Stream ecology

The aim of this study was a combined and multifaceted characterization (morphological, molecular, lipid, pigment, and ecological data) of a Lemanea (freshwater red alga) population from the south–eastern Alps, exploring its adaptive strategies to the montane habitat, (turbulent, very–cold glacial stream with extremely low–conductivity). Although the thalli were small (only up to 1 cm), the morphology was within the current circumscription of Lemanea fluviatilis. The molecular data placed this population within a clade of specimens identified as L. fluviatilis and L. fucina. This L. fluviatilis population was determined to possess lipid classes, especially phosphatidylcholine and monogalactosyldiacylglycerol with high unsaturation index (UI) and long acyl chains, which are typical adaptations for maintaining adequate membrane fluidity and consequently all the metabolic processes associated to the plasma membrane. The carotenoids profile revealed that, besides α /β– carotene, there are significant amounts of zeaxanthin and lutein. This study further demonstrated that red algae are a rich source of important food web w–3 fatty acids and may play an important role in the diets of grazers. L. fluviatilis is reported from one of the highest elevations (2,170 m a.s.l.) known for the genus Lemanea and this species. This study confirms the presence of L. fluviatilis in a cold, unpolluted, turbulent stream and this type of stream may be its preferred habitat.

Students in Environmental Field Studies class at the University of Montana Western (UMW) in Dillon, Montana conducted a baseline inventory and assessment of Poindexter Slough, a former channel of the Beaverhead River located approximately 3.0 miles south of Dillon, MT.  During the period of September 22nd to October 15th, 2014, the students assessed the stream morphology, in-stream macroinvertebrates, riparian vegetation and stream habitat for the entire 4.73-mile length of Poindexter Slough. The purpose of the study was to gather baseline data to assess a fish-related riparian restoration and improvement project by the Montana Fish, Wildlife and Parks and The Beaverhead Watershed Committee. The project was supervised by Dr. Robert C. Thomas, Professor of geology in the Environmental Sciences Department at UMW.

The study area included twenty-two cross-sections placed from the diversion of the slough from the Beaverhead River to its confluence back with the river. The cross sections were chosen to achieve a good assessment of the entire slough. The cross sections were placed across riffle-pool pairs and their positions recorded with GPS. The study was designed to (1) assess the existing conditions, and (2) make recommendations about the restoration plan. Future UMW students will use the data for a long-term assessment of the restoration project through repeated analyses. Restoration plans involve replacing existing irrigation infrastructure, mechanically modifying channel dimensions, and transplanting riparian vegetation to improve fisheries habitat and restore natural processes of habitat formation and maintenance to the slough. The majority of Poindexter Slough functions as an “A4” stream, but it should be functioning as a “C4” stream, with far less fine-grained sediment load.

Based on the assessment data, the UMW team recommended the removal and prevention of fine-grained sediment accumulation in Poindexter Slough. Since the macroinvertebrate diversity is greatest in areas of in-stream vegetation, the team recommended minimal disturbance of these areas during restoration work. The team proposed a protocol for reducing noxious weeds in the riparian areas that will be disturbed by the restoration work, and the report was submitted to Montana Fish, Wildlife and Parks to be used to modify their restoration plan for the slough.

We evaluated the influence of environmental integrity and the potential as bioindicator of larval stages of species of Trichoptera in 20 streams of first to fourth order in the Pindaı´ba river basin, Mato Grosso, Central Brazil. We measured stream integrity with the habitat integrity index (HII), establishing three levels of conservation: preserved, altered and impacted environments. We used (i) simple regression to assess the effect of habitat integrity on species abundance of Trichoptera and (ii) the indicator species analysis (IndVal) to assess the potential as bioindicator of each species. We found that 12 morphospecies showed relationship with HII: six species were bioindicators of preserved and two species of altered environments. Morphospecies that showed relationship in the two analyses (i and ii) were considered strong bioindicators, considering that the other species supported higher environmental variation, becoming evident that loss of physical structure reduces the abundance of organisms specialized in preserved environments. The results showed that the distribution and abundance of trichopterans can be an indicator of habitat integrity. Trichopteran species have bioindicator potential, corroborating the hypotheses of this work that abundance
of organisms will be smaller in environments with low integrity, and that many species are specific to preserved environments, disappearing from impacted environments, and also characteristic species of altered environments.

