j~ i eld notes 



The Chemistry of Soft-Shell Crabs 



The secret to success in the blue 

 crab business is knowing exactly when 

 the growing crustacean is going to shrug 

 off its old shell in favor of a roomier 

 one. In the vulnerable moments that the 

 crab stands naked without its calciferous 

 covering for protection, its wrinkled 

 skin distends and slowly begins to 

 harden into a new shell. 



So too inflates its value as a 

 dinnerplate delicacy. 



For several hours after 

 shedding, the body of the blue 

 crab is entirely soft, ranking it 

 with such savory seafood 

 dishes as lobster, salmon and 

 snow crab. 



And because the crab has 

 10 to 15 times more edible 

 meat in its softened state and a 

 higher value at the market, 

 fishermen work to catch blue 

 crabs that are on the verge of 

 molting. Skill at identifying 

 these premolt crabs is critical. 

 So is willingness to work hard 

 when the shedding begins; 

 shedders watch the crabs 

 struggle from their old shells 

 and pluck them from holding 

 tanks before their new cover- 

 ings begin to form. 



But a little scientific 

 understanding of the process 

 will go a long way toward 

 simplifying this tedious job of harvest- 

 ing soft-shell crabs, according to Sea 

 Grant researchers at the University of 

 North Carolina at Wilmington Center 

 for Marine Science Research. 



Specifically, researchers Robert 

 Roer, Richard Dillaman and Thomas 

 Shafer want to know what changes a 

 crab undergoes when it sheds and what 

 controls the subsequent hardening of its 

 new shell. They believe that glycopro- 

 teins in the crab's body at the time of 

 shedding play a key role in the harden- 

 ing process. 



Glycoproteins are proteins with 

 attached sugars that are found widely in 



the animal and plant kingdoms. They 

 are involved in such diverse processes 

 as immune system functions and forma- 

 tion of structural elements of bones and 

 teeth. 



The researchers believe that glyco- 

 proteins are in the cuticles that form 

 under the crab's shell and they later 

 determine when these uppermost layers 

 of the cuticle will harden. 



"The crabs make the outer two 

 layers of the new shell beneath the old 

 one when they're getting ready to molt," 

 Roer says. "They stay soft until they 

 molt and then expand with water to get 

 larger; only then do they turn on calcifi- 

 cation. The question is how the animals 

 control that switch. 



"Our research is leading us to 

 believe that they do that by altering the 

 glycoproteins that are there. They are 

 using enzymes to probably clip some 

 sugars on the glycoprotein and trigger 

 hardening." 



The two-year study is designed to 

 tell researchers whether natural inhibi- 



tors of these enzymes can keep the crabs 

 soft in a cost-effective manner. Roer and 

 his associates are analyzing the proteins 

 and glycoproteins in the shell and 

 comparing animals before and after the 

 new shell has begun to harden. But the 

 scientists have to work swiftly because 

 the transition usually occurs within two 

 hours of molting. 



If the researchers can better under- 

 stand and control the glycop- 

 roteins, they can prolong the 

 soft-shell stage by slowing 

 the formation of a new shell. 

 This will extend the amount 

 of time that crabs can spend 

 in transit to market while still 

 remaining soft and draw out 

 the time for harvesting them. 



Moreover, a better 

 understanding of the glyco- 

 proteins may be important in 

 preventing bacterial contami- 

 nation and death among blue 

 crabs. 



For North Carolina 

 crabbers, the findings may 

 mean a longer soft-shell 

 season and big business for 

 the multimillion-dollar 

 industry, which garners $1 to 

 $2 per soft-shell crab com- 

 pared to pennies for crusta- 

 ceans still shelled. 



The spring warming of 

 waters in the sounds and estuaries cues 

 the blue crabs to begin shedding their 

 winter attire for a new spring coat. After 

 a winter of dormancy, almost all blue 

 crabs molt this time of year during their 

 first growth spurt of the season. They'll 

 repeat the act 20 or more times before 

 reaching maturity. 



Watermen know the crabs' sched- 

 ule for exchanging their old clothing for 

 new. This will continue to be a neces- 

 sary skill in the soft-shell industry. But 

 the research from UNC- Wilmington 

 may buy crabbers some time in a sea- 

 sonal business where minutes and hours 

 count. Jeannie Faris 



22 MAY /JUNE 1994 



