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Abstract Microplastics (MPs) are widespread in oceans worldwide, posing a significant threat to aquatic ecosystems. The abundance of these particles in water is related to population density and urban development, functioning as a sink for MPs. However, the pollution levels due to the accumulation of MPs in the estuarine in Amazonian mangrove areas remain unknown. Here, we show that population density and fishing activities influence the distribution of MP pollution in these waters. We found the highest abundance of MPs in the inner (1.03 items/m3) and outer (0.82 items/m3) portions of the estuary, corresponding to the areas with the highest population density and fishing activity, respectively. The main morphological characteristics of MPs are fibers (89.8%), blue color (55.2%), and size of 1000–2000 μm (31.7%). The risk analysis showed a low level of danger, suggesting that the potential impact on the ecosystem is still small. Our results demonstrate that the presence of human populations and their fishing activities significantly influence the accumulation of MPs in the estuarine waters on the Amazon coast. Based on our findings, more sophisticated analysis using MPs’ spatial distribution models can be associated with hydrodynamic processes, aiming to define pollution hotspots and support the mitigation of their emerging negative effects. In addition, monitoring and generating valuable information are the main targets for developing comprehensive strategies to preserve biodiversity and sustainability in the Amazon coastal zone.

Abstract Rich freshwater biodiversity is threatened by increasing deforestation and disorderly urbanization throughout the Brazilian Amazon, especially in streams and creeks, leading to loss of aquatic habitats. Biological information combined with habitat and water quality are effective tools for rapid assessment. The impact of increasing urbanization was assessed in the Cereja River, eastern Amazonia using a Riparian Habitat Diversity Index (RHDI), benthic macroinvertebrate structure and water and sediment variables in ten areas along the Cereja using multivariate analyzes. Increasing urbanization is associated with lower RHDI, abundance, diversity and equity of benthic macroinvertebrates, higher conductivity, pH, temperature, width and percentage gravel. This information is useful for rapid identification of impacts, assessment of recovery of degraded areas and maintenance of non-degraded areas along urban streams.

Abstract Information on freshwater mussel behavior in the sediment is scarce worldwide, especially in the Amazon. Laboratory experiments were used to measure the responses of the single mussel species Castalia ambigua in relation to combinations of two co‐occurring different morphotypes (Morphotype I with an elongated shell and Morphotype II with a rounded shell), and three different densities (four, eight, and 16 mussels). Horizontal movements (cm) were calculated by summing changes in the position of each specimen and the shell exposure at the sediment–water interface was obtained by measuring (mm) the exposed part of the shell. Castalia ambigua presented different patterns of shell exposure and horizontal movements linked with shell shape and density. Castalia ambigua Morphotype I remained less exposed with 4 mussels. In contrast, this morphotype was more exposed and tended to aggregate in treatments with 8 and 16 mussels, similar to observations of Morphotype II at all densities. Morphotype II is mainly found in low hydrodynamic energy habitats, suggesting that patches with high densities may stabilize the substrate around the shells of Morphotype I, which is associated with high hydrodynamic energy habitats. We suggest that these patterns may be associated with intrinsic factors of the species, such as reproduction, sexual dimorphism and feeding. Moreover, additional studies using other mussel species belonging to the families Hyriidae and Mycetopodidae are important, since the behavior of these mussels in the sediment may provide useful information on their functional roles in river ecosystems.

Abstract Novel insights into habitat suitability for two Unionida freshwater mussels, Castalia ambigua Lamarck, 1819 (Hyriidae) and Anodontites elongatus (Swainson, 1823) (Mycetopodidae), are presented on the basis of hydraulic variables linked with the riverbed in six 500‐m reaches in an eastern Amazonian river basin. Within the reaches, there was strong habitat heterogeneity in hydrodynamics and substrate composition. In addition, we investigated stressors based on landscape modification that are associated with declines in mussel density. We measured hydraulic variables for each 500‐m reach, and landscape stressors at two spatial scales (subcatchment and riparian buffer forest). We used the Random Forest algorithm, a tree‐based model, to predict the hydraulic variables linked with habitat suitability for mussels, and to predict which landscape stressors were most associated with mussel density declines. Both mussel species were linked with low substrate heterogeneity and greater riverbed stability (low Froude and Reynolds numbers), especially at high flow (low stream power). Different sediment grain size preferences were observed between mussel species: Castalia ambigua was associated with medium sand and Anodontites elongatus with medium and fine sand. Declines in mussel density were associated with modifications linked to urbanization at small scales (riparian buffer forest), especially with percent of and distance from rural settlements, distance to the nearest street, and road density. In summary, the high variance explained in both hydraulic and landscape models indicated high predictive power, suggesting that our findings may be extrapolated and used as a baseline to test hypotheses of habitat suitability in other Amazonian rivers for Castalia ambigua and Anodontites elongatus and also for other freshwater mussel species. Our results highlight the urgent need for aquatic habitat conservation to maintain sheltered habitats during high flow as well as mitigate the effects of landscape modifications at the riparian buffer scale, both of which are important for maintaining dense mussel populations and habitat quality.

