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Advisor(s)
Abstract(s)
As populações de mexilhões de água doce (Mollusca, Bivalvia, Unionoida) são um dos grupos faunísticos mais ameaçados a nível mundial, existindo várias espécies que correm o risco de extinção. Estas espécies desempenham um papel importante no funcionamento dos ecossistemas aquáticos dado assegurarem a filtração e depuração das águas. Apresentam ainda um ciclo de vida complexo uma vez que parasitam, na fase larvar, um ou mais hospedeiros, embora na generalidade corresponda a um número restrito de peixes. A situação real destas populações de náiades está ainda mal compreendida nos rios do Nordeste Transmontano. Os objetivos do presente trabalho consistiram no estudo da bioecologia das espécies Margaritifera margaritifera, Anodonta anatina, Unio delphinus e Potomida littoralis. Mais especificamente, foi determinada a densidade e estrutura populacional, detetados os padrões de distribuição e identificados os principais fatores de regressão, bióticos e abióticos, que ameaçam estas populações de bivalves nas bacias hidrográficas dos rios Tua e Sabor.
Para a caracterização do status ecológico de diferentes cursos de água de ambas as bacias hidrográficas foram selecionados 13 locais de amostragem, tendo sido feito o registo de dados na primavera e verão de 2012 e 2013. Recorreu-se a um conjunto de análises físicas e químicas da água, à determinação de índices de qualidade do canal fluvial e dos habitas ribeirinhos e ainda à amostragem das comunidades de macroinvertebrados bentónicos e de peixes, baseada nos protocolos estabelecidos em Portugal pelo Instituto da Água, no âmbito da implementação da Diretiva Quadro da Água (DQA). As populações de náiades foram monitorizadas através da técnica de observação subaquática (snorkeling) e usado um método de varrimento completo duma extensão de rio, nunca inferior a 100 metros.
Os resultados obtidos permitiram definir as variáveis ambientais (e.g. parâmetros relacionados com a qualidade da água e hidromorfologia do canal) mais importantes na tipologia encontrada e ainda determinar a composição, distribuição e abundância das comunidades de macroinvertebrados e de peixes. Foram encontradas diferentes métricas responsáveis à degradação ambiental e identificada uma maior integridade ecológica nos setores superiores de ambas as bacias hidrográficas. Relativamente aosbivalves, a espécie M. margaritifera foi encontrada em elevadas densidades em alguns locais dos rios Rabaçal e Tuela, enquanto os unionídeos, presentes nas zonas médias e finais dos rios, mostraram uma distribuição espacial agregada em zonas específicas, nomeadamente na proximidade das margens e especialmente em braços laterais dos rios, com fluxo permanente de água. Foram construídos histogramas referentes à estrutura populacional e ao uso do habitat para cada espécie. As espécies Unio delphinus e Anodonta anatina colonizam preferencialmente pools com substrato fino, com núcleos populacionais situados entre raízes submersas, próximo de margens escavadas. Por sua vez, a espécie Potomida littoralis tem densidades superiores em zonas de maior velocidade da corrente (riffles) e com substrato mais grosseiro (seixos e pedras). Em diversos locais foi encontrada uma estrutura populacional equilibrada para a espécie M. margaritifera e para as espécies de unionídeos, com uma boa densidade de juvenis e indivíduos reprodutores.
Ao nível da fauna piscícola, detetou-se a presença quase exclusiva de espécies autóctones de peixes (e.g. Salmo trutta, Cobitis calderoni, Squalius carolitertii, Squalius alburnoides) na cabeceira dos rios onde ocorrem as populações mais viáveis de Portugal da espécie Margaritifera margaritifera (embora apenas no Alto Tua), enquanto nos troços médios e finais (colonizados por bivalves unionídeos) os ciprinídeos mais comuns e endémicos (Luciobarbus bocagei, Squalius carolitertii e Pseudochondrostoma duriense) ocorrem em proporções variáveis com espécies exóticas, muitas delas com potencial invasor (e.g. Lepomis gibbosus). Face às ameaças detetadas, caso da poluição, sedimentação e especialmente da regularização (duas grandes barragens, os Aproveitamentos Hidroelétricos do Baixo Sabor e de Foz Tua, estão em fase de construção) que conduzirão a uma redução do habitat disponível e da íctiofauna nativa (que funciona quase exclusivamente como hospedeiros destes mexilhões), é fundamental tomar medidas que visem a conservação de habitats e ecossistemas prioritários e a requalificação ambiental de troços degradados de modo a preservar as espécies de invertebrados e vertebrados autóctones fortemente ameaçadas.
