Disturbance by aquatic plant management in streams: Effects on benthic invertebrates

The effect of aquatic plant removal on benthic invertebrates and their habitat was studied in two macrophyte-rich streams of the Swiss Plateau. In each stream, habitat conditions (macrophyte biomass, current velocity, water depth) and invertebrate densities were monitored in a control reach and in a reach where plants were removed by cutting. Biological samples were taken and physical parameters measured on three dates before and six dates after plant removal in both reaches. Responses to plant removal were similar in both streams; macrophyte cutting initially decreased mean plant biomass (ca. 85%) and total number of invertebrates (ca. 65%). Variation between replicates was, however, higher in one of the streams, causing fewer effects on plants and invertebrates to be statistically significant. Plant cutting affected mainly taxa that used macrophytes as habitat (e.g. Simuliidae, Chironomidae), whereas highly mobile taxa (e.g. Ephemeroptera) and taxa living on or within the bed sediments (e.g. Trichoptera, Bivalvia) were less affected. Taxa that decreased after plant removal recovered within 4–6 months, although recovery of macrophytes was quite different in both streams. Invertebrate recovery also seemed to be seasonally dependent, with cutting having a less severe impact during summer than spring. Our results suggest that macrophytes in streams should be removed only in summer, preferably leaving some plant beds to act as refugia for phytophilous invertebrates. © 1998 John Wiley & Sons, Ltd.     

Density and distribution of epiphytic invertebrates on emergent macrophytes in a floodplain billabong

The abundance of epiphytic invertebrates living on both submerged and emergent macrophytes in lentic systems is influenced by a range of environmental features at both spatial and temporal scales. Such features include water chemistry, habitat complexity, hydrology and external influences such as climatic cycles. Dugays 2 billabong is a floodplain lake on the highly regulated, mid‐upper Murray River in southeastern Australia. Giant rush (Juncus ingens N.A. Wakefield) is the dominant habitat feature in this billabong. This plant is a simple, single‐stemmed, densely packed emergent macrophyte that fringes the littoral margins. The macrophyte habitat available to epiphytic invertebrates in this billabong is highly variable through time largely due to the variable water levels imposed by the regulated river channel for downstream irrigation needs, particularly through summer. To investigate both spatial and temporal patterns in the epiphytic invertebrates of Dugays 2 billabong, invertebrates were sampled within giant rush stands on five occasions over one year. Spatial variability in epifaunal density was generally low, while temporal densities were highly variable through time. Spatial patterns of invertebrate abundance revealed few associations with habitat structure or water quality, apart from those associated with water depth, particularly when sampling had been preceded by fluctuating water levels. High temporal variability in assemblage structure of the epifauna reflects the high background environmental variation that occurs in this system. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of plant community composition and exposure to wave action on invertebrate habitat use of Lake Huron coastal wetlands

Invertebrate communities from different coastal marsh‐plant communities were compared along wave‐exposure gradients using data from 1994, 1998 and 1999. Data were subjected to correspondence analyses to search for patterns in invertebrate communities in relation to plant‐community structure and wave exposure. In 1994, quantitative plant‐ and sediment‐invertebrate samples were taken from nine habitats: four from inland, subsurface‐connected marshes and five from littoral, emergent marshes. In 1998, sweep‐net samples were taken from 13 plant communities: six on the exposed and seven on the protected side of an island. In 1999, 2–3 plant communities/sites were sampled with sweep nets from four sites around the Bay so that intersite differences between inner, less‐exposed and outer, more‐exposed habitats could be examined. In all three studies, correspondence analyses separated inland, protected or inner sites from littoral, exposed or outer sites, suggesting differences in invertebrate‐community structure. For example, Hydracarina and Asellidae occurred in large numbers in inland sites, but were less common or absent from exposed, littoral sites. Littoral marshes also separated along an exposure gradient with Tanytarsini and Orthocladiinae collectors of organic particles occurring in very high numbers in outer, exposed areas where organic particles from the pelagic zone entered the marsh. Certain plant‐community types clustered together (e.g. wet meadow and Scirpus) while others, such as Typha, stands clustered according to exposure to waves suggesting the importance of both plant‐community structure and wave exposure in determining invertebrate‐community structure. We present a conceptual model that suggests that invertebrates in Great Lakes' marshes are distributed along gradients of decreased mixing of pelagic water and increases in sediment organic matter from outer to inner marsh and between littoral and adjacent inland marshes. Some invertebrates do best on one end of these gradients, while the majority are generalists found across habitat types.     

