Mycosporine-like amino acids in planktonic organisms living under different UV exposure conditions in Patagonian lakes

Mycosporine-like amino acids (MAAs) were studied in zooplanktonfrom 13 Argentinian lakes covering a broad range in altitude,maximum depth and physico-chemical properties of the water.Four to nine different MAAs (predominantly porphyra-334 andshinorine) were found in the copepods Boeckella gibbosa, B.gracilipes, B. meteoris and Parabroteas sarsi, and in the ciliateStentor amethystinus, while MAAs were undetectable in the cladoceranDaphnia middendorffiana. Among the different copepods, maximumMAA concentrations accounted for 0.25–1.31% of the dryweight, and contents were generally about three to seven times(up to 43 times) higher in the animals living in the clearestlakes compared to those occurring in low-UV systems. This variabilityin the content of MAAs was related to the lake altitude (r²= 0.71), and the fraction of the water column to which 1% ofthe surface UV radiation at 320 nm penetrated (r² = 0.57). Ourdata therefore underscore the role of MAAs as sunscreens todecrease the potential negative effects of solar radiation,but they also indicate that other environmental factors besidesUV transparency play a role in determining MAA concentrations.One lake was selected to obtain additional information on thequalitative composition of MAAs in seston of <100 µmbetween two sampling sites and over a 2 month study period (australsummer). Six different MAAs were detected in the samples, withporphyra-334 and palythine being predominant. In the copepodscollected simultaneously, there was low variation in MAA concentrationsbetween the two sites and over time. Thus, our results suggestthat under similar UV exposure conditions MAA contents of planktonicorganisms show low temporal variation.