Riverbank erosion is a natural process, but its measurement and prediction is still not an easy task. Bank
assessment for non-point source consequences of sediment (BANCS) model is a popular one for
evaluating stream bank erosion hazard potential (SBEHP) which includes two procedures, bank erosion
hazard index (BEHI) and near bank stress (NBS). In this paper, BANCS model has been applied for
about 20km of river Mahananda at the foothills of the Darjeeling Himalayas where bank erosion is
prominent. The results show that out of 22 sample points, 14 have high BEHI rating and 4 have a very
high and medium rating. In the case of NBS, 7 sample points have low, 9 have moderate and 6 have high
NBS rating. Field studies estimated the rate of bank erosion at 2510m /year. Less vegetation cover,
absence of surface protection at the toe of a bank, higher velocity of water, loose bank material,
fluctuation of thalweg, formation of numerous bars in the channel bed are the some of the major causes
for bank erosion in this stretch. In order to verify the suitability of BEHI and NBS rating as a predictor of
bank erosion, linear regression has been fitted that show a positive relationship between these ratings
and observed erosion rate. Hence, this model can be used as a suitable measure for predicting the
occurrence of bank erosion of the particular portion of the river.

La presente investigación tuvo como objetivo determinar el estado de restauración y calidad de dos áreas con bosque de ribera en el río Acomé y Pantaleón. En dichas áreas se consideró una unidad de análisis de 2.5 kilómetros de longitud tomando en cuenta ambas riberas del río. Asimismo, se consideró el bosque de ribera del río Popoguá como el ecosistema de referencia. Para ello, se utilizó la metodología de índice de calidad de bosques de ribera, el muestreo hábitat de arroyo y muestreo de diversidad arbórea. Con esto se determinó que la calidad del bosque de ribera del río Acomé y Pantaleón es “buena” y Popoguá calidad “muy buena”. La calidad de hábitat de Acomé y Popoguá es “excelente” y en Pantaleón “buena”. Se hallaron 35, 26 y 37 especies de árboles en el Acomé, Pantaleón y Popoguá, respectivamente. Asimismo, se determinó que las tres áreas con bosque de ribera tienen una diversidad, dominancia y equidad alta y están dominadas por Triplaris melaenodendron (Bertol.) Standl. & Steyerm., Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg. y Quararibea funebris (La Llave) Vische; en la ribera del río Acomé, Pantaleón y Popoguá, respectivamente. Finalmente se determinó que el bosque de ribera del río Acomé se encuentra rehabilitado, tanto en funcionamiento como en estructura del bosque; mientras en Pantaleón se ha recuperado el funcionamiento y estructura del bosque de ribera, respecto al bosque de referencia de Popoguá. Por ello se recomienda conservar y proteger los bosques de ribera para mantener la calidad del bosque y facilitar su restauración.

Bowman Creek is one of the most ecologically impaired tributaries of the St. Joseph River, a large river in the Lake Michigan drainage system. It has been rerouted underground through pipes and culverts for more than half of its downstream length. The City of South Bend is planning to restore portions of the stream to a more natural aboveground condition, with goals of improving hydrological, ecological, education and aesthetic values.

In this study, I investigated the effects of culverts on the physical, chemical and biological characteristics of the stream ecosystem. Deployable dataloggers were used to characterize diel respiration curves. Water samples were analyzed for ammonium, nitrate, soluble reactive phosphorus and dissolved organic carbon. Biofilm samples were analyzed for chlorophyll a concentration and ash-free dry mass. Benthic macroinvertebrate samples were used to calculate indices of biotic integrity. The effect of culverts on stream ecosystem function could not be determined from this study. However, collected baseline data can be used to assess the progress of restoration efforts. Further research and continued long-term monitoring is needed to characterize the dynamics of underground urban streams and evaluate the restoration of Bowman Creek.

The Maasnielderbeek is a lowland stream  east of Roermond (Province of Limburg, The Netherlands). The stream is largely located in an old meander. of the river Meuse The part outside the city has largely been channeled and the part in the city has been transformed into a city park. Nevertheless, the Maasnielderbeek still has many natural values, which are described in this chapter of the book 'Natuurlijk Roermond'.

