species was estimated to occupy some 77$ of the original platform 

 substrate. Some individual barnacles attained basal diameters of 3 to t 

 cm and heights of 6 to 8 cm. They characteristically grew in clusters 

 forming a three-dimensional habitat, 10 to 15 cm thick. In contrast to 

 epifauna on platforms offshore of Louisiana, bivalves comprised a 

 relatively low proportion of the epifaunal biomass. 



The dominance of the sessile epifauna by the Mediterranean barnacle 

 was a major zoogeographic finding of the program. It has been reported 

 as an incidental species in the gulf for some 20 years, and remains so 

 on most platforms offshore of Louisiana. Observations indicate that 

 this species may be the dominant barnacle on offshore platforms from 

 Galveston to offshore of West Cameron, Louisiana, but it is seldom 

 abundant on structures farther east (Gallaway et al. 1980). 



The Mediterranean barnacle, a filter feeder on particulates and 

 plankton, spawned during late spring or early summer and in fall, 

 usually somewhat later than the other competing acorn barnacles which 

 were seasonally abundant. The combination of the rapid growth and large 

 size of the Mediterranean barnacle enabled it to settle on and overgrow 

 the smaller acorn barnacles characteristic of Louisiana platforms. 



The mat portion of the sessile epifauna on platforms offshore of 

 Galveston was characterized by a virtually inseparable interspersion of 

 macroalgae, sponges, bryozoans and hydroids. The macroalgae (mostly 

 green and red algae) represented a relatively small percentage of the 

 total standing crop biomass, and were more abundant in summer than in 

 winter. The faunal component of the mat, however, bloomed during winter 

 seasons (particularly the stalked bryozoan Bugula neritina , and the 

 hydroid, Tubularia crocea ) , but declined markedly over short periods 

 during spring resulting in the characteristic low levels of mat observed 

 for summer and fall. The octocoral Teles to , characteristic on some 

 Louisiana platforms in the brown shrimp grounds, was not represented on 

 the Texas platforms. 



Polychaetes and brittle stars dominated from a biomass standpoint 

 although the numerical dominants of the cryptic assemblage associated 

 with the biofouling community were represented by microcrustaceans, 

 blennies, stone crabs, and pistol shrimp. Cryptic species which were 

 dependent upon bushy hydroids and bryozoans as cover and/or food 

 (microcrustaceans and brittle stars) also bloomed in winter and declined 

 during warm seasons. In contrast, cryptic species dependent upon 

 barnacles for habitat, and which did not outgrow the cover provided 

 (e.g. pistol shrimp, polychaetes, and blennies), were characterized by 

 stable seasonal population levels. Other cryptic species were 

 apparently recruited to the barnacle substrate from the plankton, 

 flourished and grew until they exceeded a size allowing use of the 

 habitat as cover. They were then either harvested by predators or left 

 the area before reaching a reproducing size (e.g. stone crabs). 

 Principal epifaunal grazers and predators on microcryptic species were 



40 



