Photo by Kttthy Hart 



Stan Riggs 



because there's a little layer of 

 water on top of this. It's just like a 

 soil there. And if we understand the 

 physical, biological and chemical 

 processes of that system, then we 

 ought to be able to manage that 

 system in the same way we manage 

 an agricultural field. And we ought 

 to be able to increase the produc- 

 tivity out there. 



"There's a lot that has to be done 

 before that resource is potentially 

 developed," says Riggs. "We must 

 first understand it." 



So far, what the researchers have 

 learned is that hardgrounds differ 

 greatly. Variables in their composi- 

 tion and shape affect the types of 

 communities of organisms they at- 

 tract. 



The first question Riggs asks is 

 what kind of substrate lies in cer- 

 tain areas of the shelf floor. The 

 type of rock will determine the 

 amount of organisms that will 

 grow there. The floor can be bar- 

 ren or can have whole reef devel- 

 opments on it with corals, algae, 

 fish and other marine hfe. 



Some sections of Onslow Bay are 

 made up of a fine mud or coarse, 

 mobile sand, says Snyder, a geolo- 

 gist at East Carolina University. In 



these areas, sand moves around 

 and keeps boring organisms like 

 clams and worms from attaching. 

 "The sediment waves come over 

 and bury them and kill them," says 

 Riggs. "The only kind of organisms 

 that can live on it are those that can 

 withstand the movement." 



Prolific development occurs on 

 the outcroppings that jut above the 

 loose sediments, says Snyder. With- 

 out the moving sands, larvae have 

 the chance to become established. 



Using side-scan sonar, seismic 

 data and bottom television, the 

 researchers and graduate student 

 Dave Mearns of the University of 

 South Florida located many kinds 

 of hardgrounds in Onslow Bay. 

 One group, which dates more than 

 10 million years, is small and 

 moundlike. They measure from a 

 few inches to a few feet above the 

 bottom and consist of solidified 

 muds cemented together with cal- 

 cium carbonate, or limestone. 

 These hardgrounds attract only a 

 few types of organisms. 



Younger hardgrounds — 1 or 2 

 milhon years old — offer the richest 

 substrate. Composed mostly of 

 limestone, these outcroppings rise 

 up to 10 meters above the shelf 

 floor and dot the bay. Many of 

 these mesas formed when rivers 

 cut across an exposed continental 

 shelf and created huge valleys. The 

 ledges, or scarps, produce big, nice 

 reefs, says Riggs. "These are the 

 ones fishermen are interested in; 

 the ones divers want to dive on." 

 And they're the main type he, 

 Snyder and Hine, a geologist at the 

 University of South Florida, want 

 to locate, study and map. 



One reason is that these hard- 

 grounds occur near sediments that 

 contain potential mineral resources 

 such as shell and quartz gravels, 

 gold and uranium. They also serve 

 as future sources of phosphate and 

 of sands for beach replenishment. 



These younger outcroppings win 

 their all-around popularity, how- 

 ever, for serving as attachment 

 sites for organisms that attract fish. 



The two major kinds of organisms 

 that secure themselves to the hard- 

 grounds have names like warriors 

 from the latest sci-fi flick — the 

 borers and the encrusters. 



Encrusters such as corals, sea 

 whips and barnacles tend to make 

 their home on the top of the hard- 

 ground's scarp. Generous amounts 

 of nutrients and sunlight invite 

 them to settle there. 



"The encruisters get the best real 

 estate, " says Snyder. "The borers 

 would be there if the encrusters 

 weren't." 



Instead, the borers move in on 

 the lower, vertical surfaces of the 

 scarp. Here, certain species of 

 clams, sponges and mechanical bor- 

 ers continuously chip away at the 

 limestone ledge, creating erosion. 

 This, combined with wave action, 

 shapes new surfaces where other 

 organisms can take hold. The more 

 marine life on a hardground, the 

 more fish it will attract. 



Although the maps that the re- 

 searchers will produce from these 

 studies aren't likely to excite those 

 looking for ready-made treasure, 

 they will pinpoint prime fishing 

 areas for anglers, and potential 

 sources for tomorrow's minerals. 



Photo hy Kalhy Hart 



Scott Snyder 



