spicatum ). During the period 1980-1981, 

 this introduced species became dominant in 

 Round Bay, one of the eastern bayous. By 

 1982-1983, the Myriophyllum had become 

 rooted throughout the upper East Bay area 

 (Livingston unpubl.). It is unclear how 

 spread of Eurasian watermilfoil will 

 affect the distribution of plants and 

 animals in the East Bay seagrass beds. 



Currently, the oligohaline seagrass 

 beds serve as a nursery for benthic 

 species such as the snail Neritina 

 reclivata (a major dominant! and 



epibenthic species ( Udostomia sp., 

 Gammarus macromucronatus and Taphromysis 

 bowman i )". Infaunal assemblages are 

 dominated by polychaetes ( Loandalia 

 americana , Mediomastus ambiseta ), 

 amphipods ( Grandidierella bonnieroides ) 

 and chironomid larvae ( Dicrontendipes 

 sp.). Fish populations are dominated by 

 rainwater killifish ( Lucania parva ), 

 pipefish ( Syngnathus scovell i ), 

 silvers ides ( Menidia beryl lina" )^ gobies 

 (Microgobius gulosus ), and centrarchids. 

 Many species utilize these areas (Duncan 

 1977; Livingston and Duncan 1979; Purcell 

 1977). Of the 28 dominant benthic species 

 of fishes that comprised over 98% of the 

 abundance in the area, most consumed 

 detritus, small mollusks, crustaceans, 

 epiphytes, and insect larvae. Most of the 

 penaeid shrimp, insect larvae, and fishes 

 that are found here are seasonally 

 abundant at early stages of their 

 reproductive cycles, which indicates the 

 use of these areas as primary nursery 

 grounds. Peaks of abundance are staggered 

 throughout the year. 



The predominant macrophyte species in 

 mesohaline or higher-salinity areas off 

 St. George Island in Apalachicola Bay is 

 Halodule wrighti i (Sheridan and Livingston 

 1983) . Infaunal macroinvertebrates, 

 dominated by Hargaria rapax , Heteromastus 

 f i 1 if ormis , Ampel isca vadorum and various 

 oligochaetes, reach peaks of abundance 

 during early spring. Predominant fishes 

 include silver perch ( Bairdiel la 

 chrysoura ), pigfish ( Orthopristis 

 chrysoptera ), pinfish ( Lagodon rhomboides ) 

 and spotted seatrout ( CynoscTon 

 nebulosus ) . These species are abundant 

 from May through September. Blue crabs 

 ( Cal linectes sapidus ) , pink shrimp 

 ( Penaeus duorarum ) ^and grass shrimp 



( Palaemonetes vulgaris ) are the dominant 

 invertebrates. Their densities are 

 bimodal, peaking in the winter and summer 

 months. These areas are also 

 characterized by the year-round presence 

 of larval and juvenile nekton. 



5.1.3. Litter Associations 



Leaf litter associations are 

 dominated by omnivores and detriti vores. 

 The fraction of particulate organic matter 

 (POM) large enough to be identified as 

 litter is populated with gastropod 

 mollusks ( Neritina reclivata ), amphipods 

 ( Gammarus mucronatus . Me 1 i t a spp., 

 Grandidierella bonnieroides , Corophium 

 louisianum , Gitanopsis sp.), isopods 

 ( Munna reynoldsi ) , and decapods 

 ( Palaemonetes pugio , P^. vulgaris , Penaeus 



setiferus , Cal linectes sapidus ). 



Species richness of the litter- 

 associated fauna in upper East Bay 

 (station 5A), the river mouth (station 3), 

 and the shoal qrassbeds off St. George 

 Island (station IX) peaks during August 

 and September (Figure 35). Such peaks are 

 strongly associated with salinity levels 

 at the respective study sites (Figure 36). 

 Dominant species vary from location to 

 location. The level and timing of peaks 

 of abundance also vary spatially (Figure 

 35). Upper East Bay, which is outside of 

 the direct influence of the Apalachicola 

 River, appears to be the least productive 

 part of the estuary in terms of litter- 

 associated macroinvertebrates. Areas rich 

 in detritus, such as station 3, are most 

 highly populated during March and 

 September, periods when the river is 

 flooding or macrophytes are dying off. 

 The highest numbers of litter-associated 

 macroinvertebrates occur in the Halodule 

 beds off St. George Island from April to 

 June, a period of high macrophyte 

 productivity. These data indicate that 

 while species richness may be strongly 

 influenced by salinity, the numerical 

 abundance of the litter associations is 

 more strongly aligned with the 

 availability of detritus. 



While physical factors such as 

 salinity and temperature are important 

 determinants of the distribution of 

 litter-associated organisms in the 

 estuary, recent experiments by Florida 



77 



