Salmon lice nauplii and copepodids display different vertical migration patterns in response to light

Light is a fundamental environmental cue which influences the migration of many marine organisms. For salmon louse Lepeophtheirus salmonis , light believed to drive diel vertical behaviour their planktonic larvae. Salmon lice are critical importance salmonid industry due damage they cause wild and farmed hosts. larvae have an eyespot positively phototactic, yet how intensity alters distribution remains unclear. Here, we tested (0, 0.5, 10 80 µmol m -2 s -1 ), dispersal duration (1, 4 12 h) release point (surface or bottom) influenced nauplii copepodids under controlled conditions in experimental columns. Overall, higher increased proportion that aggregated at surface. Copepodid differed from nauplii, as swam upwards both fully dark conditions, surface aggregations with duration. Results experiments did not support existing view strongly position water column. Combined previous work, our results reveal larval stages display different responses light, temperature salinity, may be explained by strategies (maximise survival dispersal) host-finding success). Our implications for models, where currently parametrised same equations. Implementing stage-specific behaviours towards improve outputs models.