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As alterações globais no planeta são grandemente responsáveis pela perda de
biodiversidade e em particular nos ecossistemas aquáticos, tidos como
extremamente vulneráveis. Para além das alterações climáticas, são várias as
pressões e ameaças à biodiversidade e integridade ecológica, como a poluição
e eutrofização da água, a fragmentação de habitats, a degradação do ecótono
ripário e a introdução de espécies exóticas. O objetivo principal do presente
estudo consistiu no estudo da biodiversidade aquática e ribeirinha do troço final
do rio Maçãs (bacia do Rio Douro), situado em Portugal. Assim, na primavera de
2023 foi monitorizada a qualidade bioecológica do sistema aquático através da
amostragem de 10 locais, espacialmente distribuídos desde a fronteira até à foz
com o rio Sabor (40 Kms de extensão). Relativamente ao elemento biológico, a
maioria dos locais amostrados apresentaram para a comunidade de
macroinvertebrados uma boa/excelente qualidade, baseado em várias métricas
(e.g., diversidade H’ Shannon-Wienner, F-IBIP - Índice Piscícola de Integridade
Biótica para Rios Vadeáveis de Portugal Continental, IPTIN - Índice Português
de Invertebrados do Norte, entre outras) embora mereça destaque a presença
assinalável de EEI - espécies exóticas e invasoras (e.g. Procambarus clarkii,
Pacifastacus leniusculus, Corbicula fluminea) que paulatinamente têm vindo a
aumentar a sua densidade e provocar alterações significativas no funcionamento
do ecossistema aquático. No que respeita à comunidade de peixes, a qualidade
determinada foi alarmante para a maioria dos locais, i.e., bem abaixo do nível
BOM exigido pela DQA - Diretiva Quadro da Água, assinalando-se a influência
negativa de barreiras (e.g. açudes), períodos de seca prolongados e a presença
massiva de EEI (e.g. especialmente Lepomis gibbosus, mas também outras
espécies como Alburnus alburnus, Micropterus salmoides). Neste
enquadramento, é de crer num futuro próximo que outras EEI possam colonizar
o Rio Maçãs (e.g. Rutilus rutilus, Sander lucioperca, Esox lucius), provenientes
da albufeira do Aproveitamento Hidroelétrico do Baixo Sabor e contribuir para a
diminuição ou extinção das espécies nativas presentes. Com efeito, para além
dos endemismos ibéricos conhecidos, caso de Squalius alburnoides, Squalius
carolitertii, Pseudochondrostoma duriense e Luciobarbus bocagei, foi
recentemente descrita uma nova espécie, Achondrostoma asturicense, presente nas bacias dos rios Sabor (Maçãs e Angueira) e Tua, que recebeu, entretanto, o
estatuto de ameaça Em Perigo (EN) pela última revisão do Livro Vermelho dos
Peixes Dulciaquícolas e Diádromos de Portugal Continental (2023). Contudo,
relativamente aos elementos de suporte, nomeadamente a qualidade da água e
da hidromorfologia mostraram, globalmente, uma boa/razoável qualidade físico-
química da água, embora as métricas hidromorfológicas (e.g. índices GQC –
Grau de Qualidade do Canal e QBR – Bosque Ribeirinho) tenham assinalado
locais com maior degradação do canal e da galeria ripícola, com destaque para
a presença de vários açudes e a elevada mortalidade de Alnus lusitanica.
Relativamente à biodiversidade da fauna ribeirinha, foram usados métodos
complementares que envolveram a foto-armadilhagem, o uso de armadilhas
terrestres e aquáticas e a procura de indícios de presença (pegadas e
excrementos) que globalmente permitiram identificar, durante 15 dias (novembro
e dezembro de 2022) e em dois setores (15 Kms de extensão), vários animais
selvagens, distribuídos por diferentes grupos faunísticos, i.e., répteis (Mauremys
leprosa e Natrix astreptophora), anfíbios (Rana iberica), aves (Garrulus garrulus,
Ardea cinerea, Corvus corone, Prunella modularis, Turdus merula, Erithacus
rubecula e Columba palumbus) e mamíferos (Genetta genetta, Martes foina, Sus
scrofa, Vulpes vulpes, Apodemus sylvaticus, Capreolus capreolus, Lutra lutra e
Neovison vison). Especial atenção foi dada à recente introdução do mustelídeo
exótico e invasor, o visão-americano, e à contribuição para o conhecimento da
sua distribuição no Rio Maçãs e consequente eliminação dos exemplares
capturados (apenas um), de acordo com a legislação vigente. Confirmou-se que
esta espécie já colonizou todo o troço final do rio Maçãs com registos de
abundância superior na proximidade de infraestruturas contruídas pelo homem,
caso de açudes rústicos de pedra, onde encontra locais adequados para refúgio
e reprodução. O baixo número de excrementos de visão-americano recolhidos
não permitiu fazer uma análise detalhada da dieta desta espécie. No caso da
lontra observou-se uma dieta maioritariamente composta por lagostins exóticos.
