INTRoDucTIoN The Mollusca is well represented in freshwaters by two classes of molluscs (or mollu... more INTRoDucTIoN The Mollusca is well represented in freshwaters by two classes of molluscs (or mollusks, depending on your preference): Gastropoda (meaning "stomach foot") and Bivalvia (referring to "two valves" or shells). The freshwater Gastropoda of the Nearctic is divided into two major groups: (1) the pulmonates which evolved from terrestrial snails and still possess a mantle cavity modified as a pulmonary cavity or "lung;" and (2) caenogastropods (formerly called prosobranchs), which have a gill and evolved directly from marine snails. The Nearctic bivalves include the native order Unionoida (primarily the abundant pearly mussels) and one order of both native (seed and mussel clams) and invasive clams and mussels. The latter (Asian clams, zebra mussels, and quagga mussels) have caused major losses of native pearly mussels as well extensive economic damage. All freshwater molluscs have one or two shells composed of a thin outer layer of proteinaceous perisostracum and a strong inner layer of mostly crystalline calcium carbonate. Molluscs are present in most Nearctic freshwater habitats other than hypersaline lakes, which are colonized by only a few snail species (Assiminea spp.). Their diversity tends to be lower in extremely soft waters, higher in lotic versus lentic habitats, and greatest in the southeastern USA. Some bivalves can survive outside of water (e.g., buried in a river bank until exposed by rising waters), and pulmonate snails regularly climb out of water on emergent vegetation or rocks to gain better access to oxygen or to avoid predators. lImITaTIoNs Identification of freshwater molluscs is primarily based on shell morphology and secondarily on color. Reliance on shell morphology may pose a serious problem, especially for snails, because the shape of the shell can be modified substantially by water currents (e.g., Britton & McMahon, 2004). Moreover, dried and preserved shells lose much of their identifying colors. Consequently, most taxonomic keys to extant
The removal of dams is frequently promoted as a cost-effective tool for some forms of river rehab... more The removal of dams is frequently promoted as a cost-effective tool for some forms of river rehabilitation, even though the scientific evidence supporting this approach is relatively rare. Our fifteen-month study assessed initial effects of removal of the Edwards Dam at three sites in the Kennebec River, Maine (USA) on zoobenthos, a critical component of a river's food web. Overall changes in both abundance and generic diversity were analysed in relation to feeding strategy. We also evaluated changes in trophic food webs by analysing stable isotope signatures of carbon and nitrogen for major functional feeding groups. The overall density of zoobenthos increased most dramatically (190 %) at the site closest to the former dam, but measures of taxonomic diversity showed variable responses. Neither generic richness nor evenness were significantly altered by removal of the dam. However, the composition of the community changed, with the addition of eight genera including caddisflies ...
Ohio River zooplankton were collected monthly or quarterly for 1 yr from littoral and pelagic (ma... more Ohio River zooplankton were collected monthly or quarterly for 1 yr from littoral and pelagic (main channel) areas in three navigation pools (constricted and floodplain) with four intrapool locations (lower pool and above, below, and within major tributaries). Total densities were minimal (1.64/L) when discharge and turbidities peaked (December-April) but were relatively high otherwise (21.63/L). Seasonal rises in rotifer density preceded increases in cladocerans and cspepods; rotifers were nearly twice as abundant as cladocesans and copepods. Diversity (species richness) was not correlated with temperature, velocity, or turbidity. Density was positively linked with temperature and negatively correlated with river velocity and turbidity. Diversities in littoral and pelagic areas were not different, but densities were higher nearshore (mostly copepods and cladocerans); rotifers were usually more common in the main channel. Neither proximity to low-head navigation dams nor channel mor...
Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires d... more Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires defining bold goals and mobilizing substantial resources to meet the challenges. While the reasons are varied, both research and conservation of freshwater biodiversity lag far behind efforts in the terrestrial and marine realms. We identify fifteen pressing global needs to support informed global freshwater biodiversity stewardship. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated action towards its sustainable management and conservation.