Temporal shifts in the biodiversity of nearshore small fishes in Lake Simcoe

Nearshore small fish species represent a large proportion of fish biodiversity in Lake Simcoe, a large inland lake in southern Ontario, Canada. Over the past 30 years, Lake Simcoe has experienced several changes to its aquatic habitat, benthic invertebrate communities and predatory fish populations. This study compared samples of the nearshore small fish community in three geographic areas of Lake Simcoe. Fish community data were grouped into two time periods: a contemporary period (2007–2009) and a historical period (1982–1995). The fish community was compared across time periods for each area to assess if observed ecological changes had an impact on the small fish community. Species richness significantly declined between time periods in two areas (Cook's Bay and the southeast shoreline), the number of individuals captured declined between time periods in one area of the lake (Kempenfelt Bay) and Simpson's diversity index declined between time periods in one area of the lake (southeast shoreline). There were no significant differences in the Shannon–Weiner evenness index between time periods in any of the study areas. Additional analyses of intra- and inter-annual variation in fish sampling results generally supported the findings that shifts in the fish community occurred between time periods. Overall, this study suggests that the nearshore small fish biodiversity of Lake Simcoe has shifted over time but these shifts are not clearly related to recent increases in water clarity, macrophyte growth and nearshore benthic invertebrate densities.     

Effects of hydropeaking on benthic invertebrate community composition in two central Norwegian rivers

Hydropower regulations can have dramatic impacts on river ecological communities. The operation of hydropower stations is related to power demands, but their releases in the receiving water body causes sudden changes in flow, which in turn affect the biota. The effects of such flow variations on benthic invertebrates is not fully understood. Here, we studied the effects of duration and intensity of hydropeaking on benthic invertebrates in two rivers over a 3.5‐year period. We used both quantitative (Surber) and semiquantitative (kick samples) sampling methods to compare the ramping zone with the permanently water covered zone downstream of the hydropower plant, and with corresponding unaffected upstream areas. The ramping zone had a different invertebrate community composition and lower benthic density than other areas, especially after hydropeaking. Mayflies and chironomids were most negatively affected by hydropeaking and oligochaetes largely unaffected. Chironomids and the mayfly Baetis rhodani were able to recolonize the ramping zone and almost reach densities similar to deeper areas within 48 days following hydropeaking. The relative abundance of filter feeders tended to increase and gatherers/collectors tended to decrease from the ramping zone towards the deep, permanently water covered areas. In corresponding areas upstream of the power plant, the relative abundance of different functional feeding groups was the same in the mid‐channel and shore sites. Our study shows that hydropeaking has clear impacts on the functional structure of benthic invertebrates below the power plants. The ecological impact of hydropeaking on invertebrate communities should thus be taken into account, for example, by reducing the amplitude and duration of flow fluctuations.     

Benthic Invertebrate Community Responses to Round Goby (Neogobius melanostomus) and Zebra Mussel (Dreissena polymorpha) Invasion in Southern Lake Michigan