Para facilitar y homogeneizar el tratamiento y la interpretación de la información generada en las redes de control biológico se presenta una colección de fichas descriptivas de los organismos fitobentónicos que incluyen: nombre científico, común, sinónimo, propiedades, descripción, ecología, ruta taxonómica e índices y métricas, foto o ilustración incluyendo la propiedad y el autor. Esta guía ha sido elaborada por la Dirección General del Agua y forma parte de una colección de cinco tomos.

The diatom Didymosphenia geminata (Lyngbye) M.Schmidt has been commonly considered a taxon restricted to pristine habitats in mountainous areas of circumboreal regions. Recent studies show that it has a broader distribution and ecological amplitude. This shift seems to have occurred recently, as it now forms large growths in rivers within its native geographical area (North America, Europe) but also mass developments have recently appeared in New Zealand, where it is considered an aggressive invasive species with dramatic ecological and economic impacts. This nuisance organism grows attached in streambeds and may impact freshwater fish and aquatic plants and insects, causing severe disturbance in food webs. This paper investigates the historic and current biogeographic range of this invasive species (and varieties) based on 1000 citations collected mainly from the scientific literature. The locations where this diatom has appeared, including both fossil and recent records, are presented in world distribution maps. Our results confirm that the native range of D. geminata is almost restricted to the Holarctic region, though its distribution area is broader than usually reported in the literature. The ecological profile of this alga, along with its nuisance effects, is also discussed. Excessive growths do not only appear in areas where this species is presumably exotic. Contrarily to general statement, reports of mass developments of D. geminata date back to the 19th century. World references to D. geminata have increased exponentially during the last decades; however; with respect to the whole diatom literature during the XIX and XX centuries, the relative frequency of citations has decreased progressively.

Монография представляет собой междисциплинарное исследование, выполненное на стыке руслове-
дения и ихтиологии. Тема — развитие русловых процессов и изменения среды обитания лососёвых рыб
Камчатки в условиях осуществления разных видов хозяйственной деятельности в долинах рек. В книге дано
региональное обобщение русловых процессов рек Камчатки, рассматриваются природные и техногенные
причины и последствия развития опасных (в техническом и экологическом аспектах) русловых процессов;
вопросы их учёта использованы для обоснования принципов организации безопасной хозяйственной дея-
тельности в долинах рек.
Настоящее издание обобщает многолетний опыт авторов в изучении опасных русловых процессов на
Камчатке и даёт региональную комплексную оценку среды обитания (речных русел) и сообществ лососё-
вых рыб в условиях осуществления разных видов хозяйственной деятельности на Камчатке. Соответству-
ющие разделы дополнены описанием истории строительства Камчатского магистрального газопровода
и автодорожных мостов через реки Камчатки, организации берегозащитных мероприятий и речного рыб-
ного промысла, создания прирусловых водозаборов.
Книга будет интересна специалистам гидрологам, геоморфологам, ихтиологам, гидробиологам,
экологам, работающим не только на Камчатке. Практические выводы, сделанные в книге, адресованы
органам законодательной и исполнительной власти Камчатского края, хозяйственникам и проектиров-
щикам всех уровней.

A new species, Pleurosigma lange-bertalotii sp. nov., is studied with light and scanning electron microscopy and described from Western Ghats, South India. The new species possesses transverse striae pattern on the external valve surface, but internal valve views show oblique striae patterns. At present the
species is assigned to the genus Pleurosigma due to the presence of oblique striation. The oblique striae pattern is continuous internally from the central nodule to the apices, and this helps to differentiate the new species from P. obscurum. The new taxon is observed only from a forested, low electrolytic stream from South Western Ghats, South India. Recent studies on diatoms suggest that the Indian sub continent is a major
geographic zone for many new diatoms, contributing to our understanding of the evolution of diatoms of this biogeographic region.

Hassar stream is a watercourse of North East of Casablanca suburban which is a tributary of Mellah river. Until the
end of 2012, Hassar stream received wastewater in crude state from Mediouna town causing a degradation of it ecological
status and adverse effects on the local population. This work aims to make a first assessment of physicochemical water
quality of this watercourse after installing the Mediouna StEp started in 2013.
The first results recorded during the first six months of the study (November 2013 to April 2014) shows an improvement in
the quality of Hassar stream with dissolved O2 values reaching up to 8,26 mg/l, COD maximum not exceeding 80 mg/l, a
maximum BOD5 of 14 mg/l, a maximum content of MES 30 mg/l, ammonium ion (NH4
+) in concentrations of 0,9 to 7,8 mg / l,
orthophosphates from 0,48 to 11,62 mg/l and nitrates from 4,7 to 25,3 mg/l. These results show that the majority of the
stations of the Hassar stream have an average to good quality and the beginning of physicochemical resilience of Hassar
stream’s waters would be initiated.
KEYWORDS: Casablanca, Hassar stream, diagnostics, quality, resilience, wastewater.

