Morphology and Ecology: Functional Basis of Feeding Constraints in Caribbean Labrid Fishes

Abstract

This study examines the role of functional morphology of the feeding apparatus in constraining the food habits of Caribbean wrasses (Labridae) in the genus Halichoeres. Like other wrasses, these fishes crush prey with powerful pharyngeal jaws. Estimates of pharyngeal jaw crushing strength were made, based on muscle size and architecture, for an ontogenetic series of fish from each of six species. The resultant scaling relationships indicated that, at any given body length, the six species differed in crushing strength. The ability to crush prey items was, therefore, predicted to vary among species. The relative importance of crushing strength and pharyngeal jaw gape in constraining predation was examined in laboratory feeding trials using three species that differed in estimated crushing strength: H. garnoti, H. bivittatus, and H. maculipinna. The feeding trials determined the largest individuals of three prey species that fishes could eat. Two hard—bodied prey species (a gastropod and a crab) and a softer bodied crab species were offered to wrasses. Feeding ability on the two hard—shelled prey was predicted best by crushing strength; fishes of equivalent crushing potential were able to eat the same maximum size prey, in spite of considerable interspecific variation in pharyngeal jaw gape and body length at any given crushing strength. The consequences of ontogenetic and interspecific differences in crushing ability for feeding habits were explored by analyzing the intestinal contents of fishes collected from the Belizean barrier reef. Crushing strength appeared to play a central role in constraining diets of these fishes. Ontogenetic diet analysis of three species revealed that fishes switched from soft—bodied to hard—shelled prey at °3—5 N crushing strength, even though this crushing strength occurred at a different body size and pharyngeal jaw gape in each species. This switch was followed by a reduction in dietary breadth as fishes specialized on hard—bodied prey. Few other Caribbean coral reef fishes are capable of crushing molluscs effectively. Wrasses thus utilize a relatively unexploited trophic niche on the prey—hardness resource dimension.