Stream Algae Research Articles

On the taxonomic richness, evenness and divergence of periphytic algae in Amazon streams

On the taxonomic richness, evenness and divergence of periphytic algae in Amazon streams

Temporal dynamics of stream algae under the combined impacts of climate and land‐use stressors

Abstract Ecosystems are increasingly challenged by the multiple facets of climate change, coupled with intensifying land‐use pressures. These co‐occurring stressors can interact in complex ways, but we lack an empirical understanding of the impact of higher‐order interactions on temporal patterns. Using 128 flow‐through circular stream mesocosms, we investigated the individual and combined effects of two climatic stressors (CO2 enrichment, flow variability) and two land‐use‐related stressors (siltation, light—as lack of shading) on algal communities and net ecosystem productivity (NPP) in a full‐factorial design. The sediment pulses coincided with high flow to mimic erosion events, whereas CO2 and light disturbances were applied continuously, as they would in nature. Sediment emerged as a key stressor for algal biomass. Land‐use stressors had more pervasive individual effects, whereas climate‐change‐related stressors were more important in up to three‐way interactions with other stressors. However, CO2 was a key driver of NPP, followed by sediment and light, whereas flow variability was only important in interactions with other stressors. The effects of sediment and flow on algal biomass depended strongly on their temporal patterns. The combined effect of an increasing number of stressors on algal biomass appeared to reach saturation with three active stressors, with no apparent additional effect caused by the fourth stressor. Synthesis. Sediment emerged as a key stressor in streams. Despite the mounting evidence and the multitude of available mitigation strategies, this problem persists worldwide. The complex interactions uncovered in our study illustrate context‐dependency that can be masked in two‐factor experiments. Our findings also highlighted that temporal patterns of individual and co‐occurring stressors can determine the ecological outcome.

Successful reintroduction of species: improving on windows of opportunity for biodiversity repair

To overcome resistance of degraded ecological communities to restorative interventions, we need to understand windows of opportunity—limited time frames when species reintroduction attempts are still successful. More specifically, we need to understand what makes these windows close, as this may enable us to stretch or reopen them. We investigated this using models of simple food web modules. We show how joint changes of bottom–up and top–down control may be applied to change windows of opportunity and increase reintroduction success. Which reintroduction densities were most effective seemed system‐specific. A more general result is that reintroduction success was strongly enhanced by low to intermediate carrying capacities of basal species (e.g. periphyton and other algae in streams). This can be seen as equivalent to low to intermediate nutrient levels. When these were too high, almost any combination of restorative measures was rendered ineffective. Interestingly, reintroducing primarily and secondarily lost species at the same time was more effective than sequential reintroductions that first attempted to fix secondary extinctions. We could further enhance the success of species reintroductions by reducing the carrying capacities of basal species before the reintroduction of primarily and secondarily lost species. We discuss our results in the light of empirical work on macro‐invertebrates in streams. This serves to exemplify how our results can be applied in the practice of ecological restoration.

Do the effects of substrate complexity influence the emergence position of microalgae on streams?

The spatial distribution of stream algae on substrates may be molded by the spatial arrangement of surface features. The variation of surface complexity on stream bottom may represent the availability of suitable areas for algal growth. Here we showed that different levels of surface complexity, at the scale used, did not affect the abundance of microalgae, however, we did note that specific areas of substrates seem to be more appropriate for initial algal establishment. Our results indicate that scale is fundamental to assess the effects of substrate on spatial distribution of benthic lotic microalgae and this may help us better understand how the different types of structural changes created by human activities in streams can affect algal colonization.

Stronger niche than dispersal effects on α‐ and β‐diversity of stream algae, insects, and fish across latitudes in the United States

