Ultraviolet (UV) radiation is damaging to life and in high doses it can be lethal. The organisms living in shallow, clearwater arctic ponds are exposed to high doses of UV because the sun never sets. Benthic organisms can hide under rocks, but planktonic species have had to develop resistance to UV exposure. Two different solutions have evolved. Some species employ melanin to block UV, just as in humans. Other species concentrate a familiar pigment, carotenoids, which doesn't block UV, but instead reduces cellular damage. Because of these adaptations, polar plankton are exceptionally colourful, ranging from orange, red, blue or black.
A water flea (R) and a cyclopoid copepod (L) showing various pigmentation colours .