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- Key exploited species as surrogates for coastal conservation in an oceanic archipelago: insights from topshells and limpets from Madeira (NE Atlantic Ocean)Publication . Sousa, Ricardo Jorge SilvaAs lapas e os caramujos estão entre os herbívoros mais bem adaptados ao intertidal do Atlântico Nordeste. Estas espécies-chave fornecem serviços ecossistémicos valiosos, desempenhando um papel fundamental no equilíbrio ecológico do intertidal e têm um elevado valor económico, estando sujeitas a altos níveis de exploração e representando uma das atividades económicas mais rentáveis na pesca de pequena escala no arquipélago da Madeira. Esta dissertação visa preencher as lacunas existentes na história de vida e dinâmica populacional destas espécies, e aferir os efeitos da regulamentação da apanha nos mananciais explorados. A abordagem conservacionista implícita ao longo desta tese pretende promover: (i) a regulamentação adequada da apanha de caramujos (Phorcus sauciatus) e (ii) a avaliação dos efeitos da regulamentação da apanha de lapas nas populações exploradas (Patella aspera, Patella candei). Atualmente, os mananciais de lapas e caramujos são explorados perto do rendimento máximo sustentável, e a monitorização e fiscalização são fundamentais para evitar a futura sobre-exploração. A regulamentação da apanha de lapas produziu um efeito positivo nas espécies de lapas exploradas, com um aumento no tamanho, na proporção de indivíduos reprodutores, no tamanho de maturação e num maior equilíbrio na proporção de sexos. A apanha de caramujos não está regulamentada e com o atual nível de exploração ocorrem alterações na estrutura de tamanhos, abundância e potencial reprodutivo das populações exploradas, pelo que urge implementar a regulamentação da apanha desta espécie, por forma a mitigar os efeitos negativos desta atividade. O efeito da proximidade das populações humanas e acessibilidade costeira na estrutura de tamanhos e abundância de gastrópodes explorados mostrou que a proporção de reprodutores e a abundância eram geralmente menores em áreas mais próximas das populações humanas e em áreas mais acessíveis. Os efeitos das Áreas Marinhas Protegidas na proteção das populações de lapas resultaram num aumento diferencial do tamanho, da maturidade sexual e da captura por unidade de esforço de acordo com o grau de proteção. O esclarecimento e envolvimento das comunidades locais, reguladores, decisores políticos e partes interessadas, baseados em informação e educação, são cruciais para uma gestão eficaz e sustentável destes gastrópodes marinhos e ecossistemas a médio e longo prazo.
- Unravelling the effects of exploitation on the size–structure of the intertidal topshell Phorcus sauciatus in harvested and non-harvested Atlantic regionsPublication . Sousa, Ricardo; Vasconcelos, Joana; Riera, RodrigoIntertidal molluscs are keystone species often used as biological indicators of human-driven pertur bations. The increasing levels of harvesting pressure on these intertidal grazers, due to the expansion of human population on coastal areas, is known to affect negatively the exploited populations by altering population size–structure and decreasing abundances. A comparative study on the effect of harvest on the size–structure of Phorcus sauciatus populations was conducted according to the exploitation level, harvested and non-harvested, throughout the intertidal zone of mainland Portugal, Azores, Madeira, and the Canaries. The comparative analysis of the size–structure of 10,480 individuals of P. sauciatus showed that the largest individuals were recorded in the Azores and the smallest in Madeira. In harvested populations, P. sauciatus showed to be under greater harvesting pressure in the archipelago of Madeira, where the lowest mean size was observed. In the Canaries the harvesting is regulated whilst in the mainland Portugal the regulation is scarce. The Azores showed no harvesting pressure. Marine Protected Areas showed individuals with the highest mean sizes supporting their effectiveness in preserving the size–structure of this species, regardless the ecoregion and thus, the harvesting pressure. The present results highlight the importance of harvesting regulation of P. sauciatus in Madeira, as well as the implementation of management measures aiming at the sustainable exploitation and conservation of this species.
