Feeding ecology, energetics, and production of pinfish Lagodon rhomboides (Linnaeus) in temperate seagrass meadows

The effects of grazing by post-larval and juvenile pinfish, Lagodon rhomboides, on amphipod abundance and densities in seagrass beds in St. Joseph Bay, Florida, USA, were estimated. Field experiments were used to estimate habitat-specific abundance and densities for pinfish and amphipods, as well as growth and production. These estimates, combined with feeding, calorimetric, respirometry, and food choice studies in the laboratory were used to develop a bioenergetics model of pinfish feeding. The bioenergetics model was then used to predict in situ consumption rates of amphipods by pinfish.; Determination of pinfish diet and/or food preference by fish size class is important in understanding the role that pinfish play in causing, or reacting to, changes in amphipod abundance. Thus, a combination of feeding studies in the laboratory, and gut content analysis on wild pinfish were also undertaken to address the questions of whether the reported shift in pinfish diet occurs with ontogeny or is a result of opportunistic feeding.; Field experiments indicated pinfish were the most abundant fish species collected in each habitat. Average pinfish size (dry weights) increased each month. Growth of individuals averaged 0.031 g d–1 in Halodule and 0.032 g d–1 in Thalassia . Average weight-specific biomass was 0.46 g m–2 dry weight in Halodule and 0.78 g m–2 dry weight in Thalassia. Daily pinfish production estimates were highest in Thalassia (0.025 g m–2 d–1 DW) compared to Halodule (0.014 g–2 d–1 DW).; Growth, consumption, and oxygen uptake by pinfish were estimated at three temperatures (20°C, 25°C, and 30°C) and three pinfish size classes (1–3g, 14–18g, and 35–38g). Laboratory results indicated that maximum pinfish growth varied by size class and temperature.; Pinfish diet changed throughout the year. Initially pinfish were totally carnivorous but switched to omnivory as they grew. Pinfish never became entirely herbivorous and seagrass material was never more than 18% of the pinfish diet by weight throughout the year.; Bioenergetic model outputs indicate pinfish in situ consumption levels were at or near the maximum rates derived in the laboratory (91.9% in Halodule and 85.9% in Thalassia). Maximum amphipod consumption occurred in the summer months and was approximately 5.9 g m–2 4d–1 AFDW in Thalassia and 1.6 g m–2 d–1 AFDW in Halodule. Based on the laboratory and field experiments, it appears pinfish may in fact be able to “graze down” amphipod standing stock and production during the summer months in both Halodule and Thalassia seagrass beds. Therefore, it appears any shift in pinfish diet may be a facultative and not obligate change and may be in response to declining numbers of preferred crustacean prey (amphipods) during the year. (Abstract shortened by UMI.)...