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Browsing CIMA by advisor "Barbosa, Ana B."
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- Bottom-up regulation of phytoplankton in the Guadiana estuaryPublication . Domingues, Rita B.; Galvão, Helena M.; Barbosa, Ana B.; Sommer, UlrichPhytoplankton are key players in the aquatic environment and they can be effectively used to understand and predict the functioning and production of aquatic ecosystems. Given that phytoplankton is affected by natural and human-induced perturbations, such as eutrophication and global climate change, it is pressing to understand which factors regulate phytoplankton communities. The main goal of this work was, therefore, to understand how phytoplankton growth and production in the turbid Guadiana estuary, particularly in the freshwater tidal zone, is regulated by bottom-up factors, namely nutrients and light. Enrichment bioassays were carried out to evaluate nutrient and light limitation of phytoplankton growth. Nutrient limitation, specifically by nitrogen, was observed during the productive period. Nitrogen, as nitrate, became limiting to phytoplankton growth at concentrations lower than 20 WM. Although nitrate was the main nitrogen source in the Guadiana estuary, an overall preference for ammonium was observed, mainly by cyanobacteria and green algae. Diatoms were the most nutrient-limited group, and they clearly preferred nitrate as their N-source. Regarding light availability, phytoplankton was not acclimated to the low light conditions that prevail in the Guadiana estuary and light limitation occurred throughout the year. Diatoms were the most light-limited group, whilst cyanobacteria seemed to be more acclimated to low light. Primary production was higher in the more turbid regions, where light availability was the lowest, but nutrient concentrations, although occasionally limiting, were the highest. Therefore, phytoplankton in such turbid regions were the most efficient in using limiting resources. River flow was a major regulator of nutrient and suspended matter inputs to the estuarine zone. Tidallyinduced variability of phytoplankton and environmental drivers in the freshwater tidal estuarine zone was low and resulted from seasonal and fortnightly variability in river flow and tidal currents.
- Movements of short-finned pilot whales (Globicephala macrorhynchus) in the Macaronesian biogeographical region: a photo-identification analysisPublication . Alessandrini, Anita; Barbosa, Ana B.The short-finned pilot whale, Globicephala macrorhynchus Gray (1846), is a marine mammal species from the family Delphinidae. It is a top predator species, with a circumglobal distribution from warm-temperate to tropical regions, at varying distances from shore, including the Macaronesia region (NE Atlantic). Population connectivity can profoundly influence the distribution, persistence and ecological impact of local marine mammal species. Understanding population connectivity and its environmental drivers is critical for effective wildlife conservation and management, namely in a context of increased marine pollution associated to toxic contaminants, ocean noise and disruption of natural food webs. The aim of this study was to compare Globicephala macrorhynchus individuals within the Macaronesian’ archipelagos. It includes data (digital photographs) from Madeira between 2003 and 2015, from Azores between 1999 and 2015, from the Canary Islands between 1993 and 2015, and from Cape Verde in 2006. This thesis represents the first study comparing individuals from this species within the four archipelagos of the Macaronesia. In this thesis, the method used to study the animals’ connectivity was photo-identification, which is based on the analyses of natural markings in dorsal fins. The dorsal fins were cropped from photographs and were matched to available photo-identification catalogues for G. macrorhynchus from Madeira and photos from the other archipelagos not catalogued yet. The comparison was made by eyes using image softwares, based on the number of nicks and notches in the dorsal fin of the different individuals. Results showed that 19 short-finned pilot whales were matched, being 11 individuals between Azores and Madeira, and eight individuals between Canaries and Madeira. Of these, 69% were categorized with a residency status of “transient”, 26% of “resident”, and 5% of “visitors”. This thesis supports the importance of the Macaronesia region for this species, and highlights the need for common conservation policies across different archipelagos/countries.
- Temporal distribution of the short-beaked common dolphin (Delphinus delphis) in the south of Madeira Island (Portugal) and relationship with oceanographic variablesPublication . Halicka, Zofia; Barbosa, Ana B.Short-beaked common dolphin (Delphinus delphis) is a small cetacean species that is among the most common marine mammals in Madeira Island. This thesis represents the first study that describes temporal distribution of D. delphis in this region and that relates it with environmental determinants. Results were based on data collected on platform of opportunity on the southern off Madeira Island during the period 2011 – 2014. They revealed that presence of D. delphis varied consistently between warm and cold seasons, with higher occurrences between December and May. This temporal distribution pattern reflects a summer migration probably directed northwards. General Additive Models showed that temperature, chlorophyll concentration, wind intensity and direction, as well as landings of sardine, curled picarel and Atlantic chub mackerel were important factors affecting D. delphis distribution. This study confirms information from previous studies revealing that common dolphin tents to avoid waters warmer than 18ºC. Moreover modelling results can also reflect a trophic cascade, between phytoplankton, pelagic schooling fish and D. delphis. Further studies are needed to evaluate seasonal migration patterns, involving animal telemetry and photo-identification, probably in cooperation with other institutions, as well as exact positioning of dolphin sightings and other potentially relevant environmental variables (e.g., depth, distance from the coast, upwelling intensity).
- Trophic dynamics between phytoplankton and microzooplankton in the Ria Formosa coastal lagoon systemPublication . Sá, Bárbara Andreia dos Santos de Sousa e; Barbosa, Ana B.Phytoplankton is a planktonic group with great importance to the aquatic ecosystems, because constitutes the base of the food web, and have an important play role in the oxygen production and carbon dioxide consumption. Grazing by phagotrophic protists (microzooplankton) is considered the major mortality source of phytoplankton in the oceans. Thus, understanding the trophic dynamics between these two planktonic groups is essential for a better understanding of the functioning and variability of aquatic ecosystems. Trophic dynamics between phytoplankton and microzooplankton in the Ria Formosa coastal lagoon system (south Portugal) was studied through a seasonal sampling, with a period of one year. The methodology used in the experiments was the dilution technique, with and without enrichment of inorganic macronutrients, in two distinct places of Ria Formosa (inner station of the lagoon system and an outer station which is in contact with the adjacent coastal region) and in different periods of time (spring and autumn). The analyses of phytoplankton biomass were done through fluorimetry, while the phytoplankton and microzooplankton composition and abundance were through epifluorescence microscopy (< 20 μm) and inverted microscopy (> 20 μm). The temperature and salinity values were under the Ria Formosa normal standers. Chl a had high seasonal variations, such that values obtained during the spring of 2015 followed the Chl a standards for the Ria Formosa, while values for the spring of 2016 did not. Cyanobacteria dominated the phytoplankton community in both seasons. It were performed six sets of experiments, and four of them had unexpected responses regarding the relationship between dilution factors and the apparent growth rate of phytoplankton. It was obtained non-significant linear regressions and positive linear regressions, showing that sometimes the dilution has a negative effect on phytoplankton. Microzooplankton removed, daily, between 44.83% and more than 100% of phytoplankton production. The growth rate of phytoplankton was between 0.05 d-1 and 2.22 d-1.