AbstractAimNiche and dispersal processes influence biodiversity, but their relative importance along latitude is unclear. We predicted that: (a) niche processes would dominate at high latitudes due to increased climatic stress, consistent with the physiological tolerance hypothesis and the Dobzhansky–MacArthur hypothesis and (b) dispersal limitation would prevail at low latitudes due to narrower niches and smaller range sizes, as postulated by the dispersal–ecological specialization trade‐off hypothesis, the latitude–niche breadth hypothesis, and Rapoport's rule.LocationCentral United States.Time period1993–2019.Major taxa studiedStream algae, insects, and fish.MethodsWe examined the relative effects of environment (climate and physicochemistry) versus space on stream biodiversity in seven latitudinal zones, spanning 19 latitudinal degrees. In each zone, species richness (α‐diversity) was analysed with multiple regression and variance partitioning. Compositional dissimilarity (β‐diversity) within zones was assessed with distance‐based redundancy analysis (dbRDA) and variance partitioning.ResultsFor α‐diversity, latitudinal variability of niche and dispersal processes conformed to our predictions in all three groups, except for dispersal processes in insects. However, the drivers of β‐diversity did not follow our predictions. The latitude–niche breadth hypothesis and Rapoport's rule were weakly supported only in fish.Main conclusionsThe importance of niche and dispersal processes varied predictably along the latitudinal gradient only for α‐diversity. However, the niche effects were driven mostly by physicochemistry, and the dispersal effects were not always linked with ecological specialization and range size. This suggests that climate‐based biodiversity theories do not have particular relevance for the streams in our study. Niche processes had a greater impact than dispersal processes across species groups and diversity metrics, emphasizing the primary role of the environment.

Lack of evidence for indirect effects from stonefly predators on primary production under future climate warming scenarios

ABSTRACT Consumptive and non-consumptive interactions of predators and prey can have strong direct and indirect effects on primary producers, such as stream algae. Increasing water temperatures may alter these interactions and thus influence productivity in streams. For each of 3 temperature treatments (‘ambient’, +2°C and +4°C), we measured the amount of algal biomass removed by grazing mayflies from 91 mesocosms after a 24-hour test period under 3 grazing treatments: lethal predators, non-lethal predators, and no predators. At all temperatures, grazers reduced algal biomass (p < 0.01), and the presence of lethal predators effectively dampened mayfly consumption of algae (p < 0.01). However, differences in algal biomass between lethal and non-lethal predator treatments were not significant, indicating that predators had no indirect behaviorally mediated effects on grazer consumption. Grazer removal of algal biomass marginally increased with increasing temperature (p = 0.051). We analyzed video data for changes in grazer foraging and drift behavior. Mayflies increased drift in the presence of lethal predators (p < 0.01) but not non-lethal predators, and no behavioral changes were seen with temperature increases. Mesocosms can help elucidate possible future shifts in trophic interactions due to climate warming. Yet, we found no evidence of indirect stonefly predator effects on grazing mayflies under these warming scenarios.

Compensatory dynamics of lotic algae break down nonlinearly with increasing nutrient enrichment.

One important mechanism governing the temporal maintenance of biodiversity is asynchrony in co-occurring competitors due to fluctuating environments (i.e., compensatory dynamics). Temporal niche partitioning has evolved in response to predictable oscillations in environmental conditions so that species may offset competition, but we do not yet have a clear understanding of how novel anthropogenic stressors alter seasonal patterns of succession. Many primary producers are nutrient limited, and enrichment may decrease the importance of environmental fluctuations that govern which species are effective competitors under naturally low nutrient regimes. Consequently, elevated nutrient concentrations may synchronize species responses to seasonality. By studying benthic algal assemblages over 2 years from 35 streams that spanned a wide gradient of nutrient enrichment, we found that compensatory dynamics characterizing seasonal succession under natural nutrient regimes broke down at relatively low levels of total phosphorus (P) enrichment (~ 25 μg/L). With increasing P more species were able to coexist at any given time, and seasonal variation in assemblage composition was characterized by synchronous swings in species biovolumes. We also observed much higher instability in assemblage biovolumes with declines in compensatory dynamics, which indicates that anthropogenic alteration of nutrient regimes can affect community stability by changing the dominant mode of seasonal succession. Our findings indicate that compensatory fluctuations of stream algae are driven by seasonality and provide insight about how nutrient enrichment alters evolved drivers of species coexistence.

Nutrient fluxes from an Arctic seabird colony to the adjacent coastal marine ecosystem

Seabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes (Rissa tridactyla) and Brünnich’s Guillemots (Uria lomvia) on stream nutrient concentrations and fluxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ13C and δ15N) was used to assess whether seabird-derived nitrogen (N) could be traced into filamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO3−) and nitrite (NO2−) peaked in July at 9200 µg N L−1 in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO43−) in seabird-impacted streams were 21.9 µg P L−1, tenfold higher than in controls. Areal fluxes from seabird-impacted study catchments of NO3− + NO2− and PO43− had estimated ranges of 400–2100 kg N km−2 and 15–70 kg P km−2, respectively. Higher δ15N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ15N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers.

