Uncertainty relationships in the estimation of settlement rates of mobile marine organisms

Abstract

Settlement is the process by which pelagic larval stages colonize the sea bottom. Variations in settlement rates can affect population dynamics and community structure. Here I study the importance of spatial and temporal scales of mobility of larvae to define settlement rates of marine species with complex life cycles, and the uncertainty in their estimation. Larvae of mobile marine species (e.g. fish, crabs) arrive at the sea bottom but still swim or crawl for several days, covering considerable distances. This behaviour affects the operational definition of settlement because an observer cannot differentiate between new and old settlers. I model the process of estimation of settlement rate for these organisms incorporating the characteristics of settlers and the process of observation. Settlers are characterised by the temporal and spatial scales of movement within a homogeneous area. The process of observation is characterised by the grain and step (= spatial and temporal resolution) of the sampling design, i.e. the size of the observed site and the time between 2 consecutive observations. As the resolution increases, the uncertainty in the estimation of settlement also increases. There are critical spatial and temporal scales below which the uncertainty is high and evaluation of patterns of settlement is not possible. Uncertainty relationships should be considered in designing sampling schemes to study patterns of settlement without the confounding effect of the subsequent movements of individuals within the settlement habitat. Relationships of this kind may also appear in other fields of ecology. © Inter-Research 2009.