Andrea Bertolo

Zooplankton egg banks are crucial in rebuilding zooplankton populations in temporary water bodies when favourable conditions return after dry periods. However, their abundance, viability, and hatching success depend on many factors, with changes in land use and flooding regimes being potentially crucial drivers. Here, we studied a large‐river floodplain to compare the egg banks of soils across a land use gradient and at different elevations, the latter affecting inundation frequency and duration. We performed experimental manipulations at both the ecosystem scale (land use in the floodplain) and in the laboratory (incubation of soils of different origins). Six land use types were considered: (i) natural maple swamp, (ii) natural wet meadow, (iii) old forage cropping, (iv) recently sown forage cropping, (v) agri‐environmental corn/soybean cropping, and (vi) conventional corn/soybean cropping implemented in collaboration with agricultural producers. Egg banks were characterized through both (i) direct egg counts and (ii) by counting the individuals emerging following the incubation of soils in the laboratory, testing the effects of land use and flooding regime (duration, frequency) on hatching success. We found no significant difference in the abundance of resting eggs of different taxa in soils across the land use gradient in frequently inundated sites at low elevation. In contrast, at high elevation, where inundation periods are less frequent and shorter, rotifer and cladoceran egg density varied across land uses, with higher abundance in old forage cropping compared to agricultural cropping. Ostracods, rotifers and copepods were the most abundant taxa that hatched in the laboratory. Their abundance varied across land use types, with natural soils supporting higher abundances than agricultural soils, and forage cropping showing intermediate abundances. Frequently inundated sites (low elevation) had higher abundances of hatchlings than the less frequently inundated (high elevation) sites. Inundation duration in incubators strongly influenced ostracod hatching only, with an overall increase after 2 weeks of inundation and a decrease thereafter for most soil types. Different taxa dominated the egg and hatchling counts. For example, cladocerans were common in the egg bank but not in hatchling samples, while ostracods were absent from the former but dominated the latter. This apparent paradox suggests that egg viability varied along the land use gradient (e.g., due to agricultural practices during summer months), that the cues required for hatching differed across taxa, or that stress (land use) modulates the likelihood that ostracods enter dormancy as eggs versus juveniles/adults. Natural wetland habitats in floodplains favour the resilience of zooplankton communities facing a disturbance (i.e., the dry period) via a high potential recovery through the emergence of resting stages. In contrast, alterations to these habitats due to agricultural intensification in floodplains hampers zooplankton community resilience via decreased emergence success. Agricultural practices leading to changes in soil properties, which influence the viability of resting stages, are the plausible explanations for this phenomenon. It is paramount to conserve natural wetlands and implement sustainable land use practices in floodplains, to allow egg banks to rebuild zooplankton communities in floodplains and sustain their productivity and ecosystem services.

Macrophytes are foundation species whose use as nature‐based solution (NbS) in aquatic ecosystems can help reduce climate change impacts while mitigating biodiversity loss. The discrepancy in research and application of macrophytes as NbS across inland and marine coastal ecosystems is an opportunity to expand the concept and learn from different approaches. We report on an initiative uniting marine and freshwater scientists that compared knowledge on macrophytes as NbS across realms, identified advances and gaps in their use, and synthesized challenges and opportunities for application. We conducted a bibliometric analysis and an expert participatory exercise around recent review papers. We reveal that most NbS papers on macrophytes are marine‐focused, with distinct topics emphasized across realms, highlighting complementarity of expertise and potential extension to inland waters. We provide recommendations to encourage researchers and stakeholders to embrace the value of macrophytes across a broad range of contexts for a more sustainable future.

The spatial organization of vegetation has been shown to be a strong indicator of ecological state in multiple ecosystems. In this study, we analyze the relationships between spatial complexity metrics in submerged aquatic vegetation (SAV) landscapes, and we explore the potential of satellite remote sensing to quantify these metrics in submerged environments. To do so, we estimated an array of complexity metrics over both simulated and real SAV landscapes of contrasted spatial organization. All these landscapes were artificially manipulated to (i) simulate remote sensing noise associated with the low signal‐to‐noise ratio (SNR) of aquatic environments and environmental noise generated by wind and waves, and (ii) reduce their spatial resolution from very high (2 m) to medium (30 m). Among these treatments, spatial resolution and low SNR (represented by sensor noise) had the strongest impacts on the perceived spatial complexity of the landscapes, while the impact of environmental noise was highly dependent on resolution. Although single metrics were deemed insufficient to characterize the spatial complexity of a landscape, a combination of informational complexity metrics such as the clumpy index, mean information gain, landscape shape index, and edge density provided a robust explanation of variation in the real and simulated datasets. These findings suggest that remote sensing has a strong potential for the ecological monitoring of SAV by contributing to establishing the link between SAV spatial structure and ecological status.

