richness and ecological complexity. Ancient lakes such as Lake Ohrid in Europe, Lake Baikal in Asia, and Lake Malawi in Africa stand out for their exceptional age, stability, and high levels of endemism, making them valuable systems for studying biodiversity and evolutionary processes. These lakes, some of the oldest and most isolated globally, function as natural laboratories, providing unique insights into ecological and evolutionary dynamics in stable freshwater environments. This research investigates meiofaunal communities across various lake habitats to reveal broader biodiversity patterns and identify the primary factors shaping community structure. To examine the environmental drivers influencing benthic communities at both local and broad scales, data from 23 studies across 129 sites and 75 lakes in central and northern Europe were compiled and analyzed. Findings demonstrate that benthic meiofauna are particularly abundant in periphyton, while their biomass is lower in oligotrophic lakes. Nematode community structure varies significantly with substrate type, especially in profundal zones of eutrophic lakes. In these deep zones, nematode diversity is lower, but individuals are larger, with omnivorous and predatory traits more commonly observed. This analysis underscores the influence of lake nutrient status and specific environmental conditions in structuring benthic assemblages, particularly nematode communities. Building on these insights, further research explored seasonal dynamics, habitat variability, and community stability in Lake Ohrid. Nematodes dominate both littoral and profundal sediments, while rotifers prevail in littoral periphyton. Profundal communities exhibit high stability and homogeneity throughout the lake, whereas littoral communities show greater heterogeneity. Over a 10-year period, littoral rotifer communities show significant seasonal changes in abundance and diversity. Rendering the profundal communities particularly useful for cross-lake comparisons as stable, isolated environments. To expand understanding of benthic eukaryotic diversity, high-throughput sequencing of 18S rRNA genes was employed to characterize eukaryotic diversity within Lake Ohrid’s littoral and profundal habitats. Results indicate a community dominated by annelids, arthropods, and protists, with distinct taxonomic and functional differences between habitats. The profundal community is primarily heterotrophic, while phototrophs are more prevalent on littoral hard substrates. Network analysis reveals that the profundal zone is both the most homogeneous and the most complex, emphasizing its stability. These findings highlight the utility of molecular techniques, like high-throughput sequencing, in uncovering hidden diversity within ancient lakes. In a global context, this dissertation contrasts meiofaunal communities across littoral and profundal habitats in Lakes Baikal, Ohrid, and Malawi to determine whether habitat characteristics or geographic separation influence community structure. Results show that profundal communities are consistent in abundance and biomass across lakes, shaped by similar environmental pressures in low-energy, resource-limited habitats. In contrast, littoral communities exhibit marked differences, likely attributable to local habitat features and nutrient levels. While chironomids, copepods, and tardigrades dominate littoral zones, nematodes are prevalent in profundal zones across all lakes, suggesting that profundal meiofaunal communities reflect stable, low-nutrient conditions, whereas littoral communities capture location specific ecological interactions. The research presented in this thesis provides a comprehensive foundation that emphasizes the ecological importance of meiofauna, particularly in nutrient cycling and sediment stability. Nematodes are highlighted as an ideal model group due to their species richness, sensitivity to environmental changes, and widespread presence across all habitats. Ancient lakes, especially their profundal zones, prove to be ideal study sites, offering unique insights into ecological and evolutionary processes due to their long-term stability and isolation. These lakes serve as hotspots for investigating highly specialized communities, making them valuable natural laboratories for holistic ecological studies. Such studies are largely lacking for meiofauna, indicating that much remains to be explored in this field in the future.