The impacts of nutrient supply and imbalance on subcontinental co‐occurrence networks and metacommunity composition of stream algae

The amounts and ratios of nutrients (nitrogen and phosphorus) are important determinants of producer community biodiversity and composition and their responses to climate and dispersal. However, the nutrient effects on co‐occurrence network topology, particularly in freshwaters, are understudied. Here, we investigate 1) whether nutrient supply and ratio constrain topological properties of algal co‐occurrence networks in streams and 2) to what extent climate and space (a surrogate for dispersal) affect co‐occurrence network topology versus metacommunity composition across nutrient supply and ratio contexts. We used a subcontinental dataset of benthic algae from 840 stream localities in the conterminous US. We constructed co‐occurrence networks representing nutrient supply contexts (oligotrophic versus eutrophic) and nutrient ratio contexts (N‐limited versus P‐limited) and statistically assessed topological variability within each pair via randomization. We then used a null model framework and direct gradient analysis to ascertain the importance of climate and space in driving, respectively, network topology and metacommunity composition. Nutrient supply was only positively related to network size (species node counts), which was driven by motile species, while other topological differences were non‐significant. Climatic and spatial variables had pronounced and for the most part comparable effects on network topology that further depended on nutrient context. A comparative assessment of topological versus compositional responses to climate and space across nutrient contexts identified both similarities and differences. While climate and space contributed to both network topology and metacommunity composition, space was a stronger predictor of compositional variability than climate, regardless of nutrient context. Our findings highlight the need for developing integrative multi‐level approaches (from metacommunities to co‐occurrence networks) to fully understand biological responses to complex and interactive abiotic forces.

Difference of ecological half-life and transfer coefficient in aquatic invertebrates between high and low radiocesium contaminated streams

The Fukushima accident emitted radioactive substances into the environment, contaminating litter, algae, sand substrate, aquatic invertebrates, and fish in freshwater streams. Because these substances have substantial effects on stream ecology over many years, it is necessary to clarify the diffusion and decay mechanisms of radiocesium. The transfer coefficient differed among aquatic invertebrate groups, likely due to the differences in habitat. The ecological half-life of cesium was longer where the air dose rate was lower. The transfer coefficient was also higher in areas with lower air dose rate. The radiocesium concentration in algae was inversely related to stream current velocity in the radiocesium-contaminated area. However, this relationship was not observed in the lower air dose rate area: the radiocesium concentration in algae in the rapid-velocity areas tended to be higher than that in the slow-velocity areas. This reverse trend would lead to a longer period of freshwater contamination. The radiocesium concentration would continue to decrease in highly contaminated areas, but it would be difficult to reduce the radiocesium concentration in less-contaminated areas because different contamination mechanisms are at work. Controlling the water flow is key to regulating radiocesium concentration in freshwater ecosystems.

Non‐native Chinook salmon add nutrient subsidies and functional novelty to Patagonian streams

Abstract The impacts of non‐native species are hypothesised to be proportional to the functional distinctiveness of invaders in their invaded ecosystems. Throughout the Patagonia region of southern South America, Chinook salmon (Oncorhynchus tshawytscha) have recently established non‐native populations, and their anadromous, semelparous life cycle could be functionally unique such that marine‐derived nutrients are delivered to streams which have historically lacked such a resource linkage with the ocean. We tested the hypothesis that salmon subsidise biofilm‐associated algae in streams throughout the Aysén province of southern Chile. Using spatial and temporal variation in the presence of salmon among multiple streams and across two spawning seasons, we found strong evidence of salmon‐subsidised algae in three out of four streams examined that have spawning salmon populations. The biofilm of subsidised streams had enriched stable isotopic ratios of nitrogen and carbon, indicating that marine‐derived nutrients were incorporated by biofilms. This nutrient uptake translated into increased algal biomass and percent of total biofilm biomass composed of algae, indicating that the incorporation of marine‐derived nutrients stimulated autotrophic production of biomass. In one stream, the incorporation of marine‐derived nutrients by biofilm occurred in only one of the two studied spawning seasons. Incorporation occurred in a year with low flows of water throughout salmon spawning (4.59 m3/s) and did not occur in a year with much higher flows (41.6 m3/s), suggesting that inter‐annual variation in discharge can mediate the subsidising effect of salmon. These results indicate that Chinook salmon have bridged the historical gap between productive marine ecosystems and nutrient‐poor stream ecosystems in Patagonia. Anadromous salmon can be a significant source of nutrients in nutrient‐limited catchments, and their ongoing expansion in southern South America is likely to entail ecological impacts in stream and riparian food webs.

