Marginal Vegetation Research Articles

DISTRIBUTION OF TADPOLES WITHIN AND AMONG BRAZILIAN STREAMS: THE INFLUENCE OF PREDATORS, HABITAT SIZE AND HETEROGENEITY

We studied the composition and richness of local tadpole assemblages in several streams at a forest site in southeastern Brazil. We initially focused on species distributions within streams, comparing the relative availability of microhabitats with the relative use of each microhabitat type by tadpoles of different species, in order to assess the existence of preference patterns. Then we assessed the role of features assumed to influence species distributions among streams, which may influence breeding site selection by adult frogs and, consequently, tadpole distribution. These features were stream size, tadpole predator abundance, structure of marginal vegetation, and microhabitat availability for tadpoles. We looked for gradients of species richness along gradients of the variables noticed to influence tadpole assemblage composition. Tadpoles of all species showed selectivity in microhabitat use. Species distribution among streams was influenced mostly by number of potential tadpole predators present, stream volume, arboreal vegetation cover at stream margins, and tadpole microhabitat diversity, though only the first two variables accounted for gradients in species richness. Even though smaller streams tend to shelter more anuran species than larger ones at sites in southeastern Brazil, we recommend the conservation of streams of a range of sizes and structural features, since anuran assemblages associated with streams vary in species composition along gradients in these characteristics.

Conveyance estimation for channels with emergent vegetation boundaries

Emergent vegetation strips occur commonly in rivers, especially along the banks, and have a significant influence on channel conveyance. A simple approach is presented for estimating the conveyance in such rivers, and the method is tested against laboratory and field data. Field data are also used to determine a realistic value of the resistance coefficient for marginal vegetation boundaries. Laboratory experiments have shown that the resistance of vegetation strips depends on the number of vegetation/ clear channel interfaces, and that the overall Manning resistance coefficient n varies strongly with flow depth. For practical purposes, conveyance can be estimated by summing the discharges in vegetated and clear channel zones, calculated separately but with allowance made for the interzonal interaction. The clear channel discharge usually makes the major contribution and can be reliably determined by application of familiar composite roughness formulae, accounting for different bed and side boundary resistance. Field data indicate a Manning's n of about 0·13 for a typical emergent vegetation side boundary. The vegetated zone discharge is invariably underestimated by using a basic vegetation resistance equation without accounting for interzonal interaction effects, especially for narrow strips, but its contribution to the total channel discharge is usually relatively small.

Alimentação de quatro espécies de Characiformes de um riacho da Floresta Atlântica, Guaraqueçaba, Paraná, Brasil

In the present study we analyzed seasonal changes in the diet, feeding behavior and food resource partitioning between juveniles and adults of four characiform species in an Atlantic Rainforest stream of the northern coast of the State of Parana, Brazil. Samples were collected monthly between September, 1999 and August, 2000 using a variety of capture techniques and underwater observations. In general, full stomach contents were more common in juveniles than in adults. Deuterodon langei Travassos, 1957 was classified as an omnivorous species, with a tendency toward herbivory, Characidium lanei Travassos 1967 was classified as an insectivore, with a tendency toward larvophagy, Hyphessobrycon griemi Hoedeman, 1957 was classified as an omnivore, and Mimagoniates microlepis Steindachner, 1876 was classified as an insectivore, with a predominance of allochtonous insects. Juveniles and adults of all studied species showed low selectivity and high opportunism in their food selection. The high frequency of allochtonous food items in stomach contents underscores the importance of marginal vegetation in their diets, being essential for the integrity of these environments and for the preservation of coastal stream fish communities.

