Settlement of benthic marine invertebrates

Settlement and recruitment of benthic marine invertebrates are complex processes, determined by the interaction of biotic and abiotic factors which operate at different temporal and spatial scales. This review analyses the settlement process, attempting to integrate aspects related to different levels of organization (i.e. ecological-physiological-molecular). This is important because many factors that act at any of these levels and at different times can explain by themselves the patterns of settlement andlor recruitment of a large number of species. From an ecological perspective, progress has been made in the identification of causal factors of vanations in larval availability for settlement. Many physical and ethological factors that act during settlement have, however, not received much attention. Likewise, since the great majority of settlement studies have been carried out at restricted spatial scales, fewer works consider different biological and physical factors acting at different scales simultaneously. Settlement patterns are frequently inferred from recruitment. In this sense, a density-independent action of post-settlement mortality has been cons~dered as prerequisite for thls type of inference. This has, however, recently been challenged on the basis that settler-recruit and mortality-settler density relationships change in time. At the physiological-molecular level, different settlement-inducing chemical cues have been identified. Those cues have, however, not yet been characterized to understand better the signal transduction mechanisms involved in larval responses. It is likely that the nervous system is involved. The use of artificial inducers would be useful in studying settlement induction, until more effective natural inducers are isolated and characterized Although few studies have analysed the acquisition of competence, stages of larval development have been related to changes in protein patterns or enzymatic levels of the nervous system. An inopportune exposure of larvae to inducers may delay settlement and may even have a negative impact on growth and subsequent survival of juveniles.