Effects of human-induced water level fluctuations on copepod assemblages of the littoral zone of Lake Maggiore

Abstract

Human-induced water level fluctuations (WLFs) are among the major pressures threatening lake ecosystems. Their effect on meiobenthic species of the littoral zone has been poorly investigated. In this study, we aimed at assessing the effects of human-induced WLFs on the composition and functionality of the benthic copepod assemblages of the littoral zone of Lake Maggiore, Italy and Switzerland. From 1942 to present, the water level of Lake Maggiore has been regulated through the Miorina Dam. We monitored copepod assemblages during different water levels defined within the period of regulation by the dam, using taxonomy- and trait-based metrics. We observed variation in the overall abundance and biomass of copepods, as well as in the number of individuals belonging to some trait classes such as ovigerous females, opportunists, omnivores and deposit feeders. None of the investigated trait class was completely lost. The results of our study suggest that ecosystem services supplied by the littoral zone of Lake Maggiore are likely altered by human-induced WLFs. Our findings provide a first picture of WLF impacts on benthic copepod assemblages, which can be useful for future research expanding on other functional traits.

Sampling and laboratory protocols to study the effects of water-level management on the littoral invertebrate fauna in deep and large temperate lakes

“…Macro-fauna samples were taken kicking the first 5 cm of sediments for 1 min (Frost et al, 1971): to ensure the capture of even the most mobile individuals, the net was passed several times through the water column above the sampled area. Concurrently, in a very close area, meiofauna semiquantitative samples were taken following the methods in Cifoni et al (2022) that involves disturbing an area of about 625 cm 2 by foot, up to 7 cm in-depth, for 30 sec (Ausden, 1997), following the methods in Pozojević et al (2019). To avoid filtering the water column, the net was quickly dragged over the disturbed area and closed at the opening before being withdrawn to the surface.…”

“…The semi-quantitative samples were sorted under a stereomicroscope (Leica M80, magnification 16), without stain addition, and standardized by picking up 150 meiobenthic animals using a glass pipette, based on a preliminary sampling survey that aimed at maximizing taxa richness at the class/order level (Metzeling and Miller, 2001). The standardization was such to capture the whole expected benthic copepod biodiversity along the lake shorelines (Cifoni et al, 2022).…”

“…Afterward, five functional traits (size, body form, locomotion and substrate relation, diet and feeding habits), described by the modalities reported in Cifoni et al (2022), were measured for each meiofaunal specimen (Tab. 4).…”

“…Here, an integrated multidisciplinary standard method (LHS application, chemical conditions and macro-and meio-faunal analyses) to assess the stress of water-level management on the littoral areas of temperate large lakes, is proposed to highlight mainly the WLFs effects on the littoral assemblage structure, biodiversity, and morphofunctional traits (body shape and volume, biomass, body size) (for results of application see this Special Issue Boggero et al, 2022).…”

“…Then, standard sampling and laboratory methods for the assessment of WLFs stress on the benthic invertebrate fauna of the littoral zone are here proposed. However, little is known about traits of macro-and meio-fauna in Lake Maggiore, and more in general in temperate lakes, and until now the trait-based approach has been applied just to benthic copepods (Cifoni et al, 2021(Cifoni et al, , 2022, which represent one of the most abundant meio-faunal taxa of the lake shorelines. That is why we decided to consider not only taxonomic diversity, but also biological traits such as body size, biomass and types of aquatic stages of macro-fauna as a proxy for stress conditions at the water/sediment interface, and of meio-fauna as a proxy for the stress at the superficial/sub-superficial sediment interface.…”