Influência da estrutura do hábitat sobre a ictiofauna de um riacho em uma micro-bacia de pastagem, São Paulo, Brasil

Este trabalho foi desenvolvido em quatro trechos de um riacho em área de pastagem no noroeste do Estado de São Paulo, com o objetivo de examinar a composição e estrutura quantitativa da ictiofauna e investigar sua relação com as características do hábitat. Os peixes foram coletados nos três meses centrais dos períodos seco e chuvoso por meio de uma passagem de pesca elétrica por mês. A análise da qualidade química da água mostrou condições boas nos quatro trechos, enquanto que a análise da integridade física do hábitat mostrou condições pobres para os trechos 2 e 3 e regulares para os trechos 1 e 4. Foram coletadas 27 espécies de peixes, totalizando 1.241 indivíduos e 5,1 kg. A estrutura quantitativa da ictiofauna demonstrou maior associação com a estrutura do hábitat do que com a sazonalidade visto que os trechos 1 e 2 foram agrupados separadamente dos trechos 3 e 4, independentemente do período de amostragem. De acordo com a análise de correspondência canônica, a elevada abundância de Gymnotus carapo Linnaeus, 1758 nos trechos 1 e 2 esteve associada principalmente com a abundância de vegetação marginal. O maior volume de hábitat no trecho 3 explicou a abundância de Piabina argentea Reinhardt, 1867, e a predominância de substratos rochosos no trecho 4 explicaram a abundância de Hypostomus nigromaculatus (Schubart, 1964).

The Use of Fossil Caddisfly Assemblages in the Reconstruction of Flow Environments from Floodplain Paleochannels of the River Trent, England

This paper examines the use of fossil larval trichopteran communities to investigate and describe the flow environment of a paleochannel network in the middle reaches of the River Trent floodplain (UK). Previous research utilising fossil insect communities (principally O. Coleoptera, O. Chironomidae) has focussed upon climate reconstruction. However, larval trichopteran communities (O. Trichoptera) also offer an aquatic signal, giving information regarding channel habitat structure and flow environments. The taxonomic diversity of each fossil community and the categorisation of each taxon into a known flow group, using the “LIFE” methodology, facilitates the reconstruction of the river flow conditions at each site based upon known faunal associations with mean flow velocity. A total of 49 trichopteran taxa were recorded from 17 paleochannels (n = 170 samples). Detrended Correspondence Analysis (DCA) identified a environmental gradient on the first DCA axis that reflected variability in flow, from rapid/fast flow to slow flowing and standing water habitats. In addition, two distinct faunal groups were identified on the second DCA axis characteristic of (i) small nutrient rich lentic habitats; and (ii) larger water bodies displaying features of both lentic, lotic and ephemeral habitats where marginal vegetation is abundant on a mineral substratum. The results demonstrate that larval Trichoptera can be used in paleolimnological research to reconstruct a flow signal and provide additional information regarding the aquatic habitat structure. Their wider use in describing the aquatic environment, in association with other proxies (e.g., Chironomidae and Coleoptera), may provide a more holistic understanding of floodplain paleoenvironment succession.

Estrutura populacional dos camarões simpátricos Potimirim glabra e Potimirim potimirim (Crustacea, Decapoda, Atyidae) no rio Sahy, Rio de Janeiro, Brasil

Este trabalho teve por objetivo obter conhecimento sobre a estrutura populacional de dois camarões de água doce simpátricos, Potimirim glabra (Kingsley, 1878) e Potimirim potimirim (Müller, 1881) no rio Sahy, Mangaratiba, Rio de Janeiro, Brasil. Os indivíduos foram coletados mensalmente durante o período de setembro de 1997 a fevereiro de 1999 utilizando-se peneiras, que foram passadas sob a vegetação marginal, superfície de rochas e pequenas poças d'água, num esforço de 15 minutos por coletor. Os animais foram separados quanto ao sexo e mensurados em relação ao comprimento total e do cefalotórax. Um total de 4.889 indivíduos foram coletados no rio Sahy: 3.281 P. glabra e 1.608 P. potimirim. A razão sexual observada foi de 1:1 para P. glabra e 1:2,3 para P. potimirim. Em ambas populações, cinco estágios de maturidade sexual foram determinados, sendo as populações constituídas principalmente por camarões adultos. O recrutamento de juvenis apresentou diferenças em ambas as espécies. O recrutamento de P. glabra ocorreu durante todo o período de estudo, exceto na primavera, enquanto que P. potimirim foi registrado somente no outono. A distribuição sazonal de fêmeas ovígeras de P. glabra é similar ao de P. potimirim, com reprodução na primavera e no verão.

