INVESTIGADORES
FERREYRA Gustavo Adolfo
artículos
Título:
Ultraviolet B radiation effects on the structure and function of lower levels of the marine planktonic food web
Autor/es:
FERREYRA, G.A., B. MOSTAJIR, I. R. SCHLOSS, K. CHATILA, M. E. FERRARIO, P. SARGIAN, S. ROY, J. PROD'HOMME, S. DEMERS
Revista:
PHOTOCHEMISTRY AND PHOTOBIOLOGY
Editorial:
American Society for Photobiology
Referencias:
Año: 2006 vol. 82 p. 887 - 897
ISSN:
0031-8655
Resumen:
The impact of UV-B radiation (UVBR; 280320 nm) on lower
levels of a natural plankton assemblage (bacteria, phytoplankton
and microzooplankton) from the St. Lawrence Estuary
was studied during 9 days using several immersed outdoor
mesocosms. Two exposure treatments were used in triplicate
mesocosms: natural UVBR (N treatment, considered as the
control treatment) and lamp-enhanced UVBR (H treatment,
simulating 60% depletion of the ozone layer). A phytoplankton
bloom developed after day 3, but no significant differences
were found between treatments during the entire experiment
for phytoplankton biomass (chlorophyll a and cell carbon)
nor for phytoplankton cell abundances from flow cytometry
and optical microscopy of three phytoplankton size classes
(picoplankton, nanoplankton and microplankton). In contrast,
bacterial abundances showed significantly higher values in the
H treatment, attributed to a decrease in predation pressure
due to a dramatic reduction in ciliate biomass (~7080%) in
the H treatment relative to the N treatment. The most
abundant ciliate species were Strombidinium sp., Prorodon
ovum and Tintinnopsis sp.; all showed significantly lower
abundances under the H treatment. P. ovum was the lessaffected
species (50% reduction in the H treatment compared
with that of the N control), contrasting with ~90% for the
other ones. Total specific phytoplanktonic and bacterial
production were not affected by enhanced UVBR. However,
both the ratio of primary to bacterial biomass and production
decreased markedly under the H treatment. In contrast, the
ratio of phytoplankton to bacterial plus ciliate carbon biomass
showed an opposite trend than the previous results, with
higher values in the H treatment at the end of the experiment.
These results are explained by the changes in the ciliate
biomass and suggest that UVBR can alter the structure of
the lower levels of the planktonic community by selectively
affecting key species. On the other hand, linearity between
particulate organic carbon (POC) and estimated planktonic
carbon was lost during the postbloom period in both
treatments. On the basis of previous studies, our results can
be attributed to the aggregation of carbon released by cells
to the water column in the form of transparent exopolymer
particles (TEPs) under nutrient limiting conditions. Unexpectedly,
POC during such a period was higher in the H
treatment than in controls. We hypothesize a decrease in the
ingestion of TEPs by ciliates, in coincidence with increased
DOC release by phytoplankton cells under enhanced UVBR.
The consequences of such results for the carbon cycle in the
ocean are discussed.a and cell carbon)
nor for phytoplankton cell abundances from flow cytometry
and optical microscopy of three phytoplankton size classes
(picoplankton, nanoplankton and microplankton). In contrast,
bacterial abundances showed significantly higher values in the
H treatment, attributed to a decrease in predation pressure
due to a dramatic reduction in ciliate biomass (~7080%) in
the H treatment relative to the N treatment. The most
abundant ciliate species were Strombidinium sp., Prorodon
ovum and Tintinnopsis sp.; all showed significantly lower
abundances under the H treatment. P. ovum was the lessaffected
species (50% reduction in the H treatment compared
with that of the N control), contrasting with ~90% for the
other ones. Total specific phytoplanktonic and bacterial
production were not affected by enhanced UVBR. However,
both the ratio of primary to bacterial biomass and production
decreased markedly under the H treatment. In contrast, the
ratio of phytoplankton to bacterial plus ciliate carbon biomass
showed an opposite trend than the previous results, with
higher values in the H treatment at the end of the experiment.