Theoretical models have spurred empirical testing to understand how anthropogenic disturbances ca... more Theoretical models have spurred empirical testing to understand how anthropogenic disturbances cause sudden shifts between alternative functional states. Most studies are done over short periods of time, making it difficult to determine the occurrence of ecological thresholds or regime shifts. This study used carbon stable isotope ratios
P opulations, communities, and ecosystem functions all rise and fall through time in accordance w... more P opulations, communities, and ecosystem functions all rise and fall through time in accordance with seasonal patterns, year-to-year changes in weather, and regulation through internal processes like predator-prey cycles (Levin 1992). These patterns, which we refer to as temporal variability, may also be influenced by human activities. Temporal variability that becomes exaggerated (ie higher peaks and lower lows) increases the risk for local extinction of animal and plant populations (Heino et al. 1997; Schindler et al. 2010), as well as outbreaks of pests and disease vectors (Bolker and Grenfell 1996; Sabo 2005). Similarly, socioeconomic systems can be impacted by unexpected temporal variability, particularly when these fluctuations occur at large spatial scales. For example, a particularly bad year for fisheries production can reduce food security and result in unsustainable harvests (Badjeck et al. 2010; Moore and Schindler 2010). Likewise, greater unreliability of pollinator services can heighten the risk of crop failure in bad years (Slingo et al. 2005; Ray et al. 2015). Understanding the drivers of temporal variability in spatially structured ecosystems is therefore critically important for both conservation planning and sustaining human livelihoods and economies. Improving knowledge about temporal variability requires consideration of how drivers interact directly and indirectly with one another across spatial scales. The emerging subdiscipline of macrosystems ecology explicitly focuses on the study of ecological dynamics at large scales, with patterns being driven by multiple factors that interact across scales (Heffernan et al. 2014). Empirical evidence suggests that temporal variability can be influenced by local and regional factors (Tilman and Downing 1994; Schindler et al. 2010), and there is growing consensus that cross-scale interactions are also important for understanding variability (Wang and Loreau 2014; Wilcox et al. 2017). For example, the Moran theorem suggests that largescale synchronous environmental fluctuations lead to largescale synchronous fluctuations in population abundance (Moran 1953). Synchronized subpopulations in a connected system may be more vulnerable to punctuated natural or anthropogenic disturbances (Wang and Loreau 2014). Here, we review the literature on drivers of temporal variability at multiple scales, identify testable hypotheses (Table 1), and provide new evidence from our own analyses. Our purpose is to illustrate how progress can be made to understand the drivers
A nearly 40-year debate on the origins of carbon supporting animal production in lotic systems ha... more A nearly 40-year debate on the origins of carbon supporting animal production in lotic systems has spawned numerous conceptual theories emphasizing the importance of autochthonous carbon, terrestrial carbon, or both (depending on river stage height). Testing theories has been hampered by lack of adequate analytical methods to distinguish in consumer tissue between ultimate autochthonous and allochthonous carbon. Investigators initially relied on assimilation efficiencies of gut contents and later on bulk tissue stable isotope analysis or fatty acid methods. The newest technique in amino acid, compound specific, stable isotope analysis (AA-CSIA), however, enables investigators to link consumers to food sources by tracing essential amino acids from producers to consumers. We used AA-CSIA to evaluate nutrient sources for 5 invertivorous and 6 piscivorous species in 2 hydrogeomorphically contrasting large rivers: the anastomosing Upper Mississippi River (UMR) and the mostly constricted lower Ohio River (LOR). Museum specimens we analyzed isotopically had been collected by other investigators over many decades (UMR: 1900-1969; LOR: 1931-1970). Our results demonstrate that on average algae contributed 58.5% (LOR) to 75.6% (UMR) of fish diets. The next highest estimated contributions of food sources were from C 3 terrestrial plants (21.1 and 11.5% for the LOR and UMR, respectively). Moreover, results from 11 individually examined species consistently demonstrated the importance of algae for most fish species in these trophic guilds. Differences among rivers in relative food source availability resulting from contrasting hydrogeomorphic complexity may account for relative proportions of amino acids derived from algae.
1994. Predicting the success of riverine populations of zebra mussels (Dreissena polymorpha) a se... more 1994. Predicting the success of riverine populations of zebra mussels (Dreissena polymorpha) a se history of early colonization and microhabitat distribution in the Ohio River.
Physical conditions are usually considered pre-eminent in controlling river plankton, but biotic ... more Physical conditions are usually considered pre-eminent in controlling river plankton, but biotic interactions may be important in slackwater areas. To begin testing this general hypothesis, we conducted a 12-day, predator-prey experiment in 3500 litre mesh enclosures in a slackwater area of the St. Lawrence River using planktivorous, juvenile yellow perch (Perca fiavescens) and Dreissena mussels. Results generally supported our hypotheses that: (1) perch would directly suppress large zooplankton via predation but benefit microzooplankton through indirect interactions; and (2) dreissenids would directly depress rotifer densities via predation and have indirect negative effects on macrozooplankton. Based on gut contents of experimental fish, cladocera were the principal prey of smaller yellow perch (c. 46-50 mm), followed by copepods, ostracods, and rotifers. Larger juvenile perch (c. 67-73 mm) fed almost exclusively on copepods and ostracods. Densities of calanoid copepodids, nauplii, and some cyclopoid copepods (Diacyclops thomasi) were significantly depressed by perch, and adult Eurytemora affinis (99% of adult calanoids) essentially disappeared from fish enclosures. Despite being a favourite prey item of small perch, densities of the small cladoceran Bosmina (Sinobosmina) spp. were significantly higher when fish were present (150% greater than control densities on Day 12). Densities of the very abundant rotifer Polyarthra were >300% greater in fish enclosures than controls by Day 12, and the rotifers Synchaeta and predaceous Ploesoma were significantly more abundant in the presence of perch. Increases in rotifers and cladocera suggest indirect, positive effects of fish related to significantly higher phytoplankton biomass or decreased densities of predaceous copepods. Densities of eight of ten zooplankton groups examined declined significantly when mussels were present, and calanoid copepodids also declined but not significantly. Chlorophyll-a concentrations were slightly lower in mussel enclosures. This evidence suggests biotic interactions play important roles among potamoplankton in slackwater habitats, but river-wide implications of these findings require further study.