Sustentabilidade da pesca na Amazônia

NO PRESENTE trabalho é feita uma síntese dos conhecimentos sobre a atividade pesqueira na Amazônia, incluindo histórico, potencial e tipos de pesca, composição do pescado e principais entraves e estratégias de manejo adotadas. Discute-se a inter-relação da pesca com as condições do ambiente aquático e a importância da vegetação ripariana ou mata ciliar como fonte de alimento, abrigo e refúgio para os peixes. Defende-se a idéia de que o manejo dos recursos pesqueiros só será bem-sucedido e eficaz se for compartilhado por todos os atores sociais direta e indiretamente envolvidos na pesca, e não apenas os pescadores, consumidores e comerciantes de peixes. O trabalho aponta a educação ambiental como a estratégia mais importante e talvez único caminho para a real sustentabilidade da pesca e, por conseguinte, dos recursos pesqueiros amazônicos.

Assessing the effectiveness of enhancement activities in urban streams: I. Habitat responses

AbstractEffects of stream enhancement on habitat conditions in five spring‐fed urban streams in Christchurch, New Zealand, were investigated. Stream enhancement consisted of riparian planting at three sites, and riparian planting and channel modifications at two sites, where a concrete dish channel and a timber‐lined channel were removed, and natural banks reinstated. Sites were surveyed prior to enhancement activities and 5 years after, and changes in riparian conditions (composition, horizontal and vertical cover), instream conditions (bank modifications, inorganic and organic material on the streambed), and hydraulic conditions (wetted perimeter, cross‐sectional area, depths and velocities) quantified. Enhanced sites generally had higher marginal vegetation cover, as well as increased overhanging riparian vegetation, reflecting planting of Carex sedges close to the water. Bed sediments changed at some sites, with the greatest change being replacement of a concrete channel with gravel and cobble substrate. Bryophyte cover declined at this site, reflecting loss of stable habitat where these plants grew. Bed sediments changed less at other sites, and cover of fine sediments increased in some enhanced sites, presumably from sediment runoff from nearby residential development. Filamentous algal cover decreased at one stream where shade increased, but increased in another stream where the removal of timber‐lined banks and creation of a large pond decreased shade. Stream enhancement increased variability in velocity at three of the five sites, but overall changes to stream hydraulics were small. Although enhancement activities altered the physical conditions of the streams, major changes occurred only to riparian vegetation and bank conditions. Lack of other major changes to instream physical conditions most likely reflected the limited range of channel morphology alterations undertaken. Moreover, the flat topography of Christchurch and naturally low stream discharge further constrained changes to instream physical conditions from enhancement activities. Sediment inputs from continuing urban development also negated the effects of adding coarse substrates. These over‐arching factors may constrain the success of future stream enhancement projects within Christchurch. Copyright © 2005 John Wiley & Sons, Ltd.

A new record of Uhlorchestia uhleri (Shoemaker, 1930) (Peracarida, Amphipoda, Talitridae) from the southern Gulf of Mexico

A total of 24 Uhlorchestia uhleri (Shoemaker, 1930) females were identified from 3,828 amphipods found in 1,402 samples from 31 sampling sites. At each locality, amphipods were collected from uncovered soft substrates and marginal vegetation, whereas sampling in coarse woody debris depended on the local availability of that habitat. Submerged aquatic vegetation consisted of Vallisneria americana (Michx.) or Cabomba palaeformis (Fassett). The amphipods were identified following Bousfield & Heard (1986) and the specimens are deposited in the Colecci?n Nacional de Crust?ceos, UNAM. Ilustrations were made with a microscope and drawing attachment. The 24 U. uhleri specimens were collected in salinities lower than 0.5%o, 20 females from the roots of the water hyacinth, Eichhornia crassipes (Mart.) in the R?o Playa, an artificial canal connected to the Rio El Moral 5.8 km inland (18?20/N 93?18'W) in the Coatzacoalcos basin, and the other four specimens from Rhizophora mangle (L.) roots in the lagoons of San Pedrito (18?23'N 92?34.5'W), El Cometa (18?27.5'N 92?26.25'W), El Coco (18?28.74'N 92?41.48/W), and