- Island effect in the shell phenotypic plasticity of an intertidal gastropodPublication . Vasconcelos, J.; Sousa, R.; Tuset, V. M.; Riera, R.The pattern of shell shape variation in populations of the top shell, Phorcus sauciatus from Madeira Island (NE Atlantic) was analysed as a function of substrate type and wave exposure, using geometric morphometrics. We hypothesized that P. sauciatus shows morphological variations to inhabit contrasting environments. Highly significant differences in shell shape were found depending on both substrate type and coastal exposure. The most marked differences were found between exposed and sheltered environments. Rounded shells in exposed environments may be explained by physiological reasons, since larger muscles are needed to ensure attachment to substrate in areas subject to harsh conditions. On the other side, conically-shaped shells may accommodate a larger body but with a smaller foot, an adaptation to sheltered environments. Slight shape variations were also observed among substrates, mostly in the degree of differentiation of some whorls. Differences could be related to a particular use of habitat and/or to the degree of exposure to water current. These results suggest that P. sauciatus is locally adapted to varying coastal hydrodynamics and may be considered as a good model in studies on adaptations of fauna to certain climate change effects.
- Disentangling exploitation of the intertidal grazer Phorcus sauciatus (Gastropoda: Trochidae) in an oceanic archipelago: implications for conservationPublication . Sousa, Ricardo; Vasconcelos, Joana; Riera, Rodrigo; Delgado, João; González, José A.; Freitas, Mafalda; Henriques, PauloHarvesting of intertidal grazers such as topshells is known to affect negatively the exploited populations by altering population structure and decreasing abundance. Phorcus sauciatus has a wide geographic distribution in the North‐eastern Atlantic Ocean and is subject to increasing levels of harvesting pressure due to the expansion of human population on coastal areas. The effect of proximity to human settlements and coastal accessibility on the size structure and abundance of P. sauciatus popula‐ tions was examined in Madeira archipelago. Mean size, proportion of reproductive individuals, and abundance of this species were generally smaller in areas closer to human settlements and in more accessible coastal areas. Marine protected areas re‐ turned the highest mean sizes evidencing their effectiveness in preserving the size structure of this species. The results highlight the necessity to regulate the harvest of P. sauciatus in Madeira archipelago, as well as the implementation of management measures aiming at the sustainable exploitation and conservation of this species, ex‐ ploited in this region since the early 15th century.
- Filling biological information gaps of the marine topshell Phorcus sauciatus (Gastropoda: Trochidae) to ensure its sustainable exploitationPublication . Sousa, Ricardo; Vasconcelos, Joana; Delgado, João; Riera, Rodrigo; González, José A.; Freitas, Mafalda; Henriques, PauloTopshells play a pivotal role in intertidal rocky ecosystems and are adapted to harsh thermal and hydric stress. Phorcus sauciatus, a common grazer in the Macaronesian region (Madeira and the Canaries), has rarely been studied due to its restricted geographic distribution com pared with Phorcus lineatus. Monthly samples were taken throughout 2017 to analyse biological parameters and evaluate the harvesting effect on the stocks of this species in Madeira. Individuals of the first age classes (<4 years) were dominant (∼89%), while immature indivi duals were more abundant during the summer season. The spawning season occurs between March and August, especially from March to June. The size at first maturity was 12.95 mm long (1.68 years), with a continuous recruitment pattern throughout the year. Yield-per-recruit analysis (Y/R) showed that maximum production is achieved at a fishing mortality of 1.7 year−1 , corresponding to a Y/R of 0.023 g. Currently, Phorcus sauciatus seems to be mod erately exploited in Madeira, but urgent conservation measures, such as a landing obligation, the establishment of a minimum catch size of 15 mm length, and a closed season (February–May), are warranted to preserve stocks of this species in the medium to long term.
- Major ocean currents may shape the microbiome of the topshell Phorcus sauciatus in the NE Atlantic OceanPublication . Sousa, Ricardo; Vasconcelos, Joana; Vera-Escalona, Iván; Delgado, João; Freitas, Mafalda; González, José A.; Riera, RodrigoStudies on microbial communities are pivotal to understand the role and the evolutionary paths of the host and their associated microorganisms in the ecosystems. Meta-genomics techniques have proven to be one of the most efective tools in the identifcation of endosymbiotic communities of host species. The microbiome of the highly exploited topshell Phorcus sauciatus was characterized in the Northeastern Atlantic (Portugal, Madeira, Selvagens, Canaries and Azores). Alpha diversity analysis based on observed OTUs showed signifcant diferences among regions. The Principal Coordinates Analysis of beta-diversity based on presence/absence showed three well diferentiated groups, one from Azores, a second from Madeira and the third one for mainland Portugal, Selvagens and the Canaries. The microbiome results may be mainly explained by large-scale oceanographic processes of the study region, i.e., the North Atlantic Subtropical Gyre, and specifcally by the Canary Current. Our results suggest the feasibility of microbiome as a model study to unravel biogeographic and evolutionary processes in marine species with high dispersive potential.