Repositório Institucional da Universidade de Aveiro
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Mercury partition in the interface between a contaminated lagoon and the ocean: the role of particulate load and composition
No full textAfter having estimated the patterns of flow to the ocean and found some seasonal and tidal differences, mainly with regard to the relative importance of dissolved and particulate fractions, mercury partitioning at the interface between a contaminated lagoon and the Atlantic Ocean was investigated during four tidal cycles in contrasting season and tidal regimes. Mercury was found to be located predominantely in the particulate fraction throughout the year, contributing to its retention within the system. Seasonal conditions, variations in marine and fluvial signals and processes affecting bed sediment resuspension influenced the character and concentration of suspended particulate matter in the water column. Variation in the nature, levels and partitioning of organic carbon in the particulate fraction affected levels of particulate mercury as well as mercury partitioning. These results highlight the dominant role of suspended particulate matter in the distribution of anthropogenic mercury and reinforce the importance of competitive behavior related to organic carbon in mercury scavenging
Changes in the fish fauna of the Ria de Aveiro estuarine lagoon (Portugal) during the twentieth century
No full textThe fish biodiversity of the Ria de Aveiro has been analysed during the 20th century, as an
indicator of the biological integrity of the ecosystem. Ninety-two distinct species and 38
families of Agnatha, Chondrichthyes and Osteichthyes occurred during the period. The family
and species richness showed two levels of magnitude, from the 1910s, with high values (26–28
families and 51–52 species), and during the last two decades with more variable values (20–27
families and 38–55 species). A total of 13 species (four non-sporadic species) have disappeared
recently. The lagoon system has been affected by large-scale anthropogenic influences mainly
the substantial development of industries and the increasing population in the watershed, in
addition to overfishing, climatic changes and dredging. In general, as shown by an analysis of
the ecotrophic guilds present, the area maintained a similar structure during the whole period.
No significant differences in time were recorded for any of the designated guilds. The
twenty-two frequent species, which occurred in six or seven surveys, were mainly estuarine
resident species or marine adventitious species, living in the substratum (benthic fish), on soft
substratum and vegetated bottoms. They were feeding either on invertebrates alone or on
invertebrates and fish, and producing pelagic or benthic eggs. The 19 sporadically-recorded
species, recorded only once, were mostly marine adventitious, demersal fishes, living above
rough bottom and vegetation, feeding strictly on invertebrates, and producing eggs benthically
or deposited into vegetation. It is concluded that the Ria de Aveiro estuarine coastal lagoon
has supported similar fish communities during the past century and that these comprise
representatives of various ecological types
Photosynthetic activity, photoprotection and photoinhibition in intertidal microphytobenthos as studied in situ using variable chlorophyll fluorescence
No full textThe photosynthetic activity of microphytobenthos biofilms was studied in situ on an intertidal mudflat of the Ria de Aveiro, Portugal. Time series of physical variables characterizing the microenvironment at the sediment photic zone (incident solar irradiance, temperature, salinity), photophysiological parameters and productive biomass of undisturbed microalgal assemblages were measured during daytime low-tide periods along one spring–neap tidal cycle, with the objective of (1) characterizing the short-term variability in photosynthetic activity in situ, (2) relating it with the changing environmental conditions and (3) with the operation of physiologically (xanthophyll cycle) and behaviorally (vertical migration) based photoprotective processes, and (4) assessing the occurrence of photoinhibition. Pulse Amplitude Modulated (PAM) fluorometry was applied to measure photosynthetic activity (the effective and maximum quantum yield of photosystem II, ΔF/Fm′ and Fv/Fm; the photosynthesis index EFY; rapid light-response curves (RLC)), the photoprotective operation of the xanthophyll cycle and photoinhibition (non-photochemical quenching, NPQ; quantum efficiency of open RCs, Fv′/Fm′), and vertical migration (productive biomass, Fo). The photosynthetic activity was found to be strongly affected by the cumulative light dose received during the morning low-tide periods. The fluorescence indices ΔF/Fm′, EFY, Fv′/Fm′ and RLC parameters were more depressed under high irradiances when clear sky was present during the morning low tide than when foggy conditions reduced the light dose