12 research outputs found
The influence of predator community composition on photoprotective traits of copepods.
Trait expression of natural populations often jointly depends on prevailing abiotic environmental conditions and predation risk. Copepods, for example, can vary their expression of compounds that confer protection against ultraviolet radiation (UVR), such as astaxanthin and mycosporine-like amino acids (MAAs), in relation to predation risk. Despite ample evidence that copepods accumulate less astaxanthin in the presence of predators, little is known about how the community composition of planktivorous fish can affect the overall expression of photoprotective compounds. Here, we investigate how the (co-)occurrence of Arctic charr (Salvelinus alpinus) and threespine stickleback (Gasterosteus aculeatus) affects the photoprotective phenotype of the copepod Leptodiaptomus minutus in lake ecosystems in southern Greenland. We found that average astaxanthin and MAA contents were lowest in lakes with stickleback, but we found no evidence that these photoprotective compounds were affected by the presence of charr. Furthermore, variance in astaxanthin among individual copepods was greatest in the presence of stickleback and the astaxanthin content of copepods was negatively correlated with increasing stickleback density. Overall, we show that the presence and density of stickleback jointly affect the content of photoprotective compounds by copepods, illustrating how the community composition of predators in an ecosystem can determine the expression of prey traits that are also influenced by abiotic stressors
The effects of hypoxia on zooplankton population estimates and migration in lakes
Many zooplankton species typically exhibit diel vertical migration (DVM), where
zooplankton migrate from the hypolimnion to the epilimnion of lakes at night.
Zooplankton exhibit this behavior to avoid visual predators and UV radiation by
remaining in the bottom waters during the day and ascending to the surface waters to feed
on phytoplankton at night. However, hypoxic conditions in the hypolimnion of lakes mayinterfere with DVM and force zooplankton to increase diel horizontal migration (DHM)
to find predation refuge in littoral zones. Climate change and eutrophication are expected
to increase the prevalence and severity of hypoxic conditions worldwide and thereby
possibly alter zooplankton migration patterns. We hypothesize that hypoxia will force
zooplankton to shift their migration patterns from predominantly DVM to DHM to avoid
oxygen-depleted bottom waters. To test our hypothesis, we are conducting a standardized
global sampling program to test whether pelagic, full water column estimates of
zooplankton are greater at night versus the day under hypolimnetic hypoxic versus oxic
conditions. Participants are aiming to sample at least one lake with an oxic hypolimnion
and one lake with a hypoxic hypolimnion during the thermally-stratified period at midday
and midnight. With our global dataset (currently expecting about 60 lakes in 22
countries), our goal is to improve our understanding of how global change may alter
zooplankton migration behavior and patterns in lakes.info:eu-repo/semantics/publishedVersio
UV radiation and freshwater zooplankton: damage, protection and recovery
While many laboratory and field studies show that zooplankton are negatively affected when exposed to high intensities of ultraviolet radiation (UVR), most studies also indicate that zooplankton are well adapted to cope with large variations in their UVR exposure in the pelagic zone of lakes. The response mechanisms of zooplankton are diverse and efficient and may explain the success and richness of freshwater zooplankton in optically variable waters. While no single behavioural or physiological protection mechanism seems to be superior, and while several unexplained and contradictory patterns exist in zooplankton UVR ecology, recent increases in our understanding are consistent with UVR playing an important role for zooplankton. This review examines the variability in freshwater zooplankton responses to UVR, with a focus on crustacean zooplankton (Cladocera and Copepoda). We present an overview of UVR-induced damages, and the protection and recovery mechanisms freshwater zooplankton use when exposed to UVR. We review the current knowledge of UVR impact on freshwater zooplankton at species and community levels, and discuss briefly how global change over the last three decades has influenced the UVR milieu in lakes
Phytoplankton and zooplankton response to ultraviolet radiation in a high-altitude Andean lake: Short- versus long-term effects
Exclusion experiments on global UV (A and B) radiation and global UVB were performed
in 460 1 mesocosms with plankton communities from the oligotrophic Andean lake Laguna Negra
(33°35'S-70°04'W; 2700 m a.s.1.). The experiments were run for 30 days during the summers of
1991-1992 and 1992-1993, and for 48 days in 1993-1994. When UVB radiation was allowed to enter
into the mesocosms (full sun), the population of Ankyra judayi (Chlorophyta) reached the highest
density, suggesting that this species can endure high levels of UV radiation. Concurrently, an increase
in chlorophyll a concentration was observed in this treatment. The cladoceran Chydorus sphaericus
and the rotifer Lepadella ovalis were strongly inhibited by UVB. Conversely, UVB radiation had no
effect on the survival of the different life stages of the calanoid copepod Boeckella graalipes, suggesting a species-specific difference in the sensitivity to solar UVB radiation. Moreover, no reduction
in the number of copepod eggs per female and the number of nauplii produced was observed. Apparently, herbivory does not strongly affect phytoplankton abundance. Moreover, the phytoplankton
species composition changed in the different treatments over the time. Fragilaria construens and
Fragilaria crolonensis were dominant in those mesocosms where UVB was excluded. Populations fluctuated depending on their life cycles and the period of time they were exposed to UVB radiation. It
is important to define the time scale of exclusion experiments, because different conclusions about
the influence of UVB irradiance result from short-, medium- or long-term exposure
Biological Weighting Function for the Mortality of Boeckella gracilipes (Copepoda, Crustacea) Derived from Experiments with Natural Solar Radiation
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 waterâsurface for âŒ24â34 h. Longâpass cutâoff filters (Schott) were used in the exposure experiments. UV radiation and PAR were measured with an ILâ1700 (International Light Inc.) and a PUVâ500 radiometer (Biospherical Instruments Inc.). A biological weighting function for UVâinduced mortality was calculated by fitting a model based on a logistic curve. Our results show that UV damage in this species is strongly wavelengthâ and doseâdependent. B. gracilipes was highly vulnerable to both UVâB (290â320 nm) and UVâA radiation (< 360 nm). The shape of the BWF obtained for B. gracilipes resembles more closely the action spectra (AS) â for UVâinduced erythema, than the AS for naked DNA.Fil: Tartarotti, Barbara. University of Innsbruck; AustriaFil: Cravero, Walter Ruben. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; ArgentinaFil: Zagarese, Horacio Ernesto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; Argentin
Survivorship of Cyclops abyssorum tatricus (Cyclopoida, Copepoda) and Boeckella gracilipes (Calanoida, Copepoda) under ambient levels of solar UVB radiation in two high-mountain lakes
We performed in situ experiments during the summer of 1995 and 1996 to assess the potential effect of solar ultraviolet B (UVB) radiation (290-320 nm) on the survival of Cyclops abyssorum tatricus Kozminski and Boeckella gracilipes Daday. These species are numerically dominant within the crustacean zooplankton living in two high-mountain lakes, one located in the Austrian Alps [Gossenkollesee (GKS), 2417 m above sea level, maximum depth 9.9 m] and another in the Chilean Andes (Laguna Negra, 2700 m above sea level, maximum depth 320 m). The copepods were incubated in quartz tubes (11) or in quartz tubes wrapped with Mylar DÂź to exclude most of the UVB radiation. The organisms were exposed at 0.5 m depth for 10-72 h on cloudless days. Both lakes were very transparent to UVB and 10% of the surface radiation at the nominal wavelength of 305 nm was still present at 9.6 m in GKS and at 12.8 m in Laguna Negra. These species migrate vertically and have a maximum daytime distribution close to