Phototactic behavior of the marine harpacticoid copepod Tigriopus japonicus related to developmental stages under various light conditions

Abstract

Marine harpacticoid copepod Tigriopus japonicus is commonly distributed in the tide-pools and shows benthic behavior. To determine its phototactic behavior, the movement pattern was investigated with different light wavelengths (white, peaks at 460 and 570 nm; blue at 470 nm; green at 525 nm; and red at 660 nm) and intensities (0.5, 2.0, 3.5, 5.0, 15.0 W/m2) related to developmental stages i.e., nauplius and adult. The eyespot of the two developmental groups efficiently absorbed the light wavelength from 400 to 550 nm, while the level of absorbance was different. For the horizontal phototactic behavior, nauplii showed negative phototaxis with the all tested light wavelengths and intensities ranging 0.5–5.0 W/m2, while they lost phototactic movement at 15 W/m2 of all conducted light wavelengths except with the red light shown negative phototaxis. The adults showed negative phototaxis at 0.5 and 3.5 W/m2, while positive phototaxis at 2.0 W/m2 regardless of light wavelengths. The vertical phototactic movement was only monitored with adults. At 2.0 and 3.0 W/m2, >40% of adults showed planktonic behavior with the blue light. The results elucidate that T. japonicus has different patterns of phototaxis related to developmental stages which can be used to manipulate its distribution for dispersal.