received during a comparable period. Productive biomass exhibited maximum values in the first hours of the morning, followed by a steep decrease when irradiance reached moderate levels, due to the downward migration of the microalgae. This photophobic migratory response appeared to display a photoprotective role, allowing ΔF/Fm′ to remain near optimum values until irradiance reached values as high as 750 μmol m−2 s−1. The response to high light also included the formation of NPQ, expected to represent mainly the operation of the xanthophyll cycle, which attained high values, above 5.9 for 1500 μmol m−2 s−1. Despite the photoprotection provided by energy-dissipation processes and photophobic behaviour, the light response of most photophysiological parameters showed a clear counter-clockwise hysteresis pattern, indicating the occurrence of photoinhibition. Hysteresis was due to the incomplete recovery of photosynthetic activity during the afternoon low tide, and its magnitude was dependent on the morning light doses
Influence of multiple stressors on the auto-remediation processes occurring in salt marshes
No full textDue to increasing global population, salt marshes have been subjected to multiple stressors such as increasing nutrient loadings and historical contamination. In order to better understand how does the salt marsh plants auto-remediation capacity (phytoaccumulation of metals) is affected by cultural eutrophication, an experiment was performed under controlled conditions. Plants were exposure to equal metal concentrations (Zn, Cu, and Ni – micronutrients, and Cd – class B metal) simulating historical contamination and three different concentrations of nitrogen (nitrate) simulating steps of cultural eutrophication. According to our study, under the tested concentrations, cultural eutrophication does not seem to affect Zn, Cu and Ni phytoremediation of H. portulacoides, but the ecosystem service of Cd phytoremediation seems to be promoted. Nevertheless, Cd high toxicity and bioaccumulation should be taken into account, as well as the vulnerability of salt marsh ecosystems, whose reduction will have drastic consequences to the ecosystem health
Accumulation of mercury in sea bass from a contaminated lagoon (Ria de Aveiro, Portugal)
No full textThis work reports the distribution of total mercury (Hg) in Dicentrarchus labrax (sea bass) and in material collected in plankton nets from an inner basin contaminated with the effluent from a chlor-alkali plant, and in other locations of a coastal lagoon (Ria de Aveiro, Portugal). Mercury concentrations were higher in material collected in 200 than in 63 μm mesh net. Mercury in seston decreased pronouncedly with the distance to the industrial source (1.3–0.015 μg g−1 on a wet weight basis), and was higher at low tide than at high tide. This indicates that mercury is exported from the contaminated basin through the first levels of the estuarine chain. Mercury was analysed in muscle, liver, gills and stomach content of sea bass. Specimens captured in the contaminated basin showed higher accumulation of mercury: levels in muscle and liver of young specimens exceeded 1 μg g−1 and 2 μg g−1, respectively; gills and stomach content also presented higher concentrations. Mercury increased more drastically in liver than in muscle of specimens exposed to high contamination, changing the liver/muscle Hg ratio. Although juveniles exhibited higher concentrations in the contaminated basin than in other areas, there is an age effect on the accumulation of mercury in sea bass at the contaminated basin. Occasionally, intermediate concentrations were found in specimens captured in other areas of the lagoon
The capacity of crab megalopae to autotomize body appendages and the consequences upon their feeding ability - the price to pay to live another day
No full textDuring the mass settlement events of brachyuran crabs, there is a significant chance of density-dependent injury in the megalopae (last larval stage) because cannibalism can occur by larger conspecifics. Laboratory observations revealed that the appendages that are more prone to injury are eyestalks, as well as first (P1) and fifth (P5) pereiopods. The ability of Carcinus maenas megalopae to autotomize these structures and the effect of such injuries in their feeding ability and metamorphosis were investigated. All tested specimens were able to autotomize one or both of their P1 and P5, but not their eyestalks. Megalopae missing a single P1, as well as one or both P5, were able to capture and ingest prey, as well as intact specimens. Megalopae with either P1 and P5 appendages or at least one damaged eyestalk failed to ingest sufficient food to reach the nutritional threshold required to successfully metamorphose
Growth and development of nauplii and copepodites of the estuarine copepod Acartia tonsa from southern Europe (Ria de Aveiro, Portugal) under saturating food conditions
