Vegetated shallows as drivers of macroinvertebrate diversity in a tropical high mountain Ramsar lake (Lago Menor, Lake Titicaca)

Integrating vertical and seasonal gradients into ecological monitoring is crucial for identifying biodiversity hotspots and understanding community dynamics in vulnerable high-Andean lakes. Benthic macroinvertebrates are sensitive indicators of ecological quality in high-altitude freshwater ecosystems, including tropical mountain lakes. We evaluated spatial and temporal patterns of benthic macroinvertebrate communities in the southern shallow basin (Lago Menor) of Lake Titicaca (Bolivia) along depth and hydrological gradients. Three bathymetry-defined biotopes were sampled (A: shallow, B: intermediate, C: deep) during three hydrological periods (dry-to-wet transition, wet season, and wet-to-dry transition). We measured physicochemical variables, submerged macrophyte biomass, Chara sp. biomass, and macroinvertebrate assemblages; only Chara sp. was recorded among charophytes. Community composition and structure were analyzed using multivariate ordination, community metrics (richness, Shannon diversity, abundance, dominance), and regression models. From 38 taxa, Amphipoda and Gastropoda dominated. Richness, diversity, and abundance declined significantly with depth, while macrophyte biomass, highest in shallow vegetated sites, was positively associated with these metrics. Chara sp. peaked at intermediate depths and was positively associated with Hyalella longipalma, suggesting a structural role in deeper, less competitive habitats. Community differentiation was strongest between shallow and deep biotopes during the dry-to-wet transition (ANOSIM R = 0.73), whereas a trend toward homogenization emerged during the wet-to-dry transition. Redundancy analysis indicated that pH, conductivity, and vegetation biomass partially explained community variation. Overall, our results highlight shallow vegetated habitats as biodiversity hotspots and support integrating depth and seasonal gradients into monitoring frameworks for high-Andean lakes.