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

Abstract

Studies were conducted in Lake Titicaca, Bolivia (16°S, 69°W, 3810 m a.s.l.) to determine the effects of solar ultraviolet radiation (UVR; 280-400 nm) and the protective role of mycosporine-like amino acids (MAAs) in the calanoid copepod Boeckella titicacae (Harding). Zooplankton samples were taken from two different radiation environments: Lake Titicaca and a tank with running lake water, which was covered with layers of neutral-density screen for over a year, receiving ∼10% of incident radiation. Samples collected from the lake had significantly higher amounts of MAAs compared with those from the tank. During short-term experiments (6-8 h incubations; six radiation treatments using sharp cut-off Schott filters), significantly higher mortality was observed in B. titicacae from the tank than from the lake. The higher sensitivity of B. titicacae containing low amounts of MAAs (compared with specimens collected from the lake) was assessed through the determination of biological weighting functions (BWFs). A 3-day-long experiment performed with specimens collected from the lake indicated an increase in mortality as a function of UVR exposure, reaching values as high as 70% at the end of day 3 for those individuals that received full radiation compared with <10% for those that received only photosynthetically active radiation (PAR; 400-700 nm). Concomitantly, a reduction in the concentration of UV-absorbing compounds as a function of UVR dose and decreasing wavelength was 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. Our results indicate that this resistance is provided by the presence of protective compounds, i.e. MAAs, which were efficiently bioaccumulated through the diet.