504 research outputs found
The influence of incubation periods on photosynthesis–irradiance curves
In phytoplankton primary production studies, samples for the determination of photosynthesis
versus irradiance relationship ( P–I) are usually incubated at several irradiance levels during a fixed
time period, commonly 2–4 h. However, it is not clear if the use of this fixed incubation time is
appropriate to study the P–I relationship in any given ecosystem. The aim of this work was to study
the influence of incubation time on the P–I relationship in natural phytoplankton populations from
three different coastal ecosystems: an open coastal area, an estuary, and a coastal lagoon. Physical
and chemical variables, phytoplankton biomass, species composition, and P–I curves were analysed.
The results showed that, in the coastal area and in the estuary, P–I relationships were time
dependent, whereas in the coastal lagoon different incubation periods produced the same P–I curve.
An underestimation of daily primary production, ranging from 13% to 42.5%, was calculated when
data from standard incubation times (2–4 h) were used in ecosystems where P–I curves present a
dynamic time-dependent behaviour. This work suggests that the response of the P–I curves to the
incubation time varies with the characteristics of the ecosystem and is related to the light regime to
which phytoplankton cells are adapted. D 2002 Elsevier Science B.V. All rights reserved
The influence of incubation periods on photosynthesis–irradiance curves
In phytoplankton primary production studies, samples for the determination of photosynthesis
versus irradiance relationship ( P–I) are usually incubated at several irradiance levels during a fixed
time period, commonly 2–4 h. However, it is not clear if the use of this fixed incubation time is
appropriate to study the P–I relationship in any given ecosystem. The aim of this work was to study
the influence of incubation time on the P–I relationship in natural phytoplankton populations from
three different coastal ecosystems: an open coastal area, an estuary, and a coastal lagoon. Physical
and chemical variables, phytoplankton biomass, species composition, and P–I curves were analysed.
The results showed that, in the coastal area and in the estuary, P–I relationships were time
dependent, whereas in the coastal lagoon different incubation periods produced the same P–I curve.
An underestimation of daily primary production, ranging from 13% to 42.5%, was calculated when
data from standard incubation times (2–4 h) were used in ecosystems where P–I curves present a
dynamic time-dependent behaviour. This work suggests that the response of the P–I curves to the
incubation time varies with the characteristics of the ecosystem and is related to the light regime to
which phytoplankton cells are adapted. D 2002 Elsevier Science B.V. All rights reserved
The relationship between phytoplankton diversity and community function in a coastal lagoon
The decrease of biodiversity related to the phenomena of global climate change is stimulating the scientific
community towards a better understanding of the relationships between biodiversity and ecosystem
functioning. In ecosystems where marked biodiversity changes occur at seasonal time scales, it is easier to
relate them with ecosystem functioning. The objective of this work is to analyse the relationship between
phytoplankton diversity and primary production in St. André coastal lagoon – SW Portugal. This lagoon is
artificially opened to the sea every year in early spring, exhibiting a shift from a marine dominated to a low
salinity ecosystem in winter. Data on salinity, temperature, nutrients, phytoplankton species composition,
chlorophyll a (Chl a) concentration and primary production were analysed over a year. Modelling studies
based on production-irradiance curves were also conducted. A total of 19 taxa were identified among
diatoms, dinoflagellates and euglenophyceans, the less abundant group. Lowest diversities (Shannon–
Wiener index) were observed just before the opening to the sea. Results show a negative correlation
(p<0.05) between diversity and chlorophyll a (Chl a) concentration (0.2–40.3 mg Chl a m-3). Higher Chl a
values corresponded to periods when the community was dominated by the dinoflagellate Prorocentrum
minimum (>90% of cell abundance) and production was maximal (up to 234.8 mg C m-3 h-1). Maximal
photosynthetic rates (Pmax) (2.0–22.5 mg C mg Chl a-1 h-1) were higher under lower Chl a concentrations.
