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The WolcoHs: Curious About Grab Behavi< 



Just before the last molt of her 

 lifetime, the female blue crab releases a 

 chemical pheromone, something like a 

 crustacean's Chanel No. 5, to attract a 

 male crab to protect her. 



The ritual is predictable and fairly 

 well-understood. 



But not so clear is how the 

 male and sexually immature 

 female crabs prepare to molt — 

 how they choose the site to shuck 

 off their own hard shell and wait 

 naked until the new one hardens. 



Do they seek out shallow, 

 covered areas? And do they tend 

 to shed in a particular area, 

 perhaps raising the need to 

 preserve that habitat? 



These questions have been 

 researched recently by Tom and Donna 

 Wolcott, professors in the Marine, Earth 

 and Atmospheric Sciences Department 

 at N.C. State University. 



Their study, funded through the 

 UNC Sea Grant Program, compared the 

 molting behavior of blue crabs in the 

 Pamlico Sound to that of Chesapeake 

 Bay crabs 250 miles north. 



What they found were blue crabs 

 tailoring their behavior to their sur- 

 roundings. 



Although blue crabs are equally 

 vulnerable to predators in their freshly 

 molted state, they were observed to seek 

 out entirely different settings to shed. 



Male crabs in North Carolina, unlike 

 their Chesapeake Bay relatives, do not 

 slip into shallow tidal creeks to shed, 

 Tom Wolcott says. They instead hug the 

 edge of the estuary in water 3 to 7 feet 

 deep — about where the females molt. 



Security is not so much a concern 

 for sexually mature females, who are 

 protected by a male while they shed. 



"There isn't anything spectacularly 

 peculiar about the habitats they've 

 selected for molting (in North 



Carolina)," Wolcott says. 



And because of their choice, there 

 appears to be no shortage of molting 

 areas for North Carolina crabs, he says. 



But plot a map of molting sites in the 

 Chesapeake Bay, and an entirely 



different picture emerges. The males 

 travel far up the salty creeks that branch 

 off the sound, safe from predators. 

 Molting females were not studied there. 



Wolcott says he believes landscape is 

 responsible for the different behaviors. 



North Carolina tidal creeks, such as 

 Pantego Creek off the Pamlico Sound, 

 are wider and deeper than those off the 

 Chesapeake Bay. So they offer soft crabs 

 less cover and protection from predators 

 — eels, pufferfish and oyster toadfish — 

 that can follow them there. 



These predators are not as likely to 

 swim up the smaller tidal creeks such as 

 Muddy Creek off the Chesapeake Bay. 



The activity of individual crabs has 

 been difficult to track in the past. But 

 new technology has changed that. The 

 Wolcotts and graduate research assistant 

 Mike Shirley were able to monitor 40 to 

 50 crabs' travel patterns with tiny 

 transmitters strapped to their backs. 



From signals beamed off the 

 estuarine floor, they tracked where and 

 when the crabs molted, and what areas 

 they had passed over. 



The same technology is now being 



used to discover how Chesapeake Bay 

 crabs forage for food and what drives 

 them to cannibalize their own. 



"The main thrust of (this study) is 

 to understand the estuarine ecology, 

 because the blue crab is a dominant 

 player," Wolcott says. "But if 

 people can figure out from that 

 how many blue crabs there will be 

 next year, great." 



Studies have shown crabs are 

 sometimes their own worst 

 enemies, preying on the smallest 

 of their numbers. Prolonged 

 cannibalism can damage a future 

 supply of adult crabs. 



In early summer, the Wolcotts 

 will team up with students and 

 other researchers to monitor the 

 feeding habits, travel patterns and body 

 language of crabs penned at the edge of 

 the lower Chesapeake Bay. 



The transmitters will tell when the 

 crabs take a bite, what movements they 

 make and how they interact over food. 



A crab with pincers extended, for 

 instance, is in the "threat display" pose 

 and probably at odds with another crab. 



The pens will be stocked with 

 clams, a favorite food of the blue crab. 

 But one pen may have a smaller clam 

 patch and bigger crabs than the next to 

 show the consequences of food supply 

 on the survival of young blue crabs. 



The Wolcotts are working on the 

 project, funded by a three-year National 

 Science Foundation grant, with the 

 Smithsonian Environmental Research 

 Center and the Virginia Institute of 

 Marine Science. 



But Wolcott says the molting 

 research has shown that findings from 

 the Chesapeake Bay cannot be directly 

 applied to North Carolina's coast. 



The study will, however, produce 

 several hypotheses for future work. 



Jeannie Faris 



COASTWATCH 21 