ABSTRACT Oyster culture has benefited traditional coastal communities along the Amazon macrotidal mangrove coast of Pará state in Brazil since 2006. Currently, seven oyster culture units in five municipalities are expanding production, but with no environmental monitoring, which is important for the control of the impacts of oyster culture on waters as well as for oyster management and conservation. Seasonal variation in environmental characteristics of the water was evaluated at all oyster culture units in Pará, from September to November 2013 (dry season) and February to April 2014 (wet season), to generate baseline data to evaluate future impacts and aid strategic planning, such as diversifying seed production. Salinity, dissolved oxygen, pH, oxidation-reduction potential, depth, temperature, and chlorophyll-a concentration were measured during flooding and ebbing tides, and compared between seasons and among culture units using uni- and multivariate statistics. All variables were significantly higher in the dry season, except depth, which was significantly greater in the wet season. Mean salinity, which varied from 2.4 to 46, explained most of the variation among culture units in relation to season, sampling date within each season and tidal state. However, dissolved oxygen, pH and depth were also important. Oyster culture units in Pará may be suitable for sustainable harvesting of seed/spat from the wild (lower salinity and pH), or for on-growing (higher salinity, higher pH, and greater depth). Seasonal variation is sufficient to allow both activities at most units at appropriate times of the year, which would help increase oyster production in Pará.

Mussels have important ecological functions in freshwater ecosystems, but populations are declining in many rivers worldwide. In the Amazon, which is undergoing widespread human-mediated alterations, information on mussel ecology is lacking. We investigated whether declines in mussel density, due to exploitation, are associated with lower macroinvertebrate assemblage taxon richness and modified habitat functioning in an Amazonian river. Between 2015 and 2017, macroinvertebrate metrics of abundance and number of families, and related habitat variables, were compared between exploited and unexploited mussel beds in the Caeté river, northeastern Pará state, Brazil. Except for Chironomidae abundance, which increased, other macroinvertebrate metrics decreased in exploited mussel beds, especially abundances of shredders and predators. Medium and high mussel densities appear to support abundant and diverse macroinvertebrate assemblages. Macroinvertebrate decreases were mainly correlated with lower organic matter in the sediment and higher dissolved solids in the water column, due to losses in mussel biodeposition and filtration functions. Amazonian freshwater mussel density is a useful indicator of abundant and diverse macroinvertebrate assemblages, and mussel beds may help prioritize locations for habitat conservation in Amazonian rivers, and indirectly for fishes that are essential for mussel dispersion. Aquatic management efforts should explicitly include mussel beds and their diverse associated macroinvertebrate assemblages.

Oysters (Ostreidae) manifest a high degree of phenotypic plasticity, whereby morphology is of limited value for species identification and taxonomy. By using molecular data, the aim was to genetically characterize the species of Crassostrea occurring along the Brazilian coast, and phylogenetically relate these to other Crassostrea from different parts of the world. Sequencing of the partial cytochrome oxidase c subunit I gene (COI), revealed a total of three species of Crassostrea at 16 locations along the Brazilian coast. C. gasar was found from Curuçá (Pará state) to Santos (São Paulo state), and C. rhizophorae from Fortim (Ceará state) to Florianópolis (Santa Catarina state), although small individuals of the latter species were also found at Ajuruteua beach (municipality of Bragança, Pará state). An unidentified Crassostrea species was found only on Canela Island, Bragança. Crassostrea gasar and C. rhizophorae grouped with C. virginica, thereby forming a monophyletic Atlantic group, whereas Crassostrea sp. from Canela Island was shown to be more similar to Indo-Pacific oysters, and either arrived in the Atlantic Ocean before the convergence of the Isthmus of Panama or was accidentally brought to Brazil by ship.

