Browsing by Author "Santos, A. Miguel P."
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- Are sardine larvae caught off northern Portugal in winter starving? An approach examining nutritional conditionsPublication . Chicharo, Maria Alexandra; Esteves, E.; Santos, A. Miguel P.; Santos, Antonina dos; Peliz, A.; Re, P.Recently, winter upwelling events off western Iberia have become more frequent. This may affect the production and survival of sardines egss and larvae through increased offshore transport. By analysis of RNA: DNA ratios, we investigated the impact of winter upwelling events on the larval conditions of Sardina pilchardus larvaeas a function of oceanographic conditions and food availability. Larvae were collected on a research cruise off northern Portugal in February 2000. Environmental parameters such as wind, water temperature, salinity microzooplankton biomass and daily egg production of the calanoid copepod Calanus helgolandicus also measured. The mean RNA:DNA ratios wererelatively high, indicating that almost all larvae collected were good condition. This was in agreement with the high microzooplankton biomass and high daily egg production of the copepod C. helgolandicus recorded during the same period. No adverse effects of upwelling causing offshore transport of larvae into poor feeding areas could be demonstrated because of the presence of a stratified warm plume with consequent high food production.
- Born small, die young: Intrinsic, size-selective mortality in marine larval fishPublication . Garrido, Susana; Ben-Hamadou, Radhouan; Santos, A. Miguel P.; Ferreira, S.; M A Teodosio; Cotano, U.; Irigoien, X.; Peck, M. A.; Saiz, E.; Re, P.Mortality during the early stages is a major cause of the natural variations in the size and recruitment strength of marine fish populations. In this study, the relation between the size-at-hatch and early survival was assessed using laboratory experiments and on field-caught larvae of the European sardine (Sardina pilchardus). Larval size-at-hatch was not related to the egg size but was significantly, positively related to the diameter of the otolith-at-hatch. Otolith diameter-athatch was also significantly correlated with survival-at-age in fed and unfed larvae in the laboratory. For sardine larvae collected in the Bay of Biscay during the spring of 2008, otolith radius-at-hatch was also significantly related to viability. Larval mortality has frequently been related to adverse environmental conditions and intrinsic factors affecting feeding ability and vulnerability to predators. Our study offers evidence indicating that a significant portion of fish mortality occurs during the endogenous (yolk) and mixed (yolk /prey) feeding period in the absence of predators, revealing that marine fish with high fecundity, such as small pelagics, can spawn a relatively large amount of eggs resulting in small larvae with no chances to survive. Our findings help to better understand the mass mortalities occurring at early stages of marine fish.
- Decapod larvae distribution and species composition off the southern Portuguese coastPublication . Pochelon, Patricia N.; Pires, Rita F. T.; Dubert, Jesus; Nolasco, Rita; Santos, A. Miguel P.; Queiroga, Henrique; dos Santos, AntoninaFor decapod crustaceans, the larval phase is the main responsible for dispersal, given the direct emission from adult habitats into the water column. Circulation patterns and behavioural mechanisms control the dispersal distance and connectivity between different areas. Information on larval distribution and abundance is required to predict the size and location of breeding populations, and correctly manage marine resources. Spatial distribution and abundance data of decapod larvae, and environmental parameters were assessed in winter surveys off the southern Portuguese coast. To better understand the oceanic structures driving larval distribution patterns, in situ physical parameters were measured and a hydrodynamical model used. Inter-annual, cross-shore and alongshore differences on decapod larvae distribution were found. Brachyuran crabs dominated the samples and similar taxa composition was observed in the most dynamic areas. Coastal taxa dominated the nearshore survey and were almost absent in the more offshore one, that registered much lower abundances. An upwelling front allowed a clear cross-shore species separation, also evident in the abundance values and number of taxa. Hydrodynamical conditions and adult habitats were the main factors explaining the observed patterns. Important missing information to understand the distribution patterns of decapod larval communities and the mechanisms behind them is given for the region.
