described by Shlnn ( 1 97 ^ ) » Soimier et al. (1976), and Gallaway et al. 

 (1979). In contrast to the low-relief, barnacle-dominated white shrimp 

 ground assemblage, bivalves dominate the sessile epifauna of brown 

 shrimp ground platforms and the communities are of high relief. 

 Near-surface areas are characterized by luxuriant growths of red and 

 green algae in which the tree oyster ( Isognomon bicolor) is often 

 present in high densities. The bivalve Chama macerophvlla and oysters 

 (Ostreacea) are the typical biomass dominants to depths of 20 m and are 

 complemented by octocorals ( Telesto sp.) and solitary hard corals 

 (Astrangia sp. and Phvllanyia sp.) in addition to various hydroids and 

 bryozoans. Below 20-m depths, colonial forms such as encrusting sponges 

 (Homocoelidae) , anemones (Zoanthidae) and ascideans (Ascidiarea) 

 predominate. There appears to be a marked drop in biomass levels of 

 sessile epifauna between 20- and 30-m depths. Biomass in the upper part 

 of the water column ranges from 8 to 11 kg/m 2 ; below 20 m biomass levels 

 are usually around 2 kg/m 2 . 



The sessile epifauna of the offshore platform assemblage is of high 



relief and supports a diverse cryptic fauna. Not only are small species 



such as microcrustaceans well represented, but relatively large species 



such as blennies, arrow crabs, stone crabs, oyster drills, and sea 

 urchins are abundant. 



The fish fauna of offshore platforms was described by Gallaway et 

 al. (1979) as dominated by species such as spadefish, lookdown, 

 bluefish, sheepshead, and gray triggerf ish (Balistes capriscus) . These 

 species were supplemented by many gray snapper, red snapper, blue runner 

 and moonfish ( Vomer setapinnis) . Large predator species such as 

 barracuda ( Sphyraena barracuda) , cobia and jack crevalle ( Caranx 

 hippos) were common. The platforms, particularly those in deeper 

 waters, had a rich tropical fish fauna. Bermuda chub ( Kvohosus 

 sectatrix) were characteristically present and associated with the algal 

 zone; blennies (Blennidae) of several species were abundant and several 

 species of damselfishes (Pomacentridae) , butterfly and angel fishes 

 (Chaetodontidae) and tangs (Acanthuridae) were usually common. 



Shinn (1974) described the general vertical zonation of fishes 

 around Louisiana platforms. He listed spadefish, barracuda, lookdown, 

 and sheepshead as characteristic of the upper water layers; red snapper 

 and large groupers (Epinephelus niqritus , £,_ ita-jara) were described 

 as predominantly bottom fish that spent some of their time in the 

 mid-water layers; and restricted to the bottom were speckled seatrout 

 ( Cvnoscion nebulosus) , sand seatrout (Cvnoscion arenarjus) , and 

 flounders ( Paralichthvs spp.). 



Sessile epifauna on petroleum platforms investigated offshore of 

 Galveston in the brown shrimp grounds (Gallaway et al. 1980) differed 

 greatly from that at similar depths on platforms investigated offshore 

 of Louisiana. The major difference was that the large Mediterranean 

 barnacle ( Balanus tintinnabulum) was the perennial dominant. This 



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