Significance of temporal changes when designing a reservoir for conservation of dragonfly diversity

While there has been much focus in biodiversity conservation that transcends place, few studies transcend time. Yet an appreciation of vegetational and hydrological succession is essential for maintaining a habitat that has been created with the aim of conserving a particular group of organisms. This is a study of changes in a dragonfly assemblage over a period of 13 years at a biodiversity-rich, southern hemisphere reservoir. A total of 30 dragonfly species were recorded in this study, compared to 12 species before the reservoir was constructed in 1988, and 26 species in 1993, with 25 species resident in both 1993 and 2001. Two of these are local endemics. One other endemic was lost to succession in 1993 but reappeared in 2001. Three other species never reappeared after succession in 1993, yet six other species appeared after this date. Multivariate analyses identified structural and compositional vegetation, especially marginal forest, percentage vegetation cover, percentage shade, as the most important environmental variables determining dragonfly species composition. Other important environmental variables were grasses of tall, medium and short height categories, submerged vegetation, water flow and amount of open water. Not surprisingly, successional changes in vegetation physiognomy and in water conditions significantly increased Odonata species richness and diversity over the years. More importantly, the study shows that to maintain both high species richness, including endemics, it is essential to maintain a variety of biotopes using selective management of the marginal vegetation without allowing succession to proceed to a point where overgrowth of the bank and silting of the bottom begin to impoverish the fauna.

Ichthyofauna of two streams (silted and reference) in the Upper Paraná river basin, Southeastern Brazil

In this study the fish assemblages of the silted Aguas Claras stream (AC) was compared with that of a reference, the São Carlos stream (SC), so as to identify potential fish indicators of integrity or degradation. Both streams, located about 5 km from one another, are part of the Upper Paraná river basin, Brazil, and present similar physiographical features. Twenty-one species were collected in AC (1,271 specimens) and 18 in SC (940 specimens). In AC, dominant species e.g., Corydoras aeneus (sandy pools), Serrapinnus notomelas, and Pyrrhulina australis (warm marginal shallow pools) were those favored by new microhabitats linked to siltation and removal of the riparian vegetation. Changes in the composition of the marginal vegetation resulted in dominance of species such as Hisonotus francirochai (marginal grasses). In SC the dominant species was Phalloceros caudimacultus, abundant in marginal shallow pools, and Trichomycterus diabolus. and Hypostomus nigromaculatus, exclusively riffle-dwelling species, which were absent in AC. Fish assemblage monitoring is recommended for use in riparian management programs in order to evaluate negative instream sedimentation effects.

Impact of major changes in flow regime on the macroinvertebrate assemblages of four chalk stream sites, 1997–2001

AbstractThe macroinvertebrate assemblages of three unshaded sites on the River Kennet and one shaded site on the River Lambourn in Berkshire, England, were sampled in summer 1997–2001. Quantitative samples were taken on gravel and on the dominant macrophyte at each site in each year and abundance data were recorded for 57 families of macroinvertebrates. The study commenced during a major drought (1997), but in subsequent years discharge prior to sampling was much higher, culminating in the exceptionally high flows of spring 2001. Both family richness and abundance varied significantly in relation to site, habitat and year. Multidimensional scaling ordination, based on Bray‐Curtis dissimilarities, also displayed significant differences between sites, habitats and years. Differences in composition between the Kennet sites were partly due to longitudinal zonation whilst on the Lambourn, faunal differences resulted from shading and the addition of families from nearby habitats, including marginal vegetation. Major changes took place in family composition and abundance between the drought year of 1997 and 1998, indicating that faunal recovery from drought was rapid. Thereafter, faunal changes between 1998 and 2000 were relatively limited. In 2001, following the prolonged period of exceptionally high discharge, overall family richness peaked on both habitats at the three Kennet sites and family abundance reached peak or second highest values on all four sites and both habitats. Thus, the recent high discharge regimes experienced by these perennial chalk stream sites have had no immediate detrimental consequences for the macroinvertebrate assemblages. Copyright © 2004 John Wiley & Sons, Ltd.