The round goby (Neogobius melanostomus Pallas), a fish native to eastern Europe, recently has become established in southwestern Lake Michigan. Because round gobies prey on zebra mussels (Dreissena polymorpha Pallas) and other benthic invertebrates, the effects of round gobies on invertebrates within zebra mussel colonies was investigated. Using a 2 × 3 factorial design, the effects of round gobies (present or absent) and zebra mussel densities (zero, low, and high) on non-mussel invertebrates was examined. Ten ceramic tiles of each mussel density were colonized in the laboratory and then anchored in Calumet Harbor, IL for 10 weeks. Round gobies had access to half the tiles while half were covered with coarse mesh screening that excluded round gobies, but allowed invertebrates to move into and out of the exclosures. Low and high zebra mussel density tiles supported significantly greater numbers of non-mussel invertebrates (p < 0.001) than zero density tiles, particularly amphipods (p < 0.001), hydroptilid caddisflies (p < 0.05), isopods (p < 0.05), and chironomids (p < 0.001). Chlorophyll a concentrations were highest (p < 0.001) at low zebra mussel densities. The presence of round gobies significantly reduced densities of total non-mussel invertebrates (p < 0.01) and leptocerid caddisflies (p < 0.05), resulting in a significant increase in chlorophyll a (p < 0.01) concentrations. A significant zebra mussel density x round goby interaction showed that total invertebrate biomass responded positively to the combined effect of high zebra mussel density and round goby absence. These results demonstrate that round gobies and zebra mussels are altering benthic invertebrate community structure and algal resources in nearshore rocky areas of southwestern Lake Michigan.     

Effects of seasonal hypoxia on macroinvertebrate communities in a small reservoir

Localized hypoxia can reduce available habitat, restrict movement and limit the abundance of aquatic invertebrates. Although cultural eutrophication, coupled with the effects of climate change, is likely to increase the frequency and extent of hypoxia in aquatic ecosystems, little is known about how oxygen gradients in small reservoirs influence spatial distribution and abundance of aquatic invertebrates. The present study evaluated the effects of environmental and biological attributes on seasonal and spatial variation of macroinvertebrates and explored how hypoxic conditions influenced littoral, benthic and pelagic macroinvertebrate communities in Lake Alvin, South Dakota. Data on reservoir conditions, in conjunction with macroinvertebrate sampling from May to October 2009–2011, were applied in an information theoretic approach to evaluate factors affecting invertebrate abundance. Hypoxic conditions were present from May to September in the lacustrine zone impacting 10%–39% of the water column. Benthic invertebrates were typically absent from the lacustrine zone during periods of severe hypoxia and were most abundant in the shallow, well-oxygenated riverine zone. Littoral invertebrates were negatively related to the per cent of the hypoxic water column, suggesting fish, confined to shallow waters by hypoxia, may be consuming a larger portion of littoral invertebrates in their diets. Cladocera and Copepoda densities were influenced primarily by water depth and monthly precipitation. The larger size of Daphnia found in the hypoxic-prone transitional and lacustrine zones suggested low oxygen concentrations may provide a refuge from fish predation. The results of the present study demonstrated spatial variations in near-bottom oxygen concentrations were important predictors of macroinvertebrate and zooplankton abundance and size structure in Lake Alvin and that macroinvertebrates, particularly benthic and littoral invertebrates, could benefit from measures taken to reduce summer hypoxia.     

Lake Champlain offshore benthic invertebrate community before and after zebra mussel invasion

Benthic invertebrates are important bio-indicators of water quality and play a significant role in aquatic systems. Lake Champlain has limited benthic invertebrate data which hinders development of food web models, assessment of invasive species impacts, and evaluation of management actions. In June 2016, we assessed benthic invertebrates along three transects in the main basin of Lake Champlain ranging from 5 to 100?m, and then compared results to densities from a limited survey in 1991 prior to the zebra mussel (Dreissena polymorpha) invasion. In 2016, total biomass and density were 1–2 orders of magnitude greater at 5?m than at 20–100?m. Zebra mussels, chironomids, oligochaetes, and gastropods were dominant at 5?m, and oligochaetes and sphaeriids were dominant at 20–100?m. Total density at the 5-m site was 94% lower in 2016 compared to 1991, but similar at the 100-m site. Diporeia, while abundant in many freshwater bodies, is historically rare in Lake Champlain and was not detected in our sampling. Because Lake Champlain benthic invertebrate densities are low and display dissimilar distributions to the Great Lakes, we hypothesize the offshore fish community is likely much more reliant on pelagic rather than benthic production. Although the current composition and biomass suggest the benthic community in Lake Champlain may not be greatly impacted by an invasion of quagga mussel (D. rostriformis bugensis), the potential for quaggas to re-route energy from pelagic to benthic habitats, as it has in the Great Lakes, could limit the Lake Champlain offshore fish community.     

