Repositório Institucional da Universidade de Aveiro
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Mercury biomagnification in a contaminated estuary food web: effects of age and trophic position using stable isotope analyses
No full textThe main aim of this study was to ascertain the biomagnification processes in a mercury-contaminated estuary, by clarifying the trophic web structure through stable isotope ratios. For this purpose, primary producers (seagrasses and macroalgae), invertebrates (detritivores and benthic predators) and fish were analysed for total and organic mercury and for stable carbon and nitrogen isotopic signatures. Trophic structure was accurately described by δ15N, while δ13C reflected the carbon source for each species. An increase of mercury levels was observed with trophic level, particularly for organic mercury. Results confirm mercury biomagnification to occur in this estuarine food web, especially in the organic form, both in absolute concentrations and fraction of total mercury load. Age can be considered an important variable in mercury biomagnification studies, and data adjustments to account for the different exposure periods may be necessary for a correct assessment of trophic magnification rates and ecological risk
Aeromonas veronii, a tributyltin (TBT)-degrading bacterium isolated from an estuarine environment, Ria de Aveiro in Portugal
No full textOrganotin compounds are used in a variety of industrial processes therefore their subsequent discharge into the environment is widespread.
Bacteria play an important role in biogeochemical transformations acting as natural decontamination agents. Therefore, screening for tributyltin (TBT)-resistant and -degrading bacteria is relevant for the selection of isolates with decontamination ability of these polluted areas. With this purpose, 50 strains were isolated from sediment and water from Ria de Aveiro and their tolerance to TBT, up to 3 mM, was evaluated. Generally, occurrence of highly TBT-resistant bacteria was observed, and Gram negative bacteria exhibited more tolerance to TBT than Gram positive bacteria. A memory response was observed when bacteria were progressively exposed to increasingly higher TBT concentrations. One isolate, Aeromonas veronii Av27, highly resistant to TBT (3 mM) uses this compound as carbon source and degrades it to less toxic compounds
Use of an intelligent CCD camera for the study of endogenous vertical migration rhythms in first zoeae of the crab Carcinus maenas
No full textThis paper describes an actographic system, based on video camera and image analysis software, which can detect small planktonic organisms and automatically determine their position in a bi-dimensional plane. This actograph was used to study swimming behaviour, under constant dark conditions in the laboratory, of the first zoea of the crab Carcinus maenas (L.), hatched from ovigerous females collected in the Ria de Aveiro, Portugal. An endogenous rhythm of vertical migration with a circatidal period was detected, in accordance with previous laboratory and field observations made on the species' first zoea from Wales and the Ria de Aveiro, respectively. The system also enabled the computation of dispersion indexes that supported the conclusion that crab zoeae use passive sinking during the descent phase of vertical migration. Mean swimming speed in the absence of light, irrespective of direction, was 0.0666 cm s–1. Vertical upward and downward components of swimming were 0.0437 and 0.0599 cm s–1, respectively. Although lower than values reported in the literature, these velocities are high enough to allow swimming throughout the water column of most estuaries during vertical migration in natural conditions at night
Sensitivity analysis of Ria de Aveiro hydro-morphodynamics to the sea level rise integration period
No full textGlobal mean sea level has been rising in the last century at a rate of 1.7± 0.5 mm/year, and it is expected that
during the 21st century it will rise at a greater rate, intensifying coastal hazards worldwide. The main aim of this
study is to evaluate the sensitivity of the hydro and morphodynamics of the Ria de Aveiro lagoon to different
local sea level rise estimates expected for the end of the 21st century. The SRES scenario A2 was considered
admitting three integration periods (Period A between 2071-2080, Period B between 2071-2100, and Period C
between 2091-2100), which are compared to the reference period of 1980-1999 (actual climate). The local sea
level rise projections were obtained from the output of the GISS-ER model and pointed to a rise of 0.29, 0.34 and
0.42 m for the periods A, B and C respectively. The morphodynamic model MORSYS2D was applied to the Ria
de Aveiro considering each forcing scenario. The residual sediment flux at the inlet region and the lagoon tidal
