SURVIVAL OF MARINE LARVAE UNDER THE COUNTERVAILING SELECTIVE PRESSURES OF PHOTODAMAGE AND PREDATION

Unlike most zooplankters, larvae of decapod crustaceans and fsh often are pigmented and may hatch and ascend to the sea surface during the d ay. Chromatophores possibly protect these larvae from ultraviolet radi ation (UVR), but may increase their visibility to planktivorous fsh. W e exposed larvae of four species of tropical crabs to sunlight and to planktivorous fish in the field to address this paradox. Most lightly pigmented larvae of three species died from exposure to sunlight withi n 1 d, and 94-97.5% of them died after 2 d. The more darkly pigmented Pachygrapsus transversus larvae survived significantly better; only 57 % of them died after 2 d of exposure to sunlight. These darkly pigment ed larvae survived encounters with fish as well as or better than larv ae of two other species that did not have large melanophores. Larval c hromatophore systems may block UVR without greatly increasing the visi bility of larvae to fish. Larvae that migrate from adult habitats to n ursery grounds in surface waters throughout the day likely have chroma tophore systems that are effective against both of these countervailin g selective pressures; however, increasing UVR may stress larvae. The timing of larval release relative to the diel cycle was not related to the susceptibility of larvae to photodamage.