Effects of flow regulation and sediment flushing on instream habitat and benthic invertebrates in a New Zealand river influenced by a volcanic eruption

I sampled five sites above and below a dam in the central North Island of New Zealand on five to six occasions to examine the effects on benthic substrates, periphyton and invertebrate communities of (i) degree of flow regulation and (ii) flushing of sediment stored behind a dam. A series of volcanic eruptions during the course of this study provided the opportunity to investigate the effects of a period of high sediment delivery on this regulated river. The operation of the dam prior to sluicing of stored sediment appeared to have little impact on substrate size distribution or fine suspendable sediment levels. Periphyton biomass was markedly higher below than above the dam when sampling was preceded by a period of stable baseflow, but over all sampling dates biomass and inorganic content of periphyton did not appear to be related to degree of flow regulation. The taxonomic richness, biomass and density of invertebrate communities were lowest directly below, rather than above, the dam on most dates, and the site below the dam differed significantly from some of the downstream sites. However, changes in invertebrate abundance and diversity generally did not follow the expected gradient of flow regulation impacts except for the mayfly Deleatidium. Multiple regression analyses implicated substrate size and the biomass and inorganic content of periphyton as significant predictor variables for invertebrate density, biomass and taxonomic richness on sampling dates not influenced by recent sediment flushes, whereas degree of flow regulation was a significant predictor for densities of the dominant chironomid Cricotopus. The volcanic eruption led to deposition of fine silt that had passed through the dam with the residual flow and coarser sediments released during subsequent dam flushes. Flushing of stored sediment during large floods increased levels of sand and gravel directly below the dam and upstream of a large island in the middle reaches of the river, and also appeared to increase scouring of periphyton and associated invertebrates downstream. Overall, invertebrate communities in the study reach appeared to be structured more by periphyton accrual patterns, changes in substrate composition, the occurrence of large floods and natural longitudinal gradients than degree of flow regulation. These findings suggest that site‐specific and large‐scale factors can obscure generalized reach‐scale patterns expected along regulated rivers. Copyright © 2002 John Wiley & Sons, Ltd.     

Periphyton and invertebrate response to wood placement in large pacific coastal rivers

Wood abundance in aquatic systems has been dramatically reduced compared to historical levels due to anthropogenic activities that led to wood removal and stream simplification. As a result, reintroduction of wood to aquatic systems is now a widely used and relatively well‐studied restoration technique for increasing habitat complexity. Although stream periphyton (biofilm) and invertebrates serve as food sources for a variety of predators including fish, birds and bats, data on how lower trophic levels respond to wood placement are relatively scarce. The purpose of this study was to test the hypothesis that periphyton biomass and aquatic invertebrate density were higher on Engineered Log Jams (ELJs) than on inorganic substrates in two large Pacific Northwest river systems. Among years and rivers, periphyton biomass and invertebrate densities were significantly higher on ELJs than on cobbles within the same reach. Invertebrate communities on ELJs were dominated by meiofauna (<500 µm), whereas cobbles were dominated by larger chironomids. We attribute these trophic level differences to substrate type, as we did not detect taxonomic differences between cobbles in reaches with and without ELJs. We show that adding wood to reaches with little or no naturally occurring wood increased overall habitat surface area and thereby the potential for increased productivity relative to reaches with low levels of wood. Finally, wood supports a unique community of invertebrates that are often overlooked in lotic system studies but may be contributing substantially to overall biological diversity. Published in 2009 by John Wiley & Sons, Ltd.     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.     

Macroinvertebrate assemblages of littoral habitats in the Macquarie and Mersey rivers,Tasmania: Implications for the management of regulated rivers