prism were computed and analysed for the actual situation and for the three sea level rise estimates. The residual
transport of sediments at the inlet region is mostly seaward both for the actual situation and for the considered
scenarios. However its magnitude is very sensitive to the sea level rise: an increase of about 72%, 94% and 123%
is expected for the periods A, B and C respectively. The tidal prism is also very sensitive to the mean sea level:
an increase of about 19%, 22% and 28% is estimated for the periods A, B and C respectively
Anchoring novel molecular biomarker responses to traditional responses in fish exposed to environmental contamination
No full textThe responses of Dicentrarchus labrax and Liza aurata to aquatic pollution were assessed in a contaminated coastal lagoon, using both traditional and novel biomarkers combined. DNA damage, assessed by comet assay, was higher in both fish species from the contaminated sites, whereas levels of cytochrome P450 1A1 gene expression were not significantly altered. The liver histopathological analysis also revealed significant lesions in fish from contaminated sites. Alterations in ras and xpf genes were analysed and additional pollutant-responsive genes were identified. While no alterations were found in ras gene, a downregulation of xpf gene was observed in D. labrax from a contaminated site. Suppression subtractive hybridization applied to D. labrax collected at a contaminated site, revealed altered expression in genes involved in energy metabolism, immune system activity and antioxidant response. The approach and results reported herein demonstrate the utility of anchoring traditional biomarker responses alongside novel biomarker responses
The leaf-bag and the sediment sample: two sides of the same ecological quality story?
No full textA growing number of studies suggest that ecological quality status assessment in transitional waters should rely upon functional indicators rather than structural indices. The experimental study of decomposition rates using leaf-bags are among the former. A recent example was conducted in Ria de Aveiro, Western Portugal, and the decomposition rates of Phragmites australis obtained through the registration of the biomass decrease in leaf samples left in the estuary for fixed periods of time (7, 15, 30 and 60 days). The leaf-bags were recollected from the field and the accompanying fauna retained, for comparison to that obtained in sediment samples taken with a hand-held corer. The study was conducted in five areas covering the full salinity gradient, in three sites per area and four replicates per site. A total of 89 taxa were registered, 70 in the leaf-bags and 50 in the sediment samples. 39 taxa were sampled only in the leaf-bags, 19 only in the corers and 31 were common. From marine to freshwater areas, average abundance increased in both types of samples, and species richness and diversity diminished, except in freshwater and in the leaf-bags. Both samplers portrayed the succession from the marine to the freshwater areas, and the benthic community was found significantly different between all areas except between the two located closer to the estuarine entrance, equally by both samplers. Despite these similarities, the benthic communities sampled by the two methods were significantly different, either dominated by annelids (corers), or by arthropods (leaf-bags), amphipods in the estuary and insects in freshwater. These differences were not significant neither in the freshwater, due to paucity of the endofauna in freshwater, nor in the fully marine area, possibly due to the high variability of samples within the area. These results indicate that the estuarine benthic invertebrates upon which the taxonomic indices are calculated and those which contribute to the functional aspects based in the study of decomposition rates, are essentially very distinct
Hydrodynamic model calibration for a mesotidal lagoon: the case of Ria de Aveiro (Portugal)
No full textRia de Aveiro is a shallow vertically
homogeneous mesotidal lagoon, located in
the Northwest of Portugal. It has
a very intricate morphology and large tidal flats area
s that cover and uncover al
ong the tidal cycle. A two-
dimensional vertically integrated hydrodynamic mode
l was considered to be adequate to simulate its
hydrodynamics and a model developed from the SIMSYS2D
model was applied. The purpose of this study is to
describe the implementation a
nd calibration of this model which is able to predict tide-induced water level and
depth integrated velocity for the entire lagoon. The
numerical bathymetry used was developed from data
concerning depth obtained from a general survey carried out
in 1987/88 and actualised for several channels in the
last years. The Monte Carlo method wa
s used to generate the rectangular
computational grid, which has 409 cells
