The Ecology of Crabs
Photo courtesy of The Blue Crab Page
Dr. Thomas Wolcott is a professor in the Department
of Marine, Earth, and Atmospheric Sciences at North
Carolina State University in Raleigh. He studies the ecology
and behavior of crabs and develops biotelemetry instruments to track and
monitor these marine invertebrates in the field.
Dr. Thomas Wolcott studies reproduction in the blue crab with his wife Dr. Donna Wolcott, an associate professor in the Department of Marine, Earth, and Atmospheric Sciences. In their investigations, they use a biotelemetry device that can be strapped to the spines of blue crabs with copper wires. The electronic "gizmos" can transmit data pertaining to eating frequencies and locations and depth in the water. He can tell how often this predator takes a bite. A different transmitter also signals when the old exoskeleton splits. During this molting process the soft-shelled crab is left vulnerable. By tracking the crab, he can know what habitat the crab finally chooses for molting. As a result of their research the Wolcotts have learned a lot about
the behaviors of blue crabs. They eat at any time, but most frequently
at dawn and dusk. They usually hunt small prey, such as clams, in a classroom-sized
patch. At times they migrate to another large feeding area which may be
several miles away. Molting sites vary. Blue crabs in the Rhode
River off the Chesapeake Bay shed in the water along creek banks away from
their numerous predators. In the Pungo River off the Pamlico Sound in North
Carolina where the predators are fewer in number, crabs molt in a variety
of locations. The female blue crab can only mate after the last shedding
of her exoskeleton. Her entire lifetime output of eggs, laid in several
broods, will have to be fertilized with the sperm she obtains at that time.
(The eggs are fertilized as they are extruded from the body to make a "sponge"
that the female carries under her tail until the eggs hatch.) When
the blue crabs mate, the females receive the sperm and store it over the
winter. To determine how long the females can keep the sperm viable
optical microscopes are used to study crab eggs and sperm cells. Fluorescent
dyes are used to sort living and dead sperm.
Dr. Wolcott has constructed a biotelemetry device called a Larval Mimic to study the planktonic (drifting) larvae of blue crabs and other animals. Since the small larvae cannot be tracked directly, he designed the device using a small fire extinguisher cylinder for a pressure housing. It behaves like a living, migrating larva. The vertically positioned robot larva has a computer 'brain," a clock, a depth sensor, a light sensor, and a GPS receiver. It can respond to environmental variables such as temperature, speed in the water, depth, and light. Tested in the Bahamas in turbulent water, one Larval Mimic was programmed to maintain a depth at 1 meter, while another was programmed to remain at a depth of 5 meters. Both of the mimics were mixed up and down in the water, but by "swimming" they maintained different average depths. The one that remained shallower was moved along much faster by the tide; the deeper one was retarded as bottom drag slowed the water. Mimics programmed to sit on the bottom for part of a tidal cycle were able to keep their position even with currents of 1 or 2 knots, providing the bottom had some topography. Dr. Thomas Wolcott enjoys doing field studies. He feels that if you want to understand how an organism lives it is important to study it in its natural environment. A college zoology professor inspired him with the importance of field research. His professor, a sharp guy, asked a lot of questions and was very observant. He emphasized that it was very important to see the environment as the animal does and think in terms of the daily challenges faced by a particular organism to survive. He recalls his professor telling a story of observing a spider in a desert environment. The surface of the desert was very hot. The spider was perched at the tip of a blade of grass. When the professor accidentally grazed the grass blade with his pant leg, the spider fell to the ground, shriveled up and died. It was incredible to think that its refuge from the extreme heat was a perch a few inches off the desert floor. This organism had met its daily challenge of surviving the desert conditions by remaining minimally aloft from the heat.