We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales fro... more We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales from headwaters to large rivers. This riverine ecosystem synthesis (RES) provides a framework for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. Rather than posing a completely new model, we arrange a conceptual marriage of eco-geomorphology (ecological aspects of fluvial geomorphology) with a terrestrial landscape model describing hierarchical patch dynamics. We modify five components of this terrestrial model for lotic ecosystems: (1) nested, discontinuous hierarchies of patch mosaics; (2) ecosystem dynamics as a composite of intra-and inter-patch dynamics; (3) linked patterns and processes; (4) dominance of non-equilibrial and stochastic processes; and (5) formation of a quasi-equilibrial, metastable state. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004. Contrasting with a common view of rivers as continuous, longitudinal gradients in physical conditions, the RES portrays rivers as downstream arrays of large hydrogeomorphic patches (e.g. constricted, braided and floodplain channel areas) formed by catchment geomorphology and climate. The longitudinal distribution of these patches, which are identifiable using standard geomorphic techniques, varies amongst rivers and is difficult to forecast above ecoregional scales. Some types of hydrogeomorphic patches may reoccur along this downstream passage. Unique ecological 'functional process zones' are formed by individual types of hydrogeomorphic patches because of physiochemical habitat differences which affect ecosystem structure and function. The RES currently includes 14 tenets predicting how patterns of individual species distributions, community regulation, lotic ecosystem processes, and floodplain interactions will vary over spatiotemporal scales, especially as they relate to the functional process zones formed by hydrogeomorphic differences in the river network.
Analyses of stable isotope (d 13 C and d 15 N) and C:N ratios of food webs within a¯oodplain and ... more Analyses of stable isotope (d 13 C and d 15 N) and C:N ratios of food webs within a¯oodplain and a constricted-channel region of the Ohio River during October 1993 and July 1994 indicate that the increasingly in¯u-ential¯ood pulse concept (FPC) does not, for either location, adequately address food web structure for this very large river. Furthermore, results of this study suggest that the riverine productivity model (RPM) is more appropriate than the widely known river continuum concept (RCC) for the constricted region of this river. These conclusions are based on stable isotope analyses of potential sources of organic matter (riparian C 3 trees, riparian C 4 grasses and agricultural crops, submerged macrophytes,
R iverine ecosystems are some of the most diverse on Earth and provide important services (Palmer... more R iverine ecosystems are some of the most diverse on Earth and provide important services (Palmer and Richardson 2009; Strayer and Dudgeon 2010). Understanding how they function is critical to sustainable management but challenging given their complex spatial and temporal structure and multi-scale processes. Riverine systems comprise hydrological-ecological networks organized by the flow of water, sediment, nutrients, and organisms downhill and downstream and the active movement of animals uphill and upstream. Rivers are multidimensional, including longitudinal (upstream-downstream), lateral (upland to channel), vertical (hyporheic, or the zone below the stream bed), and temporal components (Ward 1989; Fausch et al. 2002). Despite this multidimensionality, many ecological processes are influenced by the rapid flow of water downhill, providing strong directional connectivity (Wiens 2002). Rivers are also organized hierarchically, with fine-scale structures (eg gravel patches) embedded within channel bed features (eg riffles), which in turn are embedded within reaches, valley segments, basins, and regions (Table 1; Frissell et al. 1986; Thorp et al. 2008). Uplands are fundamental to riverine organization, with variations in land use, land cover, and soils influencing surface-water and groundwater flow paths, thereby altering water, nutrient, and sediment fluxes to rivers (eg Lewis and Grimm 2007). Rivers are also temporally variable, partially due to hydrology that varies within and across basins and climatic regions (Poff et al. 1997). Thus, we define riverine macrosystems as hierarchical dynamic networks, influenced by strong directional connectivity that integrates processes across multiple scales and broad distances through time (Figure 1; see Heffernan et al. [2014] for macrosystem definition). Ecologists have typically studied riverine ecosystems at the scale of bed features or reaches distributed longitudinally along rivers of varying size, in an attempt to understand the strong influences that upstream and watershed processes, including human modifications, can have (Poole 2010). Our conceptualization of rivers and watersheds as "macrosystems" is a logical extension of these approaches (Figure 1). We view riverine macrosystems as repeating, interacting MACROSYSTEMS ECOLOGY
Suspension feeding by bivalves exceeds that by other planktivores in many North American rivers, ... more Suspension feeding by bivalves exceeds that by other planktivores in many North American rivers, and food webs may be altered substantially by differences in feeding patterns between native unionid mussels and invading dreissenid mussels. 2. We conducted an experiment comparing zooplanktivory by one unionid and two dreissenid species that addressed several primary questions. Is benthic planktivory important in this river? Has this linkage been altered substantially by dreissenids? Do the two dreissenid species differ in planktivory , and is this ecologically important if quagga mussels extend their geographical range? 3. Our 12-day experiment consisted of controls (no mussels) and treatments with unionid (Elliptio complanata), quagga (Oreissena bugensis) or zebra (0. polymorpha) mussels in 3500-L, 80-I.Lm mesh enclosures placed in a slackwater area of the St Lawrence River. 4. The density of the most abundant calanoid copepod Eurytemora affinis increased in the presence of dreissenids, probably as an indirect food web response. By day 12, a cumulative effect was shown by the most overwhelmingly abundant rotifer, Polyarthra, whose density declined dramatically in dreissenid enclosures compared with control and unionid enclosures. Roilier densities in unionid enclosures were not different from controls, nor were dreissenid treatments different from each other. The effects on rotifers were probably from predation, as Ch1-a did not vary among treatments. 5. We conclude that benthic-pelagic coupling via planktivory is important in slackwater areas. Dreissenids have strengthened this linkage, but range extension of quaggas should not appreciably alter effects produced by a similar biomass of zebra mussels.
