Antarctic krill (Euphausia superba) acquire a UV-absorbing mycosporine-like amino acid from dietary algae

We hypothesised that Antarctic krill acquire UV-absorbing mycosporine-like amino acids (MAAs) from dietary algae, which produce MAAs in response to ul traviolet (UV) irradiation. To test this hypothesis, we grew cultures of Ph aeocystis antarctica that had been grown under either photosynthetically ac tive radiation (PAR, 400-750 nm) plus UV irradiation (UVR, 280-400 nm), or else PAR-only. Algae grown under PAR-only produced high concentrations of p orphyra-334, whereas additional UVR caused formation of high concentrations of mycosporine-glycine:valine and lower concentrations of porphyra-334. Kr ill were fed with either of these two cultures on eight occasions over 63 d ays. A third group was starved for the duration of the experiment. Animals were analysed after 36 and 63 days for MAA content. Remaining animals from all treatments were starved for a further 35 days and analysed to examine M AA retention characteristics. Our findings are that krill acquired differen t MAAs from dietary algae depending on the light conditions under which the algae were grown. Specifically, krill fed algae grown under PAR-only had h igher concentrations of porphyra-334 than starved krill. Conversely, krill fed algae grown under PAR with additional WR had high body concentrations o f mycosporine-glycine :valine. MAA concentrations in starved krill remained static throughout the experiment. However, long term starvation (35 days) caused levels of certain acquired MAAs to decline. From this we can infer t hat MAA concentrations in krill are dependent on the MAA content of phytopl ankton, and therefore the algae's response to UV exposure. This has implica tions for transfer of MAAs through marine trophic webs. (C) 2000 Elsevier S cience BN. All rights reserved.