FISHERY BULLETIN: VOL. 78, NO. 2 



confounded. Pinfish >35 mm SL nearly always 

 contained both plant and animal material in their 

 stomachs. Omnivory, of course, automatically 

 makes the fish both a "primary" and "secondary 

 consumer." Darnell's (1961) suggestion that pred- 

 ators commonly utilize food resources according 

 to their availabilities was clearly demonstrated in 

 this paper as it related to other spatial and tem- 

 poral patterns of food abundance in Apalachee 

 Bay. Although pinfish do not rely directly on detri- 

 tal material as a source of nutrition, many of its 

 prey organisms do (e.g., certain harpacticoid cope- 

 pods, amphipods, shrimps, and polychaetes). Be- 

 cause it is difficult to place detritovores in trophic 

 levels, the predatory fish also falls within no dis- 

 crete level. On these bases, the trophic level con- 

 cept is rendered inoperational for relationships 

 involving the dominant epibenthic fish in 

 Apalachee Bay. Furthermore, because of migra- 

 tion of consumers and wide variation in food 

 habits with season and consumer growth, one may 

 never assume that food webs, predator-prey rela- 

 tionships, or the functional role of a predator are 

 static. The taxonomic species is not, in many cases, 

 a functional ecological unit. At the very least, 

 ontogenetic feeding groups should be incorporated 

 in ecological models. These "trophic units" would 

 be particularly useful where the true ecological 

 role of the animal in a model is important. Except 

 in the most simple food webs, without precise 

 knowledge of variation in food habits and diet 

 breadth, models of energetic pathways and 

 predator-prey relationships and measurement of 

 niche breadth and overlap will be accurate neither 

 in theory nor in practice. 



Characteristics of prey species which mediate 

 predation include absolute and relative abun- 

 dances, conspicuousness, size, palatability, defen- 

 sive morphology and behavior, spatial distribu- 

 tion including microhabitat and aggregation, and 

 nutritional value. All of the above, however, are 

 limited or mediated by various elements of the 

 environment including temperature, turbidity, 

 dissolved oxygen, light, water motion, and struc- 

 tural aspects of the habitat. Although a great deal 

 of research has been conducted concerning the im- 

 portance of predator and prey characteristics, 

 most of the work has been done in structurally 

 simple systems, including mud bottom, freshwa- 

 ter pond, and water column habitats where the 

 number of food species is relatively low. Data from 

 this and another paper (Stoner 1979b) show 

 that seagrass blades and rhizomes provide a very 



important structural component in seagrass 

 meadows which affect both predator and prey 

 species and their interactions. Since seagrass 

 biomass, blade densities, and species compositions 

 vary over both time and space, plant-animal and 

 predator-prey relationships are in constant flux. 

 The seagrass habitat, therefore, is an extremely 

 complex system within which the ecological roles 

 of predation and habitat structure are ever chang- 

 ing. The need for further investigation is obvious. 



ACKNOWLEDGMENTS 



This research was supported by grant number 

 R-805288010 from the U.S. Environmental Pro- 

 tection Agency to Robert J. Livingston. I wish to 

 thank all of those graduate and undergraduate 

 students who helped with field collections. E. L. 

 Bousfield, H. Greening, H. Kritzler, F. G. Lewis, S. 

 L. Santos, P. F. Sheridan, and J. L. Simon provided 

 assistance with the taxonomy of various benthic 

 organisms. Aid with computer programming and 

 statistical procedures was generously provided by 

 G. C. Woodsum and D. Zahn. L. G. Abele, W. F. 

 Herrnkind, R. A. Laughlin, K. M. Leber, F. G. 

 Lewis, R. J. Livingston, R. W. Menzel, R. W. 

 Yerger, and an anonymous reviewer helped to 

 point out several inconsistencies in the manu- 

 script at various stages. 



LITERATURE CITED 



ADAMS, S. M. 



1976. The ecology of eelgrass, Zostera marina (L.), fish 

 communities. I. Structural analysis. J. Exp. Mar. Biol. 

 Ecol. 22:269-291. 

 BELL, J. D., J. J. BURCHMORE, AND D. A. POLLARD. 



1978a. Feeding ecology of a scorpaenid fish, the fortescue, 

 Centropogon australis, from a Posidonia seagrass habitat 

 in New South Wales. Aust. J. Mar. Freshwater Res. 

 29:175-185. 

 1978b. Feeding ecology of three sympatric species of leath- 

 erjackets (Pisces: Monacanthidae) from a Posidonia sea- 

 grass habitat in New South Wales. Aust. J. Mar. Fresh- 

 water Res. 29:631-643. 



Brady, K. D. 



1980. An ichthyoplankton survey of Apalachee Bay, 

 Florida. M.S. Thesis, Florida State Univ., Tallahassee. 



Brook, I. M. 



1978. Comparative macrofaunal abundance in turtlegrass 

 (Thalassia testudinum) communities in south Florida 

 characterized by high blade density. Bull. Mar. Sci. 

 28:212-217. 



Caldwell, D. K. 



1957. The biology and systematics of the pinfish, Lagodon 

 rhomboides (Linnaeus). Bull. Fla. State Mus., Biol. Sci. 

 2:77-173. 



350 



