Barbara Tartarotti

Biological Weighting Function for the Mortality of Boeckella gracilipes (Copepoda, Crustacea) Derived from Experiments with Natural Solar Radiation¶

Abstract We performed in situ experiments during the austral summer of 1998 to quantify the mortality of the freshwater copepod Boeckella gracilipes as a function of the UV dose. The copepods were exposed to solar radiation at the water-surface for ∼24–34 h. Long-pass cut-off filters (Schott) were used in the exposure experiments. UV radiation and PAR were measured with an IL-1700 (International Light Inc.) and a PUV-500 radiometer (Biospherical Instruments Inc.). A biological weighting function for UV-induced mortality was calculated by fitting a model based on a logistic curve. Our results show that UV damage in this species is strongly wavelength- and dose-dependent. B. gracilipes was highly vulnerable to both UV-B (290–320 nm) and UV-A radiation (< 360 nm). The shape of the BWF obtained for B. gracilipes resembles more closely the action spectra (AS)† for UV-induced erythema, than the AS for naked DNA.

UV-induced DNA damage in Cyclops abyssorum tatricus populations from clear and turbid alpine lakes

Zooplankton from clear alpine lakes thrive under high levels of solar UV radiation (UVR), but in glacially turbid ones they are more protected from this damaging radiation. Here, we present results from experiments done with Cyclops abyssorum tatricus to assess UV-induced DNA damage and repair processes using the comet assay. Copepods were collected from three alpine lakes of differing UV transparency ranging from clear to glacially turbid, and exposed to artificial UVR. In addition, photoprotection levels [mycosporine-like amino acids (MAAs) and lipophilic antioxidant capacity] were estimated in the test populations. Similar UV-induced DNA damage levels were observed among the copepods from all lakes, but background DNA damage (time zero and dark controls) was lowest in the copepods from the glacially turbid lake, resulting in a higher relative DNA damage accumulation. Most DNA strand breaks were repaired after recovery in the dark. Low MAA concentrations were found in the copepods from the glacially turbid lake, while the highest levels were observed in the population from the most UV transparent lake. However, the highest lipophilic antioxidant capacities were measured in the copepods from the lake with intermediate UV transparency. Photoprotection and the ability to repair DNA damage, and consequently reducing UV-induced damage, are part of the response mechanisms in zooplankton to changes in water transparency caused by glacier retreat.

The Significance of Ultraviolet Radiation for Aquatic Animals

The total amount of energy reaching the outer limit of the Earth’s atmosphere is defined as the solar constant. This is an inappropriate name for a magnitude that is known to vary over time, but it very much reflects the quotidian perception that the sun’s energy is virtually unchangeable. Such perceptions have started to change. To find the reasons for this change, we do not have to look at sun itself, but to alterations occurring within our own atmosphere. First, the release of greenhouse gases has increased the capacity of the atmosphere to capture heat. Second, ozone depletion has decreased the atmosphere’s ability to filter out some of the most damaging wavelengths within the ultraviolet region.

Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency

Summary Climate warming is accelerating the retreat of glaciers and recently, many ‘new’ glacial turbid lakes have been created. In the course of time, the loss of the hydrological connectivity to a glacier causes, however, changes in their water turbidity and turns these ecosystems into clear ones. To understand potential differences in the food‐web structure between glacier‐fed turbid and clear alpine lakes, we sampled ciliates, phyto‐, bacterio‐ and zooplankton in one clear and one glacial turbid alpine lake, and measured key physicochemical parameters. In particular, we focused on the ciliate community and the potential drivers for their abundance distribution. In both lakes, the zooplankton community was similar and dominated by the copepod Cyclops abyssorum tatricus and rotifers including Polyarthra dolichoptera, Keratella hiemalis, Keratella cochlearis and Notholca squamula. The phytoplankton community structure differed and it was dominated by the planktonic diatom Fragilaria tenera and the cryptophyte alga Plagioselmis nannoplanctica in the glacial turbid lake, while chrysophytes and dinoflagellates were predominant in the clear one. Ciliate abundance and richness were higher in the glacial turbid lake (∼4000–27 800 Ind L−1, up to 29 species) than in the clear lake (∼570–7150 Ind L−1, up to eight species). The dominant species were Balanion planctonicum, Askenasia cf. chlorelligera, Urotricha cf. furcata and Mesodinium cf. acarus. The same species dominated in both lakes, except for Mesodinium cf. acarus and some particle‐associated ciliates, which occurred exclusively in the glacial turbid lake. The relative underwater solar irradiance (i.e. percentage of PAR and UVR at depth) significantly explained their abundance distribution pattern, especially in the clear water lake. In the glacial turbid lake, the abundance of the dominating ciliate taxa was mainly explained by the presence of predatory zooplankton. Our results revealed an unexpected high abundance and richness of protists (algae, ciliates) in the glacial turbid lake. This type of lake likely offers more suitable environmental conditions and resource niches for protists than the clear and highly UV transparent lake.

