Browsing by Author "Rocha, Fernando"
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- Dissimilarity between living and dead benthic foraminiferal assemblages in the Aveiro Continental Shelf (Portugal)Publication . Alves Martins, Maria Virgínia; Hohenegger, Johann; Frontalini, Fabrizio; Dias, João Manuel Alveirinho; Geraldes, Mauro Cesar; Rocha, FernandoThis study compares living (LA) and dead (DA) benthic foraminiferal assemblages and identifies different factors that possibly cause differences in the distribution of both assemblages in the Aveiro Continental Shelf (Portugal). A total of 44 sediment samples was collected during summers of 1994 and 1995 along transects (east-west direction) and between 10 and 200 m water depth. Complex statistical analyses allow us to compare the abundance and composition of the LAs and DAs in function of depth, grain-size and total organic matter in all studied stations even in those where the numbers of individuals were rare in one or both assemblages. The highest densities and diversities of the LAs are found in the middle continental shelf on gravel deposits (coarse and very coarse sands) mostly due to the substrate stability, reduced deposition of fine sedimentary particles, availability of organic matter with high quality related to oceanic primary productivity likely induced by upwelling events, and oxygenated porewaters conditions. The DAs have, in general, higher densities and diversities than the LAs. In the outer continental shelf, the dissimilarity between both assemblages is higher due to the accumulation of tests, low dilution by sedimentary particles and scarcity of living foraminifera. Based on the comparison of LAs and DAs and considering the characteristics of the study area and the species ecology, it has been possible to understand the cause of temporal deviation between the LAs and DAs of benthic foraminifera. This deviation is much more pronounced in the inner shelf where the energy of the waves and the currents induce very dynamic sedimentary processes preventing the development of large LAs and the preservation of DAs. Some deviation also occurs in the middle shelf due to the seasonal loss of empty tests. The most well-preserved time-averaged DAs were found in the outer continental shelf.
- Evaluating loggerhead sea turtle (Caretta caretta) bycatch in the small-scale fisheries of Cabo VerdePublication . Martins, Samir; Tiwari, Manjula; Rocha, Fernando; Rodrigues, Edson; Monteiro, Ravidson; Araújo, Sónia; Abella, Elena; Loureiro, Nuno de Santos; Clarke, Leo J.; Marco, AdolfoThe incidental or target capture of sea turtles by small-scale fisheries (SSF) has been receiving increasing attention in recent years due to its high impact. Here, we evaluated the impact of the SSF on sea turtles in Cabo Verde, which hosts the largest rookery of the endangered Eastern Atlantic loggerhead turtle (Caretta caretta) population. This is the most comprehensive study evaluating the impact of SSF on sea turtles in the Cabo Verde Archipelago involving more than 85% of boats and more than 20% of the fishermen registered in the archipelago. Between the years of 2011 and 2014, 763 artisanal fishermen were interviewed at all the main ports and fishing communities of seven islands. Artisanal fishermen reported a mean annual capture of 1.5 turtles per boat indicating that a minimum of 1675 sea turtles could be landed per year in this fishing sector alone, with 65% in Santiago Island (which host the country's capital, Praia). Most captures (95.7%) occurred from May to September and coincided with the loggerhead turtle nesting season. These results suggest a severe impact of the SSF on adult loggerheads turtles in Cabo Verde as well as green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) juvenile turtles. To mitigate this impact, measures such as revising the current legislation for fisheries, the supervision and control of landings, especially in the most remote ports of the Archipelago, the regulation of the SSF during the nesting season around the main nesting areas, awareness-raising campaigns, sustainable activities, and alternative sources of income in fishing communities are recommended.
- Factors driving sediment compositional change in the distal area of the Ria de Vigo (NW Spain): oceanographic processes vs. paleopollutionPublication . Virginia Alves Martins, Maria; Cazelli, Lucas; Yhasnara, Missilene; da CristineSilva, Layla; Barros Saibro, Murilo; Bobco, Fabia Emanuela Rafaloski; Rubio, Belen; Ferreira, Bruna; Castelo, Wellen Fernanda Louzada; Santos, José Francisco; Ribeiro, Sara; Frontalini, Fabrizio; Martínez-Colón, Michael; Pereira, Egberto; Antonioli, Luzia; Geraldes, Mauro; Rocha, Fernando; Sousa, Silvia Helena Mello e; Dias, JoaoWe analyze potential Late Holocene metal contamination along a sediment core collected in the distal zone of Ria de Vigo (North Spain). Statistical treatment of the dataset based on a multiproxy approach enabled us to identify and disentangle factors influencing the depositional processes and the preservation of the records of this activity in the area over the last approximate to 3000 years BP. Some layers of the analyzed core have significant enrichment in Cu and a moderate enrichment in Ag, Mo, As, Sb, S, Zn, Ni, Sn, Cd, Cr, Co, Pb, and Li. The enrichment of these elements in some layers of this core may be related to mining activities that have taken place since classical times in the region. Successive phases of pollution were identified along the core KSGX24 related to the Late Bronze Age (approximate to 3000-2450 years BP), Iron Age (approximate to 2450-1850 years BP), Roman times (approximate to 1850-1550 years BP), Middle Ages (approximate to 1250-500 years BP), and industrial and modern (approximate to 250-0 years BP) anthropic activities. The protection of the Cies Islands, the erosive and transport capacity of the rivers in the region, oscillations of the oceanographic and climatic regime, atmospheric contamination, and diagenetic sedimentary processes might have contributed to the accumulation and preservation of this record in the distal region of the Ria de Vigo. The studied core shows that the industrial and preindustrial anthropic impacts caused an environmental liability and contributed to the presence of moderate to heavy pollution of various metals in surface and subsurface sediment layers in the distal sector of the Ria de Vigo, which could be a hazard to biota.