A factorial experiment was carried out in order to assess the effects of four treatment steps in diatom processing techniques (the quantity of hydrogen peroxide added to the sample, the time allowed to the digestion reaction, the use of centrifugation and the method used to settle the frustules onto the coverslip) on different aspects of the quality of the resulting microscopic slide: the concentration of organic and inorganic matter, the density, randomness and homogeneity of the frustule distribution in the slide, and the abundance of broken frustules and girdle views. The results show no significant effects of any of the experimental treatments on the proportion of broken frustules in the samples. No significant effects were related to the duration of the oxidation reaction in any of the aspects evaluated in the quality of the slides. A sample:hydrogen peroxide ratio of 1:1 for a 6-h oxidizing reaction can be used to optimize the protocol. Despite being more time consuming, the use of successive decantations instead of centrifuging is more appropriate to achieve better results. Slide quality can also be improved by leaving the coverslips to dry at room temperature in order to improve the distribution of frustules.

Environmental flows represent a legal mechanism to balance existing and future water uses and sustain non-use values. Here, we identify current challenges, provide examples where they are important, and suggest research advances that would benefit environmental flow science. Specifically, environmental flow science would benefit by (1) developing approaches to address streamflow needs in highly modified landscapes where historic flows do not provide reasonable comparisons, (2) integrating water quality needs where interactions are apparent with quantity but not necessarily the proximate factor of the ecological degradation, especially as frequency and magnitudes of inflows to bays and estuaries, (3) providing a better understanding of the ecological needs of native species to offset the often unintended consequences of benefiting non-native species or their impact on flows, (4) improving our understanding of the non-use economic value to balance consumptive economic values, and (5) increasing our understanding of the stakeholder socioeconomic spatial distribution of attitudes and perceptions across the landscape. Environmental flow science is still an emerging interdisciplinary field and by integrating socioeconomic disciplines and developing new frameworks to accommodate our altered landscapes, we should help advance environmental flow science and likely increase successful implementation of flow standards.

The United Kingdom Institute of Hydrology (UKIH) smoothed minima baseflow separation method originally developed for
the daily flow data of perennial streams and adopted for intermittent streams is presented. The adopted method (AdUKIH) is
the generalized version of the UKIH and hence applicable not only to intermittent streams but also to perennial streams. The
AdUKIH method is applied on three daily streamflow gauging stations from the European part of Turkey, the Thrace region.
The AdUKIH enables one to change the parameter 0Ð9 in the UKIH method and also introduces different block sizes, which
is limited to five days in the original UKIH method. The AdUKIH method is considered a useful tool in helping practitioners
and researchers to separate continuous baseflow from the daily flow in perennial and intermittent streams.

Restoration approaches such as dam removal and channel reconstruction have moved beyond the realm of small streams and are being applied to larger rivers. This development has substantial economic and ecological implications but may test gaps in our understanding of larger river systems and of restoration science. We examine how information about historical ranges of geomorphic variability can inform stream restoration in the context of the Clark Fork River, Montana, focusing on a study reach where one of the larg- est restoration projects to date was implemented, upstream of the recently removed Milltown Dam. Analysis of historical sources and aerial photographs of the Clark Fork River’s pre-mining, mining, and more recent history suggest that a wandering channel pattern has persisted despite variations in sediment supply and transport capacity. Predictive metrics for channel pattern also suggest a wandering pattern, transitional between braided and meandering, in this geomorphic setting. These analyses suggest that the creation of a single- thread meandering channel, which incorporates structures to limit erosion and channel movement, is inconsistent with the historical range of variability in this reach. The perils of restoring channels to a condition different than the historical range of variability for their geomorphic setting were illustrated on the Clark Fork by flood-induced avulsions of the restored channel that occurred soon after project construction. Application of an experimental approach to restoration, founded on the method of multiple working hypotheses, provides a means for embracing uncertainty, can maximize the potential for site-specific restoration success, and can foster advances in restoration science.
KEYWORDS: wandering; multi-thread; dam removal; historical range of variability; historical geomorphology