Freshwater mussel populations (Mollusca, Bivalvia, Unionoida) are one of the most endangered animal groups worldwide, including several species at risk of extinction. These organisms play an important role in the functioning of aquatic ecosystems, since they ensure the filtration and purification of water. Furthermore, naiads have a complex life cycle with a parasitic larvae and limited host fish populations, usually autochthonous species. The real status of these populations is still poorly understood in the northeastern rivers. The objectives of the present work consisted in the study of bio-ecology of the species Margaritifera margaritifera, Anodonta anatina, Unio delphinus and Potomida littoralis. More specifically, it was determined the density and population structure, distribution patterns and identified the main regression factors, biotic and abiotic, that threaten these populations of bivalves in the rivers Tua and Sabor. To characterize the ecological status of different streams of both river basins, 13 sites were selected. Samplings were made in the spring and summer seasons of 2012 and 2013. It was measured the physical and chemical water parameters and calculated two habitat quality indexes (river channel and riparian zones). Biota, namely benthic macroinvertebrate and fish communities, were sampled based on the protocols established in Portugal by the Water Framework Directive (WFD). Naiad populations were monitored by underwater observation technique (snorkeling) and a complete sweep up method of a stretch of river, never less than 100m, applied. The results showed the environmental variables (e.g. parameters related to water quality and hydro-morphology of the channel) most important in the river typology. Composition, distribution and abundance of macroinvertebrate and fish communities were also determined. Different metrics responsive to environmental degradation were found. The upper sectors of both rivers were classified with excellent and good ecological integrity. In the mussel bio-ecology analyses, the species M. margaritifera was found in high densities in different sampling stations of Rabaçal Tuela rivers (upper zone of River Tua), while unionid mussels colonize the middle and final areas of both rivers. These mussel populations showed a clustered distribution in specific areas, particularly near the banks and especially in lateral arms of rivers, with permanent water flow. The population structure and habitat use for each species was alsodetermined. The species Unio delphinus and Anodonta anatina colonize, preferentially, pools with thin substrate, between the submerged roots, near undercut banks. On the other hand, the species Potomida littoralis have higher densities in areas of higher flow velocity (riffles) and coarser substrate (pebbles and stones). In several sampling stations a balanced population structure was found with good density and recruitment. In terms of fish fauna , headwaters were composed almost exclusively by native species ( e.g. Salmo trutta, Cobitis calderoni, Squalius carolitertii, Squalius alburnoides) cohabiting with Margaritifera margaritifera populations, while in the middle and final sections (colonized by unionid mussels) the most common fish populations were the endemic cyprinids (Luciobarbus bocagei, Squalius carolitertii and Pseudochondrostoma duriense). In these river zones, autochthonous fish species occur in varying proportions with exotic species, many of them with invasive potential (e.g. Lepomis gibbosus). Taking into account the detected threats, like pollution, sedimentation and regularization (two big dams are in construction), a reduction of available habitat and native fish populations (the almost exclusive host fishes) will occur in future. Rehabilitation and mitigation measures are essential for the conservation of priority habitats and ecosystems in order to preserve native vertebrates and invertebrates species heavily threatened.
Freshwater mussel populations (Mollusca, Bivalvia, Unionoida) are one of the most endangered animal groups worldwide, including several species at risk of extinction. These organisms play an important role in the functioning of aquatic ecosystems, since they ensure the filtration and purification of water. Furthermore, naiads have a complex life cycle with a parasitic larvae and limited host fish populations, usually autochthonous species. The real status of these populations is still poorly understood in the northeastern rivers. The objectives of the present work consisted in the study of bio-ecology of the species Margaritifera margaritifera, Anodonta anatina, Unio delphinus and Potomida littoralis. More specifically, it was determined the density and population structure, distribution patterns and identified the main regression factors, biotic and abiotic, that threaten these populations of bivalves in the rivers Tua and Sabor. To characterize the ecological status of different streams of both river basins, 13 sites were selected. Samplings were made in the spring and summer seasons of 2012 and 2013. It was measured the physical and chemical water parameters and calculated two habitat quality indexes (river channel and riparian zones). Biota, namely benthic macroinvertebrate and fish communities, were sampled based on the protocols established in Portugal by the Water Framework Directive (WFD). Naiad populations were monitored by underwater observation technique (snorkeling) and a complete sweep up method of a stretch of river, never less than 100m, applied. The results showed the environmental variables (e.g. parameters related to water quality and hydro-morphology of the channel) most important in the river typology. Composition, distribution and abundance of macroinvertebrate and fish communities were also determined. Different metrics responsive to environmental degradation were found. The upper sectors of both rivers were classified with excellent and good ecological integrity. In the mussel bio-ecology analyses, the species M. margaritifera was found in high densities in different sampling stations of Rabaçal Tuela rivers (upper zone of River Tua), while unionid mussels colonize the middle and final areas of both rivers. These mussel populations showed a clustered distribution in specific areas, particularly near the banks and especially in lateral arms of rivers, with permanent water flow. The population structure and habitat use for each species was alsodetermined. The species Unio delphinus and Anodonta anatina colonize, preferentially, pools with thin substrate, between the submerged roots, near undercut banks. On the other hand, the species Potomida littoralis have higher densities in areas of higher flow velocity (riffles) and coarser substrate (pebbles and stones). In several sampling stations a balanced population structure was found with good density and recruitment. In terms of fish fauna , headwaters were composed almost exclusively by native species ( e.g. Salmo trutta, Cobitis calderoni, Squalius carolitertii, Squalius alburnoides) cohabiting with Margaritifera margaritifera populations, while in the middle and final sections (colonized by unionid mussels) the most common fish populations were the endemic cyprinids (Luciobarbus bocagei, Squalius carolitertii and Pseudochondrostoma duriense). In these river zones, autochthonous fish species occur in varying proportions with exotic species, many of them with invasive potential (e.g. Lepomis gibbosus). Taking into account the detected threats, like pollution, sedimentation and regularization (two big dams are in construction), a reduction of available habitat and native fish populations (the almost exclusive host fishes) will occur in future. Rehabilitation and mitigation measures are essential for the conservation of priority habitats and ecosystems in order to preserve native vertebrates and invertebrates species heavily threatened.
Description
Keywords
Ecossistemas lóticos Integridade ecológica Invertebrados Náiades Peixes