to stress. However, there is relatively 

 little in the way of detailed life-history 

 information concerninq these invertebrate 

 species. 



4. a. OYSTERS 



Oysters ( Crassostre a virqinica ) 

 represent an important part of the biota 

 of the Apalachicola estuary (Fiqure 20). 

 Such factors as temperature, rainfall/ 

 river flow (and hence salinity), 

 productivity (al lochthonous and 

 autochthonous), bottom type, and predation 

 define the life history of oysters in the 

 Apalachicola estuary. Ingle and Dawson 

 (1951, 1952) noted that temperature is 

 rarely limiting and that the spawning 

 season is one of the longest in the United 

 States (April through November). The 

 f ree-swimminq larval stage persists for 

 two weeks. Ingle and Dawson (1952) found 

 that oyster growth in Apalachicola Bay is 

 the fastest in the United States and is 

 continuous throughout the year because of 

 the relatively high year-round 

 temperatures. Successful oyster 

 development depends on an appropriate 

 substrate such as oyster shells, which can 

 be d1 anted throughout the estuary as 

 cultch to enhance growth. Whitfield and 

 Beaumariage [l^^ll) estimate that nearly 

 40^ of Apalachicola Bay is suitable for 

 growing oysters. The ample nutrients and 

 primary production of the bay also enhance 

 oyster growth. 



Oyster-bar associations also include 

 various organisms that prey on oysters 

 (Menzel et al. 1^58, 1966). These include 

 boring sponges, polychaete worms, 

 gastropod mollusks (such as Thais 

 haemastoma and Melongena corona ), and 

 crustaceans ( Menippe" mercenari a ) . 

 Salinity is the most important limiting 

 factor for oyster populations, but it has 

 been hypothesized that such influence is 

 indirect in that low salinity limits 

 predation by excluding important species 

 such as Thais and Menippe . During periods 

 of high salinity, oyster predation is 

 enhanced and can be considerable. 

 Experiments have shown that oysters over 

 50 mm in length are rare in unprotected 

 areas of high salinity relative to areas 

 where oysters are shielded from predation 

 by baskets at similar salinities (Menzel 

 et al. 1%6). 



4.5. NEKTON 



Nekton are those organisms that are 

 strong enough swimmers that they can move 

 through the water column, even aqainst 

 water currents. In the Apalachicola Bay 

 system, the nekton comprise the bulk of 

 the sport and commercial fisheries and are 

 among the more consoicuous biological 

 components of the estuarv. Eoibenthic 

 fishes and invertebrates in the 

 Aoalachicola marshes (Table IS) and ooen 

 water areas (Table 1°) are characterized 

 by high numbers of oredominant soecies, 

 with the top three species of each group 

 accounting for 70'?;-RO'3^ of the total 

 numbers taken throughout the year. The 

 relatively low number of fish and 

 invertebrate species in the bay system at 

 any given time, together with the high 

 dominance of a relatively few extremelv 

 successful species, contribute to the low 

 species diversity throughout the estuary 

 (Livingston l'376b). 



In a given year, peak numbers of 

 fishes tend to occur from February through 

 Aoril (Figure 27). This situation is due 

 largely to the presence of juvenile soot 

 and Atlantic croaker. Species numbers, on 

 the other hand, tend to oeak during 

 October. Epibenthic invertebrates reach 

 abundance peaks from August through 

 October, largely because of high numbers 

 of penaeid shrimp and, secondarily, blue 

 crabs (Figure 27). Seasonal patterns of 

 invertebrate species richness tend to 

 follow those of the fishes. The highest 

 numbers of invertebrate soecies usually 

 occur in October. The peaks of abundance 

 and species richness of fishes and 

 invertebrates are characterized by monthly 

 high variances. 



Various organisms appearing in the 

 estuary may not be estuarine dependent 

 throughout their life histories. Many 

 such organisms are migratory. The 

 anadromous soecies in the Apalachicola 

 drainage system include the Atlantic 

 sturgeon ( Acipenser oxvrhynchus ), Alabama 

 shad ( Alosa alabamae j^ and striped bass 

 ( Morone saxatil i T) (Yerqer 1<^77). The 

 skipiack herrinq ( Alosa chrysochloris ) is 

 another possible anadromous species. 

 Other species, such as the Atlantic 

 needlefish ( Stronqylura marina ) may be 

 diadromous. Catadromous species include 



60 