in the eastward direction and 966 cells in
the northward direction (dimensions of 40
×
40 m). The model
calibration was performed adjusting the bottom friction co
efficient for the entire lagoon, through the comparison
between measured and predicted time series of sea surface elevation (SSE) for a large number of stations
distributed along the main channels of the lagoon. The re
lative mean absolute error,
the root-mean square and a
skill assessment of the difference between those SSE values were determined to quantify the models
performance. Harmonic analysis was also performed in or
der to evaluate the model accuracy. According to the
results the hydrodynamic model was successfully calibrated, reproducing accurately the barotropic flows in this
complex lagoon
Channel-ocean exchange driven by tides and river flow: Espinheiro Channel (Portugal)
No full textA 3D baroclinic model (Mohid) was used to perform hindcast simulations in a tidal channel – Espinheiro
Channel (located within Ria de Aveiro, north coast of Portugal) – in order to study its hydrography. The
simulations were conducted for four distinct periods where markedly different river discharge and tides occurred
and the outputs are compared with synoptic thermohaline data. The model qualitatively reproduces alongchannel
thermohaline distributions at three different vertical levels during low-to-medium river inflow,
underestimating the salinity stratification under high river inflow (higher than 100 m3
s
-1). Once the numerical
model is fully implemented, the hydrography of the channel was analysed in terms of two main forcing factors:
river discharge and tide. Tidal currents and thermohaline data were analysed at the channel’s inlet and at a mid
channel station during two tidal cycles. The stratification and water column stability were found to vary in these
stations as a function of the estuarine Richardson number and the buoyancy frequency. Well mixed conditions
were found at the lower and mid channel area when the river flow is weak (independently of the tidal regime),
turning to highly stratified when the river flow is very high (during neap tide). The residual currents were also
analysed revealing an ebb-dominated channel, with a more intense seaward current near the surface due to the
freshwater inflow
Biodiversity patterns of epifaunal assemblages associated with the gorgonians Eunicella gazella and Leptogorgia lusitanica in response to host, space and time
No full textPatterns of biodiversity (α- and β-diversity), abundance and community structure of the epifaunal assemblages associated with two gorgonians, Eunicella gazella and Leptogorgia lusitanica, were analysed in relation to host, colony size, location and time. Colony size and time were the major factors shaping attendant assemblages. Patterns of α-diversity and β-diversity were host-dependent. Assemblages associated with E. gazella showed a significant inter-annual variability for most of the metrics analysed, while in those associated with L. lusitanica only Shannon–Wiener varied significantly between years. In L. lusitanica Hurlbert's expected number of taxa was significantly lower in small-sized than in medium- to large-sized colonies, but an opposite pattern was detected for β-diversity, reflecting the higher heterogeneity among small-sized colonies. The dbRDA analysis segregated the assemblages associated with each of the two hosts; the faunal patterns were mainly explained by colony size related attributes (area, number of branches and, to a lesser extent, width) and the “colonial” epibiont cover. However, we suggest that altogether they may act as a metacommunity, with high temporal and spatial fluidity in their composition and structure related to multiple factors including not only a component of stochasticity but also life history events, biotic interactions and response to habitat heterogeneity and environmental variability
Music, conflict and conciliation: rethinking some postcolonial approaches through the case of music in Goa
No full textThis text is a reflexive exercise based on an apparent paradox: music, as expressive behaviour, aesthetic experience and political agent, simultaneously sets a locus of conflict and conciliation. This polarity describes an ambivalent feature that also defines music as a privileged place of interlocution because it embodies both the possibility for the articulation of seemingly distant sonic languages, and especially, because it provides different ways of listening, and diverse modes of aesthetic appreciation. Music, by its own nature, may be emancipated - albeit briefly – from the universe of social conflict where it is generated, by building, at the occasion of performance, a place for conciliation which, in Homi Babha’s words, is also a place for interlocution as “the human right to narration” (2007:25)