By Daun Daemon 



In the winter months, some clams 

 brought in from North Carolina waters 

 sport a different look: green gills. The 

 condition is nothing new — clams 

 here have probably occasionally worn 

 green for millennia. 



But this greening can cause 

 problems for N.C. seafood markets 

 because most folks shy away from 

 the shellfish, believing they are 

 inedible. Biologists have traditionally 

 explained that algae on the gills 

 caused the discoloration — not a 

 palatable thought. 



When Skip Kemp, N.C. Sea 

 Grant's regional seafood marketing 

 specialist, decided to investigate the 

 issue, he found that the French 

 consider green-gilled oysters a 

 delicacy and pay premium prices for 

 the nuttier tasting, oddly colored 

 creatures. 



Kemp learned from Jean Prou, a 

 coastal zone manager with the French 

 Institute for the Exploitation of the 

 Sea, that oyster farmers in France 

 raise the shellfish in claires, ponds 

 that encourage the diatom Haslea 

 ostrearia. This single-celled alga, 

 called "the blue diatom," synthesizes 

 the blue pigment marennine. 



"Haslea releases marennine into 

 the water, giving it a bluish tinge," 

 Kemp says. "Oysters pick up the 

 water-soluble pigment in their gills as 

 they filter the water for food. When 

 the blue combines with the animal's 

 natural yellow color, the gills turn 

 green." 



Like oysters, clams are filter 

 feeders, so the greening process is the 

 same for these shellfish. 



The French have grown the 

 oysters for centuries, and their 

 scientists are currently studying 

 Haslea in hopes of improving the 



Skip Kemp 



culturing process. According to Kemp, 

 no one really understands why the 

 Haslea blooms occur in colder months 

 or which factors contribute to them. 

 For example, the diatom will flourish 

 in one claire but not in another nearby 

 with the same conditions. 



To test whether North Carolina's 

 waters hosted the diatom, Kemp 

 collected samples from Topsail Sound 

 and the Core Sound area and sent them 

 to phycologists Robert Guillard of the 

 Bigelow Oceanographic Laboratory 

 and Mike Sullivan at Mississippi State 

 University. The two algae experts 

 confirmed the presence of Haslea, thus 

 verifying that — like the French 

 oysters — the green-gilled clams here 

 result from the diatom. 



Says Kemp, "I knew then that we 

 have the condition so sought after in 

 France: a bloom of the blue diatom." 



North Carolina's coastal waters, it 

 seems, are the stuff of French haute 

 cuisine. Adventurous seafood aficiona- 

 dos who wish to sample green-gilled 

 clams should take the same precaution 

 they would with other shellfish: Check 

 the source to make sure the product 

 came from certified waters. And 

 seafood lovers with immune system 

 deficiencies or stomach disorders 

 should eat the clams cooked, not raw. □ 



COASTWATCH 25 



