Body distribution and source of mycosporine-like amino acids in the cyclopoid copepod Cyclops abyssorum tatricus

Mycosporine-like amino acids (MAAs) are an important family of photoprotective compounds accumulated by zooplankton, but little is known about their localization in the body or their source in natural lake populations. Here, we assessed first, the distribution of MAAs in the body of the copepod Cyclops abyssorum tatricus and second, measured stable isotope signatures (delta C-13, delta N-15) in different life stages of the copepod, as well as in seston and benthic primary producers to reveal the potential source of these compounds in a UV transparent alpine lake. The stable isotope analysis showed that this copepod was herbivorous throughout its ontogeny, from nauplius to adult. Mixing models based on the stable isotope signatures suggest that this copepod feeds predominantly on the <20-mu m size fraction of seston. These models also indicated that the probability of feeding in the upper water layers was high in the ice-cover period, but that the copepod switched to deep water layers in the ice-free period following the maximum of phytoplankton biomass. The higher MAA concentration found in C. abyssorum tatricus during the ice-free period was not connected with an enhanced availability in the food source, but seems to be the result of an active accumulation. The highest MAA content in the body of C. abyssorum tatricus females was found in eggs. Our results indicate that MAAs in this copepod are efficiently accumulated through the diet (mainly nanophytoplankton) and transferred to the nauplii as an important strategy to provide photoprotection for the first life stages.