Browsing by Author "Oliveira, P. B."
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- Diet and feeding intensity of sardine Sardina pilchardus: correlation with satellite-derived chlorophyll dataPublication . Garrido, Susana; Ben-Hamadou, Radhouan; Oliveira, P. B.; Cunha, M. E.; Chicharo, Maria Alexandra; Van der Lingen, C. D.Spatio-temporal variability of the diet of sardine Sardina pilchardus off Portugal was examined through analysis of the stomach contents of fish collected every 14 d from the west and south of Portugal during 2003/2004. Dietary composition of the modal sardine length class was assessed by determining the frequency of occurrence and carbon content of identified prey, and these 2 parameters were combined to estimate a modified index of relative importance of prey (mIRI). The most important prey for sardines were zooplankton, comprising crustacean eggs, copepods, decapods, cirripedes and fish eggs, dinoflagellates and diatoms (particularly the toxin-producer genus Pseudo-nitzschia), which together accounted for >90% of the estimated dietary carbon. Dietary seasonality was similar for both areas, except that the contribution of phytoplankton was higher for fish from the west Portuguese coast, where upwelling events are stronger and recurrent during spring and summer months. The predominance of prey <750 μm in sardine diet suggests that filter feeding is the dominant feeding mode used in the wild. Feeding intensity was similar for both sexes and for fish of different length classes and was higher on the west coast than in the south, which is probably related to the higher productivity of the west coast. Although there was high inter-annual variability in feeding intensity, this parameter was highest for both areas during spring and winter months. Temporal variability in satellite-derived chlorophyll a matched the temporal variability in the dietary contribution by phytoplankton and of sardine feeding intensity, suggesting further investigation of the potential use of satellite-derived chlorophyll a data as a proxy for sardine feeding intensity.
- First representation of the trophic structure and functioning of the Portuguese continental shelf ecosystem: insights into the role of sardinePublication . Veiga-Malta, T.; Szalaj, D.; Angelico, M. M.; Azevedo, M.; Farias, I; Garrido, S.; Lourenco, S.; Marçalo, Ana; Marques, V; Moreno, A.; Oliveira, P. B.; Paiva, V. H.; Prista, N.; Silva, C.; Sobrinho-Goncalves, L.; Vingada, J.; Silva, A.In this study, we analysed the structure and functioning of the Portuguese continental shelf ecosystem and investigated the role of sardine Sardina pilchardus using the Ecopath massbalance approach. An Ecopath model was configured to represent the continental shelf waters in the period 2006-2009. The model showed that biomass was concentrated in low and intermediate trophic levels as in other upwelling areas. Several low- and medium-trophic-level groups were identified as dominant groups in the ecosystem (e.g. zooplankton, macrozoobenthos, sardine, chub mackerel Scomber colias, and demersal and benthopelagic invertivorous fish). Furthermore, lowtrophic-level groups were responsible for the main energy flows, and overall higher impact on the ecosystem, emphasizing the importance of bottom-up control of the ecosystem structure. Our results are relevant to understand structure and functioning of this ecosystem and constitute an important step towards an ecosystem approach to fisheries management in the study area.
- Greenhouse climate management and control systemsPublication . Cunha, J. B.; Ruano, Antonio; Oliveira, P. B.; Couto, C.The technologies used in greenhouse production systems have developed considerably during the last decade. These improvements have taken place in several areas, such as the development of new building techniques and actuating equipments, modelling of the plant physiological processes and of the greenhouse climate, among many others. Nowadays, due to economic and environmental requirements, there is still a demand to improve the greenhouse climate management and control systems in order to optimise the production process. This paper addresses some of the software tools that are being implemented and tested with this purpose.
