Plasticity in coloration as an antipredator strategy among zooplankton

We show that marine zooplankton change their level of coloration both with depth and time of the day. The carnivorous copepod Pareuchaeta norvegica caught near the bottom in 200-400-m deep-water columns were darker than specimens caught higher in the water column. A diel rhythm in coloration occurred even at several hundred metersʹ depth, with individuals caught during night time being more pigmented than the ones caught during the day. We hypothesize that individuals actively adjust their degree of coloration to achieve optimal camouflage at the prevailing light regime.