1. The Ephemeroptera fauna of the World consists of 42 families, 400 genera and 3000 species, while the Ephemeroptera fauna of the Turkey consists of 14 families, 39 genera, 138 species and 5 subspecies.
2. The Ephemeroptera species of Turkey constitutes 4,6% of the Ephemeroptera species in the World.
3. With respect to the genera number, Ephemeroptera genera of Turkey constitutes 9,75%
of the Ephemeroptera genera in the World.
4. Ephemeroptera species play a critical role in order to define the reference sites and their fauna concerning the application of European Union Water Framework Directive (EUWFD) in Turkey.

The Water Framework Directive (WFD) requires that the European Union countries determine the biological state of their waters with respect to sites of high quality. Despite bioindicators have been widely applied in running waters and deep lakes throughout all Europe, little is known about their applicability in shallow lakes. In this context, the objective of this work is to check the effectiveness of epiphytic diatoms as indicators of the trophic state in six shallow lakes of León Province (NW Spain). Epiphyton was sampled from helophyte stems in six shallow lakes covering different ecological conditions. A significant correlation was found between the total nitrogen concentration and the diatom indices SPI (Specific Polluosensitivity Index) and BDI (Biological Diatom Index), this correlation being lower with respect to the total phosphorus concentration. The classification of the lakes according to the trophic and saprobic levels based on diatoms corresponds to that obtained from the analysis of the limnological and chemical parameters of the studied systems. Despite the use of these indices has been traditionally limited to rivers and channels, our results show the effectiveness of epiphytic diatoms as biological indicators of the quality of water in Mediterranean shallow lakes and the applicability of common diatom indices for biomonitoring purposes in these aquatic ecosystems.

The aim of this study was to support the development of ecological
stream quality assessment tools in order to provide a
method for sustainable water management in Turkey. Therefore,
we present two new or adapted indices based on benthic invertebrates.
To develop and adapt the indices, 17 streams were
studied and separated into three quality classes, which were supported
by four community indices (EPT [%], EPTCBO [%], number
of Individuals, evenness), and 23 taxa were identified as indicators
for these three quality classes. As a first biological index, we
adapted the Hindu Kush-Himalaya biotic score (HKHbios) to the
Euphrates catchment by establishing a new and ecoregion-specific
score list (Euph-Scores) by scoring 93 taxa depending on
their distribution between the quality classes. Based on these
scores, several average score per taxon values (ASPT value) were
calculated. All ASPT values of the Euph-Scores separated the quality
classes significantly. After a comparison of the different ASPT
values we recommend to use the weighted ASPT, because the
weighting enabled a sharper differentiation between the quality
classes and named it Euphrates Biotic Score (EUPHbios). As a
second biological index, we propose the proportion of habitat
specialists. To calculate this index, a habitat score was developed
by analysing the habitat preferences of several benthic invertebrates.
Habitat score values were assigned to the 20 most common
taxa from the streams in the best quality class (natural
streams). The proportion of habitat specialists, identified using the
new habitat score, differed significantly between the three quality
classes, with higher values in natural streams than in polluted
streams. In the light of the results, the presented methods appear
to be suitable for developing a multi-metric index for assessment
programs for the mountainous regions of the Middle East.

The quality and availability of water resources in tropical watersheds are threatened by increased multiple use demands by human populations. Therefore, there is a need for cost-effective ecological indicators of water body status and trends. Multimetric indices (MMIs), based on responses of biological assemblages to anthropogenic disturbances, are excellent examples of such indicators and they have been applied globally. However, creating new MMIs for each water body or study area requires considerable analytical effort and hinders our ability to make regional or global comparisons. Therefore, we tested the effectiveness of 17 published benthic macro- invertebrate MMIs for assessing the environmental quality of a tropical anthropogenically least-disturbed river basin in the Neotropical Savanna (Brazilian Cerrado) biome. We tested those MMIs through use of macro- invertebrate data sampled at 40 stream sites in the Pandeiros River basin, Brazil. Disturbances in the basin were related to local factors such as pasture, garbage, and cropland in stream riparian areas. Index performance was tested by comparing precision, bias, responsiveness and sensitivity to anthropogenic pressures and stressors. Ten indices performed satisfactorily in evaluating the environmental condition of the basin. Therefore, we do not recommend developing new benthic MMIs for rapid environmental quality assessments. On the other hand, we do recommend using standard data collection methods for evaluating conditions throughout the biome.

