The diadromous watersheds-ocean continuum: Managing diadromous fish as a community for ecosystem resilience

Diadromous fishes play important ecological roles by delivering ecosystem services and making crucial connections along the watersheds-ocean continuum. However, it is difficult to fully understand the community-level impacts and cumulative benefits of diadromous fish migrations, as these species are most often considered individually or in small groups. Their interactions at a community level (e.g., interdependencies such as predation, co-migration, and habitat conditioning) and the connections between their ecosystem roles and functions (e.g., cumulative marine-derived nutrient contributions, impacts on stream geomorphology) are yet to be fully understood. Similarly, freshwater, estuarine, and marine ecosystems are often considered as independent parts, limiting understanding of the importance of connections across systems. We argue that not considering the ecosystem interdependence and importance of diadromous fish as a community currently hinders the implementation of the large-scale management required to increase ecosystem resilience and fish productivity across the full range of these species. We developed a conceptual model, the Diadromous Watersheds-Ocean Continuum (DWOC), that uses ecosystem services to promote a more holistic approach to the management of the diadromous community and encourages an integrated understanding of the ecosystem connections made by these species. DWOC provides a framework for discussions that can help identify research and management needs, discuss the trade-offs of different management options, and analyze what pressing questions impede the implementation of large-scale management solutions toward a more ecosystem-based management approach.

Fatty acid composition of macroinvertebrate scrapers in relation to environmental conditions in subtropical mountain streams

Biochemical fatty acids (FAs) in vivo are essential to the growth and reproduction of animals including macroinvertebrates in streams and are subject to ambient abiotic variables. However, the main abiotic drivers of FA composition in macroinvertebrate scrapers are varying and uncertain. The aim of this research was to quantify the contributions of abiotic variables, including stream physical, chemical, and climatic variables, to the variation of FAs of macroinvertebrate functional feeding group-scrapers (e.g., Bellamya aeruginosa, Radix swinhoe, Heptagenia sp., and Stenelmis sp.). Stream physical, chemical, and climatic variables and the FAs of scrapers were measured in six subtropical streams during spring. The principal component analysis (PCA) indicated the parameters responsible for FA variation were mainly related to polyunsaturated fatty acids (PUFAs), saturated fatty acids (SAFAs), ω3 PUFA, and ω6 PUFA. Multiple factor analysis (MFA) showed that the FA profiles of scrapers strongly correlated with the physical variables. Specifically, the correlation analysis showed that PUFA and terrestrial FA were significantly positively associated with canopy cover, and in contrast that SAFA was negatively correlated with canopy cover. Although water quality and climate variables did not have a good relationship with FAs, they had a strong correlation with physical variables. This research suggested that the influence of environmental variables (e.g., stream physical, chemical, and climatic variables) on FAs of macroinvertebrate scrapers has complex paths. This study provides a theoretical basis for stream management and an empirical framework for the construction of an interactive network beyond food webs that includes environmental variables.

The effects of taxonomy, diet, and ecology on the microbiota of riverine macroinvertebrates

Freshwater macroinvertebrates play key ecological roles in riverine food webs, such as the transfer of nutrients to consumers and decomposition of organic matter. Although local habitat quality drives macroinvertebrate diversity and abundance, little is known about their microbiota. In most animals, the microbiota provides benefits, such as increasing the rate at which nutrients are metabolized, facilitating immune system development, and defending against pathogenic attack. Our objectives were to identify the bacteria within aquatic invertebrates and determine whether their composition varied with taxonomy, habitat, diet, and time of sample collection. In 2016 and 2017, we collected 264 aquatic invertebrates from the mainstem Saint John (Wolastoq) River in New Brunswick, Canada, representing 15 orders. We then amplified the V3-V4 hypervariable region of the 16S rRNA gene within each individual, which revealed nearly 20,000 bacterial operational taxonomic units (OTUs). The microbiota across all aquatic invertebrates were dominated by Proteobacteria (69.25% of the total sequence reads), but they differed significantly in beta diversity, both among host invertebrate taxa (genus-, family-, and order-levels) and temporally. In contrast to previous work, we observed no microbiota differences among functional feeding groups or traditional feeding habits, and neither water velocity nor microhabitat type structured microbiota variability. Our findings suggest that host invertebrate taxonomy was the most important factor in modulating the composition of the microbiota, likely through a combination of vertical and horizontal bacterial transmission, and evolutionary processes. This is one of the most comprehensive studies of freshwater invertebrate microbiota to date, and it underscores the need for future studies of invertebrate microbiota evolution and linkages to environmental bacteria and physico-chemical conditions.