Canadian Journal of Fisheries and Aquatic Sciences, 1996
A laboratory study was conducted to determine the effect of chronic turbidity (using bentonite cl... more A laboratory study was conducted to determine the effect of chronic turbidity (using bentonite clay) at medium and high temperatures on respiration of two exotic mussel species, Dreissena polymorpha and Dreissena bugensis. Populations of D. polymorpha from Lake Erie and the Ohio River and D. bugensis from Lake Erie were acclimated for 4 weeks to one of four temperature-turbidity combinations: 25°C-0 nephelometric turbidity units (NTU), 25°C-80 NTU, 15°C-0 NTU, and 15°C-80 NTU. At the end of the acclimation period, respiration was measured at both 0 and 80 NTU using a closed, flow-through system with a Clark-type polarographic microelectrode. Mass-specific respiration rates were computed as V ⋅ O 2 (= µL O 2 consumed⋅mg shell-free dry mass-1 ⋅h-1). Results showed that size, temperature, acclimation turbidity, and measurement turbidity significantly affected V ⋅ O 2 rates. An interaction between acclimation turbidity and measurement turbidity suggests that dreissenid mussels adjusted their metabolic rate in response to chronic exposure to turbidity. Mussels acclimated to higher levels (80 NTU) of turbidity did not experience as large a percent drop in V ⋅ O 2 when tested in turbid water (80 NTU) as did mussels acclimated at lower turbidity (0 NTU). Résumé : Nous avons mené une étude en laboratoire pour déterminer l'effet de la turbidité chronique (à l'aide d'argile bentonitique) à des températures moyennes et élevées sur la respiration de deux espèces de mollusques exotiques, Dreissena polymorpha et Dreissena bugensis. Les populations de D. polymorpha du lac Érié et du fleuve Ohio et de D. bugensis du lac Érié ont été acclimatées pendant 4 semaines avec l'une des quatre combinaisons suivantes de température et turbidité : 25°C-0 unités de turbidité néphélémétriques (UTN), 25°C-80 UTN, 15°C-0 UTN et 15°C-80 UTN. À la fin de la période d'acclimatement, on a mesuré la respiration à 0 et à 80 UTN à l'aide d'un système fermé en circulation avec une microélectrode polarographique de type Clark. On a calculé les taux de respiration spécifiques de la masse sous la forme V ⋅ O 2 (= µL O 2 consommé⋅mg masse sèche sans coquille-1 ⋅h-1). Les résultats ont montré que la taille, la température, la turbidité d'acclimatement et la turbidité à la mesure avaient des effets significatifs sur les taux de V ⋅ O 2. Une interaction entre la turbidité d'acclimatement et la turbidité à la mesure permet de penser que les dreissenidés ont adapté leur taux métabolique en réaction à une exposition chronique à la turbidité. Les moules acclimatées à des niveaux supérieurs (80 UTN) de turbidité n'ont pas connu une baisse aussi forte en pourcentage de V ⋅ O 2 lorsqu'on les a testées dans une eau trouble (80 UTN) que les moules acclimatées à une turbidité plus faible (0 UTN). [Traduit par la Rédaction]
Assignment of values for natural ecological benefits and anthropocentric ecosystem services in ri... more Assignment of values for natural ecological benefits and anthropocentric ecosystem services in riverine landscapes has been problematic, because a firm scientific basis linking these to the river's physical structure has been absent. We highlight some inherent problems in this process and suggest possible solutions on the basis of the hydrogeomorphic classification of rivers. We suggest this link can be useful in fair asset trading (mitigation and offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of rivers.
... Snags are an important habitat for benthic macroinvertebrates (Claflin, 1968; McLachlan, 1970... more ... Snags are an important habitat for benthic macroinvertebrates (Claflin, 1968; McLachlan, 1970; Benke et al., 1984; Thorp et al., 1985; O'Connor, 1991) and provide forage and refuge for fish (Benke et al., 1979). ... period of colonization (Thorp et al., 1985; O'Connor, 1991). ...
While the four-dimensional nature of river ecosystems has been recognized for nearly two decades,... more While the four-dimensional nature of river ecosystems has been recognized for nearly two decades, the role of lateral complexity has rarely been factored into studies of zooplankton ecology. We examined the importance of hydrologic retention areas (slackwaters) near islands and embayments of the St. Lawrence River for densities, fecundity, and diel migration of planktonic microcrustaceans. Densities of cladocera and copepods (nauplii and adult stages of cyclopoids and calanoids) were sampled from surface and deeper layers both at night (2100-0100 h, near the new moon) and during the day (1000-1400 h) for channel (deep-fast), offshore (shallow-slower), and inshore (shallow-stagnant) habitats. Average zooplankton densities increased laterally from the main channel into the slackwaters with the exception of calanoid copepods, which peaked in the intermediate depths and flows of the offshore habitats. Although the ratio of males to females for the calanoid Eurytemora affinis and the cladoceran Bosmina spp. did not differ among habitats, a greater percentage of ovigerous cladoceran females were present in slackwaters than in channel habitats. Densities of microcrustaceans were generally greater during the night than day, suggesting diel vertical migration. By demonstrating both lateral and diel differences in the spatial distribution of riverine zooplankton, we refute the view of large rivers as well-mixed homogenous systems. To the contrary, the two non-random patterns that we document imply that there is an abiotic template that at least microcrustacean potamoplankton can exploit. In turn this suggests more research into the ecological significance of the pelagic structure of other large rivers like the St. Lawrence is justified.
