INVESTIGADORES
FERREYRA Gustavo Adolfo
artículos
Título:
Variable phytoplankton response to enhanced UV-B and nitrate addition in mesocosm experiments at three latitudes (Canada, Brazil and Argentina)
Autor/es:
LONGHI, M.L., G.A. FERREYRA, I.R. SCHLOSS AND S. ROY
Revista:
MARINE ECOLOGY PROGRESS SERIES
Editorial:
Inter-Research
Referencias:
Año: 2006 vol. 313 p. 57 - 72
ISSN:
0171-8630
Resumen:
The influence of nitrate enrichment on the response of natural phytoplankton populations
to enhanced UV-B radiation was tested during a series of week-long mesocosm (1800 l) experiments
carried out in Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (southern Argentina). We set up 2 mesocosms
at each site, one was submitted to ambient UV-B levels while the other received enhanced UV-B
levels corresponding to a local 60% ozone-depletion scenario, and both were continuously mixed. Samples
from the mesocosms were incubated in UV-transparent plastic bags (4 l) floating at the surface for
24 h. Half of these received nitrate, phosphate and silicate enrichments while for the other half nitrate was
omitted. Responses in terms of photochemical yield (Fv/Fm, where Fv is variable fluorescence after dark
relaxation and Fm is maximal fluorescence following short pulses of saturating white light, pulse amplitude-
modulated [PAM] fluorescence) and high-performance liquid chromatography (HPLC) pigments,
differed among sites and over time, particularly for Rimouski, where a large bloom took place in the mesocosms.
Enhanced UV-B significantly increased photoinhibition in the surface bags, while nitrate addition
partly relieved this inhibition only during the post-bloom period. The net growth of fucoxanthin was
reduced by enhanced UV-B except during the post-bloom period, when it increased, probably because
grazing pressure was reduced under enhanced UV-B (strong decrease in ciliates). In Ubatuba, cells were
affected by the high ambient-light irradiances at the surface, and enhanced UV-B had no further effect,
irrespective of the nutrient status. At Ushuaia, enhanced UV-B prevented all increases of fucoxanthin and
chl a, with much less effect on chl b (green algae), and no nutrient response was observed. This strong and
consistent negative response to enhanced UV-B is likely to be related to the cold temperature prevailing
at Ushuaia at the time of the experiment (slowing repair) as well as the local community composition. In
contrast, no effects of enhanced UV-B were observed in the stirred mesocosms at the 3 sites, indicating
that mixing moderated the UV-B effects in all 3 experiments.(Fv/Fm, where Fv is variable fluorescence after dark
relaxation and Fm is maximal fluorescence following short pulses of saturating white light, pulse amplitude-
modulated [PAM] fluorescence) and high-performance liquid chromatography (HPLC) pigments,
differed among sites and over time, particularly for Rimouski, where a large bloom took place in the mesocosms.
Enhanced UV-B significantly increased photoinhibition in the surface bags, while nitrate addition
partly relieved this inhibition only during the post-bloom period. The net growth of fucoxanthin was
reduced by enhanced UV-B except during the post-bloom period, when it increased, probably because
grazing pressure was reduced under enhanced UV-B (strong decrease in ciliates). In Ubatuba, cells were
affected by the high ambient-light irradiances at the surface, and enhanced UV-B had no further effect,
irrespective of the nutrient status. At Ushuaia, enhanced UV-B prevented all increases of fucoxanthin and
chl a, with much less effect on chl b (green algae), and no nutrient response was observed. This strong and
consistent negative response to enhanced UV-B is likely to be related to the cold temperature prevailing
at Ushuaia at the time of the experiment (slowing repair) as well as the local community composition. In
contrast, no effects of enhanced UV-B were observed in the stirred mesocosms at the 3 sites, indicating
that mixing moderated the UV-B effects in all 3 experiments.Fm is maximal fluorescence following short pulses of saturating white light, pulse amplitude-
modulated [PAM] fluorescence) and high-performance liquid chromatography (HPLC) pigments,
differed among sites and over time, particularly for Rimouski, where a large bloom took place in the mesocosms.
Enhanced UV-B significantly increased photoinhibition in the surface bags, while nitrate addition
partly relieved this inhibition only during the post-bloom period. The net growth of fucoxanthin was
reduced by enhanced UV-B except during the post-bloom period, when it increased, probably because
grazing pressure was reduced under enhanced UV-B (strong decrease in ciliates). In Ubatuba, cells were
affected by the high ambient-light irradiances at the surface, and enhanced UV-B had no further effect,
irrespective of the nutrient status. At Ushuaia, enhanced UV-B prevented all increases of fucoxanthin and
chl a, with much less effect on chl b (green algae), and no nutrient response was observed. This strong and
consistent negative response to enhanced UV-B is likely to be related to the cold temperature prevailing
at Ushuaia at the time of the experiment (slowing repair) as well as the local community composition. In
contrast, no effects of enhanced UV-B were observed in the stirred mesocosms at the 3 sites, indicating
that mixing moderated the UV-B effects in all 3 experiments.a, with much less effect on chl b (green algae), and no nutrient response was observed. This strong and
consistent negative response to enhanced UV-B is likely to be related to the cold temperature prevailing
at Ushuaia at the time of the experiment (slowing repair) as well as the local community composition. In
contrast, no effects of enhanced UV-B were observed in the stirred mesocosms at the 3 sites, indicating
that mixing moderated the UV-B effects in all 3 experiments.