Trophic Organization of Fishes in a Coastal Seagrass System

Abstract

A long-term (8-y) field study was made concerning the trophic relationships of fishes that occupy shallow coastal grassbeds in the northeast Gulf of Mexico. Various populatlons migrate into such areas to nursery during portions of their life histories. Many fishes undergo seasonal progressions of food preferences that follow species-specific, ontogenetic patterns. While the extent of such dietary successions varies considerably among the 14 species examined, many populations follow developmental progressions that may encompass various trophic levels from herbivory to carnivory. Omnivores are relatively common in the grassbed areas and there was a range of trophic specialization among the fishes examined. Generalized food preferences were often associated with early growth stages; as they matured, various populations became more specialized in their feeding habits Through treatment of each developmental stage of trophic preference as an individual entity (or 'ontogenetic trophic unit'), it was possible to identify progressions of feeding organization through time. Varying levels of temporal partitioning of food resources were evident. Periodic interspecific overlap of food resources was noted during periods of high productivity. Most grassbed fishes were adapted to extreme seasonal changes in habitat. This adaptation was reflected in observed temporal changes in diet and would explain the difficulty of making direct, linear associations of population distribution with multivariate analyses of specific habitat characteristics. The use of the 'ontogenetic trophic unit' facilitated the examination of the relationships of complex associations of fishes to a h~g h l y variable environment.

Foraging patterns of two syngnathid fishes: importance of harpacticoid copepods

“…2). The ontogenetic switch from small prey to larger prey was also shown for S. scovellj from Appalachicola Bay, Florida (Livingston 1982(Livingston , 1984, but harpacticoids were not as prevalent in the diet as in the present study. Syngnathus fuscus from North Carolina (Adams 1976) and Chesapeake Bay (Ryer 1981) also switched from smaller to larger prey as adult fish size increased but no information is available to determine if a strong dependence on harpacticoids by juveniles of S. fuscus existed.…”

“…S, scovelll (size class unidentified) from a Texas seagrass bed also had a large proportion of copepods in gut samples (Huh & 1985). Given that the small size classes of seagrass resident fishes such as the pinfish Lagodon rhomboides (Stoner 1979, Livingston 1980, spot Leiostomus xanthurus (Sheridan & Livingston 1979), mojarra Eucinostomus gula, and silver perch Bairdiella chrysura (Livingston 1982) utilize harpacticoid copepods as prey, the dietary patterns observed for syngnathids in our study site are not unique. Moreover, because patterns of abundances for S. scovelli and H. zosterae in Tampa Bay, Florida (Tipton 1987), as well as dietary characteristics reported here, in general accord with reports from other geographical areas, a common feeding pattern emerges for these fishes in seagrass beds.…”

“…Fish predation on macrofaunal invertebrates in both temperate and tropical seagrass beds is well studied (Reid 1954, Carr & Adams 1973, Young et al 1976, Brook 1977, Nelson 1979, Stoner 1979, Stoner & Livingston 1980, Ryer 1981, Livingston 1982, Ryer & Boehlert 1983. However.…”

Dietary guild structure of the fish community in the Northeast United States continental shelf ecosystem

“…In general, the mean dietary overlap both between and within guilds in this system is considerably lower than that observed in other marine fish communities. Mean dietary overlap across guilds in systems including seagrass habitats (Livingston 1982), coral reefs (Gladfelter & Johnson 1983), and streams (Pausey et al 1995) was on the order of 0.3 to 0.5 compared to 0.23 in the Northeast shelf ecosystem. The reduced dietary overlap we observed results from several characteristics of this community.…”

Variations in structure of estuarine fish communities in relation to abundance of submersed vascular plants

“…These include: enhanced refuge from predation; increased availability of food, especially for juvenile fish; and general habitat preference. Many studies have illustrated the dependence of fish diets on the rich macroinvertebrate communities inhabiting macrophyte beds (Brook 1977, Robertson 1980, Livingston 1982, Bell & Harmelin-Vivien 1983, Huh & Kitting 1985. In some cases it appears that the physical structure of plant leaves, stems, roots and rhizomes provides sufficient protection to allow these macroinvertebrates to thrive (Heck & Thoman 1984, Summerson & Peterson 1984.…”