INTRoDucTIoN The Mollusca is well represented in freshwaters by two classes of molluscs (or mollu... more INTRoDucTIoN The Mollusca is well represented in freshwaters by two classes of molluscs (or mollusks, depending on your preference): Gastropoda (meaning "stomach foot") and Bivalvia (referring to "two valves" or shells). The freshwater Gastropoda of the Nearctic is divided into two major groups: (1) the pulmonates which evolved from terrestrial snails and still possess a mantle cavity modified as a pulmonary cavity or "lung;" and (2) caenogastropods (formerly called prosobranchs), which have a gill and evolved directly from marine snails. The Nearctic bivalves include the native order Unionoida (primarily the abundant pearly mussels) and one order of both native (seed and mussel clams) and invasive clams and mussels. The latter (Asian clams, zebra mussels, and quagga mussels) have caused major losses of native pearly mussels as well extensive economic damage. All freshwater molluscs have one or two shells composed of a thin outer layer of proteinaceous perisostracum and a strong inner layer of mostly crystalline calcium carbonate. Molluscs are present in most Nearctic freshwater habitats other than hypersaline lakes, which are colonized by only a few snail species (Assiminea spp.). Their diversity tends to be lower in extremely soft waters, higher in lotic versus lentic habitats, and greatest in the southeastern USA. Some bivalves can survive outside of water (e.g., buried in a river bank until exposed by rising waters), and pulmonate snails regularly climb out of water on emergent vegetation or rocks to gain better access to oxygen or to avoid predators. lImITaTIoNs Identification of freshwater molluscs is primarily based on shell morphology and secondarily on color. Reliance on shell morphology may pose a serious problem, especially for snails, because the shape of the shell can be modified substantially by water currents (e.g., Britton & McMahon, 2004). Moreover, dried and preserved shells lose much of their identifying colors. Consequently, most taxonomic keys to extant
The removal of dams is frequently promoted as a cost-effective tool for some forms of river rehab... more The removal of dams is frequently promoted as a cost-effective tool for some forms of river rehabilitation, even though the scientific evidence supporting this approach is relatively rare. Our fifteen-month study assessed initial effects of removal of the Edwards Dam at three sites in the Kennebec River, Maine (USA) on zoobenthos, a critical component of a river's food web. Overall changes in both abundance and generic diversity were analysed in relation to feeding strategy. We also evaluated changes in trophic food webs by analysing stable isotope signatures of carbon and nitrogen for major functional feeding groups. The overall density of zoobenthos increased most dramatically (190 %) at the site closest to the former dam, but measures of taxonomic diversity showed variable responses. Neither generic richness nor evenness were significantly altered by removal of the dam. However, the composition of the community changed, with the addition of eight genera including caddisflies ...
Ohio River zooplankton were collected monthly or quarterly for 1 yr from littoral and pelagic (ma... more Ohio River zooplankton were collected monthly or quarterly for 1 yr from littoral and pelagic (main channel) areas in three navigation pools (constricted and floodplain) with four intrapool locations (lower pool and above, below, and within major tributaries). Total densities were minimal (1.64/L) when discharge and turbidities peaked (December-April) but were relatively high otherwise (21.63/L). Seasonal rises in rotifer density preceded increases in cladocerans and cspepods; rotifers were nearly twice as abundant as cladocesans and copepods. Diversity (species richness) was not correlated with temperature, velocity, or turbidity. Density was positively linked with temperature and negatively correlated with river velocity and turbidity. Diversities in littoral and pelagic areas were not different, but densities were higher nearshore (mostly copepods and cladocerans); rotifers were usually more common in the main channel. Neither proximity to low-head navigation dams nor channel mor...
Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires d... more Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires defining bold goals and mobilizing substantial resources to meet the challenges. While the reasons are varied, both research and conservation of freshwater biodiversity lag far behind efforts in the terrestrial and marine realms. We identify fifteen pressing global needs to support informed global freshwater biodiversity stewardship. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated action towards its sustainable management and conservation.
Theoretical models have spurred empirical testing to understand how anthropogenic disturbances ca... more Theoretical models have spurred empirical testing to understand how anthropogenic disturbances cause sudden shifts between alternative functional states. Most studies are done over short periods of time, making it difficult to determine the occurrence of ecological thresholds or regime shifts. This study used carbon stable isotope ratios
