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Processos sedimentares em ilhas vulcânicas oceânicas: aferição do transporte de moluscos marinhos efetuado pelas correntes marinhas na plataforma da ilha de Santa Maria, Açores
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Abstract(s)
A ilha de Santa Maria no arquipélago dos Açores tem sido palco de diversos trabalhos científicos de diversas áreas nas últimas décadas. O arquipélago no seu todo é constituído por nove ilhas vulcânicas oceânicas, onde Santa Maria se destaca como a mais antiga. Procurando dar seguimento a trabalhos de foro científico realizados no arquipélago até à data, pretendemos desenvolver e desvendar os processos sedimentares que ocorrem nas plataformas insulares de ilhas vulcânicas oceânicas, por via do transporte de moluscos marinhos do litoral até profundidades maiores ao longo da extensão da plataforma. Para este efeito foram triadas amostra de sedimento marinho (5,2 kg) originárias da plataforma insular (-10 a -289 m) de Santa Maria, de forma a identificar espécies e a sua distribuição ao longo de cinco transectos (Norte, Sul, Sudoeste (estes dois foram agrupados), Oeste e Leste), onde foi também descrita a batimetria destes, de modo a identificar o seu bordo insular e variação de declive entre estes. Um total de 30.648 indivíduos foram contabilizados e identificados, pertencentes a 45 espécies (8 bivalves e 37 gastrópodes). Destas espécies, as que apresentaram maior abundância no litoral marinho foram analisadas de forma a avaliar a existência de transporte ao longo da plataforma e além do bordo insular. Espécies como Alvania angioyi, Alvania mediolittoralis, Bittium nanum, Gibbula delgadensis, Manzonia unifasciata, Rissoa guernei demostram uma abundância elevada de indivíduos mortos muito para além da zonação conhecida para estes animais, bem como do limite litoral estipulado para cada uma destas espécies, o que nos permite confirmar a ocorrência de transporte sedimentar ao longo da plataforma insular.
The island of Santa Maria in the Azores archipelago has been the site of several scientific studies in diverse fields over the last decades. The archipelago as a whole is made up of nine volcanic and oceanic islands, where Santa Maria stands out as the oldest. In our contribution to the scientific work carried out to date in this archipelago, we intend to develop and unravel the sedimentary processes that occur on the insular platforms of volcanic oceanic islands, through the transport of marine molluscs from the littoral area to deep sea along the shelf. To this end, marine sediment samples (5.2 kg) from the island platform (-10 to -289 m in depth) of Santa Maria were sorted in order to identify species and their distribution along five transects (North, South, Southwest, West and East), where the bathymetry of these transects was also described in order to identify the island edge and slope variation between quadrants. A total of 30,648 individuals were counted and identified for 45 different species (8 bivalves and 37 gastropods). Of these species, those with the greatest abundance and bathymetric distributions reported for the littoral area were analysed in order to understand the existence of transport along the platform and beyond the insular edge. Species such as Alvania angioyi, Alvania mediolittoralis, Bittium nanum, Gibbula delgadensis, Manzonia unifasciata, Rissoa guernei show a high abundance of dead individuals far beyond the known zonation for these animals, as well as the littoral limit stipulated for these species. This allows us to confirm the occurrence of sedimentary transport along the insular platform shores.
The island of Santa Maria in the Azores archipelago has been the site of several scientific studies in diverse fields over the last decades. The archipelago as a whole is made up of nine volcanic and oceanic islands, where Santa Maria stands out as the oldest. In our contribution to the scientific work carried out to date in this archipelago, we intend to develop and unravel the sedimentary processes that occur on the insular platforms of volcanic oceanic islands, through the transport of marine molluscs from the littoral area to deep sea along the shelf. To this end, marine sediment samples (5.2 kg) from the island platform (-10 to -289 m in depth) of Santa Maria were sorted in order to identify species and their distribution along five transects (North, South, Southwest, West and East), where the bathymetry of these transects was also described in order to identify the island edge and slope variation between quadrants. A total of 30,648 individuals were counted and identified for 45 different species (8 bivalves and 37 gastropods). Of these species, those with the greatest abundance and bathymetric distributions reported for the littoral area were analysed in order to understand the existence of transport along the platform and beyond the insular edge. Species such as Alvania angioyi, Alvania mediolittoralis, Bittium nanum, Gibbula delgadensis, Manzonia unifasciata, Rissoa guernei show a high abundance of dead individuals far beyond the known zonation for these animals, as well as the littoral limit stipulated for these species. This allows us to confirm the occurrence of sedimentary transport along the insular platform shores.
Description
Keywords
Zonação batimétrica moluscos marinhos ilhas vulcânicas oceânicas plataforma insular