Cues and context: Larval responses to physical and chemical cues

Most marine organisms have a highly specialized larval settlement stage. A major function of the settlement stage is response to environmental input that results in deposition of the larvae in a location which confers probability of survival and successful reproduction. The settlement stage is a prime target for management strategies because it is a key and vulnerable step in the colonization process. Published and unpublished work will be synthesized to provide an overview of responses of a variety of settlement stage larvae to chemical and physical cues. It is maintained that due to tiny larval brains and poor memories, it is environmental cues rather than larval choice that determines where larvae settle. Larval examples include ascidians, brachyurans, bryozoans, cirripedes, hydroids and polychaetes. Chemical cues include inorganic and organic compounds, including stimulatory peptides and odors. Physical cues include surface energy, vibration and light. The aims of this review are to find common ground with others in the field and to add to the theoretical context the consideration of environmental input for larval settlement.