The Lobster Tribes of Maine
by Sandra Dinsmore
Lobster fishermen are not the only people fascinated by the mystery of the lobster. A Dutch scientist named Jelle (pronounced Yella) Atema has been entranced with the species since coming to Woods Hole in 1970. The Woods Hole Oceanographic Institution invited him to study chemical communication in the sea, having been impressed with his post-doctoral work on chemical communication in catfish. While looking for a fish or crustacean with a big nose that could tell him something about underwater communication, Atema remembers looking at lobsters, about which he knew nothing, and thinking, They’re the right size, they walk slowly enough, there are many of them, and they're commercially important.
That first summer, Atema said, “I discovered that female lobsters put out an odor that's attractive to males.” He wrote up his discovery and published it in the important magazine, Nature. “It was a big discovery at the time,” he said of his work on lobster pheromones. It was also the beginning of Atema's love affair with lobster.
Lobsters have been giving Atema “fantastic information” ever since, information that has been far easier to obtain than that from fish because of the lobster’s receptor properties. Atema has been studying the process of sensing, including how odor molecules get into the nose.
He asked himself how a lobster uses the odor environment and found that, like humans, lobsters sniff to pick up smells, but in a different way. Lobster sniffing is called flicking. The scientist said, “If you look at any crustacean, you see that the small antennae (called the antennules) have very fast flicks: a down and then slower up and then down again.” What the lobster is doing, Atema said, is moving the water so he can smell the odor, just as humans can smell more strongly when movement in the air brings the smell closer.
After discovering how lobsters smell, the second step was finding how the lobster’s receptor cells work. Using ammonia as an odor example, Atema explained that the odor goes to a protein-binding site. The protein is the receptor and, using Pac-man to illustrate, he said, “Like Pac-man, the protein can grab things from the environment. When the Pac-man protein molecule grabs the ammonia molecule, it creates an electrical signal in the receptor cell, which sends that information to the brain. The brain now knows the scent of ammonia. It's a little bit more complicated than that,” Atema said, “but for now, it's good enough. Different Pac-man-type molecules let animals respond to different chemicals.”
How lobsters use the information for locating the source of an odor is a big part of Atema’s research. He has found that a lobster produces an odor “plume” by taking in water (the lobster's way of breathing) through gills on the sides of its carapace. A fan organ inside the gill chamber on both sides sucks water from between its legs into the gill chamber and blows it out through two small nozzles in front under the lobster's head. Atema proved this by placing food coloring underneath a lobster. It sucked the coloring up and blasted it out. “It’s such a powerful current,” Atema said, “that [the food coloring] goes seven body lengths in front of the animal.” In addition, lobsters can change the direction of the odor plume. A special fan organ can blow the plume sideways or backward.
The lobster also distributes the odor of its urine. Atema said, “We don’t know for sure, but have pretty good indirect evidence that that there is a gland near the urine bladder that produces glyco-proteins, and we have a suspicion that those actually serve a pheromone (social signal) function. “But,” he said, “This is one of the gaping holes in our knowledge. We don’t know the chemistry of these pheromones.”
What Atema does know is that chemical signals are carried from the urine into the gill current and out into the water. And that, he said, “is how lobsters, during fighting, learn the urine odor for individual recognition.” He and his team have found that a lobster that loses a fight with another lobster, when put in a tank with the winner the next day, will not fight it. The loser will fight with another lobster, but not with the one that beat it the day before. And the losing lobster will retain that olfactory [odor] memory for up to a week.
The team learned that odor stops the lobster from fighting because if researchers either block the release of urine or shave off specific sets of hairs that deal with olfaction (the sense of smell), the lobster cannot remember that particular odor.
Three years ago, Rhode Island Sea Grant, through a special Shell Disease Initiative, funded Dr. Atema’s small group of researchers and Boston University students to study shell disease. No one expected science to be able to cure the disease, but the funding gave Atema and his team an opportunity to address the fundamental questions of population structure because according to the rationale recognized by Sea Grant, Atema said, “At least you can learn about the spread of the disease. And if lobsters are living in segregated groups, then the spread of the disease from one to another is limited.”
The first experiment, in 2007-8, studied two groups of Rhode Island lobster: one in Narragansett Bay and one 20 miles away in Rhode Island Sound. They found the two populations were genetically and morphologically (structurally) separate and different. In addition, the females of each group preferred to associate with males from their own group. Tests, using the above method, showed that they did this by smell.
They did the same tests in Maine with lobster populations 20 miles apart on either side of Mount Desert Island (MDI), but in Maine the populations were not different within those 20 miles and the lobsters showed no preference.
In 2009, Atema’s team together with the Atlantic Offshore Lobstermen’s Association (AOLA) began studying offshore lobster to test anecdotal reports of links between shallow and deep-water populations. Thus far, initial results have not shown clear patterns.
Atema’s experiments on the populations of the Narragansett Bay and Rhode Island Sound lobsters showed a population barrier. If there is such a barrier, Atema said, “Then there is also a barrier for disease.” Therefore, he concluded, “If the Narragansett Bay lobsters get sick, then we don’t have to worry too much immediately about [lobsters in] Rhode Island Sound.” In terms of fisheries management, this may mean closing the fisheries in one area, but not necessarily everywhere. Through information gained in his lab, that initial shell disease study, Atema said, “Has now taken on a life of its own.” He added, “It would, of course, be interesting to continue this work with shallow and deep-water lobster populations in Maine where population may be more mixed.”
The team’s next step will be to find, “The mechanisms by which lobsters manage to make tribes.” These mechanisms, Atema said, “Are totally mysterious.” Fasci- nated by animal behavior and how animals perceive their environment, he said, “I would like to be a lobster to find out what I know. That is what drives me.”
Studying the mystery of the lobster will keep Jelle Atema busy for the rest of his life. “I know what we need to do,” he said. “It just needs to be done.”