Abstract:

Annual anomalies of Lambertian equivalent reflectivity (LER) retrieved from the total ozone mapping spectrometer spanning the period November 1978–November 2005 were studied in the Southern Hemisphere, in a region bounded by 0° S and 60° S, and their trends were estimated. With the exception of few regions where the variable may represent the contribution of both cloudiness and snow, trends in LER anomalies provided an evolution of total cloudiness. On average, the study region experienced a net increase in LER values of 0.78 reflectivity units (RU) decade−1; if only significant trend values are considered this figure increased to 1.18 RU decade−1. The region that showed the largest upward trend, up to 4 RU decade−1, was located over the eastern Pacific, off the coasts of Chile and Peru, where the presence of marine stratocumulus is frequent. Despite the overall positive trend there were regions that yielded a negative one, most notably the tropical latitudes of South America and Africa. The yearly zonal means also showed a positive trend at all latitudes, but significance occurred beyond 20° S only. Correlation maps between LER anomalies and five different circulation indices were also introduced. The indices with the highest and lowest number of significant correlation values were the Madden–Julian oscillation at 70° E and the quasi-biennial Oscillation, respectively.

Author affiliation: Yuchechen, Adrian Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires. Unidad de Investigación y Desarrollo de las Ingenierías; Argentina

Author affiliation: Lakkis, Susan Gabriela. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires. Unidad de Investigación y Desarrollo de las Ingenierías; Argentina. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Facultad de Ciencias Agrarias; Argentina

Author affiliation: Canziani, Pablo Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires. Unidad de Investigación y Desarrollo de las Ingenierías; Argentina

Abstract:

Three NILU-UV multichannel radiometers have been installed in 1999 at the Argentinian sites of Ushuaia (54S), Marambio (64S) and Belgrano-II (77S) in order to continuously monitor UV radiation, photosynthetically active radiation and total ozone. The measurements were established by INM, Spain in collaboration with FMI, Finland, DNA-IAA, Argentina and CADIC, Argentina to observe and characterize the spatial and temporal evolution of ozone and ultraviolet radiation in the Antarctic region. Special attention has been given to the quality control and quality assurance of the measurements under harsh climatological conditions. The ozone and UV time series of 2000–2006 were calibrated using a polynomial fit for lamp measurements performed every second week all year round. The gaps in these data are minimal, with almost no data missing, and the data products are available from http://www.polarvortex.org in near real time. The data products include the erythemally-weighted UV, UVB and UVA radiation, photosynthetically active radiation (PAR), total ozone (O3) and a cloud parameter (CLT). For UV data, dose rates as well as daily doses are available; from these the maximum measured UV indices (UVI), during 2000–2006, were 12.0, 9.7 and 8.1 at Ushuaia, Marambio and Belgrano-II, respectively.

Author affiliation: Redondas, A.. Izaña Atmospheric Research Center; España

Author affiliation: Torres, C.. Izaña Atmospheric Research Center; España

Author affiliation: Meinander, O.. Finnish Meteorological Institute; Finlandia

Author affiliation: Lakkala, K.. Finnish Meteorological Institute; Finlandia

Author affiliation: García, R.. Izaña Atmospheric Research Center; España

Author affiliation: Cuevas, E.. Izaña Atmospheric Research Center; España

Author affiliation: Ochoa, H.. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Direccion Nacional del Antártico; Argentina

Author affiliation: Deferrari, Guillermo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Author affiliation: Diaz, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina

Abstract:

Ultraviolet radiation (UVR) plays a key role in several biological functions, including human health. Skin exposure to UVR is the main factor in vitamin D photoconversion. There is also evidence relating low levels of vitamin D with certain internal cancers, mainly colon, breast and prostate, as well as other diseases. Several epidemiological studies have shown an inverse relationship between the above-mentioned diseases and latitude, in accordance with the ultraviolet radiation latitudinal gradient. The aim of this study is to determine whether UV irradiance levels in the southern South America are sufficient to produce suitable levels of vitamin D year around. For this purpose, vitamin D photoconversion weighted-irradiance was analyzed between S.S. de Jujuy (24.17°S, 65.02°W) and Ushuaia (54° 50′S, 68° 18′W). In addition to irradiance, skin type and area of body exposed to sunlight are critical factors in vitamin D epidemiology. Due to a broad ethnic variability, it was assumed that the skin type in this region varies between II and V (from the most to the less sensitive). All sites except South Patagonia indicate that skin II under any condition of body area exposure and skin V when exposing head, hands, arms and legs, would produce suitable levels of vitamin D year round (except for some days in winter at North Patagonian sites). At South Patagonian sites, minimum healthy levels of vitamin D year round can be reached only by the more sensitive skin II type, if exposing head, hands, arms and legs, which is not a realistic scenario during winter. At these southern latitudes, healthy vitamin D levels would not be obtained between mid May and beginning of August if exposing only the head. Skin V with head exposure is the most critical situation; with the exception of the tropics, sun exposure would not produce suitable levels of vitamin D around winter, during a time period that varies with latitude. Analyzing the best exposure time during the day in order to obtain a suitable level of vitamin D without risk of sunburn, it was concluded that noon is best during winter, as determined previously. For skin type II when exposing head, exposure period in winter varies between 30 and 130 min, according to latitude, except for South Patagonian sites. During summer, noon seems to be a good time of day for short periods of exposure, while during leisure times, longer periods of exposure without risk of sunburn are possible at mid-morning and mid-afternoon. At 3 h from noon, solar zenith angles are almost the same for sites between the tropics and North Patagonia, and at 4 h from noon, for all sites. Then, in these cases, the necessary exposure periods varied slightly between sites, only due to meteorological differences.

Author affiliation: Diaz, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Author affiliation: Vernet, María. University Of California At San Diego; Estados Unidos

Author affiliation: Paladini, Alejandro Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular; Argentina

Author affiliation: Fuenzalida, Humberto. Universidad de Chile; Chile

Author affiliation: Deferrari, Guillermo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Author affiliation: Booth, Charles R.. Biospherical Instruments Inc.; Estados Unidos

Author affiliation: Cabrera, Sergio. Universidad de Chile; Chile

Author affiliation: Casiccia, Claudio. Universidad de Magallanes; Chile

Author affiliation: Dieguez, Maria del Carmen. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Lovengreen, Charlotte. Universidad Austral de Chile; Chile

Author affiliation: Pedroni, Jorge. Universidad Nacional de la Patagonia; Argentina

Author affiliation: Rosales, Alejandro. Universidad Nacional de la Patagonia; Argentina

Author affiliation: Vrsalovic, Jazmin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Abstract:

Ultraviolet-B radiation (UV-B, 280–315 nm) is an important environmental signal that regulates growth and development in plants. Two dose-dependent UV-B response pathways were described in plants: a specific one, mediated by UVR8 (the specific UV-B receptor) and an unspecific one, activated by the oxidative damage produced by radiation. The constitutively expressed receptor appears inactive as a dimer, with the two monomers dissociating upon UV-B irradiation. The monomer then interacts with COP1, an ubiquitin ligase, hindering its ability to poly-ubiquitinate transcriptional factor HY5, thus averting its degradation and activating the photomorphogenic response. HY5 induces the synthesis of proteins RUP1 and RUP2, which interact with UVR8, releasing COP1, and inducing the re-dimerization of UVR8. This mechanism has been thoroughly characterized in Arabidopsis, where studies have demonstrated that the UVR8 receptor is key in UV-B response. Although Arabidopsis importance as a model plant many mechanisms described in this specie differ in other plants. In this paper, we review the latest information regarding UV-B response mediated by UVR8 in different species, focusing on the differences reported compared to Arabidopsis. For instance, UVR8 is not only induced by UV-B but also by other agents that are expressed differentially in diverse tissues. Also, in some of the species analyzed, proteins with low homology to RUP1 and RUP2 were detected. We also discuss how UVR8 is involved in other developmental and stress processes unrelated to UV-B. We conclude that the receptor is highly versatile, showing differences among species.

Instituto de Genética

Author affiliation: Tossi, Vanesa Eleonora. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Regalado, Jose Javier. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Iannicelli, Jesica. INTA. Instituto de Genética; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Laino, Leandro Ezequiel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina

Author affiliation: Burrieza, Hernan Pablo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina

Author affiliation: Escandon, Alejandro Salvio. INTA. Instituto de Genética; Argentina

Author affiliation: Pitta Alvarez, Sandra. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Abstract:

Experiments were conducted during the Austral Summer of 2014 to determine the effects of increased nutrient input and ultraviolet radiation (UVR) on the food consumption rate (FCR) and food preference in the amphipod Amphitoe valida. We collected specimens from the Patagonian coast (Argentina), from beaches close (Barrancas Blancas; BB) and further away (Cangrejales; C) from the Chubut River, which constitutes the potential source of eutrophication. Organisms were exposed to different radiation regimes (full radiation vs. PAR only) and fed with different macroalgae diets (i.e., from different geographical location and with different quality in terms on nutrient content). Males collected from C showed food compensation, consuming more food under low-nutrient diets, while no compensation was observed in males from BB. Regardless of their origin, UVR decreased the FCR when males where fed on ambient nutrient diets, but not when males fed on high-quality diets indicating that in the former case, individuals were in worse physiological conditions to cope with UVR; food quality, however, significantly counteracted the deleterious effects of UVR on FCR. Females collected from the two beaches showed similar FCR under high-nutrient diet and had no food compensation when fed in low-nutrient diets. Females were more vulnerable to UVR, since their FCR were lower when exposed to UV radiation independent of the diet. Our results show that under anthropogenic eutrophication and high solar UVR levels an increase in the nutrient input could favor only males of A. valida , by reducing the negative effects of UVR on their FCR. Nevertheless, these nutrient inputs might cause additional problems like anoxia, as a result of an unusual macroalgal growth, thus affecting amphipod’s survival.

Author affiliation: Valiñas, Macarena Soledad. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Bermejo, Paula. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Galbán, Lara. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina

Author affiliation: Laborda, Luciana. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina

Author affiliation: Häder, Donat P.. Universitat Erlangen-Nuremberg; Alemania

Author affiliation: Villafañe, Virginia Estela. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Helbling, Eduardo Walter. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Abstract:

The combined impact of solar ultraviolet radiation (UVR) and elevated temperature on the photosynthesis of phytoplankton communities from the two end members of the Chubut River estuary was studied using short- and long-term incubations. Samples from the river and seawater sections of the estuary were collected during the austral Spring (November 2011) and exposed to solar radiation (with and without UVR) under two temperatures: in situ and increased by 5 °C. The long-term incubations were designed to assess the potential acclimation of each phytoplankton community to the experimental conditions. Short-term incubations, at day 1 and day 5 of the acclimation period, included the determination of Photosynthesis vs. irradiance curves, Biological Weighting Functions and daily cycles of Chl-a fluorescence measurements, and were used as an estimation of the ability to cope with either increased temperature or UVR. There was a synergistic effect between UVR and temperature in the seawater community, with samples demonstrating a better photosynthetic response in the absence of UVR and at the in situ temperature. In contrast, temperature had an antagonistic effect when combined with UVR in the river community, with increased temperature counteracting the negative impact of UVR. Despite this, both communities showed an acclimation capacity toward UVR and increasing temperature. Our results point to a differential impact of global change variables on phytoplankton communities within the estuary, which affect photosynthesis and might influence the species composition with potential repercussions on the food web.

Author affiliation: Helbling, Eduardo Walter. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina

Author affiliation: Banaszak, Anastazia T.. Universidad Nacional Autónoma de México; México

Author affiliation: Villafañe, Virginia Estela. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Abstract:

Global change is associated to the increase in temperature (T), nutrient inputs (Nut) and solar radiation in the water column. To address their joint impact on the net community production [NCP], respiration [CR] and PSII performance (Φ PSII) of coastal phytoplankton communities from the South Atlantic Ocean over a seasonal succession, we performed a factorial design. For this, we used a 2 x 2 x 2 matrix set-up, with and without UVR, ambient and enriched nutrients, and in situ T and in situ T + 3ºC. The future scenario of global change exerted a dual impact, from an enhancement of NCP and F PSII during the pre-bloom to an inhibition of both processes towards the bloom period, when the in situ T and irradiances were lower and the community was dominated by diatoms. The increased inhibition of NCP and Φ PSII during the most productive stage of the annual succession could produce signi fi cant alterations of the CO2-sink capacity of coastal areas in the future.