- Field test of an autonomous observing system prototype for measuring oceanographic parameters from shipsPublication . Santos, Fernando P.; Rosa, Teresa L.; Hinostroza, Miguel A.; Vettor, Roberto; Santos, A. Miguel P.; Guedes Soares, C.A prototype of an autonomous system for the retrieval of oceanographic, wave, and meteorologic data was installed and tested in May 2021 on a Portuguese research vessel navigating on the Atlantic Ocean. The system was designed to be installed in fishing vessels that could operate as a distributed network of ocean data collection. It consists of an automatic weather station, a ferrybox with a water pumping system, an inertial measurement unit, a GNSS unit, an onboard desktop computer, and a wave estimator algorithm for wave spectra estimation. Among several parameters collected by this system’s sensors are the air temperature, barometric pressure, humidity, wind speed and direction, sea water temperature, pH, dissolved oxygen, salinity, chlorophyll-a, roll, pitch, heave, true heading, and geolocation of the ship. This paper’s objectives are the following: (1) describe the autonomous prototype; and (2) present the data obtained during a full-scale trial; (3) discuss the results, advantages, and limitations of the system and future developments. Meteorologic measurements were validated by a second weather station onboard. The estimated wave parameters and wave spectra showed good agreement with forecasted data from the Copernicus database. The results are promising, and the system can be a cost-effective solution for voluntary observing ships.
- Importance of the mesoscale in the decadal changes observed in the northern Canary upwelling systemPublication . Relvas, Paulo; Luis, Joaquim; Santos, A. Miguel P.Analysis of sea surface temperature (SST) time series since 1960 from existing data bases shows a generalized warming trend in the northern Canary upwelling system. The field of the satellite-derived SST trends off Western Iberia was built at the pixel scale (4 x 4 km) for the period 1985-2008, revealing significant spatial differences in the warming rates. Weaker warming trends fit to the known upwelling pattern off the southern part of the Western Iberia, pointing out the intensification of this feature since 1985, particularly during the peak summer months. A more regular behavior is found further north suggesting significant decadal changes in the mesoscale patterns of the northern Canary upwelling system. Citation: Relvas, P., J. Luis, and A. M. P. Santos (2009), Importance of the mesoscale in the decadal changes observed in the northern Canary upwelling system, Geophys. Res. Lett., 36, L22601, doi:10.1029/2009GL040504.
- Long-term variations in Ibero-Atlantic sardine (Sardina pilchardus) population dynamics: Relation to environmental conditions and exploitation historyPublication . Malta, T.; Santos, P. T.; Santos, A. Miguel P.; Rufino, M.; Silva, A.In the current work we modeled the relationship between global atmospheric indices, seasonal sea surface temperature and coastal upwelling on the recruitment of the Ibero-Atlantic sardine. To study long-term Ibero-Atlantic sardine population dynamics a historical recruitment index (HRI) was developed from 1947 to 2012, for the Portuguese west coast, the main recruitment area of the Ibero-Atlantic sardine stock. HRI was calculated as the number of individuals <= 16.0 cm total length per landed kg using length and weight distribution data from purse-seine fleet landings. Recruitment periodicity changed after the late 1960s from 2-3 years to 4 years cycles. Atlantic Multidecadal Oscillation (AMO), summer North Atlantic Oscillation (NAO), summer sea surface temperatures (SST) and winter upwelling were significantly related with recruitment, explaining 45.9% of recruitment variability in the generalized additive model. Possible mechanisms leading to those relationships were discussed. A complex two-way relationship between the sardine exploitation and recruitment appears to exist. High recruitments allowed the increase in total landings in the following years but high exploitation periods may have also led to a decrease of the population potential productivity in the subsequent years. (C) 2016 Elsevier B.V. All rights reserved.
