Browsing by Author "Moita, Teresa"
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- New physical and biological evidence of lateral transport affecting dinoflagellate cyst distribution in the benthic nepheloid layer along a land-sea transect off Figueira da Foz (Atlantic Iberian margin)Publication . García-Moreiras, Iria; Hatherly, Melissa; Zonneveld, Karin; Dubert, Jesus; Nolasco, Rita; Santos, Ana Isabel; Oliveira, Anabela; Moita, Teresa; Oliveira, Paulo B.; Magalhães, Jorge M.; Amorim, Anantroduction The production of resting cysts is a key dispersal and survival strategy of many dinoflagellate species. However, little is known about the role of suspended cysts in the benthic nepheloid layer (BNL) in the initiation and decline of planktonic populations.Methods In September 2019, sampling of the dinoflagellate cyst community at different water depths in the water column and in the bottom sediments, and studies of spatio-temporal changes in physical properties (temperature, salinity, density and suspended sediment concentration), were carried out along a land-sea transect off Figueira da Foz (NW Portugal) to investigate the dinoflagellate cyst distribution and the factors (physical and biological) affecting it. A clustering analysis was used to compare the BNL and sediment cyst records with the cyst rain recorded by a sediment trap at a fixed station. Furthermore, Lagrangian particle experiments enabled simulating cyst trajectories in the BNL 5 and 10 days before sampling and assessing cross-shore, vertical and alongshore transport within the studied region.Results A well-developed BNL was present during the survey, which covered a change from active (14th of September) to relaxed (19th of September) upwelling conditions. Organic-walled dinoflagellate cysts were dominant in all samples, although calcareous dinoflagellate cysts consistently occurred (at low abundances). High proportions of full cysts were observed in the BNL, of which a significant portion was viable as shown by excystment experiments. Moreover, BNL cyst records collected on the 19th of September along the land-sea transect were similar to the sediment trap cyst record but greatly differed from sediment cyst records. The heterotrophic small spiny brown cysts (SBC) and cysts of the autotrophic yessotoxin-producer Protoceratium reticulatum notably increased during the survey, in the BNL and in the water column above.Discussion The comparison of the BNL, surface sediment and sediment trap cyst records supported that the main origin of cysts in the BNL was the recent production in the water column. The spatial coincidences in the distribution of cysts and vegetative cells of Protoceratium reticulatum also supported that full cysts in the water column were being produced in surface waters. New data evidenced the presence of a significant reservoir of viable cysts in the BNL that have the potential to seed new planktonic blooms. Furthermore, back-track particle modelling evidenced that alongshore advection was the main physical mechanism controlling cyst dynamics in the BNL during most part of the survey period, being particularly intense in coastal stations (<100 m depth). Consequently, the sediment cyst signal is a mixture of locally and regionally produced cysts. We provide multi-disciplinary data evidencing that cysts recently formed in the photic zone can be laterally advected within the studied region through the BNL, contributing to a better understanding of the role of the BNL in cyst dynamics and tracing the seed sources of the new blooms.
- 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.
- Phytoplankton dynamics in southern Portuguese coastal lagoons during a discontinuous period of 40 yearsPublication . Brito, Ana; Quental, Teresa; Coutinho, Teresa; Branco, Maria; Falcão, Manuela; Newton, Alice; Icely, John; Moita, TeresaShallow coastal lagoons in southern Portugal, such as the Ria Formosa and Alvor, are considered to be highly important both ecologically and economically. Given the impact of phytoplankton in the ecosystem productivity, it is important to understand its dynamics and to consider them for the assessment of ecosystem health. All available phytoplankton data(chlorophyll a; selected species composition and abundance) within the period from 1967 to 2011 were compiled within the framework of a project to implement the Water Framework Directive. Chlorophyll a (chl a)measurements in Ria Formosa from 1967 to 1968, 1985 to 1986, 1991 to 1992, 2006 to 2008, and 2010 show similar monthly averages with some exceptions. In the 80’s the monthly averages were less than half of what was observed in the 60’s. In the 90’s, the chl a concentrations increased significantly and in the period from 2006 to 2010, chl a concentrations ranged between the values found in the 80’s. The decrease in chl a concentrations during the 80’s is likely to be associated with a peak in shellfish production. Shellfish production was recorded to have decreased from 1990 onwards. Chl concentrations in Ria de Alvor are found to vary within the same range as in Ria Formosa. However, data are limited and does not allow a detailed historical comparison. During the most important chl a peaks, the phytoplankton community was characterized by coastal species, such as Pseudo-nitzschia sp., which may be associated with upwelling events. This was found in Ria Formosa both in the 90’s and from 2000 onwards, as well as in the most recent data from Ria de Alvor. This clearly indicates the influence of the coastal dynamics in these lagoons. High chl outside the lagoon confirmed the influence of coastal waters. In addition, high chl concentrations were also observed at inner parts of the lagoon but not outside, suggesting the existence of an interior maximum. The community was mainly characterized by the existence of low salinity tolerant species, such as Kryptoperidinium foliaceum. Over the time intervals in this study, the 90th percentile values of chlorophyll a concentrations were 3.0 in Ria Formosa and 2.6 mg m 3 in the Ria de Alvor. In a five-fold classification of ecological quality from High to Bad, we propose chlorophyll a concentrations of 5.3 mg m 3 as a reference value, 8 mg m 3 for the boundary High/Good, and 12 mg m 3 for the boundary Good/Moderate. According to this, all water bodies were considered as in High status.