INVESTIGADORES
VILLAFAÑE virginia Estela
congresos y reuniones científicas
Título:
Responses of phytoplankton from mid-latitudes of Patagonia in a scenario of global change.
Autor/es:
HELBLING, E.W; V.E. VILLAFAÑE
Lugar:
Dusseldorf, Alemania
Reunión:
Congreso; 15th International Congress on Photobiology; 2009
Resumen:
Global change, as a result of anthropogenic activities, include the enhancement of ultraviolet radiation B (UV-B, 280-315 nm) due to the thinning of the ozone layer, and the increase of temperature caused by the release of greenhouse gases; both having direct and indirect effects on aquatic organisms.  Here we present results of studies carried out to assess some aspects of global change at mid-latitudes.  Along the Patagonian coast, summer marine phytoplankton assemblages are normally exposed to relatively high levels of solar radiation, especially UVR, due to a combination of low solar zenith angles, high heliophany and thermal stratification of the water column.  In addition, the wide amplitude of temperatures and strong winds produce important changes in the upper mixed layer (UML) that condition the underwater field and hence the exposure and responses / acclimation of plankton from these latitudes.  This was particularly evident in time-series studies carried out in the area where high variability in photosynthetic responses has been observed when phytoplankton were exposed to different radiation regimes.  Additionally, results from short term experiments (< day) indicated that summer phytoplankton assemblages, mainly dominated by flagellates are comparatively more resistant to UVR exposure - in terms of photosynthetic inhibition - than those from winter (dominated by diatoms).  Other intensive studies further corroborated that UVR-induced photoinhibition is not only dependant on species composition but also on the size structure of the community, with inhibition increasing when small diatoms dominated the assemblages, and lower when chlorophytes dominated.  The size-dependence of UVR-induced damage was also observed in some Patagonian sites where high CPDs (cyclobutane pyrimidine dimers) levels were determined in picoplankton but not in microplankton.  Considering that metabolism, including repair of UVR-induced damage to the DNA molecule or the photosystem are temperature-dependent we also carried out experiments to determine the effects of increased temperature on diverse processes.  Increased temperature benefited some phytoplankton species (i.e., by reducing UVR impact), as seen in experiments done with diatoms during late spring, and also with flagellates under laboratory conditions.  Hence it is evident that the effects of global change – increased UVR / temperature - on the aquatic biota are very complex but the picture is even further complicated in estuarine environments, such as one of our study sites in Argentina (Chubut River estuary) where organisms are exposed to large gradients in their physical, chemical, optical and biological properties.  Overall, the interaction radiation - temperature suggests that the outcome and the future behaviour of the system under a scenario of global change lies in a narrow line of balance between damage and repair / acclimation.