Evaluating the Effects of Habitat Patchiness on Small Fish Assemblages in a Great Lakes Coastal Marsh

Wetlands are naturally heterogeneous ecosystems with resident species adapted to patchy environments. We measured how assemblages of small fish varied among four natural patches of coastal marsh in Mismer Bay, Lake Huron, USA. We sampled patches continuously for extensive time periods to describe both spatial and temporal fish distribution patterns. Fish richness and distribution varied spatially with some species restricted to one or two patches, such as Phoxinus eos and Margariscus margarita, and others widely distributed, such as Pimephales notatus and Culaea inconstans. For ubiquitous species, patch utilization varied temporally, which was explained by variation in habitat characteristics, such as macrophyte richness and growth form diversity, emergent macrophyte stem density, water temperature and depth. Northern Great Lakes coastal marshes are not static environments, and intensive sampling illustrates the dynamic interactions between fishes and this successional marsh environment. We conclude that extended sampling protocols in patchy, temperate wetlands are preferable to short surveys for making accurate evaluations about the spatio-temporal habitat utilization of fishes.     

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.     

Characterization of natural biofilms in temperate inland waters

Community dynamics of microalgae in natural biofilms grown on 10 × 3 cm glass slides were studied in three inland water systems in Central Ontario, Canada. The periphyton communities were analyzed for species composition, diversity, density and biofilm thickness. The usefulness of periphyton community dynamics and species diversity in water quality monitoring was tested. The density of microalgae varied from 2.4 × 10⁷/cm² (Lake Couchiching) to 18 × 10⁷/cm² (Lake Simcoe) with highest species diversity at Lake Couchiching. Lake Simcoe with its moderately high phosphorus and low organic carbon showed the highest density of microalgae while Lake Couchiching with lowest total phosphorus and highest organic carbon showed the lowest density of microalgae in biofilms. The results of analysis of variance showed significant variation in the number of genera, density, biofilm thickness and diversity of microalgae in the three sampling locations. The Mill Creek site with minimum anthropogenic disturbance, minimum light availability, lower water temperature and slow but steady flowing conditions recorded the lowest species diversity and number of genera. The dominant genera of diatoms were significantly different in the three sampling locations. This study thus showed the usefulness of periphyton community dynamics in the assessment of water quality in the inland water systems.     

The Impacts of the Non-native Macrophyte Cabomba caroliniana on Littoral Biota of Kasshabog Lake,Ontario

An established population of Cabomba caroliniana now covers extensive littoral areas in the shallow waters of Kasshabog Lake (Ontario). This is the first known naturalized population of this non-native aquatic macrophyte, commonly called fanwort, on the Canadian side of the Great Lakes basin, despite the fact that it was first reported in the 1930s. High dispersal potentials combined with the ability to adapt and grow in a range of environmental conditions have made C. caroliniana a nuisance species in Australia, Japan, and parts of the United States. However, little is known about the broader ecological implications of its introduction and establishment. Using a survey approach, we conducted a preliminary assessment of water chemistry, macrophyte, epiphytic algae, and macroinvertebrate communities found in C. caroliniana beds and compared them with native macrophyte beds in Kasshabog Lake. Light penetration was significantly reduced in the C. caroliniana beds and was the only sampled physio-chemical parameter that differed between bed types. We also found several notable differences in the structure and composition of biological communities within macrophyte beds. While native macrophytes were present in dense C. caroliniana beds, abundance was considerably low and unevenly distributed. Significantly more epiphytic algae was present on C. caroliniana plants, however community composition was comparable with epiphytic algae found on native macrophytes. The taxonomic composition of macroinvertebrates was similar between C. caroliniana and native beds, while abundance was substantially higher in C. caroliniana beds, owing to high densities of coenagrionids and chironomids. These differences suggest that C. caroliniana is changing macrophyte community composition in this lake, having an impact on epiphytic algae, and creating a new habitat for some macroinvertebrates. Further studies are required to determine the extent of these ecological impacts.     