De facto, a abundância destas presas no rio Maçãs, faz pressupor que esta fonte
de alimento promoverá, no futuro, o crescimento da população de visão-
americano e consequente dispersão na rede hídrica. A área de estudo faz parte da Zona Especial de Conservação (ZEC) Rios Sabor
e Maçãs e da Reserva da Biosfera Transfronteiriça da Meseta Ibérica, pelo que
justifica a implementação de medidas de conservação orientadas para a
mitigação de impactes negativos, entre eles para o controlo continuado de EEI,
nomeadamente em habitats prioritários, de modo a assegurar a preservação dos
ecossistemas aquáticos e ribeirinhos e dos valores naturais da região.
Global changes are largely responsible for the loss of biodiversity and in particular in aquatic ecosystems, considered extremely vulnerable. In addition to climate change, there are several pressures and threats to biodiversity and ecological integrity, such as water pollution and eutrophication, habitat fragmentation, degradation of the riparian ecotone and the introduction of exotic species. The main objective of the present study was to evaluate the aquatic and riparian biodiversity of the final segment of the Maçãs River (Douro River basin), located in Northern Portugal. Thus, in the spring of 2023, the bioecological quality of the aquatic system was monitored through in 10 sampling sites, spatially distributed from the border to the mouth of the Sabor river (40 km long). Regarding the biological element, the majority of the sampled sites presented a good/excellent quality for the macroinvertebrate community, based on several metrics (e.g., H' Shannon-Wienner diversity, IPTIN, F-IBIP, among others) although the presence of notable number of exotic and invasive species - IAS (e.g. Procambarus clarkii, Pacifastacus leniusculus, Corbicula fluminea) which have gradually increased their density and caused significant changes in the functioning of the aquatic ecosystem. Regarding the fish community, the quality determined was alarming for most sites, i.e., below the GOOD level required by the WFD, highlighting the negative influence of barriers (e.g., weirs), prolonged periods of drought and the massive presence of IAS (e.g., especially Lepomis gibbosus, but also other species such as Alburnus alburnus, Micropterus salmoides). In this context, it is to be believed that soon other exotic species may colonize the Maçãs River (e.g., Rutilus rutilus, Sander lucioperca, Esox lucius), from the reservoir of the downstream big dam (Baixo Sabor Hydroelectric Powerplant), contributing to the decline or extinction of several native species. In fact, in addition to the well- known Iberian endemic freshwater species, such as Squalius alburnoides, Squalius carolitertii, Pseudochondrostoma duriense and Luciobarbus bocagei, a new species was recently described, named Achondrostoma asturicense, mostly present in the Maçãs and Angueira, belonging to the Sabor river (is also in Tua river), which has received the Endangered (EN) status by Portuguese Red Book of Freshwater and Diadromous Fishes of Continental Portugal (2023). However, regarding the support elements, namely water quality and hydromorphology, they showed, overall, a good/reasonable physical-chemical quality of the water, although hydromorphological metrics (e.g., GQC and QBR indices) highlighted sites with greater degradation, with emphasis on the presence of several weirs and the high mortality of Alnus lusitanica. Respecting to the faunal riparian biodiversity, complementary methods were used that involved photo-trapping, the use of terrestrial and aquatic traps and the search for signs of presence (footprints and excrement) that globally made possible to identify, during 15 days in November and December 2022 in two sectors (15 km of extension), several wild animals, distributed through different faunal groups, i.e., reptiles (Mauremys leprosa, Natrix astreptophora), amphibians (Rana iberica), birds (Garrulus garrulus, Ardea cinerea, Corvus corone, Prunella modularis, Turdus merula, Erithacus rubecula, Columba palumbus) and mammals (Genetta genetta, Martes foina, Sus scrofa, Vulpes vulpes, Apodemus sylvaticus, Capreolus capreolus, Lutra lutra and Neovison vison). Special attention was given to the recent introduction of the exotic and invasive mustelid, the American mink, and the contribution to the knowledge of its distribution in the River Maçãs and the consequent elimination of captured specimens (only one), in accordance with current legislation. It was confirmed that this species has already colonized the entire final section of the River Maçãs with records of higher abundance in the proximity of man-made infrastructures, such as rustic weirs, where it finds suitable places for refuge and reproduction. The low number of American mink excrement collected did not allow for a detailed analysis of the diet of this species. In the case of the otter, the native semiaquatic mustelid, the diet was mainly composed of exotic crayfishes. In fact, the abundance of these preys in the River Maçãs suggests that this food source will promote, in the future, the growth of the American mink population and consequent dispersion in the river network.
