DISTRIBUTION OF FISHES IN SEAGRASS MEADOWS: 

 ROLE OF MACROPHYTE BIOMASS AND SPECIES COMPOSITION 1 



Allan W. Stone r : 

 ABSTRACT 



Large spatial variation was found in the abundance and species composition of ichthyofauna in seagrass 

 meadows of Apalachee Bay and Indian River lagoon, Florida. Abundance of fishes was a direct function of 

 aboveground seagrass biomass in Apalachee Bay where seagrass meadows were dominated by turtlegrass, 

 Thalassia testudinum, but the relationship did not hold across monospecific beds of 7" testudinum; manatee 

 grass, Syringodium filiforme; and shoal grass, Halodule wrightii, in Indian River lagoon. Rather, the shoal 

 grass site, with lowest seagrass biomass, yielded the largest number of fishes, while manatee grass, with 

 biomass near that of shoal grass, had fewest fishes. Across seagrass species, blade density was a better pre- 

 dictor offish abundance than seagrass biomass. Seasonal patterns offish abundance at all of the sites were 

 related to macrophyte biomass. Although lowest numbers of fish species were collected at an unvegetated 

 site, species richness was not related to seagrass biomass or blade density; habitat heterogeneity appeared to 

 be more important. Abundance of prey and protection from piscivorous predators were hypothesized as the 

 best explanations for high fish abundance associated with high seagrass biomass and with shoal grass. Dif- 

 ferential distribution in pinfish, Lagodon rhnmboides, of various size classes was related to foraging behavior 

 of individual trophic stages. 



The great abundance and diversity of ichthyofauna in 

 seagrass meadows are well established (Hoese and 

 Jones 1963; Kikuchi 1966; Adams 1976; Weinstein 

 and Heck 1979; Robertson 1980), but little is known 

 concerning the mechanisms which control the dis- 

 tribution and diversity of fishes within beds. 

 Although a few researchers have compared the 

 ichythofauna of vegetated and unvegetated sub- 

 strata (Briggs and O'Connor 1971; Weinstein et al. 

 1977; Orth and Heck 1980) and changes in fish com- 

 munities associated with pollution-induced reduc- 

 tions in seagrass cover have been examined (Kikuchi 

 1974; Livingston 1975), studies have not been 

 designed specifically to test the role of seagrass 

 biomass in the organization offish assemblages. Only 

 one study has examined ichthyofauna of different 

 seagrass species (Martin and Cooper 1981). Suchin- 

 vestigations require seagrass beds of different blade 

 density or species composition within a restricted 

 geographic range and beds which are characterized 

 by similar physical and chemical conditions. 



In this study I first discuss the ichthyofauna of four 

 beds which have different seagrass biomass. Then, I 

 compare the fish assemblages collected at three beds 

 characterized by monotypic stands of three seagrass 



'Contribution No. 365 of the Harbor Branch Foundation, Inc., Fort 

 Fierce, FL 33450. 



2 Harbor Branch Institution, Inc., R.R. 1, Box 196-A, Fort Pierce, 

 Fla; present address: Center for Energy and Environment Research, 

 University of Puerto Rico, Mayagiiez, PR 00708. 



species. The criteria for similar physical-chemical 

 conditions were met within each of the two systems 

 studied (Apalachee Bay and Indian River lagoon, 

 Florida). Patterns of abundance, species composi- 

 tion, species richness, and fish size are discussed in 

 terms of the life history of individual fish species, 

 abundance of prey at the sites, and foraging behavior 

 of numerically dominant species. 



METHODS 

 Sampling Sites 



Trawl surveys were made in two Florida localities: 

 Apalachee Bay in the northern Gulf of Mexico and In- 

 dian River lagoon, 8 km north of Fort Pierce, on the 

 east coast of Florida. Apalachee Bay is shallow and 

 open to the Gulf of Mexico with seagrass beds 

 (primarily turtle grass, Thalassia testudinum, and 

 lesser amounts of manatee grass, Syrintfodiurn fili- 

 forme) which cover hundreds of square kilometers. 

 Four stations were chosen on the basis of long-term 

 macrophyte data for the area (Zimmerman and 

 Livingston 1976, 1979) and are identical to the 

 stations discussed by Stoner (1980a). Fenholloway 

 station 11 (F-ll) was characterized by a very sparse 

 and patchy seagrass flora with a mean aboveground 

 biomass of only 9.3 g dry wt/m : . Station F-ll will be 

 termed the unvegetated site. Fenholloway 12 (F-12) 

 had a mean macrophyte biomass of 141 g dry wt/m : ; 



Manuscript accepted .lune 198M. 



FISHERY BULLETIN: VOL. 81. NO. 4. 1983. 



837 



