Horizontal migration of Acartia pacifica Steuer (copepoda) in response to UV-radiation.

It is known that zooplankton migrate vertically to avoid UV-radiation (UVR, 280-400nm), but little is known if such avoidance happens horizontally. Here, we showed that the copepod Acartia pacifica avoided UV irradiated fields horizontally. Exposure of A. pacifica to PAR or PAR+UV-A for 30min did not make any difference in the horizontal distribution of the individuals. However, addition of UV-B radiation, that is PAR+UV-A+B, resulted in uneven distributions among the treatments, with significant less individuals compared to the PAR or PAR+UV-A treatments. More carotenoids and UV-absorbing compounds were found in the A. pacifica individuals that chose to stay under the radiation treatments with UV. It is concluded that A. pacifica can migrate horizontally to avoid UV-related harms and those contains more protective compounds were less sensitive to UVR.