Periphyton contribution to nitrogen dynamics in the discharge from a wastewater treatment plant

To evaluate the importance of periphyton to nitrogen dynamics in the discharge from wastewater treatment plants (WWTPs), we examined changes in total and inorganic nitrogen content downstream from a WWTP on the Kurose River in Hiroshima Prefecture, Japan. At 0.7 km downstream of the WWTP (point A), NH₄⁺?N was the dominant form of inorganic nitrogen, but concentrations decreased rapidly to 5 km downstream (point B). In contrast, no significant change in the [NO₂^?+ + NO₃^?]?N concentration was observed between the two points. Total nitrogen (TN) load decreased significantly between the two points, suggesting that sorption and/or denitrification occurred in the river channel. Potential rates of nitrogen sorption and transformation by periphyton were determined in a loboratory experiment in which changes in the nitrogen content of river water were examined in an acrylic chamber with periphyton. Nitrification and nitrogen removal occurred mainly in the periphyton. The contributions of periphyton activity to TN and NH₄⁺?N decrease in the field, as estimated from the results of the laboratory experiments, were 6–18% and 23–72%, respectively. These results suggest that periphyton plays an important role in decreasing NH₄⁺?N concentration in the discharge from wastewater treatment plants.     

Effects of Food Type,Habitat, and Fish Predation on the Relative Abundance of Two Amphipod Species,Gammarus fasciatus and Echinogammarus ischnus

We evaluated the abundance patterns of Gammarus fasciatus and Echinogammarus ischnus in dreissenid and macrophyte areas in Hatchery Bay, Lake Erie before (1997) and after round goby (2001, 2002) invaded the area. Total amphipod abundance was higher before round goby invasion in both habitats. In mussel beds, E. ischnus abundance was similar or significantly higher than G. fasciatus. In macrophytes, G. fasciatus was significantly more abundant than E. ischnus. In laboratory experiments, we compared amphipod survivorship and growth when fed mussel feces and pseudofeces (F+P) or macrophytes with epiphytes (M+E). Gammarus fasciatus survivorship and growth were higher when fed F+P than M+E. Echinogammarus ischnus showed similar survivorship under both diets, but significantly higher growth when fed M+E than F+P. Therefore inter-habitat differences in food resources cannot explain the abundance patterns observed in the lake. We also estimated the relative vulnerability of G. fasciatus and E. ischnus to yellow perch (Perca flavescens) and round goby (Neogobius melanostomus) predation in laboratory feeding trials using mussel colonies or macrophyte beds as substrate. Both fish strongly preferred E. ischnus in macrophytes, but consumed relatively more G. fasciatus than E. ischnus in dreissenid habitats. Our results suggest that dreissenid establishment may have facilitated the invasion of E. ischnus. However, habitat-specific differences in vulnerability to fish predation may mediate the coexistence of G. fasciatus and E. ischnus by minimizing expansion of E. ischnus to macrophyte areas. Our results also suggest that round goby invasion can alter amphipod abundance patterns in Lake Erie.     

Impacts of different weed cutting practices on macrophyte species diversity and composition in a Danish stream

Various effects of stream management on biotic communities have been suggested on the basis of observations and investigations in regularly managed streams throughout Europe, but only very sparse information is available about if and how stream management can be combined with maintaining a natural and diverse stream flora. Our study was carried out to investigate how weed cutting practice and frequency can affect macrophyte communities to provide knowledge for future decisions regarding management in streams. We chose an experimental approach and applied four different weed cutting practices (cutting full width, central channel, diagonal channels and no cutting) and frequencies within one stream reach for four years. We found only very limited changes over the four years in overall macrophyte diversity parameters following different management practices and there were no changes in macrophyte diversity parameters either as a function of the weed cutting frequency or method applied. In contrast we found directional changes in macrophyte composition following frequent cuttings of either the whole stream channel or a less comprehensive cutting of only one central channel for four years. In both cases the macrophyte communities changed towards a more Ranunculus dominated community while Potamogeton natans became less important in the community. This change seemed to reflect a higher tolerance of Ranunculus towards disturbance. On the basis of these results, we recommend that the management frequency in streams is limited and, if several cuttings are needed to prevent bank over‐flow, cutting in several narrow channels is preferable to cutting in one central channel as directional changes in plant communities are avoided. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of pulsed flows on nuisance periphyton growths in rivers: a mesocosm study