Data on macrofauna density and diversity, and the height and density of Spartina brasiliensis, were obtained from salt marsh beds of a tropical estuary in northern Brazil. Sampling was carried out at four distinct times of the year, during the wet and dry seasons and in the transition periods between these. Sampling was also carried out in salt marshes of three size classes, small, medium and large. Variables were analyzed in relation to time of year and salt marsh size class. Overall, 46 taxa were found, with polychaetes, isopods and the gastropod Neritina virginea dominating the fauna. Macrofauna density and diversity were positively correlated with culm density, indicating a possible role in protection from predation. All the three variables were higher during the transitional periods between the wet and dry seasons and seasonal changes in rainfall, salinity and light availability may influence mortality, food availability and settlement of the macrofauna. There was no effect of salt marsh size on either the macrofauna or the vegetation.Dados sobre a densidade e diversidade da macrofauna em relação à altura e densidade de Spartina brasiliensis foram obtidos em bancos de marismas em um estuário tropical no norte do Brasil. A amostragem foi realizada quatro vezes durante um ano, nas estações chuvosa, seca e nos períodos de transição entre estas. A amostragem foi realizada em marismas de três classes de tamanho: pequeno, médio e grande. As variáveis foram analisadas em relação às estações do ano e das classes de tamanho das marismas. Um total de 46 táxons foram encontrados, com os poliquetos, isopodos e o gastropódo Neritina virginea dominando a fauna, resultados similares a estudos realizados em marismas no sul do Brasil. A densidade e a diversidade da macrofauna foram correlacionadas positivamente com a densidade de colmos da vegetação, indicando um possível papel da vegetação em proteção contra predação. Todas as três variáveis foram maiores durante os períodos transicionais entre as estações chuvosa e seca e mudanças sazonais em precipitação, salinidade e disponibilidade de luz possam influenciar mortalidade, disponibilidade de alimento e assentamento da macrofauna. Não houve um efeito de tamanho da marisma sobre a macrofauna ou a vegetação. O efeito beneficial da vegetação sobre a macrofauna é apoiado por outros estudos de marismas brasileiras.

Os rios são os agentes mais importantes no transporte dos sedimentos para as áreas mais baixas dos continentes e para o mar. Além dos efeitos diretos do clima local, a cobertura vegetal atua no controle da descarga e no suprimento de sedimentos. Sendo assim, o presente trabalho enfoca o padrão de distribuição granulométrica do rio Urumajó (nordeste paraense) em relação ao estado de preservação da mata ciliar. Cinco estações (A-E) foram estabelecidas de forma a registrar um transecto da nascente à foz do rio. Nessas estações, procedeu-se com a caracterização da mata ciliar, bem como do seu grau de preservação. Além disto, elaborou-se um perfil transversal ao canal para cada estação, com coleta de cinco amostras de sedimentos em cada perfil. Estes foram submetidos à análise granulométrica, que resultou na obtenção de valores da média, mediana, seleção, assimetria e curtose. Com os resultados foi possível reconhecer as características sedimentares normais do rio, onde areia média é a principal classe granulométrica transportada. Foram observadas nas estações A e C a clara tendência das amostras serem moderadamente bem selecionadas e aproximadamente simétricas, com dominância absoluta de areia média, o que está diretamente relacionado ao seu bom estado de preservação. Significativas variações granulométricas nas estações B, D e E foram associadas com o processo erosivo das margens do rio, conseqüência da degradação da mata ciliar. Além disso, foi constatada a influência das correntes de maré na sedimentologia da estação E, subsidiando também a delimitação do ambiente estuarino que se encontra associado ao canal fluvial.Rivers are the main ways of sediment transport from inland to the coastal zone and oceans. Despite direct influence of climate, the vegetation coverage plays a central role in liquid and solid fluvial discharge. In this context, the present work aimed to study the fluvial sedimentology of the Urumajó River (Pará, Brazil) in relation to the preservation state of riparian vegetation. Sediment samples were collected at five sites (A to E), including a five-sample transversal profile at each site. The sites were distributed from the source to the estuarine area. The characteristics and preservation state of the riparian vegetation were analyzed at each site as well. The collected sediments were submitted to grain size analysis, where mean grain size, median, asymmetry, selection and kurtosis were obtained. The results made it possible to recognize the regular characteristics (sites A and C), which included median sand as the main sediment class and well-sorted and approximate symmetric grain size distribution, directly related to the well-preserved riparian vegetation at sites A and C. On the other hand, sites B, D and E showed substantial differences in relation to the regular pattern. This fact could be associated to the vegetation degradation at those sites, resulting in margin erosion. Furthermore, at site E, reflexes of tide influence on the sediment characteristics could be observed, subsidizing the estuary delimitation.

