Trophic interactions in the sea: An ecological role for climate relevant volatiles?

When attacked by herbivores, land plants can produce a variety of volatile compounds that attract carnivorous mutualists. Plants and carnivores can benefit from this symbiotic relationship, because the induced defensive interaction increases foraging success of the carnivores, while reducing the grazing pressure exerted by the herbivores on the plants. Here, we examine whether aquatic phytoplankton use volatile chemical cues in analogous tritrophic interactions. Marine algae produce several classes of biogenic gases such as non-methane hydrocarbons, organohalogens, ammonia and methylamines, and dimethylsulfide. The grazing-induced release of marine biogenic volatiles is poorly understood, however, and its effect on the chemical ecology of plankton and the foraging behavior of predators is essentially unknown. We outline grazing-induced defenses in algae and highlight the biogenic production of volatiles when phytoplankton are attacked by herbivores. The role of chemical signaling in marine ecology presents several possible avenues for future research, and we believe that progress in this area will result in better understanding of species competition, bloom development, and the structuring of food webs in the sea. This has further implications for biogeochemical cycles, because several key compounds are emitted that influence the chemistry of the atmosphere and global climate.