Distribution 



On exposed jetties the supral ittoral 

 fringe is blackened by blue-green algae, 

 over which wanders the occasional isopod 

 Lyqia exotica (Figure 5; Van Dolah et al . 

 1984; Fox and Ruppert 1985). Below this 

 is a barnacle zone, usually with 

 Chthamalus fraqilis occupying the highest 

 levels and various species of Balanus at 

 lower levels (Figure 5). Barnacles can be 

 abundant, approaching 100% cover (Ortega 

 1981). Below the barnacle zone at mid- 

 intertidal levels, is a zone where the 

 oyster Crassostrea virqinica reaches its 

 highest abundance, although this rarely 

 exceeds 20% cover in exposed habitats 

 (Figure 5; Ortega 1981). Below the 

 barnacle and oyster zones is a zone with 

 high densities of the mussel Brachidontes 

 exustus , which reaches to mean low water 

 (Figure 5). This pattern of zonation is 

 found with minor modifications throughout 

 the South Atlantic Bight, although in 

 northern Florida we begin to see a more 

 tropical fauna. Balanus spp. give way to 

 the larger barnacle Tetracl ita squamosa 

 and the siphonarid limpet Siphonari a 

 pectinata becomes abundant in the mid- 

 intertidal zone (Stephenson and Stephenson 

 1972). 



A similar pattern of zonation is seen 

 on more protected rubble structures except 

 that the lower intertidal zone is 

 dominated by the oyster Crassostrea 

 vi rgi ni ca instead of the mussel 

 Brachidontes exustus (Ortega 1981). 



Subtidally, our information is biased 

 towards shaded habitats in protected 

 waters of North Carolina, where most work 

 has been conducted. The hallmark of the 

 shallow subtidal community is change. In 

 their studies at Beaufort, NC, Sutherland 

 and Karl son (Sutherland and Karl son 1977; 

 Karl son 1978; Sutherland 1981) found that 

 the longevity of most community members 

 was less than a year. Few species 

 appeared able to tolerate the entire 25 °C 

 annual temperature range at Beaufort. 

 Hydroids and tunicates were especially 

 seasonal. Short life spans also 

 contributed greatly to seasonal changes in 

 species composition. 



Characteristically, mature benthic 

 assemblages were invaded by the tunicate 



Styel a pi icata each spring. Small 

 individuals often grew epizootically (on 

 top of other invertebrates) and after a 

 summer of rapid growth became too heavy 

 for their attachment sites. S^ pi icata 

 commonly sloughed off in the fall, taking 

 many other adhering organisms with it. 

 This process produced bare spaces on the 

 substrate, which were most often filled 

 with newly recruiting larvae. Variations 

 in larval recruitment produced winter 

 assemblages dominated by a variety of 

 sponges, hydroids, and bryozoans. Summer 

 assemblages were dominated by the solitary 

 tunicate S^ pi icata and the foliose 

 bryozoan Buqul a neri tina (Sutherland 

 1981). 



With increasing depth, annual changes 

 in species abundance are fewer (Karl son 

 1978). Much space is occupied by 

 relatively long-lived organisms such as 

 the hydroid Hvdracti ni a echinata , the 

 sponge Xestospongia hal ichondroides , the 

 anemone Pi adumene 1 eucol ena (Karl son 

 1978), and the coral Ocul ina arbusculum 

 (McCloskey 1970). 



In the South Atlantic Bight near Cape 

 Canaveral, FL, annual changes in species 

 abundance are fewer even in shallow water 

 assemblages (Mook 1976, 1980, 1981, 

 1983b). Balanus spp. and the tube 

 building amphipod Corophi urn 1 acustre 

 dominate these communities throughout the 

 year. 



Patterns of Recruitment 



When substrate has been 

 experimentally cleared (Ortega 1981) or 

 when new jetties are constructed (Van 

 Dolah et al . 1984), the general pattern of 

 intertidal zonation is restored or created 

 by recruitment within a year. Near 

 Beaufort, NC, Ortega (1981) reports most 

 intertidal recruitment of Bal anus spp. 

 during summer and of Crassostrea virqinica 

 and Brachidontes exustus in fall, but it 

 is unknown whether this pattern is typical 

 for the Atlantic Bight. Recruitment of 

 oysters is much higher in protected waters 

 than on jetties and pilings on the open 

 coast, while the reverse is true for 

 mussels (Ortega 1981). It is likely that 

 recruitment is lowest from January to 

 March when temperatures are minimal (e.g. 

 Sutherland and Karl son 1977). 



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