A Hard Rock Oasis 



Under T h 



S e 



By Carlo B. Burgess 



There's something exciting under 

 the ocean floor off the coast of 

 southeastern North Carolina. It's 

 seeping from beneath beds of 

 limestone, phosphate and other 

 sedimentary rock 

 that make up the 

 continental shelf, 

 and it may 

 dissolve a perplex- 

 ing mystery 

 surrounding the 

 abundance of 

 marine life on 

 rocky reefs known 

 as hardbottoms. 



It's groundwa- 

 ter, says Sea Grant 

 researcher and 

 East Carolina 

 University 

 geologist Stan 

 Riggs, and it has 

 immersed scien- 

 tists into a new 

 understanding of 

 these underwater 

 ecosystems. 



For years, the 

 productivity of the 

 rocky seafloor outcroppings that 

 occur throughout Onslow Bay — the 

 coastal waters that extend from Cape 

 Lookout to Cape Fear's Frying Pan 

 Shoals — seemed a paradox. Some 

 of the rocky hardbottoms are veri- 

 table oases covered with algal 

 meadows, sponges, soft whip corals, 

 tropical fishes and territorial and 

 predatory animals. These habitats 

 provide shelter and food to sustain 



valuable commercial and recreational 

 fish such as grouper and snapper, 

 worth millions of dollars to the 

 state's economy. More than 300 

 species of fish and hundreds of 

 thousands of invertebrates call these 



Hardbottoms Project Team 



reefs home. Yet, the waters above the 

 shelf are often nutrient-poor; few 

 coastal rivers empty into Onslow 

 Bay, and most sediments are trapped 

 in the sounds behind barrier islands 

 and the nutrients used by estuarine 

 organisms. 



"Biologists and chemical ocean- 

 ographers for years have said there 

 are more organisms out there than we 

 can account for — there are not 



enough nutrients," says Riggs. 

 "They've always known that nutri- 

 ents came from upwellings below the 

 Gulf Stream or down the rivers and 

 out of the estuaries. But they analyze 

 the water and don't find enough 



nutrients. Some 

 researchers have 

 concluded that 

 there's got to be 

 another source of 

 nutrients, but 

 nobody knew 

 what that source 

 was." 



The answer 

 may lie in the 

 submarine 

 groundwater 

 discharges, which 

 appear to be 

 dissolving 

 nutrients from the 

 sedimentary rock 

 and releasing 

 ammonia and 

 phosphorus into 

 the water column. 



"What we've 

 got is an in-house 

 fertilizer system 

 that's helping to make Onslow Bay 

 very productive," says Riggs. 



Riggs and his colleagues will be 

 unveiling their groundwater theory to 

 the scientific community in papers to 

 be submitted for publication this 

 spring; other surprises are sure to 

 follow. After all, little is known about 

 the structure and function of hard- 

 bottom habitats, and until recently, 

 dollars for research were as scarce as 



2 MARC HI APRIL 1993 



