Intensity differences in bioluminescent dinoflagellates impact foraging efficiency in a nocturnal predator

Abstract

Bioluminescence in dinoflagellates is thought to function as a alarm, alerting visual predators to the presence of dinoflagellate grazers. However, many bioluminescent dinoflagellates, particularly those associated with harmful algal blooms (HABs), have a much lower bioluminescence capacity that seems less well-adapted for attracting the attention of distant secondary predators. The present study was motivated by a question regarding the impact of extreme differences in bioluminescence potential among dinoflagellates, particularly those with the capacity to form HABs. This study examined the function of bioluminescence in the bright emitter, Pyrocystis noctiluca (Murray, 1876), compared to the much dimmer HAB species, Lingulodinium polyedrum F. Stein (Stein 1883). The foraging efficiency of the nocturnal teleost, Apagon maculatus (Poey, 1860), was determined at a range of cell concentrations with both dinoflagellate species. At low cell concentrations of P. noctiluca, both the foraging efficiency and the orientation distance of the fish to the prey increased, indicating that bioluminescence functions as a burglar alarm. However, neither fish foraging efficiency nor orientation distance increased in the presence of luminescent L. polyedrum at low cell concentrations. At higher concentrations, the bioluminescence of L. polyedrum improved the foraging efficiency of the fish, but the orientation distance to the prey was no greater than with non-luminescent cells, indicating that at low cell concentrations, bioluminescence does not function as a burglar alarm in L. polyedrum. The role of bioluminescence as a possible aposematic signal in L. polyedrum is discussed, along with the implications for the role of bioluminescence in HAB dynamics.