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Abstract(s)
Na bacia hidrográfica do Rio Tua, no Nordeste de Portugal, estão referenciadas as últimas populações viáveis duma espécie ameaçada a nível nacional e mundial, o mexilhão-de-rio Margaritifera margaritifera Linnaeus 1758. Apesar de existirem trabalhos acerca da distribuição e densidade da espécie em Portugal, são poucos os estudos que analisam os requisitos ecológicos desta náiade em sistemas aquáticos da região transmontana. Neste estudo fez-se uma abordagem global da qualidade ecológica de sistemas lóticos da bacia do Tua e, mais especificamente, uma análise detalhada da qualidade da água e sedimentos e do habitat/microhabitat usado pela náiade na cabeceira dos rios Tuela e Rabaçal.
O bom estado de integridade ecológica detectado nos cursos de água do Alto Tua, ao nível abiótico (bom estado de conservação de habitats aquáticos e ribeirinhos e boa qualidade da água) e biótico (domínio de espécies estenobiontes e composição faunística autóctone) contrastou com sinais de perturbação presentes em troços amostrados no Baixo Tua (e.g. poluição, regularização, degradação de habitats e presença de espécies exóticas). Relativamente aos requisitos ecológicos da náiade, foi caracterizado o habitat (River Habitat Survey) e o microhabitat usado pela espécie. Foram seleccionados 30 transectos por cada troço de rio e determinadas as variáveis da profundidade, substrato dominante e sub-dominante, velocidade da corrente, medida na coluna de água e no leito, e cobertura para cada área amostrada (0,25 m2). Verificou-se que a M. margaritifera apresentou uma distribuição espacial muito agregada. As curvas de preferência detectaram diferenças entre juvenis, presentes maioritariamente em habitats com corrente, menor profundidade e substrato grosseiro (pedras) e adultos, também presentes em zonas lênticas, com maior profundidade e substrato de granulometria fina (areias). Paralelamente, foi ainda encontrada uma similitude de comportamento entre a M. margaritifera e os juvenis e alevins de Salmo trutta, o que permite confirmar a importância assumida pelo hospedeiro na preservação da náiade. Apesar da boa qualidade da água foi encontrada alguma influência antrópica dada a presença de coliformes totais na água e sedimentos.
No futuro, será importante proceder regularmente à monitorização dos sistemas aquáticos e avaliar os efeitos de potenciais impactos (e.g. regularização, poluição, sobrepesca) com o intuito de evitar a regressão assinalada noutros rios de Portugal e definir e aplicar medidas de conservação orientadas especificamente para a espécie mas também para os ecossistemas aquáticos e ribeirinhos, nomeadamente nos sectores localizados no Parque Natural de Montesinho.
The last viable populations of pearl mussel populations Margaritifera margaritifera Linnaeus 1758, a threatened national and world species, are reported in the River Tua basin, northeastern Portugal. Despite of the knowledge about species distribution and density, there is a lack of information related with ecological quality of aquatic systems of the region. In this study, it was made a global approach of ecological quality of lotic systems and, in detail, a particular analysis of sediment and water quality and the habitat/microhabitat used by the pearl mussel populations in the headstreams of Tuela and Rabaçal rivers. The good ecological integrity status detected in the water courses of Upper Tua, in terms of abiotic (i.e. good aquatic and riparian habitats and excellent water quality) and biotic features (dominance of autochthonous species with high ecological requirements) differed, markedly, from some sampled reaches in the Lower Tua, where different signs of disturbance (e.g. pollution, regulation, habitat disruption and presence of alien species) were found. The ecological requirements of pearl mussel populations were evaluated through the habitat characterization (River Habitat Survey) and the microhabitat used by M. margaritifera. 30 transects were selected in each river reach and measured the following variables: total depth, dominant and sub-dominant substrate, water current into the water column and near the bottom and cover for each sampled area (0.25 m2). It was found an aggregated spatial distribution by the pearl mussel populations. Preference curves detected differences between juvenile, mainly present in riffle zones, with lower depth and coarse substrate (cobbles) and adult pearl mussels, also present in pool zones with higher depths and fine substrate (silt and sand). The same behaviour for the microhabitat used was found between M. margaritifera and Salmo trutta, namely with young-of-year and juveniles, confirming the importance assumed by this unique obligatory host species in the preservation of the bivalve species. Despite of the good water quality, typically found in these headwater streams, it was found some microbiological contamination of water and sediments. In the future, it will be important promote a regular monitoring of aquatic systems and the evaluation of potential impacts (e.g. regulation, pollution, over-fishing) in order to avoid the regression of pearl mussel populations reported in other Portuguese rivers. At the same time, conservation measures must be defined and applied not only for this species but also for all the aquatic and riparian ecosystems where this species is present, namely in segments located inside of Montesinho Natural Park.
The last viable populations of pearl mussel populations Margaritifera margaritifera Linnaeus 1758, a threatened national and world species, are reported in the River Tua basin, northeastern Portugal. Despite of the knowledge about species distribution and density, there is a lack of information related with ecological quality of aquatic systems of the region. In this study, it was made a global approach of ecological quality of lotic systems and, in detail, a particular analysis of sediment and water quality and the habitat/microhabitat used by the pearl mussel populations in the headstreams of Tuela and Rabaçal rivers. The good ecological integrity status detected in the water courses of Upper Tua, in terms of abiotic (i.e. good aquatic and riparian habitats and excellent water quality) and biotic features (dominance of autochthonous species with high ecological requirements) differed, markedly, from some sampled reaches in the Lower Tua, where different signs of disturbance (e.g. pollution, regulation, habitat disruption and presence of alien species) were found. The ecological requirements of pearl mussel populations were evaluated through the habitat characterization (River Habitat Survey) and the microhabitat used by M. margaritifera. 30 transects were selected in each river reach and measured the following variables: total depth, dominant and sub-dominant substrate, water current into the water column and near the bottom and cover for each sampled area (0.25 m2). It was found an aggregated spatial distribution by the pearl mussel populations. Preference curves detected differences between juvenile, mainly present in riffle zones, with lower depth and coarse substrate (cobbles) and adult pearl mussels, also present in pool zones with higher depths and fine substrate (silt and sand). The same behaviour for the microhabitat used was found between M. margaritifera and Salmo trutta, namely with young-of-year and juveniles, confirming the importance assumed by this unique obligatory host species in the preservation of the bivalve species. Despite of the good water quality, typically found in these headwater streams, it was found some microbiological contamination of water and sediments. In the future, it will be important promote a regular monitoring of aquatic systems and the evaluation of potential impacts (e.g. regulation, pollution, over-fishing) in order to avoid the regression of pearl mussel populations reported in other Portuguese rivers. At the same time, conservation measures must be defined and applied not only for this species but also for all the aquatic and riparian ecosystems where this species is present, namely in segments located inside of Montesinho Natural Park.
Description
Margaritifera margaritifera, qualidade da água, habitat, biomonitorização
Keywords
Citation
Claro, Ana Marília Barreira (2010). Estudo de populações de mexilhão-de-rio (Margaritifera margaritifera L.): análise da qualidade ecológica de ecossistemas lóticos da bacia hidrográfica do Rio Tua (NE Portugal). Bragança: Escola Superior Agrária. Dissertação de Mestrado em Gestão de Recursos Florestais
Publisher
Instituto Politécnico de Bragança, Escola Superior Agrária