Rivers regulated by dams are typically characterized by altered biotic communities and habitat structure in downstream reaches. In the Jackson River (Alleghany Co., VA), a relatively constant flow regime below Gathright Dam and anthropogenic nutrient loading have apparently contributed to nuisance levels of periphyton (>300 mg chlorophyll a m^?2). These nuisance growths cause low dissolved oxygen concentrations in the water column and altered benthic habitats in the Jackson River. The use of periodic pulsed flows has been suggested as a restoration practice that could potentially reduce periphyton biomass. We investigated the effects of increased flow on periphyton chlorophyll a (chl a), ash‐free dry mass (AFDM), % organic matter (%OM) using streamside channels in which periphyton‐colonized tiles were subjected to near‐bed velocities ranging from 20 (control) to 240 cm s^?1. Analysis of variance (ANOVA) and regression were used to examine periphyton responses to velocity treatments. There was a significant decrease in chl a and AFDM, and significant increase in %OM in velocity treatments of 150, 180 and 240 cm s^?1 (p < 0.001), but not in lower velocity channels. Regression analyses showed a significant positive relationship with %OM (r² = 0.88) and significant negative relationship with chl a (r² = 0.77) and AFDM (r² = 0.63). Algal taxa were dominated by Cladophora glomerata, Melosira varians and Pleurosira laevis. There was a significant positive relationship between treatment velocity and % C. glomerata (p = 0.007, r² = 0.87) as diatoms were differentially removed with increasing treatment velocity. Our results demonstrate that pulsed flows can reduce periphyton standing crops in the Jackson River, but the discharge required to achieve this reduction would probably need to produce near‐bed velocities >100 cm s^?1. Further study is needed to establish specific flow targets and evaluate the direct and indirect effects of pulsed flows on ecological conditions in the Jackson River. Copyright © 2009 John Wiley & Sons, Ltd.     

Large variation in periphyton δ13C and δ15N values in the upper Great Lakes: Correlates and implications

Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) are frequently used to examine food web structure. Despite periphyton's importance to lake food webs, little is known about spatial variation of periphyton δ¹³C and δ¹⁵N values in the Great Lakes. We present periphyton δ¹³C and δ¹⁵N values from 28 sites the upper Great Lakes, including Lake Superior, the north shore of Lake Michigan, and Green Bay. We also examined variation in periphyton isotope values relative to several water quality parameters (TP, TN, TKN, NO₃⁻, K_d) as well as periphyton C:N. There was a large range in both periphyton δ¹³C (range = 13.5‰) and δ¹⁵N (range = 10.2‰) among sites. Periphyton in more eutrophic sites had more depleted δ¹³C and more enriched δ¹⁵N compared to more oligotrophic sites. Our finding of high variability in periphyton isotope values in the Upper Great Lakes has implications for stable isotope-based reconstructions of food web structure.     

Phosphorus uptake and active growth of Elodea canadensis Michx. and Elodea nuttallii (Planch.) St. John

Two related submerged freshwater macrophyte (Elodea nuttallii (Planch.) St. John and Elodea canadensis Michx.) were used in a combination of in- and outdoor experiments to compare growth rates and routes of phosphorus uptake, translocation and possible excretion. Elodea nuttalli had a higher growth rate than Elodea canadensis both in the field and under laboratory conditions.The uptake and translocation of phosphorus was studied using ³²P in a partitioned container. Roots and leaves were supplied with ³²P separately and simultaneously Both macrophyte species were able to take up phosphorus both with leaves and roots. The uptake rate of ³²P by roots was higher in Elodea nunallii when tracer was supplied to the root compartment only. Leaf uptake was stimulated by the supply of phosphate to both compartments, and the uptake was faster and reached a higher level than when the tracer was injected to the leaf compartment only. The ³²P uptake by either roots or leaves was translocated. Shoot-to-root translocation predominated over the reverse. There was no significant difference between both species in root uptake rates, but leaf uptake was significantly higher in Elodea canadensis. The two studied Elodea species do not have a strong preferential source of phosphorus.     

