Biomass loss and change in species dominance shift stream community excretion stoichiometry during severe drought

Hopper, Garrett W.; Gido, Keith B.; Pennock, Casey A.; Hedden, Skyler C.; Guinnip, James P.; Fisher, Molly A.; Tobler, Courtney M.; Hedden, Crosby K.; Bruckerhoff, Lindsey A.

doi:10.1111/fwb.13433

Cited by 14 publications

(11 citation statements)

References 77 publications

(114 reference statements)

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“…We found a strong relationship between aggregate excretion rates and suites of species corresponding to particular rivers, a result we attribute to the variable dominance by species with steeper scaling of per capita N and P excretion rates. This pattern has been observed in fish occurring among habitat types (Hopper et al., 2020; McIntyre et al., 2008) and mussel assemblages with contrasting species dominance patterns within the same river (Atkinson & Vaughn, 2015). These results highlight the roles of taxonomic diversity, stoichiometric traits and biomass distribution of assemblages in governing the balance of nutrients cycled in ecosystems.…”

Section: Discussionmentioning

confidence: 60%

“…For example, a ~10‐fold shift in the mean body size of an aggregation would result in a ~10‐fold shift in the flux of DOM, N and P (Figure 3). Such influence of body size on biogeochemical processes has far‐reaching implications across ecosystems as size structure can shift as a result of habitat alterations leading to shift in net community excretion rates (Hopper et al., 2020).…”

Section: Discussionmentioning

confidence: 99%

“…Understanding these mechanisms is essential to predicting how ecosystems may respond to human‐driven disturbances that alter the biomass, composition and ecological stoichiometry of animal communities. Net nutrient contributions from animal communities often depend on which species are dominant (Atkinson et al., 2017), yet even common species are declining, leading to shifts in species dominance patterns and subsequently nutrient recycling (Capps & Flecker, 2013; Hopper et al., 2020). These changes likely are affecting interactions in green and brown food webs since nutrient and organic matter provisioning increases nutrient and resource heterogeneity.…”

Section: Discussionmentioning

confidence: 99%

“…Understanding the functional role of animal communities as sources of bioavailable energy and nutrients in ecosystems is a key for predicting biogeochemical processes and stream food web dynamics following disturbances that alter animal abundance and distribution (Hopper et al., 2020; Larson et al., 2018). Using diverse mussel communities as a model, our objectives were to (a) quantify how species identity and body size influence the quantity, chemical composition and bioavailability of excreted DOM and N and P; (b) test how spatial differences in assemblage biomass and structure would impact local DOM, N and P availability through aggregate excretion.…”

Section: Introductionmentioning

confidence: 99%

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Aggregated filter‐feeders govern the flux and stoichiometry of locally available energy and nutrients in rivers

et al. 2021

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Biogeochemical cycling has often been characterized by physical and microbial processes, yet animals can be essential mediators of energy and nutrients in ecosystems. Excretion by aggregated animals can be an important local source of inorganic nutrients in green food webs; however, whether animals are a source of dissolved energy that can support brown food webs is understudied. We tested whether animal aggregations are a substantial flux of bioavailable dissolved organic matter (DOM) by studying spatially stable, biogeochemical hotspots formed by filter‐feeding freshwater mussels. We used parallel‐factor analysis to quantify DOM fluorescent components composition of mussel excretion and expected digestive breakdown of particulate food sources would lead to excretion of labile DOM. Next, we combined measured excretion rates of DOM, ammonium (NH4+, N) and phosphorous (SRP; P) for 22 species with biomass estimates for 14 aggregations to quantify contributions of DOM, N and P to local availability. Because mussels occupy distinct stoichiometric niches, we anticipated that differences in species biomass and assemblage structure would elicit different flux and stoichiometries of aggregate excretion. Aggregate dissolved organic carbon (DOC) excretion was minor (1%–11%) compared to N (12%–2,860%) and P (1%–97%), yet generalities across assemblages emerged regarding organic matter transformation by mussels towards labile protein‐like compounds compared to abundant aromatic, humic compounds in ambient water. Aggregate excretion of labile DOM was a substantial pool of bioavailable energy, contributing 2%–114% of local labile DOM. Spatial differences in assemblage structure led to strong differences in aggregate flux and stoichiometry driven by biomass and stoichiometric trait expression of species with contrasting dominance patterns. Under the nutrient conditions of our study (high C:nutrient), biogeochemical hotspots associated with low‐trophic position animal biomass may indirectly control energy flow to the brown food web by shifting C:nutrient stoichiometry available to microbes or directly by increasing the flux of microbially available DOM. Collectively, our results highlight a potentially substantial flux of labile energy and nutrients to microbial communities through the transformation of ingested organic matter by aggregations of animals and emphasize that shared functional trait classification may not translate into shared ecological function. A free Plain Language Summary can be found within the Supporting Information of this article.

