FEEDING ECOLOGY OF LAGODON RHOMBOIDES 

 (PISCES: SPARIDAE): VARIATION AND FUNCTIONAL RESPONSES 



Allan W. Stoner* 



ABSTRACT 



Five major ontogenetic stages were found in the diet of pinfish, Lagodon rhomboides, from Apalachee 

 Bay, Florida, but diet and dietary breadth showed high degrees of variation with space (both local and 

 geographic), and seasonal variation within size classes was often as dramatic as ontogenetic variation. 

 Lagodon rhomboides demonstrated planktivory, omnivory, strict camivory, and strict herbivory at 

 different times, places, and developmental stages. 



Ontogenetic pattern in food habits was primarily a fimction of mouth size and changing dentition of 

 the predator. Until it reaches 35 mm standard length, the pinfish is an obligate carnivore. Spatial and 

 temporal variation in the food habits of pinfish was a complex function of absolute and relative 

 abundances of food items in the field. Changes in plant consumption by fish larger than 35 mm standard 

 length may be due to changing plant abundance or protection of prey species by macrophyte cover at a 

 given station. Since seagrass biomass and the functional role of a single predator vary over both space 

 and time, plant-animal and predator-prey relationships change continually; however, the life history 

 of L. rhomboides is well adapted to seasonal patterns of productivity in food organisms. Multi- 

 dimensional variation in diets rendered the trophic level concept inoperational. It is concluded that 

 food webs are static neither in time nor in space and that taxonomic species may not be functional 

 components in models of energetic pathways and predator-prey relationships. 



In recent years, much research effort has been 

 expended on experiments for testing the role of 

 predation in seagrass meadows (Young et al. 1976; 

 Young and Young 1977, 1978; Orth 1977; Nelson 

 1978; Reise 1978); yet few experimental ecologists 

 have concerned themselves with variation in the 

 feeding behavior or functional responses of the 

 predators involved in their experiments. The prob- 

 lem is illustrated by empirical data which show 

 the potential for wide variation in the diets of 

 fishes with season (Keast and Welsh 1968; Bell et 

 al. 1978a, b), time of day (Hobson 1974; Hobson 

 and Chess 1976; Robertson and Howard 1978), age 

 or size of the animal (Carr and Adams 1973; Hob- 

 son and Chess 1976; Ross 1978), and with locality 

 (Feller and Kaczynski 1975; Love and Ebeling 

 1978). However, very few scientists have 

 adequately characterized interactions of spatial, 

 temporal, and ontogenetic variations (Keast 1970, 

 1979; Nakashima and Leggett 1975). Also, field 

 studies that have examined relationships between 

 prey selection by fish and structure of prey as- 

 semblages are largely limited to fishes that in- 

 habit structurally simple mud bottom or water 



'Department of Biological Science, Florida State University, 

 Tallahassee, Fla.; present address: Harbor Branch Institution, 

 hic, R.R. 1, Box 196- A, Fort Pierce, FL 33450. 



Manuscript accepted December 1979. 

 FISHERY BULLETIN: VOL. 78. NO. 2, 1980. 



column habitats (Feller and Kaczynski 1975; 

 Nakashima and Leggett 1975; Repsys et al. 1976; 

 Stein 1977). To date, only two field studies provide 

 data on the functional responses of fish to prey 

 abundance in seagrass habitats. Robertson and 

 Howard (1978) reported that short-term (diel) 

 dietary shifts in fishes inhabiting beds oiZostera 

 muelleri and Heterozostera tasmanica were due to 

 vertical movements of holoplankton and faculta- 

 tive zooplankton. Stoner (1979b) showed that the 

 selectivity of prey by pinfish, Lagodon rhom- 

 boides, was mediated by standing crop of benthic 

 macroph)^es. I concluded that increased seagrass 

 biomass resulted in a higher degree of selectivity 

 for certain amphipod species by juvenile fish. 



The pinfish is the numerically dominant fish on 

 Thalassia testudinum meadows in the shallow 

 subtidal areas of the Gulf of Mexico (Hoese and 

 Jones 1963; Hansen 1969) and onZ. marina beds 

 along the Atlantic coast of the United States south 

 of Cape Hatteras, N.C. (Adams 1976). The pinfish 

 is one of the most important predators on macro- 

 benthic organisms of seagrass meadows and has 

 been shown to play a role in the organization of 

 faunal assemblages (Young et al. 1976; Young and 

 Young 1978; Nelson 1978). Data have accumu- 

 lated on the food habits of pinfish; however, most of 

 the early work reviewed by Caldwell (1957) and 



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