Inadequacy of species-level designations for ecological studies of coastal migratory fishes

Synopsis The species is not always appropriate as a unit of measure when used in quantitative ecological studies. Analyses of fish trophic relationships in coastal areas indicate that, in many instances, more substantial ecological differences exist among life stages of a given species than among similar trophic units of different species. The use of a species in quantitative ecological studies can lead to problems of interpretation concerning the relationships of coastal fishes to complex habitats. Use of the species as a convenient unit of measure substitutes a basically taxonomic entity for more relevant life-history stages in ecological determinations. Niche breadth of a given species can be so extensive that quantitative determinations of significant ecological processes are difficult to make. Migratory coastal fishes undergo diverse ontogenetic trophic transformations. Without adequate recognition of the complex ecological stages that characterize such fishes, the oversimplification that characterizes many ecological studies in coastal areas will continue. This simplification, and the attendant overgeneralization that follows, tends to add to the continuing problem of unverified models and the inability to identify causal relationships in estuarine and coastal systems. Quantitative ecological studies would benefit from an approach that includes the use of identifiable, ontological trophic entities.