Diatom Red List Species Reveal High Conservation Value and Vulnerability of Mountain Lakes

Abstract

Mountain lakes are unique and often isolated freshwater habitats that harbour a rich biotic diversity. This high conservation value may be reflected by diatoms, a group of algae that is known for its reliability as a bioindicator, but which has not been studied extensively in mountain lakes of the northern European Alps. In this study, the conservation value of these lakes was assessed by characterizing the number, share, and abundance of diatom Red List (RL) taxa and their relationship with environmental variables, diatom α and β diversity (assemblage uniqueness). For this purpose, linear regression models, generalized linear models, and generalized additive models were fitted and spatial descriptors were included when relevant. Of the 560 diatom taxa identified, 64% were on the RL and half of these were assigned a threat status. As hypothesized, a decreasing share of RL species in sediment and littoral samples at higher trophic levels was reflected by higher total phosphorous content and lower Secchi depth, respectively. Species-rich lakes contained a high number of RL taxa, contrasting our hypothesis of a logarithmic relationship. In turn, RL abundance increased with uniqueness, confirming our initial hypothesis. However, some of the most unique sites were degraded by fish stocking and contained low abundances of RL species. The results demonstrate the importance of oligotrophic mountain lakes as habitats for rare freshwater biota and their vulnerability in light of human impact through cattle herding, tourism, damming, and fish stocking. Additional conservation efforts are urgently needed for mountain lakes that are still underrepresented within legal conservation frameworks. Species richness and uniqueness reflect complementary aspects of RL status and thus should be applied jointly. Uniqueness can indicate both pristine and degraded habitats, so that including information on human impacts facilitates its interpretation.

Sedimentary, littoral and planktic diatoms show different diversity patterns and assembly mechanisms in mountain lakes of the northern European Alps

“…The significant correlation of TP with the sedimentary and planktic diatom β-diversity reveals a sensitive reaction of the assessed assemblages towards nutrient conditions that ranged from ultraoligotrophic to mesotrophic. These findings confirm previous results, suggesting an influence of anthropogenic pressure on the share and abundance of Red List species (Ossyssek et al, 2022).…”

“…These may lead to priority effects that have already been documented for ostracods (Castillo-Escrivà et al, 2017), aquatic plants (García-Girón et al, 2021) and zooplankton (Leibold et al, 2010;Mergeay et al, 2011). In our dataset, such processes may be caused by the introduction of fish (Chen et al, 2011;Hobbs et al, 2016;Ossyssek et al, 2022) or land-use changes (Martin et al, 2017). Identifying lakes that have been affected by such events and transferring the analytical scheme of this study to downcore assemblages may help interpret historical legacies, yet there are doubts about the completeness and correctness of such information, affecting the ability to track responses of biotic assemblages over time.…”

Diversity, Composition and Environmental Relations of Periphytic Rotifer Assemblages in Lentic Freshwater Bodies (Flanders, Lower Belgium)

“…All these criteria may be used, preferably in combination, to pinpoint sites of higher conservation value, although little concordance is expected in view of their limited correlation. Moreover, caution is required because degradation and disturbance easily lead to ecological uniqueness relative to less impaired conditions [36,57,202], as also clearly shown by the present study. Rotifer assemblages from the most acid water bodies, particularly those with high aluminium concentrations, were all quite unique, but in the absence of pristine conditions, the acidification footprint should be borne in mind and restoration, rather than conservation, may be more in order here.…”

Are protected areas effective in preserving alpine stream morphology and biodiversity? An experience in the first Italian National Park

“…At the same time, this trend was negative (although not significant) considering habitat modification score, which means that poor communities are typical of the most impacted sites. Moreover, according to Ossyssek, Hofmann, Geist, & Raeder (2022), we found a good correlation between total diatom richness and endangered species.…”