P opulations, communities, and ecosystem functions all rise and fall through time in accordance w... more P opulations, communities, and ecosystem functions all rise and fall through time in accordance with seasonal patterns, year-to-year changes in weather, and regulation through internal processes like predator-prey cycles (Levin 1992). These patterns, which we refer to as temporal variability, may also be influenced by human activities. Temporal variability that becomes exaggerated (ie higher peaks and lower lows) increases the risk for local extinction of animal and plant populations (Heino et al. 1997; Schindler et al. 2010), as well as outbreaks of pests and disease vectors (Bolker and Grenfell 1996; Sabo 2005). Similarly, socioeconomic systems can be impacted by unexpected temporal variability, particularly when these fluctuations occur at large spatial scales. For example, a particularly bad year for fisheries production can reduce food security and result in unsustainable harvests (Badjeck et al. 2010; Moore and Schindler 2010). Likewise, greater unreliability of pollinator services can heighten the risk of crop failure in bad years (Slingo et al. 2005; Ray et al. 2015). Understanding the drivers of temporal variability in spatially structured ecosystems is therefore critically important for both conservation planning and sustaining human livelihoods and economies. Improving knowledge about temporal variability requires consideration of how drivers interact directly and indirectly with one another across spatial scales. The emerging subdiscipline of macrosystems ecology explicitly focuses on the study of ecological dynamics at large scales, with patterns being driven by multiple factors that interact across scales (Heffernan et al. 2014). Empirical evidence suggests that temporal variability can be influenced by local and regional factors (Tilman and Downing 1994; Schindler et al. 2010), and there is growing consensus that cross-scale interactions are also important for understanding variability (Wang and Loreau 2014; Wilcox et al. 2017). For example, the Moran theorem suggests that largescale synchronous environmental fluctuations lead to largescale synchronous fluctuations in population abundance (Moran 1953). Synchronized subpopulations in a connected system may be more vulnerable to punctuated natural or anthropogenic disturbances (Wang and Loreau 2014). Here, we review the literature on drivers of temporal variability at multiple scales, identify testable hypotheses (Table 1), and provide new evidence from our own analyses. Our purpose is to illustrate how progress can be made to understand the drivers
A nearly 40-year debate on the origins of carbon supporting animal production in lotic systems ha... more A nearly 40-year debate on the origins of carbon supporting animal production in lotic systems has spawned numerous conceptual theories emphasizing the importance of autochthonous carbon, terrestrial carbon, or both (depending on river stage height). Testing theories has been hampered by lack of adequate analytical methods to distinguish in consumer tissue between ultimate autochthonous and allochthonous carbon. Investigators initially relied on assimilation efficiencies of gut contents and later on bulk tissue stable isotope analysis or fatty acid methods. The newest technique in amino acid, compound specific, stable isotope analysis (AA-CSIA), however, enables investigators to link consumers to food sources by tracing essential amino acids from producers to consumers. We used AA-CSIA to evaluate nutrient sources for 5 invertivorous and 6 piscivorous species in 2 hydrogeomorphically contrasting large rivers: the anastomosing Upper Mississippi River (UMR) and the mostly constricted lower Ohio River (LOR). Museum specimens we analyzed isotopically had been collected by other investigators over many decades (UMR: 1900-1969; LOR: 1931-1970). Our results demonstrate that on average algae contributed 58.5% (LOR) to 75.6% (UMR) of fish diets. The next highest estimated contributions of food sources were from C 3 terrestrial plants (21.1 and 11.5% for the LOR and UMR, respectively). Moreover, results from 11 individually examined species consistently demonstrated the importance of algae for most fish species in these trophic guilds. Differences among rivers in relative food source availability resulting from contrasting hydrogeomorphic complexity may account for relative proportions of amino acids derived from algae.
1994. Predicting the success of riverine populations of zebra mussels (Dreissena polymorpha) a se... more 1994. Predicting the success of riverine populations of zebra mussels (Dreissena polymorpha) a se history of early colonization and microhabitat distribution in the Ohio River.
Physical conditions are usually considered pre-eminent in controlling river plankton, but biotic ... more Physical conditions are usually considered pre-eminent in controlling river plankton, but biotic interactions may be important in slackwater areas. To begin testing this general hypothesis, we conducted a 12-day, predator-prey experiment in 3500 litre mesh enclosures in a slackwater area of the St. Lawrence River using planktivorous, juvenile yellow perch (Perca fiavescens) and Dreissena mussels. Results generally supported our hypotheses that: (1) perch would directly suppress large zooplankton via predation but benefit microzooplankton through indirect interactions; and (2) dreissenids would directly depress rotifer densities via predation and have indirect negative effects on macrozooplankton. Based on gut contents of experimental fish, cladocera were the principal prey of smaller yellow perch (c. 46-50 mm), followed by copepods, ostracods, and rotifers. Larger juvenile perch (c. 67-73 mm) fed almost exclusively on copepods and ostracods. Densities of calanoid copepodids, nauplii, and some cyclopoid copepods (Diacyclops thomasi) were significantly depressed by perch, and adult Eurytemora affinis (99% of adult calanoids) essentially disappeared from fish enclosures. Despite being a favourite prey item of small perch, densities of the small cladoceran Bosmina (Sinobosmina) spp. were significantly higher when fish were present (150% greater than control densities on Day 12). Densities of the very abundant rotifer Polyarthra were >300% greater in fish enclosures than controls by Day 12, and the rotifers Synchaeta and predaceous Ploesoma were significantly more abundant in the presence of perch. Increases in rotifers and cladocera suggest indirect, positive effects of fish related to significantly higher phytoplankton biomass or decreased densities of predaceous copepods. Densities of eight of ten zooplankton groups examined declined significantly when mussels were present, and calanoid copepodids also declined but not significantly. Chlorophyll-a concentrations were slightly lower in mussel enclosures. This evidence suggests biotic interactions play important roles among potamoplankton in slackwater habitats, but river-wide implications of these findings require further study.
