Large variability in the concentration of mycosporine-like amino acids among zooplankton from lakes located across an altitude gradient

The qualitative and quantitative composition of mycosporine-like amino acid s (MAAS), a family of intracellular UV-absorbing compounds, were investigat ed in zooplankton from 15 takes located in the Central Alps between 913 and 2,485 m above sea level. The lakes differed in their UV water transparency (1% attenuation depth, Z(1%), at 320 nm: 1.1-25.6 m.) and maximum depth (Z (max): 3-133 m), thus offering the possibility to test the influence of dif ferent UV exposure conditions of zooplankton on the concentration of MAAS. Seven distinct MAAS were detected, but shinorine (maximum absorption: 334 n m) was the predominant compound. In the copepods Cyclops abyssorum, C. abys sorum tatricus, and Acanthodiaptomus denticornis, the total MAA concentrati on ranged from 0.01 to 3.1% of the dry weight. In the rotifers Keratella co chlearis and Polyarthra dolichoptera, MAAS were also found: however, these compounds were undetectable in Asplanchna priodonta as well as in the clado cerans Daphnia hyalina, D. longispina, Bosmina longispina, and Chydorus sph aericus. The total concentration of MAAs in populations of Cyclops spp. and phytoplankton collected simultaneously was not associated (r(2) = 0.09, P > 0.05), suggesting a different dynamic in the accumulation of these compou nds. The variability in the concentration of MAAS, however, was related wit h the diffuse attenuation coefficient at 320 nm (r(2) = 0.74, P < 0.001) an d the fraction of the water column to which 1% of the surface irradiance at 320 nm (Z(1%):Z(max)) penetrated (r(2) = 0.86, P < 0.001). These relations hips suggest that the prevailing UV exposure condition in the lakes is a ma jor determinant of the concentration of MAAS found in zooplankton. Our data support the hypothesis that MAAs, together with other photoprotective comp ounds, play a major role in minimizing the damaging effects of solar UV rad iation in zooplankton from transparent takes.