No full textA temperature-dependent growth model is presented for nauplii and copepodites of the estuarine calanoid copepod Acartia tonsa from southern Europe (Portugal). Development was followed from egg to adult in the laboratory at four temperatures (10, 15, 18 and 22°C) and under saturating food conditions (>1,000 μg C l−1). Development times versus incubation temperature were fitted to a Belehradek’s function, showing that development times decreased with increasing incubation temperature: at 10°C, A. tonsa need 40.3 days to reach adult stage, decreasing to 8.9 days when reared at 22°C. ANCOVA (homogeneity of slopes) showed that temperature (P<0.001) and growth phase (P<0.01) had a significant effect on the growth rate. Over the range of temperatures tested in this study, highest weight-specific growth rates were found during naupliar development (NI–NVI) and varied from 0.185 day−1 (10°C) to 0.880 day−1 (22°C) with a Q 10 equal to 3.66. During copepodite growth (CI–CV), the weight-specific growth rates ranged from 0.125 day−1 (10°C) to 0.488 day−1 (22°C) with a Q 10 equal to 3.12. The weight-specific growth rates (g) followed temperature (T) by a linear relationship and described as ln g=−2.962+0.130 T (r 2=0.99, P<0.001) for naupliar stages and ln g=−3.134+0.114T (r 2=0.97, P<0.001) for copepodite stages. By comparing in situ growth rates (juvenile growth and fecundity) for A. tonsa taken from the literature with the temperature-dependent growth model defined here we suggest that the adult females of A. tonsa are more frequently food limited than juveniles
Acute toxicity testing with the European estuarine amphipod Corophium multisetosum
No full textThis study reports on the use of the estuarine amphipod Corophium multisetosum in acute toxicity testing. The species was successfully acclimated to the laboratory and was used in a water-only whole effluent 96 h acute bioassay and in a 10 days whole estuarine sediment test. C. multisetosum response was compared to other species in 96 h bioassays, testing boiling cork effluent and iron filings lixiviates. The amphipod showed high sensitivity and the results were similar to those obtained with others species namely, the freshwater cladoceran Daphnia magna, the estuarine amphipod Gammarus chevreuxi and the seawater annelid Sabellaria alveolata. In a 10 days static exposure to natural impacted estuarine sediments, the response of the species was compared to a fertilization bioassay with the sea-urchin Paracentrotus lividus. Both species indicated the same sediment samples as the most potentially toxic. These samples were collected in sites where the resident macrofauna benthic community is also the most affected, with strong reduction of the species richness, abundance and biomass. The results revealed that C. multisetosum presents high potential to be used in routine acute toxicity testing in the estuarine environment
Determination of organic mercury in biota, plants and contaminated sediments using a thermal atomic absorption spectrometry technique
No full textA simple, rapid procedure for the determination of organic mercury in sediments, plants and fish tissues has been developed and validated. Extraction and separation of organic mercury compounds from the sample matrix was achieved by an established procedure based on an acid leaching of the sample (H2SO4/KBr/CuSO4), followed by extraction of the organic mercury halide with toluene and back-extraction with an aqueous solution of thiosulphate. Detection and quantification of mercury, in the liquid extracts, was made by atomic absorption spectrometry (AAS), following thermal decomposition of the sample. The method was evaluated using Certified Reference Material (CRM) BCR 463 (tuna fish), BCR 580 (estuarine sediment), IAEA-140TM (sea plant homogenate) and NRCC TORT-2 (lobster hepathopancreas). The recovery factors for organic mercury in all tested CRM were between 81–107%. The precision of the method has relative standard deviations of less than 10% for sediments and fish tissues and of less than 16% for plant material. The method was successfully applied to natural samples of sediments, plants, macroalgae and fish tissues collected from an estuarine ecosystem and could, therefore, be used for routine analyses
Capital structure determinants in the context of listed family firms
No full textThis paper provides an analysis of the capital structure in the context of Portuguese listed family firms, covering the period
from 1999 to 2010. Using a panel data approach, we find that family controlled firms differ from non-family firms in several aspects.
Family firms use more debt than non-family firms and have a lower proportion of independent directors. In addition, they finance new
projects with debt financing and are sensitive to the cost of debt and the crisis periods, whereas non-family firms with higher levels of
cash have more debt financing. Overall, we find a negative relationship between profitability and non-debt tax shield and debt and a
positive relationship between firms’ age and debt