A Decade after Invasion: Evaluating the Continuing Effects of Rusty Crayfish on a Michigan River

In 2004, we revisited a Michigan stream invaded by rusty crayfish (Orconectes rusticus) to determine if this species continued to expand its downstream range and negatively impact the stream food web. Compared to a 1992 study, we predicted that rusty crayfish would increase in density and downstream distribution from a small lake, resulting in further reduction of in-stream resources such as organic matter, benthic invertebrates, and periphyton. To determine current crayfish distributions and impacts, we conducted a longitudinal survey of crayfish abundance, ran a 28-d leaf breakdown experiment, and sampled benthic substrates. Leaf packs of sugar maple (Acer saccharum) leaves were placed at three sites with differing crayfish densities (high, intermediate, and none). Breakdown rates were compared across the three sites and for two treatments (closed leaf bags excluding crayfish and open bags allowing crayfish access). Benthic invertebrates were sampled from leaf bags and invertebrates and periphyton were sampled from cobbles. In contrast to 1992, we found that the maximum downstream distance of rusty crayfish declined from 4 km to less than 3 km downstream from the lake. Leaves in open bags decayed significantly faster (k = 0.143) than did leaves in closed bags at all sites (k = 0.079) (p = 0.0005). The site lacking crayfish had significantly higher densities of invertebrates compared to both high and intermediate crayfish density sites (p = 0.005). Although we found that rusty crayfish reduced standing stocks of leaves and invertebrates, we did not detect measurable changes in periphyton biomass. Therefore, rusty crayfish have not dispersed further downstream since 1992, but where present, these omnivores significantly reduce resource availability via the consumption of leaf material and benthic invertebrates.     

Periphyton in the Clear and Colored Water Masses of the St. Lawrence River (Quebec,Canada): A 20-Year Overview

Periphyton was collected on navigational buoys in the Montreal island sector of the St. Lawrence River during 1994–95 to compare biomass and species composition in the transparent “green” waters originating from the Great Lakes with those found in the colored, more turbid “brown” waters coming from the Ottawa River. Periphyton biomass (chlorophyll a, ash free dry mass, density and biovolume) was depressed in brown waters and differences in species composition were observed at the class (i.e., diatoms more important in brown waters) and species level (i.e., Melosira varians more abundant in brown waters). Comparison of 1994 and 1995 with 1982 and 1973 data supported the observed differences in biomass between brown and green waters, yet showed no major temporal shifts in periphyton species composition despite reductions in phosphorus loadings to the Great Lakes and the St. Lawrence River during that 20-yr period. Biomass (density and biovolume) of Cladophora and relative abundance of chlorophytes appeared much higher in 1982 than recorded in 1994 and 1995. Cladophora influences diatom community composition by providing a substratum for epiphytes and thus represents a key species controlling the structure of periphyton assemblages. Future monitoring efforts in the St. Lawrence River should focus on this species and include a standardization of sampling and enumeration methods.     

Establishing spatial trends in water chemistry and stable isotopes (δ15N and δ13C) in the Elwha River prior to dam removal and salmon recolonization

Two high‐head dams on the Elwha River in Washington State (USA) have changed the migratory patterns of resident and anadromous fish, limiting Pacific salmon to the lower 7.9 km of a river that historically supported large Pacific salmon runs. To document the effects of the dams prior to their removal, we measured carbon and nitrogen stable isotope ratios of primary producers, benthic macroinvertebrates, and fish, and water chemistry above, between and below the dams. We found that δ¹⁵N was significantly higher in fish, stoneflies, black flies, periphyton and macroalgae where salmon still have access. Fish and chloroperlid stoneflies were enriched in δ¹³C, but the values were more variable than in δ¹⁵N. For some taxa, there were also differences between the two river sections that lack salmon, suggesting that factors other than marine‐derived nutrients are structuring longitudinal isotopic profiles. Consistent with trophic theory, macroalgae had the lowest δ¹⁵N, followed by periphyton, macroinvertebrates and fish, with a range of 6.9, 6.2 and 7.7‰ below, between, and above the dams, respectively. Water chemistry analyses confirmed earlier reports that the river is oligotrophic. Phosphorous levels in the Elwha were lower than those found in other regional rivers, with significant differences among regulated, unregulated and reference sections. The removal of these dams, among the largest of such projects ever attempted, is expected to facilitate the return of salmon and their marine‐derived nutrients (MDN) throughout the watershed, possibly altering the food web structure, nutrient levels and stable isotope values that we documented. Published in 2010 by John Wiley & Sons, Ltd.     