Four Brazilian populations of Anomalocardia brasiliana were tested for mutual genetic homogeneity, using data from 123 sequences of the mtDNA cytochrome oxidase c subunit I gene. A total of 36 haplotypes were identified, those shared being H3 (Canela Island, Prainha and Acupe) and both H5 and H9 (Prainha and Acupe). Haplotype diversity values were high, except for the Camurupim population, whereas nucleotide values were low in all the populations, except for that of Acupe. Only the Prainha population showed a deviation from neutrality and the SSD test did not reject the demographic expansion hypothesis. Fst values showed that the Prainha and Acupe populations represent a single stock, whereas in both the Canela Island and Camurupim stocks, population structures are different and independent. The observed structure at Canela Island may be due to the geographic distance between this population and the remainder. The Camurupim population does not share any haplotype with the remaining populations in northeastern Brazil. The apparent isolation could be due to the rocky barrier located facing the mouth of the Mamanguape River. The results highlight the importance of wide-scale studies to identify and conserve local genetic diversity, especially where migration is restricted.

The current taxonomy of the Teredinidae (shipworms) is wholly based on morphology and up to now no molecular studies of the phylogeny of this group have been published. In the present study the relationships between four genera of the subfamilies Teredininae and Bankiinae were established and the efficiency of the 16S rRNA gene in characterizing four Teredinidae species was tested. Phylogenetic trees support the grouping of Bankia fimbriatula with Nausitora fusticula and of Neoteredo reynei with Psiloteredo healdi, but the genetic distances do not justify the classification of these species into two distinct subfamilies. The results show that B. fimbriatula, N. reynei and P. healdi specimens from the coast of the Brazilian state of Pará have five distinct 16S rRNA haplotypes, with one N. reynei haplotype differing from the other haplotypes in respect to at least seven sequences sites, indicating the existence of two very distinct sympatric lineages.

This paper records for the first time the presence of Corbicula fluminea (Philipi, 1844) in the Brazilian Amazon Basin. This exotic bivalve was found in localities on the Amazonas, Pará and Tocantins rivers. Density and population size structure were measured in some localities. Mean density is between 6.66 and 7.3 individuals m-2. Population size structure and the dates of the first records suggest that the introductions may have occurred between 1997 and 1998. The introductions may have been mediated by ocean-going vessels visiting the ports of Manaus and Belém. The potential impact of the invasion on native freshwater bivalves is discussed along with the need for monitoring and prevention of further introductions of non-indigenous bivalves in Brazil.

Microplastics (MPs) are widespread in oceans worldwide, posing a significant threat to aquatic ecosystems. The abundance of these particles in water is related to population density and urban development, functioning as a sink for MPs. However, the pollution levels due to the accumulation of MPs in the estuarine in Amazonian mangrove areas remain unknown. Here, we show that population density and fishing activities influence the distribution of MP pollution in these waters. We found the highest abundance of MPs in the inner (1.03 items/m3) and outer (0.82 items/m3) portions of the estuary, corresponding to the areas with the highest population density and fishing activity, respectively. The main morphological characteristics of MPs are fibers (89.8%), blue color (55.2%), and size of 1000–2000 μm (31.7%). The risk analysis showed a low level of danger, suggesting that the potential impact on the ecosystem is still small. Our results demonstrate that the presence of human populations and their fishing activities significantly influence the accumulation of MPs in the estuarine waters on the Amazon coast. Based on our findings, more sophisticated analysis using MPs' spatial distribution models can be associated with hydrodynamic processes, aiming to define pollution hotspots and support the mitigation of their emerging negative effects. In addition, monitoring and generating valuable information are the main targets for developing comprehensive strategies to preserve biodiversity and sustainability in the Amazon coastal zone. [ABSTRACT FROM AUTHOR]