Littoral habitats in large rivers are influenced to varying degrees by changes in discharge. Irrigation abstractions can increase the amount of habitat that would naturally be dewatered during low flow periods and therefore it is important to have some knowledge of the potential impact this may have on riverine macroinvertebrates. The macroinvertebrate assemblages of common littoral habitats in riffles, pools and runs in two reaches each of the Macquarie and Mersey Rivers, northern Tasmania, Australia were compared from samples collected during the low flow and irrigation season, between December 1991 and April 1992. The area under water of these habitats, riffle substrata, macrophyte beds and coarse woody debris, responded differently to changes in discharge. Within a reach, the same taxonomic groups often dominated the total number of macroinvertebrates for all habitats, but there were differences in the proportions contributed by these taxa to the different habitats. In general, taxa characteristic of slow-flowing or lentic habitats, such as ostracods and amphipods, were dominant in macrophyte beds in pools and runs, whereas taxa such as larval elmid beetles and hydropsychid caddisflies were dominant in riffles. A substantial component of the fauna from each habitat within a reach was unique to that habitat, but there was always a similar number of taxa common to all habitats. Classification and ordination grouped samples from both rivers firstly by habitat and secondly by month and reach. Total density and family richness of invertebrates differed by reach, habitat and month in both rivers, except for richness in the Mersey River where habitat was not significant. Differences in densities and numbers of invertebrate families among habitats were not consistent between reaches for each river. This study has highlighted the differences in macroinvertebrate assemblages of several littoral habitats in two lowland rivers in Tasmania. Differences in taxonomic composition, density and richness among habitats within reaches strongly imply the uniqueness of these habitats in terms of the invertebrate faunas that occupy them. We suggest that if maintenance of biotic diversity is an aim of instream flow management, water allocations that address low flows should place a high priority on the maintenance of a diversity of habitats.     

Responses of lake macrophyte beds dominated by Eurasian watermilfoil (Myriophyllum spicatum) to best management practices in agricultural sub-watersheds: Declines in biomass but not species dominance

Long-term studies of macrophyte beds growing near streams in Conesus Lake, New York, have revealed a high biomass and continuing dominance of the invasive rooted species Eurasian watermilfoil (Myriophyllum spicatum). We tested whether agricultural best management practices (BMPs) designed to reduce tributary nutrient and soil loss from the watershed could reduce populations of Eurasian watermilfoil downstream in the lake littoral. Six macrophyte beds were monitored during a 3-year baseline period (2001–2003) prior to the implementation of BMPs and for a 4-year experimental period after a variety of agricultural BMPs were implemented in three sub-watersheds. For three macrophyte beds downstream from sub-watersheds managed as part of our project, quadrat biomass decreased by 30–50% and was statistically lower than Pre-BMP baseline values in 7 of 11 experimental sample years. Biomass loss primarily in the form of the dominant Eurasian watermilfoil ranged from 6.2 to 10 t wet weight for each bed. The declines in biomass coincided with significant annual and January–August decreases in the concentrations and fluxes of dissolved nutrients, total phosphorus, and total suspended solids in nearby streams. For three macrophyte beds downstream from watersheds in which landowners applied less extensive or no new agricultural management, biomass was statistically indistinguishable from Pre-BMP baseline values in all 12 experimental sample years. Milfoil remained the overwhelmingly dominant species at all sites during the entire study period. These results provide impetus for the use of watershed nutrient management to control the nuisance growth of Eurasian watermilfoil on a local scale in the lake littoral.     

Effects of water level fluctuations on Vallisneria nana in the Burnett River in Southeast Queensland,Australia

Changes in aquatic macrophyte populations in the Burnett River in southeast Queensland, Australia are described with respect to the effects of water level fluctuations and possible impact on the Queensland lungfish (Neoceratodus forsteri). This protected fish relies on macrophyte beds as spawning and nursery areas. Studies were conducted prior to, during and following construction of a new weir on the river. Comparative results of impounded and non‐impounded sites were conducted to investigate seasonal and inter‐annual changes in macrophytes and the effects of both a rapid rise in water level when the impoundment first filled and a decline, on new plants in shallow water. Macrophyte communities in newly inundated areas were studied to determine the time taken for seedlings to emerge and reach a cover sufficient to represent spawning habitats for the lungfish. Vallisneria nana dominated the macrophyte beds, which were scoured from the river by a large flow event in May 1998, the effects of which persisted for at least 1 year. Most newly emerging seedlings of Vallisneria perished following a small decline of 7 cm in water level. Decrease in plant biomass and death of established plants in highly turbid water resulted within 6–9 weeks following larger water level rises of 4.0–5.5 m in the new impoundment. In the period leading up to the lungfish‐spawning season at least 5 months is required for submerged plants to reach the 90% cover preferred for spawning. Implications of the results for water level management and lungfish populations are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Planktonic interactions with an austral bias: Implications for biomanipulation