Macroinvertebrate Associations with Aquatic Macrophytes and Artificial Substrates

Macroinvertebrate populations associated with Myriophyllum exalbescens, Potamogeton richardsonii, and Vallisneria americana were compared with those on plastic ‘plants’ similar in morphology to P. richardsonii. The density of organisms varied according to macrophyte species (Myriophyllum ? Potamogeton > Vallisneria). The plastic imitations did not differ significantly from Potamogeton in the total numbers of macrophytes they harboured at two different sampling periods during the growing season. A similar macroinvertebrate species composition occurred in association with the three plant species and with the artificial substrates.     

Invertebrate drift patterns in a regulated river: dams,periphyton biomass or longitudinal patterns?

Macroinvertebrate drift was sampled at 15 sites along the Tongariro River, New Zealand above and below two hydroelectric dams. Sixty‐seven invertebrate taxa were collected in the drift. Trichoptera (31) were the most diverse, followed by Diptera (13), Ephemeroptera (8) and Plecoptera (8). However, chironomidae were the numerically dominant taxa in the drift throughout the river and represented over 80% of all animals collected. Of these, Orthocladiinae and Diamesinae were the most abundant. Taxonomic richness declined with distance downstream and peaked at sites with intermediate levels of periphyton biomass. The per cent of Ephemeroptera, Plecoptera and Trichoptera (EPT) was 3–4 times higher in the unregulated section of the river and declined exponentially with both distance downstream and increase in periphyton biomass, but densities were similar along the river. Of the measured environmental variables periphyton biomass was most closely linked with drift community structure. Periphyton biomass was six times higher in the lower section of the river than the upper unregulated section. The autocorrelation between periphyton biomass and distance downstream complicates the interpretation of results. However, because of the distinct differences between above and below dam sections of river in periphyton biomass and the strong link between it and invertebrate drift we suggest that the alteration of flow patterns by the hydroelectric dams and the associated shift in periphyton biomass is the most likely explanation for invertebrate drift patterns in the river. Copyright © 2009 John Wiley & Sons, Ltd.     

附着性藻类生长-迁移模型及其在南水北调中线工程中的应用

附着性藻类广泛存在于自然水体中,有很强的生命力且能通过释放孢子/配子等多种方式进行繁殖与迁移。传统附着藻类生长模型往往仅考虑了藻类生长过程及水动力影响,但藻类的繁殖迁移过程也是附着藻类生活史的重要部分。通过在传统附着藻类生长模型中引入繁殖迁移过程,构建了适用于附着性藻类的生长-迁移模型,并通过相关实验结果进行了率定验证。针对南水北调中线工程中藻类增殖问题的定性研究表明：当干渠内水流流速小于0.4 m/s时,附着藻类容易大量增殖,故附着性藻类容易聚集在水渠弯道处及两侧边壁。通过增大总干渠输水流量可提高渠内水流平均流速,从而控制渠内附着藻类平均生长密度,当干渠流量为350 m³/s时,干渠中附着藻类平均密度仅为流量为180 m³/s时的20%。模拟结果符合南水北调中线工程中附着藻类的实际分布规律,研究成果可为南水北调中线工程中附着性藻类增殖问题的进一步治理提供参考。     

Effect of fine sediment deposition and channel works on periphyton biomass in the Makomanai River,northern Japan

The Makomanai River in northern Japan has suffered considerable fine sediment deposition, especially in a reach where channel works have been constructed. Four contiguous reaches were examined for deposition of fine sediment and the effects of such on periphyton biomass; two of the reaches had channel works and bank protection, respectively, the other two being unmodified. The influence of fine sedimentation on epilithic periphyton biomass (chlorophyll a weight and organic matter weight) and the autotrophic index (AI), and the relationship between these and hydraulic variables was emphasized. Fine sediment increased, chlorophyll a decreased and AI increased in the reach with channel works and in the unmodified reach immediately upstream. In addition, the current velocity and Froude number tended to decrease in the reach with channel works. Correlation analysis showed that with an increase in fine sediment, chlorophyll a decreased and non‐living periphyton, indicated by AI, increased. It was also confirmed that fine sediment increased with an increase in weight of periphyton organic matter and decreased with an increase in current velocity or Froude number. These results suggest that accumulation of fine sediment, which substantially reduces light penetration for photosynthesis under low current velocity conditions, results in lowered periphyton levels. The channel works have lowered the current velocity, thus promoting deposition of fine sediment and an increase in non‐living periphyton. Copyright © 2002 John Wiley & Sons, Ltd.     