Information on freshwater mussel behavior in the sediment is scarce worldwide, especially in the Amazon. Laboratory experiments were used to measure the responses of the single mussel species Castalia ambigua in relation to combinations of two co‐occurring different morphotypes (Morphotype I with an elongated shell and Morphotype II with a rounded shell), and three different densities (four, eight, and 16 mussels). Horizontal movements (cm) were calculated by summing changes in the position of each specimen and the shell exposure at the sediment–water interface was obtained by measuring (mm) the exposed part of the shell. Castalia ambigua presented different patterns of shell exposure and horizontal movements linked with shell shape and density. Castalia ambigua Morphotype I remained less exposed with 4 mussels. In contrast, this morphotype was more exposed and tended to aggregate in treatments with 8 and 16 mussels, similar to observations of Morphotype II at all densities. Morphotype II is mainly found in low hydrodynamic energy habitats, suggesting that patches with high densities may stabilize the substrate around the shells of Morphotype I, which is associated with high hydrodynamic energy habitats. We suggest that these patterns may be associated with intrinsic factors of the species, such as reproduction, sexual dimorphism and feeding. Moreover, additional studies using other mussel species belonging to the families Hyriidae and Mycetopodidae are important, since the behavior of these mussels in the sediment may provide useful information on their functional roles in river ecosystems. [ABSTRACT FROM AUTHOR]

As a result of phenotypic plasticity, the cupped oysters (Crassostrea) are difficult to identify by means of their morphology. However, molecular DNA markers are a useful means of discriminating among these species. Cupped oysters are one of the most widely cultured marine invertebrates and correct species identification is important in aquaculture. Moreover, the molecular phylogeny of the genus Crassostrea and the subfamily Crassostreinae is still not clear. In order to identify the Brazilian cupped oysters and to clarify the phylogenetic relationships of these species, we sequenced a fragment of mitochondrial DNA (16S rRNA gene) from 120 specimens collected at nine different sites distributed along the Brazilian coast. The results identified two native species of oyster: Crassostrea gasar, from the Amazon to the Parnaíba delta; and Crassostrea rhizophorae, from the northeast (Fortim) to the south of Brazil. An exotic Crassostrea species, closely related to Indo-Pacific Crassostrea, was found in one location in the north of Brazil. Crassostrea showed monophyly and the Atlantic oysters are clearly separated from the Indo-Pacific cluster. [ABSTRACT FROM AUTHOR]

Melo, K.R., Tagliaro, C.H. and, Beasley, C.R., 2013.Seasonal changes in the subtidal benthic macrofauna of a mangrove coast Mangrove coasts in northern Brazil are subject to seasonal discharges of freshwater input from rivers and terrestrial runoff. However, little is known about the effects of freshwater discharge on the subtidal benthos in the region. Thus, three sites, each representing a different level of seasonal discharge, Canela island (low), Ajuruteua beach (medium), and the Caeté Bay (high) were sampled in the dry (October) and wet (April/May) seasons of 2007 and 2008, respectively. Sampling was carried out using a Petersen grab and a bottom dredge (total n=74). Additional replicas (n=12) were obtained by grab for sediment analyses. Salinity and turbidity of the bottom waters, and percentage of silt/clay in the sediment were also measured. Benthic macrofauna and environmental data were analyzed using uni- and multivariate techniques. A total of 661 individuals were distributed among 47 taxa of which polychaetes and crustaceans dominated at all three sites. No significant differences in macrofaunal abundance were found among sites and dates. At all sites, in the wet season, the number of taxa was low and dominance was high, especially in the Caeté Bay. The polychaete Nephtys fluviatilis only occurred in the Caeté Bay in the wet season, and yet was the dominant taxon (22.7% of total abundance). The Ajuruteua beach and Canela island samples were composed of typically marine taxa. The polychaete Armandia sp., the gastropod Olivella minuta, mysiid and phoxocephalid crustaceans and the echinoderm family Mellitidae were most abundant in the dry season at Canela island. Salinity was the most important environmental factor associated with high numbers of taxa in the dry season. Silt and turbidity were associated with low numbers of taxa in the wet season. In conclusion, the subtidal benthic macrofauna at Canela island, Ajuruteua beach and the Caeté Bay is mainly composed of polychaetes and crustaceans. The higher freshwater discharge in the wet season, resulting in lower salinity, higher percentage silt and greater turbidity, is associated with lower abundance, fewer taxa and a different faunal composition at Canela and Ajuruteua, and strong dominance of an oligohaline polychaete in the Caeté Bay [ABSTRACT FROM AUTHOR]