The conceptual model of trophic structure in a typical north temperate lake that underlies attempts at biological manipulation to improve water quality is reviewed in relation to the trophic structure and community composition of planktonic food webs in New Zealand and Australian lakes. New Zealand's relatively simple food webs are characterized by an absence of obligate piscivores and few vertebrate and invertebrate planktivores; manipulation of fish stock to improve water quality has not been attempted. The largest crustacean zooplankton in Australasia, and potentially the most effective grazers of phytoplankton, are Daphnia carinata and calanoid copepods (Boeckella spp.). Their potential capacities to remove algae and colonial cyanobacteria (Microcystis, filamentous forms) from waterways are discussed in relation to colony size and concentration, toxicity, selectivity, and digestibility. The potential of D. carinata to suppress rates of increase in phytoplankton biomass may be lowered by its sensitivity to crowding and starvation, and its susceptibility to predation by fish. Decisions to use biomanipulation as a management tool to improve water quality should be based on the results of a whole lake study and take into consideration relevant obligations to preserve the biodiversity of native species, and curb the spread and dominance of exotic species. Programmes that are based on reductions in biomass of planktivorous fish should be complemented by control of nutrient loads (integrated management).     

Effects of Three Consecutive Rotenone Treatments on the Benthic Macroinvertebrate Fauna of the River Ogna,Central Norway

The effects of piscicides on aquatic invertebrates are often studied after one treatment, even though piscicides may be repeatedly applied within river management. Here we investigate the impacts of repeated piscidie treatment on riverine benthic invertebrates. The River Ogna, Norway, was treated with rotenone three times over a 16‐month period. The two first treatments caused temporary density reduction of a few rotenone sensitive benthic invertebrate taxa. Effects of the third treatment were variable with some taxa unaffected while all Plecoptera, were locally extinct. The toxic effect of rotenone increases with water temperature and high water temperature (20 °C) combined with high rotenone concentration was probably the main reason why the benthic community in the third treatment was more negatively affected than during the two previous treatments (4 and 8 °C). Eight months after the treatment benthic densities had not reached pre‐treatment levels, but most taxa had recolonized the treated area within a year. Our data suggest that the severe effects of the third treatment were not influenced by the two former ones. This implies that the timing of piscicide treatment has a greater impact on the benthic invertebrate community than the number of treatments. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamics of river fish populations in response to hydrological conditions: a simulation study

Increasing multi‐sectoral demands on water resources have led to water abstraction and transfer activities, and the construction of dams and embankments that have significantly altered the flood regimes of rivers throughout the world resulting in the loss of fish production and biodiversity. The current emphasis on sustainable development and biodiversity conservation is leading efforts to mitigate these impacts by means of interventions such as the release of artificial floods downstream of dams and the manipulation of water levels within impounded floodplains. Whilst much work has been done to determine the hydrological requirements for the maintenance of salmonid populations, few equivalent studies are available from which to develop criteria for the management of hydrological regimes for fishes and fisheries in large floodplain–river systems such as the Mekong. The population dynamics of fish in such rivers are believed to respond to hydrological conditions in a density‐dependent manner. An age‐structured population dynamics model incorporating sub‐models describing density‐dependent growth, mortality and recruitment was used to explore how hydrological conditions within a theoretical floodplain–river system affect the dynamics of a common floodplain–river fish species. Graphical summaries of the response of exploitable biomass to a range of different drawdown rates, dry and flood season areas and volumes, and flood season durations are presented under five different model assumptions concerning density‐dependent processes. Optimal flooding patterns are also described for the model species and theoretical river system. The patterns of predictions that emerge from the simulations provide guidelines for managing or manipulating hydrological conditions in river systems for both fixed and variable volume hydrological scenarios. As a general rule of thumb, exploitable biomass is maximized by minimizing the rate of drawdown and maximizing the flood duration and flood and dry season areas or volumes. However, experiences from dam and other hydraulic engineering projects suggest that these predictions should be treated with caution until we better understand the influence of hydrology on spawning behaviour, system primary production, and critical habitat availability. Copyright © 2004 John Wiley & Sons, Ltd.     

