Trophic Organization of Fishes in a Coastal Seagrass System

Abstract

A long-term (8-y) field study was made concerning the trophic relationships of fishes that occupy shallow coastal grassbeds in the northeast Gulf of Mexico. Various populatlons migrate into such areas to nursery during portions of their life histories. Many fishes undergo seasonal progressions of food preferences that follow species-specific, ontogenetic patterns. While the extent of such dietary successions varies considerably among the 14 species examined, many populations follow developmental progressions that may encompass various trophic levels from herbivory to carnivory. Omnivores are relatively common in the grassbed areas and there was a range of trophic specialization among the fishes examined. Generalized food preferences were often associated with early growth stages; as they matured, various populations became more specialized in their feeding habits Through treatment of each developmental stage of trophic preference as an individual entity (or 'ontogenetic trophic unit'), it was possible to identify progressions of feeding organization through time. Varying levels of temporal partitioning of food resources were evident. Periodic interspecific overlap of food resources was noted during periods of high productivity. Most grassbed fishes were adapted to extreme seasonal changes in habitat. This adaptation was reflected in observed temporal changes in diet and would explain the difficulty of making direct, linear associations of population distribution with multivariate analyses of specific habitat characteristics. The use of the 'ontogenetic trophic unit' facilitated the examination of the relationships of complex associations of fishes to a h~ghly variable environment.