Mussels provide important ecological functions in freshwater ecosystems but the associations between Amazonian mussels, macroinvertebrate assemblage and habitat quality remain poorly understood. We investigated whether changes in macroinvertebrate assemblage structure and ecological functioning were associated with mussel presence. We compared sites with and without mussels, with similar habitat conditions, in an eastern Amazonian river, using field measurements of macroinvertebrate structure, hydrological variables and sediment organic matter, and laboratory experiments of mussel clearance rate and biodeposition. Sites with mussels were associated with higher macroinvertebrate abundance and number of taxa, especially for trichopterans Marilia (shredder), Oecetis (predator) and Antarctoecia (collector). Decreased chlorophyll-a in the water column and increased sediment organic matter were positively associated with mussel presence. Laboratory experiments corroborated these patterns, which were stronger with higher mussel density. Mussel filtration and biodeposition may be associated with habitat quality for other invertebrates by lowering phytoplankton density in the water column and increasing inputs of sediment organic matter. This suggests a potential role of freshwater mussels in ecosystem function associated with high taxonomic and functional diversity in the macroinvertebrate assemblages of an eastern Amazon river, enhancing the already high mussel conservation priority. [ABSTRACT FROM AUTHOR]

Novel insights into habitat suitability for two Unionida freshwater mussels, Castalia ambigua Lamarck, 1819 (Hyriidae) and Anodontites elongatus (Swainson, 1823) (Mycetopodidae), are presented on the basis of hydraulic variables linked with the riverbed in six 500‐m reaches in an eastern Amazonian river basin. Within the reaches, there was strong habitat heterogeneity in hydrodynamics and substrate composition. In addition, we investigated stressors based on landscape modification that are associated with declines in mussel density. We measured hydraulic variables for each 500‐m reach, and landscape stressors at two spatial scales (subcatchment and riparian buffer forest). We used the Random Forest algorithm, a tree‐based model, to predict the hydraulic variables linked with habitat suitability for mussels, and to predict which landscape stressors were most associated with mussel density declines. Both mussel species were linked with low substrate heterogeneity and greater riverbed stability (low Froude and Reynolds numbers), especially at high flow (low stream power). Different sediment grain size preferences were observed between mussel species: Castalia ambigua was associated with medium sand and Anodontites elongatus with medium and fine sand. Declines in mussel density were associated with modifications linked to urbanization at small scales (riparian buffer forest), especially with percent of and distance from rural settlements, distance to the nearest street, and road density. In summary, the high variance explained in both hydraulic and landscape models indicated high predictive power, suggesting that our findings may be extrapolated and used as a baseline to test hypotheses of habitat suitability in other Amazonian rivers for Castalia ambigua and Anodontites elongatus and also for other freshwater mussel species. Our results highlight the urgent need for aquatic habitat conservation to maintain sheltered habitats during high flow as well as mitigate the effects of landscape modifications at the riparian buffer scale, both of which are important for maintaining dense mussel populations and habitat quality. [ABSTRACT FROM AUTHOR]

Floodplain lakes are good metacommunity systems to study the environmental and spatial processes structuring local assemblages. They are more connected during high-water periods and are more isolated during low-water periods. We evaluated the effects of lake spatial patterning and water and sediment conditions on Unionida species assemblages. Moran Eigenvector Maps were used to generate spatial variables representing spatial patterns at different scales. We sampled 35 lakes from the Pantanal floodplain, Brazil. To understand the effects of environmental and spatial variables, we performed Redundancy Analyses and variation partitioning to separate environmental and spatial pattern effects. Environmental variables explained almost twice the variation in the Pantanal mussel assemblages than did spatial variables. Unionida species presence was driven mainly by variations in sediment coarse sand and silt contents. The weak spatial patterns observed may be related to increased connectivity between lakes during floods, which facilitates mussel host fish dispersal. Mussel abundances were driven mainly by organic matter availability, but varied between species. Changes in lake connectivity can affect the regional sediment dynamics and affect mussel assemblages. [ABSTRACT FROM AUTHOR]

