Niche Partitioning in Early Life History Stage, Estuarine-Dependent Fishes (Sciaenidae)

Abstract

Although the form and function of feeding apparatus structures and diet composition are linked in adult fishes, it is often not clear when during ontogeny ecomorphological patterns develop, enabling early life history stage (ELHS) fishes to partition foraging niches and reduce competition. Species of drums (Sciaenidae) demonstrate tremendous variability in the structure of the feeding apparatus, which allows sympatric species to exploit a broader range of foraging habitats as adults than any other family of fishes in the coastal systems of the western Atlantic. The feeding apparatus (i.e., oral and pharyngeal jaw elements) and stomach contents were examined in ELHS and juvenile sciaenids from the Chesapeake Bay representing three foraging guilds: pelagic, generalist, and benthic. Stomach contents were examined and specimens were cleared and double-stained to measure elements of the feeding apparatus. Regardless of foraging guild, a single diet shift was observed in the size range of fishes examined. Benthic sciaenids were the first to undergo a diet shift at 16 mm SL, which was attributed to changes in the feeding apparatus. Pelagic sciaenids underwent a diet shift at 17 mm SL, which was attributed to a previously studied shift in the sensory modality. The generalist sciaenids were the last to undergo a diet shift at 20 mm SL, which was attributed to changes in both the feeding apparatus and sensory abilities. These ecomorphological patterns identify the developmental events to the feeding apparatus and sensory systems necessary for ELHS sciaenids to begin partitioning their foraging niches, reducing their susceptibility to competition and bottom-up processes in estuarine ecosystems.