Spatial and temporal distribution of "curvina" larvae (Plagioscion squamosissimus Heckel, 1840) and its relationship to some environmental variables in the Upper Paraná River floodplain, Brazil.

With the objective of studying the spatial and temporal distribution of "curvina" Plagioscion squamosissimus larvae and verifying respective spawning sites, monthly sampling was carried out from March 1993 to February 1994 on the Upper Paraná River floodplain. Using a conical-cylindrical plankton net (0.5 mm mesh), samples were taken from the surface of the water bodies, and in the marginal vegetation a strainer and a dragnet ("picaré") were used. Water samples were collected for environmental variable analysis (temperature, dissolved oxygen, water pH, and electrical conductivity). Water level data were obtained from hydrometric stations. High average density of larvae was found from December 1993 to February 1994 due to high temperature and water level. The Baía sub-area was shown to be the most important in the larvae catch, probably due to its semi-lotic characteristics. Larvae size distribution was shown to be more frequent in the 4.0 mm standard length class, indicating that the sampling stations were next to the spawning sites.

Response of the flora and macroinvertebrate fauna of a chalk stream site to changes in management

SUMMARY1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50‐m section of a chalk stream in Berkshire, England between June 1975–79 and June 1997–2001.2. The site was part of a trout fishery in 1975–79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997–2001, the site was heavily shaded by trees and riparian vegetation.3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat.4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975–79 than in 1997–2001, total family richness for the site in each year did not differ significantly between sampling periods.5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975–79 and 57 in 1997–2001. This small increase in site family richness may be due to the invading marginal plants.6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation.7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources.8. Whereas macroinvertebrate family richness has been conserved under the recent ‘no management’ regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout.

Effect of sports fisherman activities on dragonfly assemblages on a Hungarian river floodplain.

We studied the dragonfly fauna along a 15 km stretch of thefloodplain of the regulated, first-order river Tisza, Hungary. Data on capturedand observed adults, larvae and exuvia were recorded. Observations were madefrom May to October 1998 and 1999 on 34 species, which is 52% of theHungarian fauna. Classification on the basis of faunistic similarity revealedthat habitat-level differences, associated with various degrees of physicalanthropogenic impact on bank vegetation, can exceed variation among the waterbodies of different types (backwater, pond, marsh, canal, river). The richestsites were dominated by structurally diverse macrophyte vegetation, while flowing waters (river and canal) were poorest in species. Odonata were found tobe reliable indicators of small-scale habitat patterns, reflecting vegetationdifferences even within single water bodies where the sampling spots werearranged just a few hundred metres apart. Along a gradient of utilisationintensity, the species number of Odonata assemblages and the summed relativeabundance of the five rarest species of the study area decreased linearly withincreasing fragmentation of the marginal vegetation. Sports fishermanactivities, implying disruption of the littoral marsh zone by establishment ofclearings and excessive trampling of the banks, can also be monitored bydragonfly faunistic investigations. Our results demonstrate that conservation ofthese varied floodplain water bodies requires the control of sports fishingactivity, suggesting that (i) to maintain the representative odonate fauna ofthe water bodies, some non-fragmented shores must be provided; and (ii) permanentfishing stands should not exceed 8 m mean width and should beseparated by at least 12 m of intact riparian sections.