Distribution of Eurasian Watermilfoil,Myriophyllum Spicatum,in the St. Clair-Detroit River System in 1978

Submersed macrophytes were surveyed at 595 stations located throughout the St. Clair-Detroit River system between Lakes Huron and Erie, 23 August to 13 October 1978. Eurasian watermilfoil (Myriophyllum spicatum), first recorded in the system in 1974, became the fourth most common submersed macrophyte in the system by 1978. However, it has not been reported as a widespread nuisance in this system as it has in many other large water bodies in the United States. Observations made during the present study, and interpretation of an aerial photograph, suggest that M. spicatum was a minor nuisance to small boat navigation in portions of the system. Information presented in this study provides a baseline against which future changes in the occurrence of M. spicatum in the St. Clair-Detroit River system can be measured.     

Changes in Distribution and Abundance of Submerged Macrophytes in the Inner Bay at Long Point,Lake Erie: Implications for Foraging Waterfowl

Submerged aquatic macrophytes in Long Point Bay provide food for several species of migrating waterfowl, particularly diving ducks. The percent occurrence of several plant species in the diets of six species (207 birds) of diving ducks were studied between 1992 and 1994. Of 29 plant species consumed, Vallisneria americana was the most commonly occurring in the diet. Chara vulgaris, Potamogeton spp., Polygonum spp., and Najas flexilis/quadalupensis were also important dietary items. The seeds of a number of emergent macrophyte species were also consumed. Submerged macrophytes were sampled at 312 locations in the Inner Bay of Long Point, Lake Erie, in 1991, 1992, and 1995. Distribution and percent abundance were compared with a similar study in 1976 and with observations of macrophytes in 1962. In comparison with the 1976 study, Chara vulgaris is still dominant over much of the Bay. V. americana and N. flexilis/N. guadalupensis have expanded their ranges, probably a result of increasing light penetration associated with the filtering of suspended material by introduced zebra mussels Dreissena polymorpha. The continued widespread distribution of C. vulgaris, and the expansion of V. americana and N. flexilis/N. guadalupensis, has probably benefitted waterfowl, as these species have a high nutritive value and are readily consumed by diving ducks at Long Point. Myriophyllum spicatum, an exotic species introduced in the early 1970s, increased in distribution between 1976 and 1991 but decreased in distribution and percent abundance by 1995. Increased light transparency may have contributed to this decline, as M. spicatum typically grows best in turbid, eutrophic environments. The decline of this species has probably been beneficial to waterfowl because it commonly out-competes native plants and it is underutilized by ducks at Long Point. Ceratophyllum demersum appears to be a more prominent member of the submerged macrophyte communities in the 1990s, as it was not reported previously. In comparison with 1962, major changes have occurred in species composition and relative abundance: M. spicatum, Najas spp., and Elodea canadensis have increased, Potamogeton spp. and Nitella spp. have declined. Macrophyte distribution and abundance on the Inner Bay is influenced by environmental, biological, geomorphological and geological variables. However, the anthropogenic introduction of two exotic species, M. Spicatum and the zebra mussel, appears to have had a pronounced influence on the community structure of submerged macrophytes in Long Point Bay.     

A review of the effect of river regulation on mayflies (Ephemeroptera)

Impoundment and diversion of watercourses for power production and water supply can have profound effects on the mayfly fauna. To explain such effects a species-specific approach is adopted on account of differing habitat requirements and life histories in the order and even within genera. Environmental conditions such as discharge and flow patterns, temperature, food availability, and predation may be changed. This leads to changes in the density and species composition of the mayfly community, especially when there is a hypolimnion drain from reservoirs. Temperature changes below such reservoirs may remove obligatory life cycle thresholds. Prolonged periods of low discharge lead to the dominance of genera, such as Paraleptophlebia, Choroterpes, Siphlonurus, and Pseudocloen, typical of slow-flowing and lentic habitats. The life cycle plasticity and opportunism shown by Baetis rhodani in Europe and B. tricaudatus in North America have undoubtedly contributed to their success in regulated rivers. The life history characteristics of Tricorythodes are also advantageous below dams. The increased growth of periphyton and mosses below many dams favour certain Ephemerellidae, but restrict or eliminate many Heptageniidae. In order to survive adverse conditions, flexible life cycles or a short period of rapid nymphal growth coupled with a long period of egg development, are advantageous.