These results are explained by the changes in the ciliate
biomass and suggest that UVBR can alter the structure of
the lower levels of the planktonic community by selectively
affecting key species. On the other hand, linearity between
particulate organic carbon (POC) and estimated planktonic
carbon was lost during the postbloom period in both
treatments. On the basis of previous studies, our results can
be attributed to the aggregation of carbon released by cells
to the water column in the form of transparent exopolymer
particles (TEPs) under nutrient limiting conditions. Unexpectedly,
POC during such a period was higher in the H
treatment than in controls. We hypothesize a decrease in the
ingestion of TEPs by ciliates, in coincidence with increased
DOC release by phytoplankton cells under enhanced UVBR.
The consequences of such results for the carbon cycle in the
ocean are discussed.Strombidinium sp., Prorodon
ovum and Tintinnopsis sp.; all showed significantly lower
abundances under the H treatment. P. ovum was the lessaffected
species (50% reduction in the H treatment compared
with that of the N control), contrasting with ~90% for the
other ones. Total specific phytoplanktonic and bacterial
production were not affected by enhanced UVBR. However,
both the ratio of primary to bacterial biomass and production
decreased markedly under the H treatment. In contrast, the
ratio of phytoplankton to bacterial plus ciliate carbon biomass
showed an opposite trend than the previous results, with
higher values in the H treatment at the end of the experiment.
These results are explained by the changes in the ciliate
biomass and suggest that UVBR can alter the structure of
the lower levels of the planktonic community by selectively
affecting key species. On the other hand, linearity between
particulate organic carbon (POC) and estimated planktonic
carbon was lost during the postbloom period in both
treatments. On the basis of previous studies, our results can
be attributed to the aggregation of carbon released by cells
to the water column in the form of transparent exopolymer
particles (TEPs) under nutrient limiting conditions. Unexpectedly,
POC during such a period was higher in the H
treatment than in controls. We hypothesize a decrease in the
ingestion of TEPs by ciliates, in coincidence with increased
DOC release by phytoplankton cells under enhanced UVBR.
The consequences of such results for the carbon cycle in the
ocean are discussed.and Tintinnopsis sp.; all showed significantly lower
abundances under the H treatment. P. ovum was the lessaffected
species (50% reduction in the H treatment compared
with that of the N control), contrasting with ~90% for the
other ones. Total specific phytoplanktonic and bacterial
production were not affected by enhanced UVBR. However,
both the ratio of primary to bacterial biomass and production
decreased markedly under the H treatment. In contrast, the
ratio of phytoplankton to bacterial plus ciliate carbon biomass
showed an opposite trend than the previous results, with
higher values in the H treatment at the end of the experiment.
These results are explained by the changes in the ciliate
biomass and suggest that UVBR can alter the structure of
the lower levels of the planktonic community by selectively
affecting key species. On the other hand, linearity between
particulate organic carbon (POC) and estimated planktonic
carbon was lost during the postbloom period in both
treatments. On the basis of previous studies, our results can
be attributed to the aggregation of carbon released by cells
to the water column in the form of transparent exopolymer
particles (TEPs) under nutrient limiting conditions. Unexpectedly,
POC during such a period was higher in the H
treatment than in controls. We hypothesize a decrease in the
ingestion of TEPs by ciliates, in coincidence with increased
DOC release by phytoplankton cells under enhanced UVBR.
The consequences of such results for the carbon cycle in the
ocean are discussed.P. ovum was the lessaffected
species (50% reduction in the H treatment compared
with that of the N control), contrasting with ~90% for the
other ones. Total specific phytoplanktonic and bacterial
production were not affected by enhanced UVBR. However,
both the ratio of primary to bacterial biomass and production
decreased markedly under the H treatment. In contrast, the
ratio of phytoplankton to bacterial plus ciliate carbon biomass
showed an opposite trend than the previous results, with
higher values in the H treatment at the end of the experiment.
These results are explained by the changes in the ciliate
biomass and suggest that UVBR can alter the structure of
the lower levels of the planktonic community by selectively
affecting key species. On the other hand, linearity between
particulate organic carbon (POC) and estimated planktonic
carbon was lost during the postbloom period in both
treatments. On the basis of previous studies, our results can
be attributed to the aggregation of carbon released by cells
to the water column in the form of transparent exopolymer
particles (TEPs) under nutrient limiting conditions. Unexpectedly,
POC during such a period was higher in the H
treatment than in controls. We hypothesize a decrease in the
ingestion of TEPs by ciliates, in coincidence with increased
DOC release by phytoplankton cells under enhanced UVBR.
The consequences of such results for the carbon cycle in the
ocean are discussed.