Polyunsaturated fatty acids in fish tissues more closely resemble algal than terrestrial diet sources

The River Continuum Concept implies that consumers in headwater streams have greater dietary access to terrestrial basal resources, but recent studies have highlighted the dietary importance of high-quality algae. Algae provide consumers with physiologically important omega-3 (n-3) polyunsaturated fatty acids (PUFA), particularly eicosapentaenoic acid (EPA). However, terrestrial plants and most benthic stream algae lack the long-chain (LC) n-3 PUFA docosahexaenoic acid (DHA, 22:6n-3), which is essential for neural development in fish and other vertebrates. We sampled subalpine streams to investigate how the PUFA composition of neural (brain and eyes), muscle, and liver tissues of freshwater fish is related to their potential diets (macroinvertebrates, epilithon, fresh and conditioned terrestrial leaves). The PUFA composition of consumers was more similar to epilithon than to terrestrial leaves. Storage lipids of eyes most closely resembled dietary PUFA (aquatic invertebrates and algae). However, DHA and arachidonic acid (ARA, 20:4n-6) were not directly available in the diet but abundant in organs. This implies that algal PUFA were selectively retained or were produced internally via enzymatic PUFA conversion by aquatic consumers. This field study demonstrates the nutritional importance of algal PUFA for neural organs in aquatic consumers of headwater regions.

The Structure of Riparian Vegetation in Agricultural Landscapes Influences Spider Communities and Aquatic-Terrestrial Linkages

Riparian habitats are important ecotones connecting aquatic and terrestrial ecosystems, but are often highly degraded by human activities. Riparian buffers might help support impacted riparian communities, and improve trophic connectivity. We sampled spider communities from riparian habitats in an agricultural catchment, and analyzed their polyunsaturated fatty acid (PUFA) content to quantify trophic connectivity. Specific PUFAs are exclusively produced by stream algae, and thus are used to track uptake of aquatic resources by terrestrial consumers. Riparian spiders were collected from 10 site pairs situated along agricultural streams, and from five forest sites (25 sites total). Each agricultural site pair comprised an unshaded site with predominantly herbaceous vegetation cover, and a second with a woody riparian buffer. Spider communities differed between site types, with web-building spiders dominating woody buffered sites and free-living spiders associated with more open habitats. PUFA concentrations were greatest overall in free-living spiders, but there was also evidence for increased PUFA uptake by some spider groups when a woody riparian buffer was present. Our results reveal the different roles of open and wooded riparian habitats in supporting terrestrial consumers and aquatic-terrestrial connectivity, and highlight the value of incorporating patches of woody vegetation within riparian networks in highly modified landscapes.

Friends or foes? The ecological relationships between micro- and macroalgae in low-order tropical streams

Streambeds are abundantly colonized by benthic algal assemblages. Environmental factors are the most assessed to find out predictable correlations between algal presence and habitat conditions, but biological interactions can also be important determinant of species composition in stream algae communities. Although there is plenty of information about algal ecology, the mechanisms leading their spatial distribution remain insufficiently clarified. Herein, we contribute to a better understanding regarding this latter issue, carrying out an experimental study to assess possible interactions between micro- and macroalgae during a successional process (75 days) in nine streams, using artificial substrates. The experimental analyses revealed the following main results: (i) streams with higher abundance of macroalgae also registered higher microalgal densities; (ii) the relative interaction index showed values greater than zero for all sampling dates, suggesting positive interaction between micro- and macroalgae during colonization process; and (iii) the multiple partial regression analyses (redundancy, pRDA) showed that environmental variables and microalgae density together explained 25% of macroalgal variation. These results indicate that interactions between stream micro- and macroalgae may contribute to shape the community structure during the successional process on the streambed. As observed previously, microalgae are early successional settlers and macroalgae are late successors, but both community components, besides their inherent competition, seem to cooperate in order to keep their coexistence. Based on this perspective, some typical ecological concepts related to the stream macroalgae, specially from tropical regions, may be expanded. For instance, studies have reported that the highest richness and abundance of lotic macroalgae in tropical/subtropical streams are determined basically by variation in climatic and environmental factors. Our results showed that, in addition to climatic and environmental factors, the increase in richness and abundance of stream macroalgae may also be affected by biotic interactions. In this context, our results suggest that the higher abundance of microalgae on the streambed seems to allow a better development of the benthic algal community, reaching to the later successional stages, in which the relative occurrence of larger and more complex algae (i.e., macroalgae) become more evident.

