Lobsters Use Smell Test to ID Buddies, Bullies

John Roach
for National Geographic News
January 13, 2006
Jelle Atema says when he first encountered lobsters as a young marine
biologist in the 1970s, he was surprised at how peaceful the giant-clawed crustaceans behaved toward each other.

"I'd swim around and see lobsters meet each other, give a display, raise their claws. But there was not much fighting," the professor at Boston University's Marine Program in Woods Hole, Massachusetts, said.

Now he understands that those lobsters already knew each other. A few swishes of their small antennae were all they needed to pick up the other's scent and recall their earlier battle that established who was dominant.

Yes, lobsters' small antennae work like the human nose, only the crustaceans' sense of smell is keener. They recognize individuals purely by their odor, Atema says.

The antennae are packed with chemical sensors called aesthetascs. Odor molecules diffuse onto these sensors, which route a signal to a region of the brain where smells are processed and identified.

Atema and colleague Meg Johnson reported the finding on individual odor recognition in the July issue of the Journal of Experimental Biology.

"Being able to show lobsters can identify each other individually by odor is quite a feat because lobsters don't communicate the way we do," said Diane Cowan, president of the Lobster Conservancy in Friendship, Maine.

Cowan, who has collaborated with Atema on research in the past, adds that any finding on how lobsters navigate their environment is helpful to her organization's goal of sustaining a thriving lobster fishery.

"Without lobsters successfully finding each other to mate and reproduce there is no future for the lobster industry," she said.

Lobster Boxing

Recognizing individuals is important for lobsters because it allows the crustaceans to know where they fit in the pecking order, Atema says. The hierarchy establishes which lobster is the most dominant and thus can claim the most protected shelter in the neighborhood.

And when a female lobster comes sniffing around for a mate, she's on the prowl for the most dominant male.

Atema and his students made their discovery on the lobsters' use of smelling sensors by analyzing a series of boxing matches they staged in an aquarium tank.

The researchers placed eight lobsters of equal size that had never met before in the tank and watched as they engaged in often bruising battles to establish dominance. An hour later, however, the lobsters were relatively calm and settling into their digs.

"It makes sense," Atema said. "They live ultimately in a small community where they are relatively local and meet the neighbors on a regular basis. Why waste time fighting with the neighbors?"

When the same lobsters were reintroduced after a days' separation, they only interacted long enough to catch a whiff of each other and recall who was the more dominant. "The loser says, Oh no, I know that guy, and goes away," Atema said.

But if the loser is introduced to a new lobster, he'll engage in a fresh battle. As well, familiar lobsters fought anew when their smelling sensors on the end of their small antennae were shaved off.

This indicates that lobsters need the structures to recognize each other, Atema and Johnson concluded in their paper.

Underwater Perception

Atema aims to ultimately explain how creatures such as lobsters use chemical signals to understand their underwater environment. "It's not something many people study," he said.

In addition to smelling sensors on their small antennae, lobsters have tiny hairs on their feet and the appendages around their mouths that give the crustaceans a sense of taste.

In other words, Atema says, they can grab a piece of food with the little claws on their feet, taste it, then bring it up to their mouth and taste it again.

The system of two sets of taste, which Atema says is fairly common in the underwater world, acts as a safeguard against eating spoiled food.

Cowan, of the Lobster Conservancy, says that as biologists discover how much lobsters rely on chemical sensors to interact with their environment, fishery managers are gaining a better understanding of how to maintain a healthy lobster industry.

For example, she says, many lobsters reside in the near-shore environment and thus are susceptible to human impacts along the shoreline, such as pollution.

"Many pollutants can mess up [lobsters'] sense of smell, which would be very detrimental, because they are using it to communicate and find each other and reproduce," she said.

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