The shells of unionid freshwater mussels are highly morphologically variable, making species identification difficult and thus hampering conservation efforts. Shell shape variation is associated with several factors, of which hydrodynamic variables are the most common. Using geometric morphometrics, shell shape was evaluated on the basis of both external (entire margin including alate processes) and internal (pallial line and positions of muscle scars and teeth) landmarks in Triplodon corrugatus, Paxyodon syrmatophorus and Prisodon obliquus. Samples of these species were collected from 2–5 sites on six rivers, which were classified as either small or large drainages, in the eastern Amazon region, Pará state, northern Brazil. Interspecific comparisons in shell shape were also made among all three species where they co-occurred. Shell shape differed significantly among individuals of the same species from different sites and, in cross-validation tests, 94–96% of mussels were correctly classified into their river of origin according to their shape. For all three species, canonical variates analysis consistently differentiated between mussels from sites in large and small rivers, with the greatest difference in shell shape occurring between large and small rivers. Mussels from the large, clear or whitewater Tapajós, Amazon and Tocantins sites had a triangular shape with prominent posterodorsal and anterior winged processes, whereas those from the small, clearwater Trombetas, Irituia and Piriá sites had a rounded shape, and lacked or had reduced dorsal winged processes. Where all three species co-occurred in the Tapajós and Trombetas sites, shell shape tended to converge. Paxyodon syrmatophorus from the Tapajós sites was most distinct, with very pronounced dorsal processes and a reduced shell disc. In all three species, most of the shell shape variation occurred in the posterodorsal winged process, posterior and ventral margins, and to a lesser degree, in the anterior winged process. The shape differences among Amazonian freshwater mussels agree with those of freshwater mussel species from other regions, characterized by wide variation in hydrodynamics. [ABSTRACT FROM AUTHOR]

Triplodon corrugatus is a freshwater bivalve (Hyriidae) endemic to the Amazon, Orinoco and Tocantins basins, and the Piriá river. Our understanding of hyriid diversity at, and below, the species level, remains poor. The genetic diversity of T. corrugatus from the Tapajós, Amazon, Tocantins, Irituia and Piriá rivers in the north-eastern Brazilian Amazon was investigated. Except for the Irituia, where a single COII–COI haplotype had been fixed, all the other populations had medium to high haplotype diversities, and all populations had low nucleotide diversities. Pairwise fixation indices indicated that all populations were structured, except for comparisons between the Tapajós and Amazon, and the Amazon and Tocantins rivers, which may be explained by a stepping-stone model of migration. AMOVA detected that 81.28% of the variation was among populations. However, STRUCTURE analyses corroborated only the Piriá river specimens as comprising a distinct population, which is being maintained by allopatry due to the current isolation between the Piriá, and the Amazon and Tocantins basins. [ABSTRACT FROM AUTHOR]

Shipping has facilitated dispersion of exotic marine species, the genetic diversity of which may allow determination of their geographic origins. The economically important African brown mussel ( Perna perna) is widely distributed along the southeastern and southern Brazilian coasts, and for which information on genetic diversity and origins is scarce. Five populations, along 2,500 km of Brazilian coast, were genetically characterized to test for homogeneity, verify haplotype and nucleotide diversity levels, and infer relationships among Brazilian and African P. perna. Mitochondrial COI gene sequences of 488 bp were obtained from 158 Brazilian P. perna, and from GenBank for other locations. The nuclear fragment rRNA18S-ITS1 was used as a species-specific marker. The five Brazilian locations were homogeneous, being composed of two mitochondrial haplogroups: haplogroup 1, with low genetic diversity, was linked to Tunisia, Morocco, and Mauritania, and haplogroup 2, with high genetic diversity, shared haplotypes with Brazil, Venezuela, western South Africa, Namibia and Angola. Haplotypes from southeastern Africa and from Oman were not found in Brazil. Patterns in genetic structure, diversity, and haplotype relationships of haplogroup 2 appear related to past trade routes between former African colonies and Brazil, whereas the low diversity of haplogroup 1 suggests more recent invasions. [ABSTRACT FROM AUTHOR]