PERSISTING EFFECTS OF RIVER REGULATION ON EMERGENT AQUATIC INSECTS AND TERRESTRIAL INVERTEBRATES IN UPLAND FORESTS

River regulation can alter the structural complexity and natural dynamics of river ecosystems substantially with negative consequences for aquatic insects. However, there have been few studies of regulation effects on the export of emergent insects into terrestrial ecosystems. In northern Scandinavia, we compared emerged aquatic insect and terrestrial invertebrate biomass between four strongly regulated and four free‐flowing rivers using fortnightly measurements at three upland‐forest blocks in each over one summer. The biomass of emerged aquatic insects was significantly lower along regulated rivers than free‐flowing rivers. Biomass in Linyphiidae, Opiliones, Staphylinidae, total Coleoptera, Formicidae and total terrestrial invertebrates was also lower along regulated rivers. Aquatic insect biomass did not explain the entire regulation effect on terrestrial invertebrates but did explain significant variations among Linyphiidae, total Coleoptera, Formicidae and total terrestrial biomass. Variations in Formicidae also explained significant variance among several terrestrial taxa, suggesting some keystone role in this group. Overall, our results suggest that river regulation affects upland‐forest invertebrate communities, with at least some of these effects arising from links between aquatic emergence and terrestrial predators. The data highlight the need to consider areas beyond the riparian zone when assessing the effects of river regulation. Copyright © 2012 John Wiley & Sons, Ltd.     

Fish species richness is a key predictor of community biomass and productivity in littoral regions of Severn Sound,an embayment of southern Georgian Bay,Lake Huron

Catches from standardized littoral electrofishing (EF) surveys (1990–2016) at various locales in Severn Sound, Georgian Bay, were analyzed. Catches were adjusted for size-selectivity using published results of laboratory immobilization experiments. Adjusted abundance-mean size relationships were consistent with the metabolic theory of ecology where body size has a central role in structuring community features. Relationships among species richness and areal estimates of biomass and annual production of the adjusted catches were assessed. Richness was the key variable driving other community metrics and was, in turn, largely driven by habitat fetch metrics and sampling time of day. Richness, biomass, and production decreased with increasing maximum effective fetch. Richness increased with time after sunset. Year and locale had smaller roles in variation of community metrics with more vegetated/ less urbanized areas having higher values. Higher fish production is expected in sheltered areas where the contributions of allochthonous and benthic primary production are expected to be greater. Further analyses using additional EF datasets from Great Lakes’ littoral zones should increase understanding of the differences between littoral and offshore fish productivity and help guide management of littoral habitats to ensure healthy fish communities.     

Fish and Macroinvertebrate Communities in Tributary Streams of Eastern Lake Erie with and without Round Gobies (Neogobius melanostomus, Pallas 1814)

Round gobies have had significant impacts on benthic fish and invertebrate communities in nearshore habitats of the Great Lakes. As round gobies have become more abundant in lake habitats, there has been an expansion of their populations into tributary streams and rivers. We compared stream invertebrate and fish communities in New York tributaries to Lake Erie with round gobies present and absent. Four of six benthic invertebrate metrics differed between streams with and without round gobies. Streams with round gobies present had reduced Shannon diversity, EPT richness, and EPT/chironomid ratios, and increased macroinvertebrate density relative to streams without round gobies, but there was no difference in non-Diptera density, or total taxa richness. None of the four fish metrics examined differed between streams with and without round gobies. However, darters occurred in all streams lacking round gobies, but did not occur in any streams with round gobies. Comparisons with historical fish and macroinvertebrate distributional data support our suspicion of goby-induced community changes. In these New York streams, round gobies seem to have had significant impacts on invertebrate communities via their consumptive behavior, whereas the impacts on fish communities are less evident. If round gobies continue to expand their distribution inland, the resultant alterations in macroinvertebrate communities may impact the suitability of tributary streams as spawning and nursery habitat for several sport fish species and for energy dynamics in tributary streams.