Sex and life stage dependent phototactic response of the marine copepod Calanus finmarchicus (Copepoda: Calanoida)

Stage V copepodites and adult females displayed negative phototaxis, and the threshold for phototactic response was 9.8 × 10− 6 μmol photons m− 2 s− 1. Adult males displayed positive phototaxis and the corresponding threshold value was 9.9 × 10− 7 μmol photons m− 2 s− 1. The results from the experiments were used to estimate the depths at which phototaxis is elicited in natural light conditions by conducting light simulations for an ocean scenario and a fjord scenario during peak spring bloom conditions. The estimated depths for irradiances that elicit a phototactic response corresponded to approximate depths of 158-186 m in the ocean scenario and 48-57 m in the fjord scenario. These depths are within the range of depth distributions of C. finmarchicus reported for ocean and fjord populations.