The results of this work suggest that decreases in diversity are associated with increases in biomass and
production, whereas increases correspond to opposite trends. It is suggested that these trends, contrary to
those observed in terrestrial and in some benthic ecosystems, may be a result of low habitat diversity in the
water column and resulting competitive pressure. The occurrence of the highest photosynthetic rates when
Chl a is low, under some of the highest diversities, suggests a more efficient use of irradiance under low
biomass–high diversity conditions. Results suggest that this increased efficiency is not explained by
potential reductions in nutrient limitation and intraspecific competition under lower biomasses and may be
a result of niche complementarity
The relationship between phytoplankton diversity and community function in a coastal lagoon
The decrease of biodiversity related to the phenomena of global climate change is stimulating the scientific
community towards a better understanding of the relationships between biodiversity and ecosystem
functioning. In ecosystems where marked biodiversity changes occur at seasonal time scales, it is easier to
relate them with ecosystem functioning. The objective of this work is to analyse the relationship between
phytoplankton diversity and primary production in St. André coastal lagoon – SW Portugal. This lagoon is
artificially opened to the sea every year in early spring, exhibiting a shift from a marine dominated to a low
salinity ecosystem in winter. Data on salinity, temperature, nutrients, phytoplankton species composition,
chlorophyll a (Chl a) concentration and primary production were analysed over a year. Modelling studies
based on production-irradiance curves were also conducted. A total of 19 taxa were identified among
diatoms, dinoflagellates and euglenophyceans, the less abundant group. Lowest diversities (Shannon–
Wiener index) were observed just before the opening to the sea. Results show a negative correlation
(p<0.05) between diversity and chlorophyll a (Chl a) concentration (0.2–40.3 mg Chl a m-3). Higher Chl a
values corresponded to periods when the community was dominated by the dinoflagellate Prorocentrum
minimum (>90% of cell abundance) and production was maximal (up to 234.8 mg C m-3 h-1). Maximal
photosynthetic rates (Pmax) (2.0–22.5 mg C mg Chl a-1 h-1) were higher under lower Chl a concentrations.
The results of this work suggest that decreases in diversity are associated with increases in biomass and
production, whereas increases correspond to opposite trends. It is suggested that these trends, contrary to
those observed in terrestrial and in some benthic ecosystems, may be a result of low habitat diversity in the
water column and resulting competitive pressure. The occurrence of the highest photosynthetic rates when
Chl a is low, under some of the highest diversities, suggests a more efficient use of irradiance under low
biomass–high diversity conditions. Results suggest that this increased efficiency is not explained by
potential reductions in nutrient limitation and intraspecific competition under lower biomasses and may be
a result of niche complementarity
Analysis of the deep chlorophyll maximum across the Azores Front
Physical, chemical and biological observations made in late July and August 1997 across the Azores Front (37ºN, 32ºW to 32ºN, 29ºW) are presented. The objectives of the study were: (1) to analyse horizontal and vertical
profiles of temperature, salinity, density, nutrients and chlorophyll-a (Chl a) of the top 350 m; (2) to identify the
main differences in the deep Chl a Maximum (DCM) and hydrographic structure between the water masses that
pass north and south of the Azores Front; and (3) to estimate phytoplankton primary production in these water
masses. Horizontal and vertical profiles of salinity, temperature, density, nutrients and phytoplankton pigments in
the top 350 m were analysed. The Front separates two distinct water types: the 18 ºC ModeWater (18MW) of subtropical
origin, and the 15 ºC ModeWater (15MW) of sub-polar origin. Differences in the DCM and hydrographic
structure between 18 MW and 15 MW were observed in the contour plots of each section. The average Chl a
concentration between 5 and 200 m depth decreased significantly from 15 MW to 18 MW. The same pattern was
observed for the Chl a concentration at the DCM depth. A vertical one-dimensional model was used to estimate
the phytoplankton primary production in the 15 MW and 18 MW and led to an estimated water column average
gross primary productivity (GPP) between 1.08 and 2.71 mg C
Analysis of coastal lagoon metabolism as a basis for management
This work was carried out in a shallow eutrophic coastal lagoon (St. André lagoon, SW Portugal) which is artificially
opened to the sea each year in early spring. Macrophytes, mainly Ruppia cirrhosa, are keystone species in
this ecosystem covering up to 60% of its total area with peak biomasses over 500 g DWm−2. The main objectives
were to study ecosystem metabolism, to evaluate the metabolic contribution to the community of the macrophyte
stands and their influence in the development of thermal stratification and bottom oxygen depletion.
