STONER: SEAGRASS ICHTHYOFAL'XA 



trawls were made for night collections, as opposed to 

 seven in the daytime, variation around the mean 

 values was low; the three beds yielded no statistically 

 similar collections of pinfish or total number of in- 

 dividuals. There were, however, no significant dif- 

 ferences among the three beds in numbers of 

 non- pinfish individuals or numbers of species collect- 

 ed. Although night collections yielded higher num- 

 bers of individuals than daytime collections, there 

 were few qualitative differences between samples. In 

 January, the relative abundance of pinfish was slight- 

 ly greater in night collections than in daytime collec- 

 tions in Halodule and Syringodium; there were slight 

 decreases at all stations in July (<14%) (Tables 8, 

 10). Certain cryptic species, such as Syngnathus 

 scocelli, (lobiosoma robustum, and Myrophis 

 punctata*, were more abundant in night collections 

 than in daytime samples, but only one species, sea 

 catfish. Alius felis, was captured only at night. 



DISCUSSION 



Comparisons of vegetated and unvegetated 

 habitats have demonstrated the importance of 

 seagrass habitats to a wide variety of juvenile fishes 

 (Reid 1954; Livingston 1975; Weinstein et al. 1977; 

 Orth and Heck 1980). From the present study, it is 

 clear that there is a close relationship between struc- 

 tural complexity of a seagrass bed and patterns of 

 fish abundance. Aboveground biomass was a good in- 

 dicator of ichthyofaunal abundance in one type of 

 meadow ( Thalassia), but when examining monotypic 



TABLE 10.— Nighttime abundance of fishes and fish species in three 

 seagrass beds in Indian River lagoon, Fla. Values are mean numbers 

 per trawl ± SD (n — 2). * indicate mean values that were not statis- 

 tically different on a given date (ANOVA and Duncan's multiple 

 range test, P < 0.05; F values are provided). 



beds of several seagrass species, blade density, 

 rather than biomass, proved to be best correlated 

 with fish abundance. 



The observed relationships between fish abundance 

 and structural complexity or type of seagrass 

 meadow are governed by the dispersal of fishes to the 

 beds, habitat preferences of the fishes, and their sur- 

 vival in the meadows. Because most of the fishes on 

 temperate seagrass beds are seasonal residents 

 (Kikuchi and Peres 1977) and because the majority 

 are juveniles, seasonal abundance is related to time 

 of spawning. Many of the most numerous seagrass 

 associates, including Lagodon rhomboides, Leio- 

 stomus xanthurus, Bairdiella chrysoura, and Diplodus 

 holbrooki, spawn offshore in midwinter (Brady 1981). 

 Differential dispersal of larvae to various field sites, 

 therefore, could have a major influence on the abun- 

 dance of fishes at a given field location. In a study of 

 ichthyoplankton in Apalachee Bay, Brady (1981) 

 found highest numbers of fish eggs and larvae at sta- 

 tion F- 1 2 which yielded the smallest trawl collections 

 of all vegetated sites. Lowest numbers of eggs and 

 larvae were collected at station E-12 where juvenile 

 and adult fishes were most abundant. Similarly, there 

 was no correlation between the abundance of eggs 

 and larvae as determined by Brady and the number 

 of juveniles and adults collected by trawl for species 

 such asL. rhomboides andL. xanthurus. Clearly, dif- 

 ferential dispersal of eggs and larvae does not explain 

 the distributional pattern for juvenile and adult 

 fishes in Apalachee Bay. Because late postlarval fish 

 were collected at all stations in Indian River lagoon 

 and because the sites were in very close proximity (all 

 within a radius of 300 m), differential dispersal of 

 fishes seems unlikely to explain ichthyofaunal dif- 

 ferences among sites in the lagoon. 



Individual fish species or age groups may actively 

 seek particular habitat types. Two characteristics of 

 seagrass meadows attract fishes — abundance of food 

 and shelter. In earlier studies (Stoner 1980a) it was 

 shown that spatial patterns in the abundance of 

 benthic macroinvertebrates in Apalachee Bay are 

 directly related to seagrass biomass. Because the 

 benthic samples were taken concurrently with fish 

 collections, and on the same stations, strong cir- 

 cumstantial evidence exists for a functional 

 relationship between food abundance and fish dis- 

 tribution. Also, experimental data on the foraging 

 behavior of Lagodon rhomboides (Stoner 1982) pro- 

 vide support for the hypothesis that predator and 

 prey distribution may be related to predatory ef- 

 ficiencies of the fishes. Lagodon rhomboides was 

 found to be most successful in capturing amphipod 

 prey in habitats composed of Halodule; capture rate 



843 