- Multi-marker DNA metabarcoding for precise species identification in ichthyoplankton samplesPublication . Ferreira, André O.; Barroso, Cristina; Azevedo, Olga Mouteira; Duarte, Sofia; Egas, Conceição; Fontes, João T.; Ré, Pedro; Santos, A. Miguel P.; Costa, Filipe O.Ichthyoplankton monitoring is crucial for stock assessments, offering insights into spawning grounds, stock size, seasons, recruitment, and changes in regional ichthyofauna. This study evaluates the efficiency of multi-marker DNA metabarcoding using mitochondrial cytochrome c oxidase subunit I (COI), 12S rRNA and 16S rRNA gene markers, in comparison to morphology-based methods for fish species identification in ichthyoplankton samples. Two transects with four coastal distance categories were sampled along the southern coast of Portugal, being each sample divided for molecular and morphological analyses. A total of 76 fish species were identified by both approaches, with DNA metabarcoding overperforming morphology-75 versus 11 species-level identifications. Linking species-level DNA identifications with higher taxonomic morphological identifications resolved several uncertainties associated with traditional methods. Multi-marker DNA metabarcoding improved fish species detection by 20-36% compared to using a single marker/amplicon, and identified 38 species in common, reinforcing the validity of our results. PERMANOVA analysis revealed significant differences in species communities based on the primer set employed, transect location, and distance from the coast. Our findings underscore the potential of DNA metabarcoding to assess ichthyoplankton diversity and suggest that its integration into routine surveys could enhance the accuracy and comprehensiveness of fish stock assessments.
- 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.
- Reproduction and respiration of a climate change indicator species: effect of temperature and variable food in the copepod Centropages chierchiaePublication . Cruz, Joana; Garrido, Susana; Pimentel, Marta S.; Rosa, Rui; Santos, A. Miguel P.; Re, PedroThe abundance of the calanoid copepod Centropages chierchiae has increased at the northern limits of its distribution in recent decades, mainly due to oceanic climate forcing, suggesting this as a key species in monitoring climate change. Laboratory experiments were conducted to study the combined effect of temperature, food type and concentration on the egg production rate (EPR) and hatching success (HS) of C. chierchiae. Females were fed on two monoalgal diets (Gymnodinium sp. and Phaeodactylum tricornutum) at two food concentrations and at three different temperatures (13, 19, 24C). Respiration rates of both genders were measured at four different temperatures (8, 13, 19, 24C). EPR was significantly different between temperatures and food concentrations, the maximum EPR being attained when the copepods were exposed to high food levels and at 19C. Prey type significantly influenced EPR; feeding on P. tricornutum resulted in higher egg production than Gymnodinium sp. HS was significantly lower at 13C than at 19 and 24C and higher with Gymnodinium sp. Respiration rates were sex independent and increased exponentially with temperature. To maintain basal metabolism, the minimum food intake of P. tricornutum ranged between 0.4 and 1.8 g C and for Gymnodinium sp. between 0.03 and 0.13 g C. Food intake was always higher than the metabolic demands, except for the highest temperature tested (24C). The present results confirm the sensitivity of C. chierchiae to temperature variations and may help in understanding the successful expansion of its distribution towards northern latitudes.
- Review and prospects for autonomous observing systems in vessels of opportunityPublication . Rosa, Teresa L.; Santos, A. Miguel P.; Vettor, Roberto; Soar, C. GuedesThis paper focuses on the state of the art on Autonomous Observing Systems (AOS) used in Vessels of Opportunity (VOO) for collecting in situ atmospheric, oceanic and biogeochemical data. The designation Vessels of Opportunity includes all kinds of ships, even if not having scientific goals, which may carry proper devices that autonomously measure environmental variables. These vessels can be merchant, military, research, cruise liners, fishing, ferries, or even private yachts or sailing boats. The use of AOS can provide the opportunity for highly refined oceanographic data and improved derived data estimation, for local, regional or global scales studies. However, making the collected information accessible, both for scientific and technical purposes, provides a challenge in data management and analysis, which must, above all, ensure trusted useful data to the stakeholders. An overall review of the systems implemented is presented. This includes the definition of objectives, the recruitment of vessels and a review on the installation of proper acquisition devices; the selection and collection of Essential Oceanic Variables (EOV); the mechanisms for transmitting the information, and the quality control analysis and dissemination of data. The present and future capabilities of VOO for measuring EOV, within the Portuguese context are referred.