We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales fro... more We propose an integrated, heuristic model of lotic biocomplexity across spatiotemporal scales from headwaters to large rivers. This riverine ecosystem synthesis (RES) provides a framework for understanding both broad, often discontinuous patterns along longitudinal and lateral dimensions of river networks and local ecological patterns across various temporal and smaller spatial scales. Rather than posing a completely new model, we arrange a conceptual marriage of eco-geomorphology (ecological aspects of fluvial geomorphology) with a terrestrial landscape model describing hierarchical patch dynamics. We modify five components of this terrestrial model for lotic ecosystems: (1) nested, discontinuous hierarchies of patch mosaics; (2) ecosystem dynamics as a composite of intra-and inter-patch dynamics; (3) linked patterns and processes; (4) dominance of non-equilibrial and stochastic processes; and (5) formation of a quasi-equilibrial, metastable state. Our conceptual model blends our perspectives on biocomplexity with aspects of aquatic models proposed from 1980-2004. Contrasting with a common view of rivers as continuous, longitudinal gradients in physical conditions, the RES portrays rivers as downstream arrays of large hydrogeomorphic patches (e.g. constricted, braided and floodplain channel areas) formed by catchment geomorphology and climate. The longitudinal distribution of these patches, which are identifiable using standard geomorphic techniques, varies amongst rivers and is difficult to forecast above ecoregional scales. Some types of hydrogeomorphic patches may reoccur along this downstream passage. Unique ecological 'functional process zones' are formed by individual types of hydrogeomorphic patches because of physiochemical habitat differences which affect ecosystem structure and function. The RES currently includes 14 tenets predicting how patterns of individual species distributions, community regulation, lotic ecosystem processes, and floodplain interactions will vary over spatiotemporal scales, especially as they relate to the functional process zones formed by hydrogeomorphic differences in the river network.
Analyses of stable isotope (d 13 C and d 15 N) and C:N ratios of food webs within a¯oodplain and ... more Analyses of stable isotope (d 13 C and d 15 N) and C:N ratios of food webs within a¯oodplain and a constricted-channel region of the Ohio River during October 1993 and July 1994 indicate that the increasingly in¯u-ential¯ood pulse concept (FPC) does not, for either location, adequately address food web structure for this very large river. Furthermore, results of this study suggest that the riverine productivity model (RPM) is more appropriate than the widely known river continuum concept (RCC) for the constricted region of this river. These conclusions are based on stable isotope analyses of potential sources of organic matter (riparian C 3 trees, riparian C 4 grasses and agricultural crops, submerged macrophytes,
R iverine ecosystems are some of the most diverse on Earth and provide important services (Palmer... more R iverine ecosystems are some of the most diverse on Earth and provide important services (Palmer and Richardson 2009; Strayer and Dudgeon 2010). Understanding how they function is critical to sustainable management but challenging given their complex spatial and temporal structure and multi-scale processes. Riverine systems comprise hydrological-ecological networks organized by the flow of water, sediment, nutrients, and organisms downhill and downstream and the active movement of animals uphill and upstream. Rivers are multidimensional, including longitudinal (upstream-downstream), lateral (upland to channel), vertical (hyporheic, or the zone below the stream bed), and temporal components (Ward 1989; Fausch et al. 2002). Despite this multidimensionality, many ecological processes are influenced by the rapid flow of water downhill, providing strong directional connectivity (Wiens 2002). Rivers are also organized hierarchically, with fine-scale structures (eg gravel patches) embedded within channel bed features (eg riffles), which in turn are embedded within reaches, valley segments, basins, and regions (Table 1; Frissell et al. 1986; Thorp et al. 2008). Uplands are fundamental to riverine organization, with variations in land use, land cover, and soils influencing surface-water and groundwater flow paths, thereby altering water, nutrient, and sediment fluxes to rivers (eg Lewis and Grimm 2007). Rivers are also temporally variable, partially due to hydrology that varies within and across basins and climatic regions (Poff et al. 1997). Thus, we define riverine macrosystems as hierarchical dynamic networks, influenced by strong directional connectivity that integrates processes across multiple scales and broad distances through time (Figure 1; see Heffernan et al. [2014] for macrosystem definition). Ecologists have typically studied riverine ecosystems at the scale of bed features or reaches distributed longitudinally along rivers of varying size, in an attempt to understand the strong influences that upstream and watershed processes, including human modifications, can have (Poole 2010). Our conceptualization of rivers and watersheds as "macrosystems" is a logical extension of these approaches (Figure 1). We view riverine macrosystems as repeating, interacting MACROSYSTEMS ECOLOGY
Suspension feeding by bivalves exceeds that by other planktivores in many North American rivers, ... more Suspension feeding by bivalves exceeds that by other planktivores in many North American rivers, and food webs may be altered substantially by differences in feeding patterns between native unionid mussels and invading dreissenid mussels. 2. We conducted an experiment comparing zooplanktivory by one unionid and two dreissenid species that addressed several primary questions. Is benthic planktivory important in this river? Has this linkage been altered substantially by dreissenids? Do the two dreissenid species differ in planktivory , and is this ecologically important if quagga mussels extend their geographical range? 3. Our 12-day experiment consisted of controls (no mussels) and treatments with unionid (Elliptio complanata), quagga (Oreissena bugensis) or zebra (0. polymorpha) mussels in 3500-L, 80-I.Lm mesh enclosures placed in a slackwater area of the St Lawrence River. 4. The density of the most abundant calanoid copepod Eurytemora affinis increased in the presence of dreissenids, probably as an indirect food web response. By day 12, a cumulative effect was shown by the most overwhelmingly abundant rotifer, Polyarthra, whose density declined dramatically in dreissenid enclosures compared with control and unionid enclosures. Roilier densities in unionid enclosures were not different from controls, nor were dreissenid treatments different from each other. The effects on rotifers were probably from predation, as Ch1-a did not vary among treatments. 5. We conclude that benthic-pelagic coupling via planktivory is important in slackwater areas. Dreissenids have strengthened this linkage, but range extension of quaggas should not appreciably alter effects produced by a similar biomass of zebra mussels.
