5.1.4. Oyster Bars 



Oyster bars represent a relatively 

 significant habitat in the estuary (Table 

 1). The main concentrations of oysters 

 ( Crassostrea virqinica ) (Fiqure 20) lie in 

 St. Vincent Sound and western portions of 

 St. George Sound, Oyster distribution is 

 dependent upon substrate, temperature, 

 salinity, and available food. Oyster 

 bars, themselves, provide habitat and food 

 for a variety of organisms. The oyster 

 associated community includes sponges 

 ( Cliona vastifica), bryozoans 

 ( Membranipora sp.), flatworms ( Stylochus 

 frontalis ), annelids ( Neanthes succinea . 

 Polydora websteri ), various arthropod 

 crustaceans ( Callinectes sapidus , Menippe 

 mercenaria , Neopanope spp., Petrolisthes 



armatus ),~ gastropods ( Crepidula plana , 

 Melongena corona , Thais haemastroma 



and 



pelecypods ( Brachidontes exusta, Chi one 

 cancel lata ) (Menzel et al . 1966). Fishes 

 include blennies ( Hypsoblennius spp.) and 

 toadfish ( Opsanus beta ). These organisms 

 use the reef for shelter and/or feeding. 



Salinity controls oyster-bar 

 community organization. When salinities 

 are high, various stenohaline gulf species 

 are able to move Into the oyster-rich 

 areas and feed on the oysters. Low 

 salinity limits such predation by acting 

 as a barrier to those organisms. Species 

 richness and diversity of the oyster- 

 associated populations vary directly with 

 seasonal increases in salinity. During 

 warmer months, extensive oyster mortality 

 in the Apalachicola estuary has been 

 attributed to infestation by the pathogen 

 Perkinsus marinus (formerly called 

 Dermocyctidium marinum ) (Menzel 1983). 

 Young oysters are unaffected by this 

 disease, although up to 505^ of adult 

 oysters may be killed annually. The 

 relatively long period of high water 

 temperature in the gulf estuaries 

 contributes to such mortality. A long- 

 term study is currently under way to 

 determine the response of the Apalachicola 

 oyster associations to various stimuli 

 including habitat features (water quality, 

 substrate), predation, competition, 

 disease, and possible over-fishing 

 (Livingston et al., unpubl.). 



5.1.5. Subtidal (Soft-Sediment) 

 Communities 



Almost 70% of the Apalachicola Bay 

 system can be characterized as a subtidal, 

 unvegetated, soft-sediment area (Table 1). 

 The muddy bottom substrate is inhabited 

 primarily by polychaetes ( Mediomastus 

 ambiseta , Streblospio benedict i ) and" 

 amphipods ( Grandidierella bonnleroides ). 

 The polychaetes are deposit and suspension 

 feeders with a high reproductive capacity 

 and considerable tolerance for low 

 salinity and variable environmental 

 conditions. Productivity trends, habitat 

 type, and the ecological characteristics 

 of the various populations contribute to 

 what is a temporally variable but highly 

 persistent assemblage of organisms in 

 terms of species richness, relative 

 abundance, and recruitment. In 

 oligohaline areas of the estuary, the 

 benthic macroinvertebrate assemblages are 

 characterized by high dominance, low 

 species richness, low diversity, and 

 varying standing-crop biomass and 

 numerical abundance (Livingston 1983c, d). 

 Areas around the mouth of the river have 

 much higher numbers of infaunal 

 macroinvertebrates than areas outside of 

 the region of general flow. Such 

 differences have been attributed 

 (Livingston 1983c, d) to the deposition of 

 nutrients and detritus by the river during 

 periods of flooding (Figure 9) and 

 Increased activity and abundance of the 

 benthic macroinvertebrates (Figure 27). 



The general community characteristics 

 of the soft-bottom assemblages change as 

 salinities increase temporally and 

 spatially. In mesohaline and polyhaline 

 portions of the system, overall numerical 

 abundance Is lower than in oligohaline 

 areas, but species richness and diversity 

 increase significantly (Livingston et al. 

 1983). Such trends are evident in the 

 associations of epibenthic fishes and 

 invertebrates, which are an Important part 

 of the soft-sediment communities. 

 Dominant populations such as Atlantic 

 croaker, spot, penaeid shrimp, and blue 

 crabs feed extensively on organisms within 

 the muddy bottom of the estuary. 



The soft-sediment community 

 (invertebrates and fishes) of the 



79 



