Ignoring spatial effects results in inadequate models for variation in littoral macroinvertebrate diversity

Environmental drivers alter PUFA content in littoral macroinvertebrate assemblages via changes in richness and abundance

Shallow littoral areas in lakes are productive and highly diverse ecotonal zones, providing habitats for both invertebrate and vertebrate species. We developed a Bayesian modeling framework to elucidate the relationships between environmental drivers (lake typology, habitat, water chemistry, and latitude) and taxon richness, abundance, as well as the content of polyunsaturated fatty acids (PUFAs) in littoral macroinvertebrate communities in 95 boreal lakes. PUFAs, particularly arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are critical micronutrients to maintain normal physiological functions in consumers. Lake typology was a significant predictor for PUFA content in the invertebrate assemblages, which was connected to taxon richness and/or abundance. Benthic communities in large humus-poor or nutrient-rich lakes displayed higher abundance, taxon richness, and more PUFA-rich taxa, whereas those in medium- and large-sized humic (color 30-90 mg Pt/L) and humus-rich lakes (color >90 mg Pt/L) were characterized by decreased abundance and subsequently low PUFA content. The abundance, taxon richness, and nutritional quality of the communities were also strongly related to latitude. Lakes with lower pH were characterized by lower benthic invertebrate diversity and low frequency of taxa with high somatic EPA and DHA content. The complexity of littoral habitats dominated by various macrophyte assemblages creates an environment that favors higher benthic abundance and increased presence of taxonomic groups with high PUFA content. Nutritional quality of benthic invertebrates for upper trophic levels can be modulated by a complex interplay between external stressors and abiotic factors that typically shape the structure of littoral benthic communities.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00027-023-00996-2.

Responses of multiple facets of macroinvertebrate alpha diversity to eutrophication in floodplain lakes

The accelerated eutrophication of freshwater lakes has become an environmental problem worldwide. Increasing numbers of studies highlight the need to incorporate functional and phylogenetic information of species into bioassessment programms, but it is still poorly understood how eutrophication affects multiple diversity facets of freshwater communities. Here, we assessed the responses of taxonomic, phylogenetic and functional diversity of benthic macroinvertebrates to water eutrophication in 33 lakes in the Yangtze River floodplain in China. Our results showed that macroinvertebrate assemblage structure was significantly different among four lake groups (river-connected, macrophyte-dominated, macrophyte-algae transition, and algae-dominated). Three taxonomic, two phylogenetic and two functional diversity indices were significantly different among the lake groups. Except for the increasing trend of Lambda⁺, these metrics showed a clear decreasing trend with increasing levels of eutrophication, with highest values detected in river-connected and macrophyte-dominated lakes, followed by macrophyte-algae transition lakes and algal-dominated lakes. Although differing in the number and identity of key environmental and spatial variables among the explanatory models of different diversity indices, environmental factors (eutrophication-related water quality variables) played more important role than spatial factors in structuring all three facets of alpha diversity. The predominant role of environmental filtering can be attributed to the strong eutrophication gradient across the studied lakes. Among the three diversity facets, functional diversity indices performed best in portraying anthropogenic disturbances, with variations in these indices being solely explained by environmental factors. Spatial factors were mostly weak or negligible in accounting for the variation in functional diversity indices, implying that trait-based indices are robust in portraying anthropogenic eutrophication in floodplain lakes. However, variation in some taxonomic and phylogenetic diversity indices were also affected by spatial factors, indicating that conservation practitioners and environmental managers should use these metrics with caution when providing solutions for addressing eutrophication in floodplain lakes.

Disentangling the relative roles of natural and anthropogenic-induced stressors in shaping benthic ciliate diversity in a heavily disturbed bay

Coastal areas are facing biodiversity loss and degradation of habitats due to intensified human activities. However, our understanding of the relative contribution of natural gradients and human induced disturbance to biodiversity is limited. Here, we investigated the response of three facets of alpha and beta diversity of benthic ciliates to environmental gradients in a highly disturbed estuarine bay in China. We used linear regression and distance-based redundancy analysis to determine the key driving factors for biodiversity. Variation partitioning was further used to examine the relative influence of natural gradients and anthropogenic disturbances on ciliate communities. Our results revealed that ciliate alpha diversity and functional composition remained similar despite notable variation in species composition along salinity gradient. Sediment grain size, together with heavy metals were the strongest determinants in shaping both alpha and beta diversity. After controlling for the effect of natural factors, heavy metals still had significant impacts on beta diversity. Human induced nitrogen enrichment was positively correlated with algivorous functional group with possible impacts on benthic food webs. These results suggest that beta diversity is overall more sensitive to anthropogenic stressors than alpha diversity and give important insights into the role of anthropogenic disturbance on coastal diversity, being also useful for developing ecosystem protection and conservation strategies.