While it is well‐accepted that predation plays a key role in shaping both size structure and species composition in natural ecosystems, fine‐scale variation in predation risk within ecosystems has been largely neglected. The objective of this study was to use normalised size spectra (NSS) to investigate whether small‐scale spatial variation in predation risk (by fish) can modulate zooplankton community structure at the within‐lake level in a small temperate lake. We tested the difference in the NSS between two hydrologically well‐connected basins of a lake exhibiting contrasting thermal regimes. The first is a well‐mixed shallow basin (max. depth 2.5 m) that is inaccessible to brook charr (Salvelinus fontinalis) during summer because the temperature is too warm. The second is a deeper basin (max. depth 18 m) offering a thermal refuge during summer because of lake stratification. As a consequence of these differences in fish accessibility, the fishless basin should contain larger and more abundant zooplankters, inducing a change in NSS slope and height. Our results showed that both the zooplankton size structure and taxonomic composition were distinct in the two basins, with a higher proportion of small individuals and a higher abundance of zooplankton in the shallow basin compared to the deep one. Furthermore, following cooling of the epilimnion in late summer, the zooplankton communities of both basins exhibited a clear shift in size structure and species composition: in autumn, there were smaller individuals and larger proportions of Bosminidae and Daphniidae compared to colonial rotifers than in summer. These results suggest a potential effect of the change in the spatial distribution of brook charr which feed preferentially on large individuals, reducing the average body size of the zooplankton community. Our results show that predation risk by fish can induce a spatial and temporal variation in zooplankton community structure within small temperate lake ecosystems exhibiting contrasted thermal regimes. Other potential predators also influenced the zooplankton community structure, creating a complex interplay that has to be taken into account to disentangle ecological processes and predict their future changes.

Herein, we used zooplankton as a study model for determining how biodiversity components as well as taxonomic and functional attributes reflect lake typology in the natural southern boreal lakes. We estimated the regional and local variation in zooplankton diversity and the community structure across a set of fourteen lakes within a national park. Regional diversity (γ diversity) accounted for 40 species including 20 rotifers, 10 cladocerans and 8 copepods. Local diversity (α diversity) averaged 15 species per lake. Spatial variation in β diversity was inversely related to spatial variation in α diversity. Inter-lake variation in zooplankton communities based on taxonomy, functional traits and biotic indices was explained by two major limnological gradients: namely lake trophic status and fish community. The community structure reflected a gradient of rotifer to calanoid copepod dominance in response to trophic status. Several key species of rotifers (Kellicottia longispina and Conochilus unicornis) and of small (Bosmina and Diaphanosoma birgei) or large (Daphnia catawba and Holopedium gibberum cf glacialis) cladocerans were good indicators of lake zooplankton typology, as in other boreal lakes. We distinguished two main groups of lakes: (1) oligotrophic lakes inhabited by brook trout and dominated by the calanoid copepods and (2) mesotrophic lakes inhabited by northern pike and dominated by rotifers. Overall, our study can help managers better define monitoring and conservation strategies for lake ecosystems in natural parks.

Despite being recognized as a key component of shallow-water ecosystems, submerged aquatic vegetation (SAV) remains difficult to monitor over large spatial scales. Because of SAV’s structuring capabilities, high-resolution monitoring of submerged landscapes could generate highly valuable ecological data. Until now, high-resolution remote sensing of SAV has been largely limited to applications within costly image analysis software. In this paper, we propose an example of an adaptable open-sourced object-based image analysis (OBIA) workflow to generate SAV cover maps in complex aquatic environments. Using the R software, QGIS and Orfeo Toolbox, we apply radiometric calibration, atmospheric correction, a de-striping correction, and a hierarchical iterative OBIA random forest classification to generate SAV cover maps based on raw DigitalGlobe multispectral imagery. The workflow is applied to images taken over two spatially complex fluvial lakes in Quebec, Canada, using Quickbird-02 and Worldview-03 satellites. Classification performance based on training sets reveals conservative SAV cover estimates with less than 10% error across all classes except for lower SAV growth forms in the most turbid waters. In light of these results, we conclude that it is possible to monitor SAV distribution using high-resolution remote sensing within an open-sourced environment with a flexible and functional workflow.