Mycosporine-like amino acids protect the copepod Boeckella titicacae (Harding) against high levels of solar UVR

Studies were conducted in Lake Titicaca, Bolivia (16°S,69°W, 3810 m a.s.l.) to determine the effects of solar ultravioletradiation (UVR; 280–400 nm) and the protective role ofmycosporine-like amino acids (MAAs) in the calanoid copepodBoeckella titicacae (Harding). Zooplankton samples were takenfrom two different radiation environments: Lake Titicaca anda tank with running lake water, which was covered with layersof neutral-density screen for over a year, receiving ~10% ofincident radiation. Samples collected from the lake had significantlyhigher amounts of MAAs compared with those from the tank. Duringshort-term experiments (6–8 h incubations; six radiationtreatments using sharp cut-off Schott filters), significantlyhigher mortality was observed in B. titicacae from the tankthan from the lake. The higher sensitivity of B. titicacae containinglow amounts of MAAs (compared with specimens collected fromthe lake) was assessed through the determination of biologicalweighting functions (BWFs). A 3-day-long experiment performedwith specimens collected from the lake indicated an increasein mortality as a function of UVR exposure, reaching valuesas high as 70% at the end of day 3 for those individuals thatreceived full radiation compared with <10% for those thatreceived only photosynthetically active radiation (PAR; 400–700nm). Concomitantly, a reduction in the concentration of UV-absorbingcompounds as a function of UVR dose and decreasing wavelengthwas determined. The relatively high UVR dose threshold for mortality(~300 kJ m^–2), as well as a comparison with related species,demonstrated the high resistance of B. titicacae to UVR. Ourresults indicate that this resistance is provided by the presenceof protective compounds, i.e. MAAs, which were efficiently bioaccumulatedthrough the diet.