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Section: Discussionmentioning

confidence: 60%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aggregated filter‐feeders govern the flux and stoichiometry of locally available energy and nutrients in rivers

et al. 2021

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“…We calculated individual excretion rates as the difference in nutrient concentration between containers with sculpin and control containers without fish (e.g. Atkinson et al., 2013; Hopper et al., 2020).…”

Section: Methodsmentioning

confidence: 99%

Effects of increased temperature on arctic slimy sculpin Cottus cognatus is mediated by food availability: Implications for climate change

et al. 2020

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Lakes are vulnerable to climate change, and warming rates in the Arctic are faster than anywhere on Earth. Fishes are sensitive to changing temperatures, which directly control physiological processes. Food availability should partly dictate responses to climate change because energetic demands change with temperature, but few studies have simultaneously examined temperature and food availability. We used a fully factorial experiment to test effects of food availability and temperature (7.6, 12.7, and 17.4°C; 50 days) on growth, consumption, respiration, and excretion, and effects of temperature (12 and 19.3°C; 27 days) on habitat use and growth of a common, but understudied, mid‐level consumer, slimy sculpin Cottus cognatus, in arctic lakes. We also used bioenergetics modelling to predict consumptive demand under future warming scenarios. Growth rates were 3.4× higher at 12.7°C in high food compared to low food treatments, but the magnitude of differences depended on temperature. Within low food treatments, there was no statistical difference in growth rates among temperatures, suggesting food limitation. Consumption, respiration, and nitrogen excretion increased with temperature independent of food availability. Lower growth rates coincided with lower phosphorus excretion at the highest temperature, suggesting that fish selectively retained phosphorus at high temperatures and low food. In habitat choice experiments, fish were more likely to use the 12°C side of the tank, closely matching their optimal temperature. We predicted a 9% increase in consumption is required to maintain observed growth under a 4°C warming scenario. These results highlight considering changes in food resources and other associated indirect effects (e.g. excretion) that accompany changing temperatures with climate change. Depending on how food webs respond to warming, fish may cope with predicted warming if density‐dependent feedback maintains population sizes.

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Drought in intermittent river and ephemeral stream networks

2021

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Intermittent rivers and ephemeral streams (IRES), those watercourses that periodically cease to flow or dry, are the world's most widespread type of river ecosystem.Our understanding of the natural hydrology and ecology of IRES has greatly improved, but their responses to extreme events such as drought remain a research frontier. In this review, we present the state of the art, knowledge gaps and research directions on droughts in IRES from an ecohydrological perspective. We clarify the definition of droughts in IRES, giving recommendations to promote transferability in how ecohydrological studies characterize droughts in non-perennial stream networks. Based on a systematic search of the literature, we also identify common patterns and sources of variation in the ecological responses of IRES to droughts and provide a roadmap for further research to enable improved understanding and management of IRES during those extreme hydrological events. Confusion in the terminology and the lack of tools to assess the hydrological responses of IRES to drought may have hindered the development of drought research in IRES. We found that 44% of studies confused the term drought with seasonal drying and that those that measure droughts in a transferable way are a minority. Studies on ecological responses to drought in IRES networks are still rare and limited to a few climatic zones and organisms and mainly explored in perennial sections. Our review highlights the need for additional research on this topic to inform IRES management and conservation.

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Biomass loss and change in species dominance shift stream community excretion stoichiometry during severe drought

Cited by 14 publications

References 77 publications

Aggregated filter‐feeders govern the flux and stoichiometry of locally available energy and nutrients in rivers

Aggregated filter‐feeders govern the flux and stoichiometry of locally available energy and nutrients in rivers

Effects of increased temperature on arctic slimy sculpin Cottus cognatus is mediated by food availability: Implications for climate change

Drought in intermittent river and ephemeral stream networks

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