The freshwater red algae (Batrachospermales, Rhodophyta) of Africa and Madagascar I. New species of Kumanoa, Sirodotia and the new genus Ahidranoa (Batrachospermaceae)

Our knowledge of the diversity of African freshwater red algae is rather limited. Only a few reports exist. During our field work in the last five years we frequently encountered freshwater red algae in streams in Rwanda and Madagascar. Here we describe four new species and one new genus of freshwater red algae from the Batrachospermales, based on morphological and molecular evidence: Kumanoa comperei from the Democratic Republic of the Congo and Rwanda is related to K. montagnei and K. nodiflora; Kumanoa rwandensis from Rwanda is related to K. ambigua and K. gudjewga; Sirodotia masoalensis is related to S. huillensis and S. delicatula; and the new genus and species Ahidranoa madagascariensis from Madagascar is sister to Sirodotia, Lemanea, Batrachospermum s.str. and Tuomeya. There is also evidence for the presence of Sheathia, which was recorded as yet-unidentifiable Chantransia stages. These are among the first new descriptions since 1899 from the African continent and since 1964 from Madagascar. A short history of the exploration of freshwater red algae from Africa and Madagascar is provided. All new taxa are accompanied by illustrations and observations on their ecology.

Food Shortage Amplifies Negative Sublethal Impacts of Low-Level Exposure to the Neonicotinoid Insecticide Imidacloprid on Stream Mayfly Nymphs

Interactions of pesticides with biotic or anthropogenic stressors affecting stream invertebrates are still poorly understood. In a three-factor laboratory experiment, we investigated effects of the neonicotinoid imidacloprid, food availability, and population density on the New Zealand mayfly Deleatidium spp. (Leptophlebiidae). Larval mayflies (10 or 20 individuals) were exposed to environmentally realistic concentrations of imidacloprid (controls, 0.97 and 2.67 μg L−1) for nine days following five days during which individuals were either starved or fed with stream algae. Imidacloprid exposure had severe lethal and sublethal effects on Deleatidium, with effects of the lower concentration occurring later in the experiment. The starvation period had delayed interactive effects, with prior starvation amplifying imidacloprid-induced increases in mayfly impairment (inability to swim or right themselves) and immobility (no signs of movement besides twitching appendages). Few studies have investigated interactions with other stressors that may worsen neonicotinoid impacts on non-target freshwater organisms, and experiments manipulating food availability or density-dependent processes are especially rare. Therefore, we encourage longer-term multiple-stressor experiments that build on our study, including mesocosm experiments involving realistic stream food webs.

Soft-bodied benthic algae in pristine Brazilian streams: from acid to karst

ABSTRACT This study evaluated soft-bodied benthic algae from seven streams located in protected areas of central Brazil (Parque Nacional de Brasilia, Parque Nacional da Chapada dos Veadeiros and Parque Estadual de Terra Ronca), and related them to abiotic factors. We addressed the following questions: A) how algal community structure in Cerrado streams is influenced by the marked seasonality typical of the region; and B) how karst geology influences algal communities in Parque Estadual de Terra Ronca, as compared to streams in other Cerrado areas. Samples were collected between 2012 and 2013 from a single site in each stream, and upstream and downstream of caves present in Parque Estadual de Terra Ronca. Altogether, 159 taxa were recorded. Algal community structure varied significantly among sites, but not between seasons, despite relatively lower abundances during the rainy season, likely due to a negative influence of the faster currents in streams during this period. Some alkaliphilic species were observed only at sites near caves (e.g. the cyanobacterium Tolypothrix distorta), while acidophilic taxa were more frequent in the other streams (e.g. desmids and Cyanobacteria such as Scytonema caldarium, Hapalosiphon stuhlmannii and Stigonema ocellatum). We observed a rare green alga, Microthamnion kuetzingianum, and reported the cyanobacterium Rivularia aquatica for the first time in Brazil.