Lakes in the era of global change: moving beyond single-lake thinking in maintaining biodiversity and ecosystem services

The Anthropocene presents formidable threats to freshwater ecosystems. Lakes are especially vulnerable and important at the same time. They cover only a small area worldwide but harbour high levels of biodiversity and contribute disproportionately to ecosystem services. Lakes differ with respect to their general type (e.g. land-locked, drainage, floodplain and large lakes) and position in the landscape (e.g. highland versus lowland lakes), which contribute to the dynamics of these systems. Lakes should be generally viewed as 'meta-systems', whereby biodiversity is strongly affected by species dispersal, and ecosystem dynamics are contributed by the flow of matter and substances among locations in a broader waterscape context. Lake connectivity in the waterscape and position in the landscape determine the degree to which a lake is prone to invasion by non-native species and accumulation of harmful substances. Highly connected lakes low in the landscape accumulate nutrients and pollutants originating from ecosystems higher in the landscape. The monitoring and restoration of lake biodiversity and ecosystem services should consider the fact that a high degree of dynamism is present at local, regional and global scales. However, local and regional monitoring may be plagued by the unpredictability of ecological phenomena, hindering adaptive management of lakes. Although monitoring data are increasingly becoming available to study responses of lakes to global change, we still lack suitable integration of models for entire waterscapes. Research across disciplinary boundaries is needed to address the challenges that lakes face in the Anthropocene because they may play an increasingly important role in harbouring unique aquatic biota as well as providing ecosystem goods and services in the future.

Responses of macroinvertebrate functional traits to riverbed structure of typical debris flow gullies in the upper reaches of the Yangtze River, China

Debris flow is a typical natural disaster in mountainous areas. Its occurrence has serious impacts on the ecological environment and the life, property safety of local people. The structure of mountain riverbed plays an important role in maintaining the ecological stability of debris flow gullies (DFGs) and improving the ecological condition. However, the effects of hydro-geomorphological processes induced by riverbed structure on local macroinvertebrates have not been well examined. A functional approach was applied to macroinvertebrate data collected in a field survey at sites with different riverbed structure to investigate the response of macroinvertebrate functional traits and environment factors to riverbed structure-induced processes. Riverbed structure was quantitatively calculated by concavity-convexity degree. The results showed that (a) Macroinvertebrates were mainly composed of individuals with the ability of avoiding risks and recovering quickly in DFGs. (b) The environmental factors affecting macroinvertebrates (i.e., average particle size, velocity, flow rate, water depth, and gradient) had a great relationship with riverbed structure. (c) Only 3 (trophic habit, attachment and drift) of the 10 benthic functional traits in the study area had a good correlation with riverbed structure. This study thus found that riverbed structure, as a complex of various environmental factors directly or indirectly affected the community structure and functional traits of macroinvertebrates in DFGs. Besides, it was more suitable for macroinvertebrates of different species to live, and more conducive to the maintenance of ecological stability when the concavity-convexity degree value was about 0.075. Because 5 environmental factors affecting macroinvertebrates were moderate when the degree of concavity was about 0.075. These results can provide scientific basis for ecological conservation and management in DFGs where eco-environment is very fragile.

Discriminating the effects of local stressors from climatic factors and dispersal processes on multiple biodiversity dimensions of macroinvertebrate communities across subtropical drainage basins

Metacommunity ecology emphasizes that community structure and diversity are not only determined by local environmental conditions through environmental filtering, but also by dispersal-related processes, such as mass effects, dispersal limitation and patch dynamics. However, the roles of dispersal processes are typically ignored in bioassessment approaches. Here, we simultaneously explored the potential influences of four groups of factors: local stressors, climatic factors, within-basin spatial factors and basin identity in explaining variation in diversity indices of macroinvertebrate assemblages from seven subtropical tributary rivers. A total of 12 biodiversity indices based on species identities, functional traits and taxonomic relatedness were calculated and used in the subsequent statistical analysis. Our results showed that, although differing in their relative importance, the four explanatory factor groups all played important roles in explaining variation in biodiversity indices. Of the pure fractions, index variation was best explained by local environmental stressors, whereas the other three explanatory factor groups appeared less influential. Furthermore, diversity indices from species, functional and taxonomic dimensions responded distinctly to the focal ecological factors, and differed in their abilities to portray the effects of human disturbances on macroinvertebrate communities. Taxonomic distinctness indices performed best, with the highest amount of variation associated to local stressors and hardly any variation explained by other factors, implying that these indices are robust in portraying human disturbances in streams. However, species diversity and functional diversity indices were also affected by spatial processes and climatic factors, suggesting that these indices should be used with caution in bioassessment. We hence conclude that environmental assessment of riverine ecosystems should not rely entirely on the perspective of species sorting. In contrast, both roles of spatial processes and environmental variables related to human disturbances and climatic variation should be incorporated in management and conservation of riverine ecosystems.

Relative roles of spatial processes, natural factors and anthropogenic stressors in structuring a lake macroinvertebrate metacommunity

Studies of aquatic metacommunities have so far been focused almost entirely on relatively isolated systems, such as a set of streams, lakes or ponds. Here, we aimed to quantify the relative importance of spatial processes, natural factors and anthropogenic stressors in structuring of a macroinvertebrate metacommunity within a large, highly-connected shallow lake system. The roles of different drivers were evaluated for the entire metacommunity, 10 trait-based deconstructed metacommunities and four common species by incorporating extensive sampling and a large number of abiotic explanatory variables. Contrary to our expectations, we found that variation in community structure among sites was mostly correlated to spatial and wind-wave variables rather than anthropogenic disturbance factors even though the lake presented strong environmental gradients associated with long-term human pressures. In addition, the relative importance of the three groups of drivers varied slightly among the deconstructed trait matrices (i.e. based on dispersal ability, feeding mode and degree of occurrence). Importantly, the distributions of the most common species showed significant and strong spatial autocorrelation, indicating the prominent role of high dispersal rate for their distributions. These findings suggest that the influences of high dispersal rates and natural disturbance may even override the roles of anthropogenic stressors in metacommunity organization in highly-connected aquatic systems. Hence, we strongly encourage that spatial processes and natural drivers are taken into account in the development of bioassessment approaches in highly-connected aquatic systems.