Canadian Journal of Fisheries and Aquatic Sciences, 1996
A laboratory study was conducted to determine the effect of chronic turbidity (using bentonite cl... more A laboratory study was conducted to determine the effect of chronic turbidity (using bentonite clay) at medium and high temperatures on respiration of two exotic mussel species, Dreissena polymorpha and Dreissena bugensis. Populations of D. polymorpha from Lake Erie and the Ohio River and D. bugensis from Lake Erie were acclimated for 4 weeks to one of four temperature-turbidity combinations: 25°C-0 nephelometric turbidity units (NTU), 25°C-80 NTU, 15°C-0 NTU, and 15°C-80 NTU. At the end of the acclimation period, respiration was measured at both 0 and 80 NTU using a closed, flow-through system with a Clark-type polarographic microelectrode. Mass-specific respiration rates were computed as V ⋅ O 2 (= µL O 2 consumed⋅mg shell-free dry mass-1 ⋅h-1). Results showed that size, temperature, acclimation turbidity, and measurement turbidity significantly affected V ⋅ O 2 rates. An interaction between acclimation turbidity and measurement turbidity suggests that dreissenid mussels adjusted their metabolic rate in response to chronic exposure to turbidity. Mussels acclimated to higher levels (80 NTU) of turbidity did not experience as large a percent drop in V ⋅ O 2 when tested in turbid water (80 NTU) as did mussels acclimated at lower turbidity (0 NTU). Résumé : Nous avons mené une étude en laboratoire pour déterminer l'effet de la turbidité chronique (à l'aide d'argile bentonitique) à des températures moyennes et élevées sur la respiration de deux espèces de mollusques exotiques, Dreissena polymorpha et Dreissena bugensis. Les populations de D. polymorpha du lac Érié et du fleuve Ohio et de D. bugensis du lac Érié ont été acclimatées pendant 4 semaines avec l'une des quatre combinaisons suivantes de température et turbidité : 25°C-0 unités de turbidité néphélémétriques (UTN), 25°C-80 UTN, 15°C-0 UTN et 15°C-80 UTN. À la fin de la période d'acclimatement, on a mesuré la respiration à 0 et à 80 UTN à l'aide d'un système fermé en circulation avec une microélectrode polarographique de type Clark. On a calculé les taux de respiration spécifiques de la masse sous la forme V ⋅ O 2 (= µL O 2 consommé⋅mg masse sèche sans coquille-1 ⋅h-1). Les résultats ont montré que la taille, la température, la turbidité d'acclimatement et la turbidité à la mesure avaient des effets significatifs sur les taux de V ⋅ O 2. Une interaction entre la turbidité d'acclimatement et la turbidité à la mesure permet de penser que les dreissenidés ont adapté leur taux métabolique en réaction à une exposition chronique à la turbidité. Les moules acclimatées à des niveaux supérieurs (80 UTN) de turbidité n'ont pas connu une baisse aussi forte en pourcentage de V ⋅ O 2 lorsqu'on les a testées dans une eau trouble (80 UTN) que les moules acclimatées à une turbidité plus faible (0 UTN). [Traduit par la Rédaction]
Assignment of values for natural ecological benefits and anthropocentric ecosystem services in ri... more Assignment of values for natural ecological benefits and anthropocentric ecosystem services in riverine landscapes has been problematic, because a firm scientific basis linking these to the river's physical structure has been absent. We highlight some inherent problems in this process and suggest possible solutions on the basis of the hydrogeomorphic classification of rivers. We suggest this link can be useful in fair asset trading (mitigation and offsets), selection of sites for rehabilitation, cost-benefit decisions on incremental steps in restoring ecological functions, and general protection of rivers.
... Snags are an important habitat for benthic macroinvertebrates (Claflin, 1968; McLachlan, 1970... more ... Snags are an important habitat for benthic macroinvertebrates (Claflin, 1968; McLachlan, 1970; Benke et al., 1984; Thorp et al., 1985; O'Connor, 1991) and provide forage and refuge for fish (Benke et al., 1979). ... period of colonization (Thorp et al., 1985; O'Connor, 1991). ...
While the four-dimensional nature of river ecosystems has been recognized for nearly two decades,... more While the four-dimensional nature of river ecosystems has been recognized for nearly two decades, the role of lateral complexity has rarely been factored into studies of zooplankton ecology. We examined the importance of hydrologic retention areas (slackwaters) near islands and embayments of the St. Lawrence River for densities, fecundity, and diel migration of planktonic microcrustaceans. Densities of cladocera and copepods (nauplii and adult stages of cyclopoids and calanoids) were sampled from surface and deeper layers both at night (2100-0100 h, near the new moon) and during the day (1000-1400 h) for channel (deep-fast), offshore (shallow-slower), and inshore (shallow-stagnant) habitats. Average zooplankton densities increased laterally from the main channel into the slackwaters with the exception of calanoid copepods, which peaked in the intermediate depths and flows of the offshore habitats. Although the ratio of males to females for the calanoid Eurytemora affinis and the cladoceran Bosmina spp. did not differ among habitats, a greater percentage of ovigerous cladoceran females were present in slackwaters than in channel habitats. Densities of microcrustaceans were generally greater during the night than day, suggesting diel vertical migration. By demonstrating both lateral and diel differences in the spatial distribution of riverine zooplankton, we refute the view of large rivers as well-mixed homogenous systems. To the contrary, the two non-random patterns that we document imply that there is an abiotic template that at least microcrustacean potamoplankton can exploit. In turn this suggests more research into the ecological significance of the pelagic structure of other large rivers like the St. Lawrence is justified.
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