Light and Substrate Color Preferences in the Marine Isopod Cymodoce japonica

Marine herbivorous isopods can have negative impacts on cultivated marine macroalgae, in the same way that terrestrial insects can negatively affect plant communities. Color preference of harmful insects has been studied and applied in controlling their populations, but that of isopods has rarely been examined. This study examined the substrate and light color preferences of the marine isopod Cymodoce japonica, a species impacting the cultivation of brown macroalgae in northeastern Japan. The number of isopods positioning themselves on blue-colored substrates was lower than that on red-, orange-, and yellow-colored substrates. There was no difference in the time spent in a dark compartment compared with a compartment illuminated with red light, but the time spent in a compartment illuminated with blue or green light was shorter than in a dark compartment. Moreover, the time spent in compartments irradiated with blue light was shorter compared with compartments irradiated with red light. These results indicate that this species is more sensitive to blue substrates and light than to other colors under the tested conditions. These behavioral characteristics of this species provide important insights for developing methods to suppress the aggregation and herbivory of this species in marine macroalgal farms.