In this paper we reinvestigated seven Surirella species described or reported by Gandhi and two taxa which were not reported by Gandhi using his collections from Peninsular India. Among these, S. langebertalotii Karthick, Hamilton & Kociolek stat. & nom. nov. is a new name for Surirella robusta f. minor.
Surirella leyana Bramburger & Hamilton and S. pinnigera Bramburger & Hamilton were new records to India. Surirella lanceolata Gandhi is a synonym of the cosmopolitan species S. ovalis Brébisson 1838 and for the fi rst time the ultrastructural details of S. shyamae Gandhi, S. capronioides Gandhi, and Surirella capronii Brebisson & Kitton are presented. This study confi rms that members of Surirella show different levels of endemism, such as some being locally endemic, some regionally distributed and others cosmopolitan. It is also evident that Peninsular India and the Malay Archipelago share a similar regional diatom fl ora.

Douglas Rodríguez-Olarte, Alexis Araujo Quintero, Guillermo Bianchi Pérez, Salvador Boher, Otto Castillo, Yadira Cordero Perozo, Juan Escudero, Ángel Fernández, Juan Elías García, Oscar Lasso-Alcalá, Margarita Martínez, Críspulo Julián Marrero, José Manuel Mendoza, Vilisa Morón Zambrano, Pedro Rodríguez Bueno, Samuel Segnini, Andrés Eloy Seijas, Julio Velásquez

Aim: Knowledge of expanding and contracting ranges is critical for monitoring invasions and assessing conservation status, yet reliable data on distributional trends are lacking for most freshwater species. We developed a quantitative technique to detect the sign (expansion or contraction) and functional form of range-size changes for freshwater species based on collections data, while accounting for possible biases due to variable collection effort. We applied this technique to quantify stream-fish range expansions and contractions in a highly invaded river system.
Location: Upper and middle New River (UMNR) basin, Appalachian Mountains, USA.
Methods: We compiled a 77-year stream-fish collections dataset partitioned into ten time periods. To account for variable collection effort among time periods, we aggregated the collections into 100 watersheds and expressed a species' range size as detections per watershed (HUC) sampled (DPHS). We regressed DPHS against time by species and used an information-theoretic approach to compare linear and nonlinear functional forms fitted to the data points and to classify each species as spreader, stable or decliner.
Results: We analysed changes in range size for 74 UMNR fishes, including 35 native and 39 established introduced species. We classified the majority (51%) of introduced species as spreaders, compared to 31% of natives. An exponential functional form fits best for 84% of spreaders. Three natives were among the most rapid spreaders. All four decliners were New River natives.
Main conclusions: Our DPHS-based approach facilitated quantitative analyses of distributional trends for stream fishes based on collections data. Partitioning the dataset into multiple time periods allowed us to distinguish long-term trends from population fluctuations and to examine nonlinear forms of spread. Our framework sets the stage for further study of drivers of stream-fish invasions and declines in the UMNR and is widely transferable to other freshwater taxa and geographic regions.
KEYWORDS conservation assessment, functional form, introduced species, native invaders, range expansion, species declines

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant–herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore–plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore–plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant–herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants.

In 2000 the European Parliament and The European Union Council recommended that member countries assess water quality using diatoms, as part of the phytobenthos. In Italy this recommendation has given new impetus to the study of diatom communities and the application of biotic indices. During the summer of 2004, a total of 11 rivers of the Trentino province (Northern Italy) were sampled, revealing the presence in low abundances of the diatom Didymosphenia geminata (Lyngbye) M. Schmidt. The sites where this diatom occurred were characterised by a low pollution impact; they were also lake fed or had a regulated flow regime, although with different geologies. Morphological features of D. geminata frustules were analysed using LM and SEM and specimens could be referred to the morphotype "geminata". In many countries this species is expanding its distribution and in New Zealand it is considered an invasive alga. This work provides an initial report on the presence of D. geminata in the Trento province, and contributes to increasing the knowledge on its distribution in Italy and its ecology in the Alps.