UV protective compounds transferred from a marine dinoflagellate to its copepod predator

Planktonic organisms living in surface waters can be exposed to harmful levels of ultraviolet radiation (UVR), but few studies have examined accumulation of UV protective compounds in marine zooplankton. Zooplankters are suggested to lack the ability to synthesize these substances and hence must accumulate them from their algal food. Here, we show that both phytoplankton (dinoflagellates) and their zooplankton grazers (copepods) respond strongly to UVR exposure by, respectively, synthesizing and accumulating the natural sunscreens mycosporine-like amino acids (MAAs). In our experiment, the MAAs content increased approximately four times in dinoflagellates exposed to UVR and PAR, as compared to non-UVR controls only receiving PAR (PAR = photosynthetically active radiation). The elevated MAAs level in the dinoflagellates was mirrored in the copepods, which accumulated more MAAs when exposed to UVR as compared to a non-UVR treatment. Overall, copepods accumulated approximately 2–5% of the total MAAs pool. Other UV protective compounds, like carotenoids, were however not accumulated by the copepods. The ability of some species to produce or accumulate photoprotective compounds may lead to increased fitness, and thus these taxa may become more dominant in plankton communities.