Copepod luminescence revisited

Bioluminescence is abundant in marine taxa, including copepods. Bioluminescent copepods flash or spout a cloud of bright blue light to stun, deter, or distract their predators in the dark depths of the midwater. Despite their sophisticated survival strategies, bioluminescent copepods are heavily preyed upon by a variety of predators, including bioluminescent fishes, squids, and decapods. Copepod bioluminescence is commonly attributed to the enzymatic oxidative reaction of coelenterazine, a substrate also used for luminescence reactions in wide range of marine bioluminescence across various taxa. It has been confirmed that some of those animals, such as hydrozoan jellies, a lophogastrid shrimp, and brittle stars are unable to biosynthesize coelenterazine. Instead, they acquire it from their diet to produce their own light, a process known as ‘semi-intrinsic bioluminescence’. Bioluminescent copepods, such as Metridia pacifica, can biosynthesize coelenterazine from three amino acids: one phenylalanine and two tyrosines. It is likely that other bioluminescent copepods also share this capability. As a consequence, bioluminescent copepods are considered a major source of bioluminescent substrate for a wide range and quantity of marine bioluminescent animals. This connection helps account for the richness of bioluminescence in marine midwater fauna.