Photo courtesy of the Smithsonian Marine Station at Fort Pierce It is important, Dr. Wolcott stresses, to ask the real life questions. What might cause the blue crab to become endangered? What is the niche of this animal in the real world? In the past, our society has treated the environment as a natural mine without regard to conserving its species. For instance, after years of harvesting oysters in the Chesapeake Bay, the population has decreased. Now we have become appreciative of the fact that they used to filter huge amounts of water every few days and kept our water clear. Dr. Wolcott came to North Carolina from California where the coastline has rocky pools filled with marine invertebrates. After studying the limpet to earn his doctorate, he wondered what organism he would study in North Carolina. He became interested in ghost crabs so assigned one of his students at North Carolina State University the task of finding out what happens to the oxygen supply in a North Carolina ghost crab's burrow when the tide came in and covered it with water. As it turned out, little seemed to be known about ghost crabs and Dr. Wolcott became even more interested. He noted that ghost crabs are built for speed to catch live prey whereas slower fiddle crabs eat organic particles from the sediment. The Park Service was asking, "What's the impact of Off-Road
Vehicle use on populations of beach-nesting birds?" Dr. Wolcott did
some investigation and told them, "That information already exists...but
we'll look at beach invertebrates, if you like!" They bought it.
"We censused crab holes, and conducted experiments. One was to sample
sand from truck tracks and adjacent undisturbed areas; none of the little
clams or mole crabs in the tracks was killed because the sand absorbed
the force. We also put crabs to sleep with CO2, put them down artificial
burrows, and drove trucks over. Ghost crabs deeper than the width
of a man's hand also are safe from tires. We also drove along the
beach at night on three-wheelers to see how many crabs would be killed
by vehicles driving on
Dr. Thomas Wolcott graduated magma cum laude with a B.A. in zoology from the University of California, Riverside. He studied for one year Goettingen, West Germany. He earned his Ph.D. in Zoology from the University of California, Berkeley. For his doctorate dissertation he studied the small limpet, which is like an uncoiled snail. Dr. Donna Wolcott graduated summa cum laude with a B.A. in Biology from the University of California, Riverside. She earned her Ph.D. in Zoology from the University of California, Berkeley. Dr. Wolcott tells students to work hard, study hard and attend a university with a challenging program. He noted that more advanced degrees allow you to achieve more freedom, but to earn one also involves more responsibility to accomplish as much as possible. When you earn a Ph.D. and become involved in research, the exploration is never done. Research projects involve much hard work and commitment. He emphasizes that it is important to take enriching liberal arts courses as well as the sciences. It is good to "get a well-rounded education." He enjoyed his opportunity to study abroad for a year in Goettingen, West Germany. Universities offer a buffet of courses and career paths. He advises, "Don't decide what you want to do too early." He thinks it is a good idea to take time to explore your interests and be exposed to a variety of ideas. For example his wife, Donna Wolcott started out as a math major but her first semester of biology "clicked" and she went on to pursue a doctorate in Zoology at the University of California in Berkeley. He emphasized that today there are many opportunities in science for women. "Take advantage of your choices." Today there are many opportunities for undergraduates to get involved in fieldwork and to get supervised research experience. The National Science Foundation pays students to do research as undergraduates. Through their research in marine biology, the Wolcotts and their son and daughter have had many opportunities to travel. They have been able to sail to Bermuda and fly to Panama and the Virgin Islands to carry out their research on crabs. During these extensive trips Dr. Donna Wolcott home schooled their children. His research has also taken him to international conferences in Australia, England, and Italy. Dr. Wolcott has many different interests and hobbies. He likes to sing as part of a madrigal group and plays piano and flute. He even combined his enjoyment of woodworking and music to build a harpsichord. He loves the water. In junior high school, a friend took him out sailing. He enjoyed the experience so much that he taught himself how to sail. Recently he bought a sailboat and was able to sail down the East Coast. As for the future he believes that there may be a trend to swing back to natural history We have taken a look at an animal's genes, its biochemistry but there is a need to understand the animal as a whole in addition to what goes on at the molecular or cellular level. If you enjoyed this article, you might also enjoy these related links:
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Dr. Wolcott with SciBlast Reporters
Ruby, Supriya, and Rosemary
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