Global changes are largely responsible for the loss of biodiversity and in particular in aquatic ecosystems, considered extremely vulnerable. In addition to climate change, there are several pressures and threats to biodiversity and ecological integrity, such as water pollution and eutrophication, habitat fragmentation, degradation of the riparian ecotone and the introduction of exotic species. The main objective of the present study was to evaluate the aquatic and riparian biodiversity of the final segment of the Maçãs River (Douro River basin), located in Northern Portugal. Thus, in the spring of 2023, the bioecological quality of the aquatic system was monitored through in 10 sampling sites, spatially distributed from the border to the mouth of the Sabor river (40 km long). Regarding the biological element, the majority of the sampled sites presented a good/excellent quality for the macroinvertebrate community, based on several metrics (e.g., H' Shannon-Wienner diversity, IPTIN, F-IBIP, among others) although the presence of notable number of exotic and invasive species - IAS (e.g. Procambarus clarkii, Pacifastacus leniusculus, Corbicula fluminea) which have gradually increased their density and caused significant changes in the functioning of the aquatic ecosystem. Regarding the fish community, the quality determined was alarming for most sites, i.e., below the GOOD level required by the WFD, highlighting the negative influence of barriers (e.g., weirs), prolonged periods of drought and the massive presence of IAS (e.g., especially Lepomis gibbosus, but also other species such as Alburnus alburnus, Micropterus salmoides). In this context, it is to be believed that soon other exotic species may colonize the Maçãs River (e.g., Rutilus rutilus, Sander lucioperca, Esox lucius), from the reservoir of the downstream big dam (Baixo Sabor Hydroelectric Powerplant), contributing to the decline or extinction of several native species. In fact, in addition to the well- known Iberian endemic freshwater species, such as Squalius alburnoides, Squalius carolitertii, Pseudochondrostoma duriense and Luciobarbus bocagei, a new species was recently described, named Achondrostoma asturicense, mostly present in the Maçãs and Angueira, belonging to the Sabor river (is also in Tua river), which has received the Endangered (EN) status by Portuguese Red Book of Freshwater and Diadromous Fishes of Continental Portugal (2023). However, regarding the support elements, namely water quality and hydromorphology, they showed, overall, a good/reasonable physical-chemical quality of the water, although hydromorphological metrics (e.g., GQC and QBR indices) highlighted sites with greater degradation, with emphasis on the presence of several weirs and the high mortality of Alnus lusitanica. Respecting to the faunal riparian biodiversity, complementary methods were used that involved photo-trapping, the use of terrestrial and aquatic traps and the search for signs of presence (footprints and excrement) that globally made possible to identify, during 15 days in November and December 2022 in two sectors (15 km of extension), several wild animals, distributed through different faunal groups, i.e., reptiles (Mauremys leprosa, Natrix astreptophora), amphibians (Rana iberica), birds (Garrulus garrulus, Ardea cinerea, Corvus corone, Prunella modularis, Turdus merula, Erithacus rubecula, Columba palumbus) and mammals (Genetta genetta, Martes foina, Sus scrofa, Vulpes vulpes, Apodemus sylvaticus, Capreolus capreolus, Lutra lutra and Neovison vison). Special attention was given to the recent introduction of the exotic and invasive mustelid, the American mink, and the contribution to the knowledge of its distribution in the River Maçãs and the consequent elimination of captured specimens (only one), in accordance with current legislation. It was confirmed that this species has already colonized the entire final section of the River Maçãs with records of higher abundance in the proximity of man-made infrastructures, such as rustic weirs, where it finds suitable places for refuge and reproduction. The low number of American mink excrement collected did not allow for a detailed analysis of the diet of this species. In the case of the otter, the native semiaquatic mustelid, the diet was mainly composed of exotic crayfishes. In fact, the abundance of these preys in the River Maçãs suggests that this food source will promote, in the future, the growth of the American mink population and consequent dispersion in the river network.
Descrição
Palavras-chave
Espécies exóticas invasoras Ameaças de rios Integridade Ecológica Gestão de ecossistemas