STONER: FEEDING ECOLOGY OF LAGODON RHOMBOIDES 



Plant consumption was inversely related to poly- 

 chaete field density at all three stations and rela- 

 tionships with amphipod abundance were mixed. 

 Multiple regression did not provide a satisfactory 

 model for variation in plant matter consumed at 

 Fenholloway 12, but plant and food item abun- 

 dances explained 78.6 and 95.5'7f of the variation 

 at Econfina 12 and 10. Explanation of temporal 

 variation in shrimp consumption by multiple re- 

 gression methods was successful only for fish from 

 Econfina 10 (r^ = 0.741). Shrimp intake increased 

 with shrimp abundance in the field and decreased 

 with plant and polychaete abundances. Other cor- 

 relations were low. Harpacticoid copepod con- 

 sumption was positively related to plant biomass 

 and negatively correlated with amphipod abun- 

 dance; however, multiple correlation coefficients 

 were not computed since no data were available on 

 harpacticoid abundance. 



Diet of large pinfish (>80 mm SL) showed little 

 seasonality at Econfina 10, where plant material 

 made up at least 809c of the stomach contents on 



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C 

 (D 



c 

 o 

 U 



u 



E 

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■t-> 



1 1 1 



3 4 5 6 



(93) (118) (115) (113) (121) (116) (113) (100) (96) 



Month 



Figure 8. — Seasonality in diet of Lagodon rhomboides >80 mm 

 SL from two stations (F 12-top, E 10-bottom) in Apalachee Bay, 

 Fla. (March to November 1977). Diet is given as the relative 

 proportion of the dry weight of stomach contents. Codes for the 

 dietary components are given in Table 1 . Numbers in parenthe- 

 ses are the mean lengths offish. 



all dates. At Fenholloway 12, however, benthic 

 vegetation was less abundant than at Econfina 10 

 and major changes in diet occurred with season 

 (Figure 8). Clearly, large pinfish were carnivorous 

 during winter and early spring at Fenholloway 12, 

 but became herbivorous in May. Winter diet in- 

 cluded polychaetes, bivalves, amphipods, and 

 isopods. Animal material was unimportant in the 

 diets of fish taken during the rest of the year. 



Temporal variation in the diets of adult fish was 

 not adequately explained with multiple regres- 

 sion, as obvious trends in plant consumption did 

 not follow seasonal patterns in macrophyte abun- 

 dance. Lack of temporal variation in diet at 

 Econfina 10 is due to the fact that plants were 

 readily available at that station when adult 

 pinfish were present (March through October). On 

 the other hand, at Fenholloway 12, macrophytes 

 were patchy in distribution and a high biomass in 

 April (Table 3) was composed largely of T. tes- 

 tudinum which was generally not consumed by 

 pinfish. Abundance of alternative prey organisms, 

 such as isopods and bivalves, may also explain 

 earn ivory of adult pinfish at Fenholloway in the 

 spring. 



Breadth of diet in pinfish was examined by cal- 

 culating Shannon-Weiner diversity indices, H', 

 and by tabulating the number of food items that 

 individually contributed >1.0% of the total mass 

 of stomach contents for each fish size class, sam- 

 pling date, and station (Table 6, Figure 9). Dietary 

 diversity of pinfish between 16 and 80 mm was 

 lowest at the unvegetated site because two food 

 items, amphipods and calanoid copepods, over- 

 whelmed the importance of other foods. Low 

 abundance of alternative prey such as shrimp, 

 shrimp postlarvae, and benthic macrophytes 

 probably explain this occurrence. For fish >80 



Table 6. — Dietary diversity, H', and number of food types 

 (individually contributing >1.0'7c of the total mass of stomach 

 contents) in Lagodon rhomboides from four stations in 

 Apalachee Bay, Fla. (mean ± SD). Within a fish size group, no 

 mean values were significantly different (AN OVA and Duncan's 

 multiple range test, P>0.05). 



Size group (mm) 



Fen 11 



Fen 12 



Econ 10 



Econ 1 2 



Dietary diversity. H' 



— — 0.57±0.39 0.54±0.64 

 0.99r0.50 1.68 = 0.17 1.28 = 0.59 1.45 = 0.13 

 1.27 = 0.46 1.68 = 0.44 1.64=0.44 1.58=0.25 



— 0.92 = 0.44 0.50 = 0.36 0.41=0.22 



11-15 



16-35 



36-80 



>80 



11-15 



16-35 



36-80 



>80 



Number of food types 



— — 2.2 = 0.9 2.7 = 2.0 

 5.0 = 2.8 7.5=2.1 5.5 = 2.3 5.8 = 1.2 

 6.2 = 1.7 8.6=2.4 8.1=3.0 7.2=1.2 



— 6.2 = 2.3 4.4=1.7 4.5=0.7 



345 



