FISHERY BULLETIN: VOL. 81. NO. 4 



the seagrass cover here was occasionally broken by a 

 bare sand substratum. Econfina 10 (E- 10) and 12 (E- 

 12) had standing crops of 215 and 320 g dry wt/m : , 

 respectively, and were characterized by continuous, 

 uniform seagrass cover. All of the stations were 

 polyhaline, about 1.2 m in depth, and characterized 

 by low levels of water color and turbidity. The 

 physical- chemical and sedimentological similarity of 

 the Apalachee Bay stations was established in an 

 earlier report (Stoner 1980a). 



Seagrass beds in Indian River lagoon are composed 

 of three different species. Large monospecific stands 

 of Thalassia testudinum (110 g dry wt/m : ), 

 Syringodium filiforme (48 g dry wt/m : ), and shoal 

 grass, Halodule wrightii (34 g dry wt/m : ) were sam- 

 pled near the western shore of the lagoon in shallow 

 (1.0 m) polyhaline water. The beds were adjacent to 

 one another and biomass values were representative 

 of beds in the lagoon. Biweekly sampling showed that 

 the Indian River stations were statistically similar to 

 each other in depth, salinity, temperature, and other 

 water conditions (Stoner 1983). 



Biological Collections 



In Apalachee Bay, fishes were collected with a 5 m 

 otter trawl (1.9 cm mesh wing; 0.6 cm mesh liner) 

 which was towed in a straight line near permanent 

 station markers at a speed of 2 kn for 2 min. Seven 

 replicate tows were made at each bed on a monthly 

 basis from December 1976 through November 1977. 

 The seven-trawl strategy was found to be appro- 

 priate for an asymptotic accumulation of species 

 (Livingston 1975). In Indian River lagoon, a smaller 

 net and a more rigid trawl strategy were required so 

 that only monospecific seagrass beds were sampled. 

 A 3 m otter trawl, with mesh identical to that used in 

 Apalachee Bay, was towed at 2 kn in a straight line 

 between floats at the ends of a 70 m transect or in a 

 line close to and parallel to the line of the floats. 

 Seven replicate tows were made at each bed on a 

 quarterly basis after preliminary analysis showed 

 that the seven replicates yielded an asymptotic 

 species accumulation curve for fishes. Despite the 

 restricted area of a trawl site, replicate tows did not 

 overlap in the area covered and no change in species 

 composition was observed over the collection period 

 which normally spanned several hours. Collections 

 were made at midday in October 1979, and in 

 January, April, and July 1 980. Because the efficiency 

 of capturing fishes (Ryan 1981) and invertebrates 

 (Greening and Livingston 1982) varies diurnally and 

 because certain species move to and from seagrass 

 beds on a diurnal basis (Randall 1965; Ogden and 



Buckman 1973; Ogden and Zieman 1977), midnight 

 collections were made at the Indian River stations. 

 Two tows were made at each bed in January and in 

 July. All fishes reported in this study were preserved 

 in a Formalin'-seawater mixture, identified to 

 species, counted, and measured for standard 

 length (SL). 



Macrophyte collections were made at each bed and 

 on each date of fish collection. As described by 

 Livingston et al. (1976), aluminum hoops (0.25 m by 

 0.25 m) were thrown haphazardly into the sampling 

 site and all macrophytes within each hoop were 

 collected by diving. Eight replicates were collected 

 including leaves, stems, roots, and rhizomes. Sam- 

 ples were placed in plastic bags and taken to the 

 laboratory for identification and weighing. Plants 

 were divided into aboveground and belowground 

 parts, dried at 80 -100 C for 12 h, and weighed by in- 

 dividual species and fractions. For an estimate of 

 blade density at Indian River beds, the number of 

 seagrass blades in each sample was determined and 

 extrapolated to yield numbers of seagrass blades per 

 square meter. 



Certain limitations are inherent in the present 

 study. The inefficiency of trawl sampling is known 

 (Kjelson and Johnson 1978), and it is not possible to 

 provide abundance data in absolute terms; only a 

 comparison of collections is valid. It may also be 

 argued (correctly) that trawl efficiencies decrease 

 with seagrass biomass. Although visual surveys of 

 ichthyofauna, made in Apalachee Bay and in Indian 

 River lagoon during the surveys, helped to confirm 

 the spatial patterns of abundance for large, mobile 

 species, visual surveys are rarely quantitative and 

 underestimate the abundance of cryptic species. 

 Low water transparence further restricted the value 

 of visual surveys in the two sampling areas. 



RESULTS 

 Role of Seagrass Biomass 



A total of 8,002 fishes representing 53 species were 

 collected in the 12-mo survey in Apalachee Bay. The 

 total number of individuals collected at a given sta- 

 tion, however, varied from 7 14 to 3,1 71 (Table 1) and 

 was a direct function of mean macrophyte biomass (r 

 = 0.988; P < 0.001) (Table 2). The close linear 

 relationship was largely a result of a linear increase in 

 abundance of pinfish, Lagodon rhomboides (r = 

 0.998; P < 0.001); however, when all other species 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



838 