The work combined an experimental and a modelling methodology. The experimental approach included open
water, mesocosm and microcosm seasonal experiments. During these experiments several physical, chemical
and biological parameters were monitored in the lagoon and in plastic enclosures (mesocosms) for periods of
24 hours. The microcosm experiments followed the light-dark bottle technique. The simultaneous use of these
different methodologies allowed the analysis of the contribution of the planktonic and benthic compartments to the
ecosystem’s oxygen budget.
The modelling work was based on the mathematical simulation of heat and gas exchanges in a vertically
resolved water column, under different macrophyte densities. Several simulations were carried out, in order to
investigate the importance of the macrophytes in the development of water column stratification and anoxia.
The simulation results suggest that macrophytes may greatly influence thermocline and oxycline development.
This influence is proportional to their biomass and canopy height. It is suggested that controlled macrophyte
biomass removal of up to 25% of available biomass in summer, may be useful in preventing bottom anoxia without
compromising benthic net primary production
Analysis of coastal lagoon metabolism as a basis for management
This work was carried out in a shallow eutrophic coastal lagoon (St. André lagoon, SW Portugal) which is artificially
opened to the sea each year in early spring. Macrophytes, mainly Ruppia cirrhosa, are keystone species in
this ecosystem covering up to 60% of its total area with peak biomasses over 500 g DWm−2. The main objectives
were to study ecosystem metabolism, to evaluate the metabolic contribution to the community of the macrophyte
stands and their influence in the development of thermal stratification and bottom oxygen depletion.
The work combined an experimental and a modelling methodology. The experimental approach included open
water, mesocosm and microcosm seasonal experiments. During these experiments several physical, chemical
and biological parameters were monitored in the lagoon and in plastic enclosures (mesocosms) for periods of
24 hours. The microcosm experiments followed the light-dark bottle technique. The simultaneous use of these
different methodologies allowed the analysis of the contribution of the planktonic and benthic compartments to the
ecosystem’s oxygen budget.
The modelling work was based on the mathematical simulation of heat and gas exchanges in a vertically
resolved water column, under different macrophyte densities. Several simulations were carried out, in order to
investigate the importance of the macrophytes in the development of water column stratification and anoxia.
The simulation results suggest that macrophytes may greatly influence thermocline and oxycline development.
This influence is proportional to their biomass and canopy height. It is suggested that controlled macrophyte
biomass removal of up to 25% of available biomass in summer, may be useful in preventing bottom anoxia without
compromising benthic net primary production
Reproduction of the blue jack mackerel, Trachurus picturatus, in western Portugal: microscopic gonad analysis reveals indeterminate fecundity and skipped spawning patterns
Blue jack mackerel, Trachurus picturatus, is the fifth most landed fish species in mainland Portugal, but
information on its reproductive biology is scarce. From September 2018 to August 2019, 626 specimens
were collected from commercial vessels to clarify the reproductive strategy of the T. picturatus population
off the west coast of Portugal. The proportion and length range of males and females were similar. Only
three of the specimens collected were categorized as immature, indicating that the fish caught in the
fishery are primarily mature. The spawning season lasted from late January until the end of March, with
gonadosomatic indices being similar for males and females. Fecundity was indeterminate, and estimated
batch fecundity ranged between 6,798 (at 25.4 cm TL) and 302,358 oocytes (at 33.8 cm TL). The low
number of females showing direct evidence of imminent or recent spawning suggests a low number
of spawning events. In addition, 12.7% of females were considered non-reproductive due to ovary
abnormalities including parasitic infection by Kudoa species, atretic structures and skipped spawning
events. This study highlights the importance of accounting for skipped spawning events and ovary
abnormalities in the management of species fisheries.info:eu-repo/semantics/publishedVersio
Clinical outcomes of patients with acute myeloid leukemia: evaluation of genetic and molecular findings in a real-life setting
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