“Slip, Slop, Slap”—it’s a phrase we hear regularly throughout summer, so as good Kiwis heading to the beach we slop on some sunscreen. However, I am sure that the swimmers at St Kilda’s beach in Dunedin were unaware that the phytoplankton surging beyond them in Otago’s coastal waters are also capable of slopping on some sunscreen.
Mycosporine-like amino acids (MAA’s) are one of nature’s answers to ultraviolet radiation. These naturally occurring sunscreen compounds are synthesised by many species of phytoplankton and are subsequently incorporated into many other marine organisms that feed on them, which are incapable of synthesising these compounds themselves.
Undine Riemer and colleagues at the University of Otago have recently published one of the few in-situ examples where MAA concentrations in phytoplankton have been correlated with seasonal UV levels. They found that the concentration of MAA compounds increased in summer, matching greater UV exposure at that time. Effectively phytoplankton were actively protecting themselves against harmful UV radiation.
It has been hypothesised that such seasonal increases in MAA in phytoplankton could prevent UV damage in other organisms that feed on them, such as krill. However, in the same study Riemer found that MAA’s, although present in Nyctiphanes australis (a species of krill), did not vary in concentration with the seasons.