Ontogenetic Patterns in Diet and Feeding Morphology in Sympatric Sparid Fishes from Seagrass Meadows

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Abstract
The sparids Lagodon rhomboides and Diplodus holbrooki were spatially and temporally sympatric and demonstrated similar growth patterns on seagrass meadows of Apalachee Bay, Florida [USA]. Both species took a wide variety of food items over the growth period, but distinctly different trophic stages exist for both fishes and dietary overlap between the species was small. Ontogenetic and interspecific variation in the diets of the fishes was correlated with differences in external morphology related to locomotion, mouth dimensions and ontogeny of dentition. With an elongated body form, large mouth and sharp incisors as a juvenile, Lagodon is a generalized predator dependent upon motile epibenthic invertebrates. Diplodus specializes on hydroids and microepiphytes; this is related to early development of chisel-type incisors, deep-bodied form and small mouth. Consumption of seagrasses as a primary food source was associated with the presence of vertically opposed, straight-edged incisors in Lagodon. Consumption of epiphytes and sponges in adult Diplodus was related to the development of long, rounded and protruding incisors, greater numbers of posterior teeth and strong jaws. The hypothesis that ontogenetic and interspecific differences in the diets of fishes are related to morphological characteristics is supported and the usefulness of the ontogenetic trophic unit concept is affirmed.