Distribution of Fishes in Seagrass Meadows: Role of Macrophyte Biomass and Species Compositioni

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, 7Iwla""ia I".<ludinum, but the relationship did not hold across monospecific beds of T. t".<ludinum; manatee grass, 8yrinl-:{)dium /ili/orm,,; and shoal grass, Halodule wri/ihtii, 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 speries, blade density was a better predictor of fish 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"m unvegetated site, species richness was not related to seagrass biomass or blade density; habitat heterogeneity appeared to be more important. Ab4ndance 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. Differential distribution in pinfish, Lal-:odon rhomboid"", ofvarious 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 distribution and diversity of fishes within beds. Although a few researchers have compared the ichythofauna of vegetated and unvegetated substrata (Briggs and O'Connor 1971; Weinstein et aL 1977; Orth and Heck 1980) and changes in fish communities associated with pollution-induced reductions 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). Such investigations 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 P 'Contrihution No. a65 of the Harbor Branch Foundation, Inc., Fort lerce, FL a:J450. 'Harbor Branch Institution, Inc., R.R. 1, Box 196-A, Fort Pierce, Fla; present address: Centerfor Energy andEnvironmentResearch, University of Puerto Rico, Mayagiiez, PR 00708. M;;;,u,cript aceepted .June 19H:1. ~'ISHERY BULLETIN: VOL. HI. :"0. 4. 19H~. 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 composition, 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.