Author affiliation: Cabrerizo, Marco J.. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Universidad de Granada; España

Author affiliation: Carrillo, Presentación. Universidad de Granada; España

Author affiliation: Villafañe, Virginia E.. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Helbling, Eduardo Walter. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Abstract:

The combined impact of solar ultraviolet radia- tion (UVR) and elevated temperature on the photosynthesis of phytoplankton communities from the two end members of the Chubut River estuary was studied using short- and long-term incubations. Samples from the river and seawater sections of the estuary were collected during the austral Spring (November 2011) and exposed to solar radiation (with and without UVR) under two temperatures: in situ and increased by 5 °C. The long-term incubations were designed to assess the potential acclimation of each phyto- plankton community to the experimental conditions. Short- term incubations, at day 1 and day 5 of the acclimation period, included the determination of Photosynthesis vs. irradiance curves, Biological Weighting Functions and daily cycles of Chl-a fluorescence measurements, and were used as an estimation of the ability to cope with either increased temperature or UVR. There was a synergistic effect be- tween UVR and temperature in the seawater community, with samples demonstrating a better photosynthetic re- sponse in the absence of UVR and at the in situ tempera- ture. In contrast, temperature had an antagonistic effect when combined with UVR in the river community, with increased temperature counteracting the negative impact of UVR. Despite this, both communities showed an acclima- tion capacity toward UVR and increasing temperature. Our results point to a differential impact of global change variables on phytoplankton communities within the estuary, which affect photosynthesis and might influence the species composition with potential repercussions on the food web.

Author affiliation: Helbling, Eduardo Walter. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Union. Estación de Fotobiología Playa Union; Argentina

Author affiliation: Banaszak, Anastazia T.. Universidad Nacional Autónoma de México; México

Author affiliation: Villafañe, Virginia Estela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Union. Estación de Fotobiología Playa Union; Argentina

Abstract:

Se estudió la estructura trófica del mesozooplancton con énfasis en Appendicularia y Copepoda en la región norpatagónica, poniendo atención en su variación espacial y estacional. Adicionalmente, se realizaron estudios con especies dominantes en esta zona para evaluar cómo factores ambientales pueden afectar las relaciones tróficas en este ecosistema. Para ello, se analizó experimentalmente el efecto subletal de la radiación ultravioleta en las tasas de alimentación de copépodos. En todo el ciclo estacional dominaron los copépodos y la fracción nanoplanctónica de fitoplancton. En verano se destacó una menor diversidad de especies, entre las que dominó Euterpina acutifrons. Asimismo, se observó que la RUV inhibe la alimentación de dicha especie y que en sus estadios larvales son capaces de realizar foto-reparación. En cuanto a la variación espacial, en el sistema frontal de Península Valdés dominaron las menores tallas del mesozooplancton (‹ 500 μm) (copépodos calanoideos, ciclopoideos, nauplii y apendicularias) y las larvas de Engraulis anchoita en la zona homogénea. La distribución de la Chl-a y la estratificación térmica de la columna de agua fueron los principales factores que influyeron en las diferencias observadas en la distribución y composición del mesozooplancton. La apendicularia Oikopleura dioica, presentó una distribución vertical similar de día y de noche en la zona homogénea, en cambio en la zona de transición se encontraron las mayores tallas e individuos maduros por encima de la termoclina durante la noche. Este trabajo brinda nueva información sobre la comunidad mesozooplanctónica que sostiene especies ícticas de alto valor comercial en la zona de estudio. En este sentido, los datos aportados por esta tesis sobre el efecto de la RUV en la alimentación de una especie dominante, plantea un punto de partida para nuestro entendimiento de cómo los factores asociados al cambio global pueden modificar las relaciones tróficas.

The present thesis report studies on the trophic structure of mesozooplankton focusing on Appendicularia and Copepoda in the North Atlantic Patagonian region, with special attention to its spatial and seasonal variations. Furthermore, it studies the dominant species in this area to evaluate how environmental factors can affect trophic relationships in this ecosystem. To do so, the sublethal effect of ultraviolet radiation on feeding rates of copepods, were experimentally examined. Both copepods and the nanoplanktonic fraction of phytoplankton dominated during the whole seasonal cycle. Lower diversity of species was found during summer, being Euterpina acutifrons the dominant one. It was also observed that the UV radiation inhibits the feeding of this species and that they are able to photo-repair in their larval stages. As for the spatial variation in the frontal system of Peninsula Valdés, small sizes (‹ 500 μm) such as mesozooplankton (calanoids, ciclopoyds, nauplii and appendicularians) and Engraulis anchoita dominated in the homogeneous area. The distributions of Chl-a and the thermal stratification of the water column were the main factors influencing the observed differences in the distribution and composition of mesozooplankton. The appendicularian Oikopleura dioica showed a similar vertical distribution both during day and night in the homogeneous area, whereas in the transition area larger sizes and more mature individuals were found above the thermocline at night. This work provides new information about the mesozooplankton community that supports fish species of high commercial value. In this sense, the data provided by this thesis concerning the UVR effect on the feeding of a dominant species represents a starting point for our understanding of how the factors associated with global change can alter the trophic relationships in this region.