- Physical-biological interactions in the life history of small pelagic fish in the Western Iberia Upwelling EcosystemPublication . Santos, A. Miguel P.; Chicharo, Maria Alexandra Teodosio; Santos, Antonina dos; Moita, Teresa; Oliveira, P. B.; Peliz, A.; Re, P.This paper reviews relevant investigations conducted in the Western Iberia Upwelling Ecosystem (WIUE) on the dynamics of small pelagic fish (SPF), its relationship to climate changes and processes related to the ‘ocean triad’ (enrichment, concentration, transport/retention). In the last decades, a decline in the productivity of several SPF species (e.g., sardine and horse mackerel) was observed in the WIUE, which is partially explained by environmental variability (e.g., changes in coastal upwelling). The main mechanism proposed to explain this decline is the increased frequency and intensity of upwelling events during the spawning season (winter) of these species, which is typically a period when convergence conditions prevail. Thus, this ‘anomalous’ situation promotes egg and larval dispersal away from the favourable coastal habitat (the shelf) and consequently has a negative impact on their survival and recruitment. However, the variability of local features like the Western Iberia Buoyant Plume (WIBP) and the Iberian Poleward Current (IPC) introduce important fluctuations in the transport patterns of the region, and could modulate the impact of these winter upwelling events in the survival of larvae. The retention on the shelf of larval sardine along convergence zones formed by the interaction of these two features plays an important role in their survival. Furthermore, the WIBP is a suitable environment for the growth of phytoplankton and for larval fish survival. From these findings it is clear that simplified Ekman transport models could not explain larval fish transport/retention patterns in this region and more realistic biophysical models should be used to simulate the local oceanographic conditions to understand larval dynamics and the success of recruitment of SPF in the Western Iberia.
- Phytoplankton distribution and physical processes off NW Iberia during two consecutive upwelling seasonsPublication . Oliveira, P. B.; Amorim, F. N.; Dubert, J.; Nolasco, R.; Moita, TeresaThis work presents the results of two oceanographic surveys conducted off NW Iberia during successive summer upwelling seasons, aiming at the identification of the physical processes underlying the phytoplankton distribution in the area. Mooring (ADCP and thermistors) and ship-based CTD-F observations corroborate previous results that wind-driven upwelling circulation, (sub)mesoscale eddies and the stratification induced by the Western Iberia Buoyant Plume (WIBP) are the main processes affecting the chlorophyll distribution, but also provide new insights on key oceanographic structures governing the shelf circulation and phytoplankton structuring, namely (i) the link between frontal activity along the shelf break south of similar to 41 degrees N, the flow bifurcation at that latitude and the establishment of a cyclonic area with low frontal activity over the mid-shelf; (ii) the measurement of a previously unreported, remarkably persistent (> 1 month), near bottom poleward flow at the 30 m isobath, interpreted as the response to the alongshore pressure gradient driven by the stronger upwelling intensity north of 41 degrees N; (iii) the impact of low salinity buoyant plumes expressed on the shallowing of the Ekman layer, with the consequent frictional (Ekman) currents intensity increase, their low chlorophyll content contrary to previous winter/spring observations, and the lack of a direct relationship between plume salinities and river runoff; and (iv) the strong coupling between the chlorophyll distribution and the small-scale (O(1 - 10)km) oceanographic features providing further evidence that the phytoplankton distribution off NW Iberia in the summer upwelling season is strongly coupled to submesoscale processes.
- Validation of standard and alternative satellite ocean-color chlorophyll products off Western IberiaPublication . Sá, Carolina; D'Alimonte, Davide; Brito, A.; Kajiyama, T.; Mendes, C. R.; Vitorino, J.; Oliveira, P. B.; da Silva, J. C. B.; Brotas, V.Chlorophyll a concentration (Chl) product validation off theWestern Iberian coast is here undertaken by directly comparing remote sensing data with in situ surface reference values. Both standard and recently developed alternative algorithms are considered for match-up data analysis. The investigated standard products are those produced by the MERIS (algal 1 and algal 2) and MODIS (OC3M) algorithms. The alternative data products include those generatedwithin the CoastColour Project and Ocean Color Climate Change Initiative (OC-CCI) funded by ESA, as well as a neural net model trained with field measurements collected in the Atlantic off Portugal (MLPATLP). Statistical analyses showed that satellite Chl estimates tend to be larger than in situ reference values. The study also revealed that a non-uniform Chl distribution in the water column can be a concurring factor to the documented overestimation tendency when considering larger optical depth match-up stations. Among standard remote sensing products, MODIS OC3M and MERIS algal 2 yield the best agreement with in situ data. The performance of MLPATLP highlights the capability of regional solutions to further improve Chl retrieval by accounting for environmental specificities. Results also demonstrate the relevance of oceanographic regions such as the Nazaré area to evaluate how complex hydrodynamic conditions can influence the quality of Chl products.