They would blend right into the algae, which would also fluoresce red, but they've got great vision, and they go through this long mating ritual, and perhaps they're using it in that effect.
Il se fond complètement dans les algues, qui peuvent virer aussi rouge fluorescent, mais ils ont une excellente vue, ils accomplissent ce long rituel d'accouplement, et il se peut qu'ils l'utilisent à cet effet.