Distribution and UV protection strategies of zooplankton in clear and glacier-fed alpine lakes

Zooplankton, a group of aquatic animals important as trophic link in the food web, are exposed to high levels of UV radiation (UVR) in clear alpine lakes, while in turbid glacier-fed lakes they are more protected. To study the interplay between behavioral and physiological protection responses in zooplankton from those lakes, we sampled six lakes of different UVR transparency and glacial turbidity. Copepods were absent in the upper water layers of the clearest lake, while in glacier-fed lakes they were more evenly distributed in the water column. Across all lakes, the weighted copepod mean depth was strongly related to food resources (chlorophyll a and rotifers), whereas in the fishless lakes, glacial turbidity largely explained the vertical daytime distribution of these organisms. Up to ~11-times (mean 3.5) higher concentrations of photo-protective compounds (mycosporine-like amino acids, MAAs) were found in the copepods from the clear than from the glacier-fed lakes. In contrast to carotenoid concentrations and antioxidant capacities, MAA levels were strongly related to the lake transparency. Copepods from alpine lakes rely on a combination of behavioral and physiological strategies adapted to the change in environmental conditions taking place when lakes shift from glacially turbid to clear conditions, as glacier retreat proceeds.

Seasonal plasticity in photoprotection modulates UV‐induced hsp gene expression in copepods from a clear lake

Abstract Zooplankton from clear alpine lakes is exposed to stressful levels of solar UV radiation (UVR). As these pelagic organisms experience high UVR and large changes in solar radiation conditions between ice‐free and ice‐cover periods, they have evolved various strategies to minimize UVR exposure and damage. Here, we studied the relation between photoprotection levels (mycosporine‐like amino acids, carotenoids), antioxidant capacities, and gene expression of heat shock proteins (hsps) as indicator of stress in the copepod Cyclops abyssorum tatricus during the course of a year. Expression of hsp60, hsp70, and hsp90 was measured in the field (baseline expression [BE]) and after UVR exposure in the laboratory. The BE differed among genes and seasons (hsp60: high during summer, hsp70 and hsp90: high during the ice‐cover period). The gene expression of hsp70 was upregulated after exposure to UVR (up to 5.2‐fold change), while hsp60 and hsp90 were only constitutively expressed. A strong seasonal pattern was found in the photoprotective compounds and antioxidant capacities, with highest levels during the ice‐free period. The extent of upregulation of hsp70 gene expression increased with decreasing photoprotection levels and peaked 24 h post UVR exposure (9.6‐fold change) at the time of lowest photoprotection (February). Our data suggest that hsp70 gene expression is modulated by seasonal plasticity in photoprotection. This ability of adequate stress response is essential for survival in highly variable ecosystems such as alpine lakes.

The Impact of UV Radiation on Paramecium Populations from Alpine Lakes

Paramecium populations from a clear and a glacier‐fed turbid alpine lake were exposed to solar simulated ultraviolet (UVR) and photosynthetically active radiation (PAR) at 8 and 15 °C. The ciliates were tested for DNA damage (comet assay), behavioral changes, and mortality after UVR + PAR exposure. High DNA damage levels (~58% tail DNA) and abnormal swimming behavior were observed, although no significant changes in cell numbers were found irrespective of the lake origin (clear, turbid), and temperatures. We conclude that environmental stressors such as UVR and their effects may influence the adaptation of ciliates living in alpine lakes.

Auswirkungen der UV-Strahlung auf heterotrophe aquatische Organismen

Die Wirkungen der UV-B-Strahlung konnen auf drei Organisationsstufen des Lebens (Individuum, Population, Lebensgemeinschaft) studiert werden. Auf der Stufe des Individuums bzw. seiner Untereinheiten (Zellen, Organellen, Molekule) werden die Primar- und Folgeprozesse analysiert, die zum Tod oder zu subletalen Beeintrachtigungen des Individuums fuhren konnen (Strahlenbiologie und Okophy- siologie) (Abb. 2.47). Dementsprechend ist die Beziehung zwischen der UV-B-Dosis (= Dosisrate x Bestrahlungsdauer) und der Mortalitat bzw. bei subletalen Beeintrachtigungen verschiedener Fitnesparameter (Lebensdauer, Korperwachstum, Reproduktionsgrose) Gegenstand der Untersuchungen. Im Gegensatz zur Toxikologie wird die Dosis nicht auf die Masse der Testobjekte bezogen, sondern auf die Flacheneinheit der Ebene, in welcher sie sich aufhalten bzw. durch die Versuchsanordnungen festgehalten werden: Wm-2.1=Jm-2.