Author affiliation: Spinelli, Mariela Lorena. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Abstract:

Esta tesis investiga los efectos de la radiación ultravioleta sobre organismos acuáticos. En particular se estudiaron los efectos sobre el zooplancton, sobre sus principales depredadores, las larvas de peces, y sobre la interacción entre presa y depredador. Este trabajo se realizó en distintos ambientes y diferentes escalas. Los ambientes incluyeron varios lagos del Noroeste Patagónico y la Península Antártica. Las ecalas variaron desde experimento de laboratorio hasta muestreos de campo. Los resultados indican que la radiación ultravioleta tiene efectos negativos, tanto sobre el zooplancton, como sobre sus depredadores. Dichos efectos son claramente dependientes de la dosis a la que los organismos son expuestos, y por lo tanto, varían con la profundidad y la transparencia de cada ambiente en particular. Se anaizó también las distintas estrategias utilizadas por los organismos para contrarrestar los efectos negativos de la RUV. Los resultados sugieren fuertemente que dichas estrategia están condicionadas por el ambiente físico y el entorno ecológico. Por ejemplo, en ambientes profundos, como los grandes lagos pedemontanos Patagónicos,el zooplancton puede encontrar refugio en profundidad durante el verano. Por el contrario en ambientes menos profundos, muchos organismos recurren a otro tipo de estrategias, tales como la fotorrespiración mediante la acumulación de ompuestos capaces de bloquear la radiación, o la foto-reparación, a través de mecanismos enzimáticos. La posibilidad de foto-reparación parece estar muy limitada en ambientes fríos, presumiblemente debido a la baja eficiencia de la enzima fotoliasa a baja temperatura. Por otra parte, el empleo de compuestos fotoprotectores parece estar condicionado, al menos en parte, por la presencia de depredadores visuales, como los estadios juveniles de peces. Se investigó también la posibilidad de que los peces pudieran utilizar las longitudes de onda dentro del espectro ultravioleta para localizar a sus presas. Estos estudios se llevaron a cabo con juveniles de trucha arco iris, los cuales se sabe que cuentan con receptores de UV en sus retinas. Sin embargo, nuestros experimentos produjeron resultados negativos. La falta de utilización de longitudes de onda dentro del UV para la localización de presas no resulta llamativa, dado que en ambientes transparentes, tanto los peces, como sus presas evitan las aguas superficiales, refugiandose en aguas relativamente profundas donde no penetra la RUV.

In this work, we investigated the effects of ultraviolet radiation on aquatic organisms. Particulary, we studied the effects on zooplankton and their main predators, namely larval fish, as well as on the interactions between preys and predators. This work was performed on various environments and at different scales. The study sites included a number of lakes located in North-western Patagonia and the Antartic Peninsula. The scales ranged from laboratory experiments to whole-lake field samplings. The results show that ultraviolet radiation has negative effects on both zooplankton and their predators. Such effects are remarkably dependant on the doses to which the organisms are exposed, and consequently vary with lake depth and water transparency. The study also considered the different counteracting strategies used by the organisms to cope with high ultraviolet radiation levels. The results suggest that such strategies are strongly constrained by the physical environment and the ecological assembly. For example, in the large lakes typical of low elevation valleys of Patagonia the zooplankton appears to seek a deep refuge during summertime. In contrast, in more shallow lakes, many organisms use other strategies, such as photoprotection through the accumulation of sun blocking compounds, or photorecovery through photoenzymatic repair. In Turn, the extent of photorecovery appears to be very limited in cold habitats, presumably because of the low efficiency of the photolyase enzyme at low temperatures. On the other hand, the use of photoprotective compounds appears to be constrained by the presence of visual predators, such as the early life stages of fish. Qe also explored the possibility that fish predators could take advantage for ultraviolet radiation wavelength to locate their preys. These experiments were conducted using rainbow trout juveniles, which are known to posses retinal UV detectors. However, our investigation produced negative results. The lack of reliance on UV wavelength to locate preys is not comletely unexpected, given that in transparent habitats both fish and their preys avoid the surface waters and refuge at depth were UV radiation has already been depleted by the absorption of the water.

Author affiliation: Rocco, Vanina E.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.