Niche dimensionality and herbivory control stream algal biomass via shifts in guild composition, richness, and evenness.

We developed a framework for the hierarchical pathways of bottom-up (niche dimensionality) and top-down control (herbivory) on biomass of stream algae via changes in guild composition (relative abundance of low profile, high profile, and motile guilds), species richness, and evenness. We further tested (1) the contrasting predictions of resource competition theory vs. the benthic model of coexistence on how the number of added nutrients constrains species richness, (2) the relationship between species richness and evenness, and (3) the biodiversity-ecosystem-function paradigm. Implementing a combination of field and lab experiments that manipulated for the first time in benthic algae herbivory and/or niche dimensionality, i.e., the number of added nutrients (NAN), including nitrogen, phosphorus, iron, and manganese, we made the following discoveries. First, important predictors of guild composition were herbivory (field) and NAN (lab); of richness, NAN (field) and NAN and guild composition (lab); of evenness, guild composition (field and lab) and herbivory (field); and of biomass, guild composition, NAN, and richness + evenness (field and lab). Herbivory increased the proportions of the low profile and motile guilds but decreased the proportion of the high profile guild. In the absence of grazing, greater proportions of the high profile guild resulted in elevated richness and biomass but diminished evenness, whereas in the presence of grazing, these relationships generally disappeared. Second, both experiments confirmed the prediction of the benthic model that species richness increases with NAN, a pattern inconsistent with resource competition theory. Third, supplementation with manganese and/or iron increased algal richness, indicating that micronutrients, which have generally been overlooked in stream ecology, added dimensions to the algal niche. Fourth, the richness-evenness relationship, observed only in the absence of herbivory, depended on the size of the species pool. It was positive at richness lower than 49 species (lab), implying complementarity and facilitation, while at higher richness (field and lab), this relationship was negative, consistent with negative interspecific interactions. Finally, the greater dependence of biomass production on guild composition and NAN than on richness and evenness suggests that more comprehensive, environmentally explicit, and trait-based approaches are necessary for the study of the biodiversity-ecosystem-function paradigm.

STATUS, DISTRIBUTION AND HABITAT SPECIFICITY OF BENTHIC MACRO-INVERTEBRATES: A CASE STUDY IN FIVE TRIBUTARIES OF BUDDHIGANGA RIVER IN WESTERN NEPAL

Benthic macro-invertebrates are organisms that inhabit the bottom of substrates such as sediments, debris, logs, macrophytes and filamentous algae of streams, rivers and lakes for some span of their lifecycle. They are important part of food chain since they are source of food for different species of fishes and process organic matters. These organisms are considered vital tools to assess any environmental change caused by anthropogenic interference in the river ecosystems. In this study, we sampled macro-invertebrates from 5 different rivers across altitudinal ranges of 600- 800 m and 1500-1700 m above sea level. We observed that the macro-invertebrate diversity varied substantially across altitudinal ranges. The diversity of macro-invertebrates was higher in lower altitudinal range, where 11 families were found, more than the higher altitudinal range. Some rare and dominant families were also identified in our study. We also examined the substrate specificity of macro-invertebrates. Results revealed that Ephemeroptera,Tricoptera, Coleoptera, Diptera and Odonata were found in all seven substrates namely bedrock, boulder, cobble, stone, pebble, gravel and sand. The richness and abundance of macro-invertebrates were documented in cobble, stone and pebble substrates. Similarly we also investigated the ecological river quality class of rivers using Ganga River System Biotic Score-Average Score per Taxon (GRS-BioS/ASPT) system which indicated good status. The outcomes of this study serve as a baseline data since no prior research has been done in these rivers.

The immatures of Bezziachilensis Spinelli & Ronderos, 2001 (Diptera, Ceratopogonidae).

The fourth instar larva and the pupa of Bezziachilensis Spinelli & Ronderos, 2001 are described for the first time. The immature stages were collected from macrophytes and filamentous algae in streams of the Patagonian steppe, in the provinces of Neuquén and Chubut, Argentina. The described stages were photographed and illustrated with a phase-contrast microscope and scanning electron microscope. Data on the bionomics of the species, new records and tables for characters of the known larvae and pupae of Bezzia Kieffer, 1899 from the Neotropical region are provided.