Spatial and Temporal Trends in Diet for Pinfish (Lagodon rhomboides) from Turtle Grass (Thalassia testudinum) Beds with Contrasting Environmental Regimes in the Lower Laguna Madre, Texas

Seagrass meadows in far South Texas are dominated by turtle grass (Thalassia testudinum), and juvenile pinfish (Lagodon rhomboides) are abundant grazers of seagrass epifauna. As they grow, pinfish exhibit an ontogenetic dietary shift and begin consuming increasing amounts of plant material. In this study, contrasting environmental regimes in two seagrass meadows were examined to identify how they might affect pinfish diets, diet shifts, and growth across the growing season. The eastern site was sheltered from prevailing southeasterly winds by a barrier island, while the western site was shallower and subjected to higher wind energy and turbidity. Gut contents from 290 pinfish were quantified from May through October 2016 and multivariate analyses showed strong but overlapping separation of diets and temporal change in feeding habits. Although there were spatial and temporal differences between the two sites, a site by time interaction indicated different temporal trends. Nonetheless, ooze (amorphous detritus) and aquatic invertebrates (primarily amphipods) were the primary diet items consumed at both localities across time. Pinfish at both sites consumed seagrass, which increased in importance as the growing season progressed, although volume and consumption rate did not differ between sites. Growth rates of pinfish were similar at both sites, but pinfish from the western site were larger and fewer in number across the study. Although pinfish diets differed under different environmental regimes, they were generalist consumers in South Texas seagrass meadows with high diet variability that trended towards herbivory in late summer and fall.