evident. Tnfaunal numerical abundance and 

 dry weiqht biomass (Figure ?7) in East 

 Bay, Apalachicola Bay, and St. George 

 Sound usually peak during winter and early 

 spring months (Mahonev and Livingston 

 1982; Livingston l'583b, c; Livingston et 

 al. 1983). Numbers of infaunal species 

 reach the highest levels during winter and 

 spring months (Figure ?J) . Monthly 



variance follows the trends of numerical 

 abundance and soecies richness. Sheridan 

 and Livingston (1983), working in shoal 

 grass ( Halodule wrightii ) meadows on the 

 north shore of St. George Island, found 

 infaunal densities exceeding 104,000 

 individuals m"'' in April 1^15. 



Spatial gradients of salinity, 

 oroductivity, and sediment types influence 

 the infaunal community composition 

 (Livingston et al. 1983). While physical 

 ■•"actors appear to predominate in the 

 infaunal community relationships in the 

 upper estuary near the river mouth, other 

 factors such as predation pressure and 

 competition mav be important determinants 

 of such interspecific interactions in 

 polyhaline portions of the bay system 

 (Livingston et al . 1983). 



Overall, infaunal soecies fall into 

 four general categories: crustaceans, 

 polychaetes, mollusks, and a miscellaneous 

 qroup that includes insect larvae and 

 oligochaete worms. Predominant species in 

 East Bay include Mediomastus ambiseta , 

 Steblospio benedicti , Heteromastus 

 fil iformis , Ampel isca vadorum , Hobsonia 

 florida , Hargeria rapax , and 

 Grandidierel la bonnieroides . The tanaid 

 Hargeria raoax is most abundant in or near 

 grass beds in Apalachicola Bav from 

 February to April. Other dominant grass- 

 bed soecies include Heteromastus 

 fil iformis and Hob soni a florida . The 



bonnieroides 



amphipod 

 ranges 



Grandidierel 1 a 



throughout the East 

 Bay-Apal achicola Bay complex, with peak 

 abundances during early spring and late 

 summer. Soft-sediment polyhaline 

 assemblages are dominated by Mediomastus 

 ambiseta , Paraorionospio pinnata , and 

 immature tubificid worms (Livingston et 

 al. 1^83). The sedentary polychaete 

 Heteromastus fil iformis is largely 

 restricted to grass beds and is most 

 abundant during April. The amphipod 

 Ampel i sca vadorum occurs primarily in the 



Apalachicola Bay seagrass meadows during 

 winter and early fall months. The poly- 

 chaete Mediomastus ambiseta is found in 

 fine mud bottoms throughout the bay, with 

 peaks of abundance in March. The 

 ubiquitous polychaete Streblospio 

 benedicti utilizes a variety of habitats 

 throughout the estuary, with peak 

 abundance during winter months. The 

 polychaete Hobsonia florida is found 

 throuqhout the bay from qrass beds to soft 

 sediment (unveqetated areas). Peak 

 abundance is noted during early fall 

 months. Tn general, the polychaete 

 species are eurythermal and euryhaline and 

 include selective and nonselective deposit 

 feeders. Sheridan and Livingston (1983) 

 noted that the dominant tanaids and 

 amphipods are detritivores and deposit 

 feeders. 



Because considerable amounts of 

 detrital matter are usually swept into the 

 estuary by the Apalachicola River during 

 winter-spring periods, the organic litter 

 forms an important habitat for various 

 macroinvertebrates. Organisms associated 

 with leaf litter and detritus have been 

 described by Livingston (1978) and 

 Livingston et al. (1976b, 1977). Litter 

 fauna is dominated by isopods, amphipods, 

 and decapods, which utilize particulate 

 matter and litter-associated microbes for 

 food and/or shelter. Dominant species in 

 East Bay and Apalachicola Bay include 

 Neritina reclivata , Palaemonetes spp., 

 Corophium louisianum , Gammarus spo., 

 Grandidierella bonnieroides , Mel ita spo., 

 and Munna reynoldsi . Salinity appears to 

 be an important orqanizinq feature of 

 litter associations (Livinqston unpubl.). 



Life-history strategies of dominant 

 infaunal and litter-associated 

 macroinvertebrate populations are dictated 

 by substrate type, temperature, salinity, 

 and biological factors (Table 17). Most 

 dominant infaunal populations reach peaks 

 of numerical abundance during late winter 

 and spring periods of low salinity and 

 increasing temperature. Most such soecies 

 are euryhaline and eurythermal. 

 Reproduction of some infaunal populations 

 occurs throughout the year while others 

 reproduce only between spring and fall. 

 Individual species have different patterns 

 of distribution within the estuary depen- 

 ding on recruitment patterns and response 



55 