Partição ambiental de Potimirim glabra (Kingsley) e Potimirim potimirim (Müller) (Crustacea, Decapoda, Atyidae) no rio Sahy, Mangaratiba, Rio de Janeiro, Brasil

This work aims to determinate the spatial distribution of two sympatric freshwater shrimp species, Potimirim glabra (Kingsley, 1878) and Potimirim potimirim (Muller, 1881) in Sahy River, municipality of Mangaratiba. The populations were collected from September, 1997 to February, 1999. The animals were collected monthly by sieving the marginal vegetation, on rocky surface and among litter on river bottom. The animals were sorted sexed. Their carapace length measured and total length measured. A total of 4,889 animals were collected in Sahy River: 3,281 P. glabra and 1,608 P. potimirim. The spatial distribution of P. glabra and P. potimirim showed an environmental partition. Potimirim glabra occurred in abundance at the farthest stations from the beach, wilst and P. potimirim, at the nearest stations from the sea.

The effects of bankside management on chalk stream invertebrate communities

SUMMARY 1. Communities of aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects were investigated from short stretches of English chalk streams with two different bankside vegetation types: simply structured grazed grass (grazed) and structurally complex herbaceous vegetation with scattered trees (ungrazed). Macroinvertebrates were sampled in spring, summer, autumn and winter 1996–97 from three aquatic habitats: mid‐channel gravel, patches of the aquatic macrophyte Ranunculus and marginal emergent macrophytes. The terrestrial adult phases of aquatic insects were sampled in spring, summer and autumn from bankside vegetation.2. Total macroinvertebrate abundance did not differ between stretches with different bankside vegetation. Taxon richness of mid‐channel gravel was, however, significantly higher in ungrazed compared with grazed stretches and Shannon diversity (H′) of mid‐channel gravel and marginal vegetation was significantly higher in ungrazed compared with grazed stretches. Total abundance, taxon richness and Shannon diversity (H′) of the terrestrial adult phases of aquatic insect were significantly higher from the bankside vegetation of ungrazed compared with grazed stretches.3. Ordination of communities of aquatic macroinvertebrates and terrestrial adults demonstrated that individual families of both groups were generally more abundant in ungrazed stretches. Many more families were significantly associated with ungrazed stretches than with grazed stretches.4. This investigation has shown that high structural diversity of bankside vegetation along lowland chalk streams is accompanied at the reach scale by increased diversity of both aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects. The conservation potential of such streams may thus be lowered by management practices that result in the removal or simplification of bankside vegetation along extensive stream stretches.

Conveyance of meandering channels with marginal vegetation

Vegetation along the margins of meandering channels affects conveyance under both in bank and overbank flow conditions. Experiments using simulated vegetation with different channel and floodplain geometries have shown that vegetation increases resistance by introducing stem drag, but may also decrease it by reducing separation at tight bends. For in bank flows, bend resistance (including vegetation effects) is better accounted for by a bend curvature parameter than by sinuosity alone. Conveyance for overbank flows with marginal vegetation and straight floodplains can be predicted satisfactorily using the James and Wark method with adjustment for vegetation density.

Conveyance of meandering channels with marginal vegetation

Vegetation along the margins of meandering channels affects conveyance under both in bank and overbank flow conditions. Experiments using simulated vegetation with different channel and floodplain geometries have shown that vegetation increases resistance by introducing stem drag, but may also decrease it by reducing separation at tight bends. For in bank flows, bend resistance (including vegetation effects) is better accounted for by a bend curvature parameter than by sinuosity alone. Conveyance for overbank flows with marginal vegetation and straight floodplains can be predicted satisfactorily using the James and Wark method with adjustment for vegetation density.

Conveyance of meandering channels with marginal vegetation

Vegetation along the margins of meandering channels affects conveyance under both in bank and overbank flow conditions. Experiments using simulated vegetation with different channel and floodplain geometries have shown that vegetation increases resistance by introducing stem drag, but may also decrease it by reducing separation at tight bends. For in bank flows, bend resistance (including vegetation effects) is better accounted for by a bend curvature parameter than by sinuosity alone. Conveyance for overbank flows with marginal vegetation and straight floodplains can be predicted satisfactorily using the James and Wark method with adjustment for vegetation density.