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The wars of the tidal worlds

For those about to sting another anemone, we salute you. A look into the secret, volatile life of tide pool inhabitants.

War is hell, both for humans and sea anemones, it turns out.

Anemones, those flowery looking animals that seem to gently in tide pools, actually live in a state of chronic warfare, according to researchers at the University of California at Davis and the University of Wollongong in Australia.

The research, which focused on tidal dwellers Anthopleura elegantissima, gives new insight into an animal that is largely thought of as peaceful. When the tide comes in, scouts on the front line of a colony patrol its borders for vacant or enemy territory to occupy, according to the study. When the scouts encounter the neighbors, larger, well-armed "warriors" then move to the front, swinging inflated tentacles that leave patches of stinging cells on an opponent. Polyps three or four rows away from the front will also reach over their comrades to engage in fights.

But it's not dulce et decorum est for everyone. Poorly armed "reproductive" anemones move away from the front to conduct the business of breeding.

Warrior anemones
Credit: Rick Grosberg/UC Davis
Warrior anemones reach over
from several rows behind
the front to attack animals
from a neighboring colony.

The fighting strategies differ from colony to colony, said Rick Grosberg at Davis and Wollongong's David Ayre, who studied the creatures. Differentiation into warriors seems to depend on a combination of signals from enemy stings and the genetics of the individual colony. Different colonies react differently to similar signals.

The colonies breed by cloning, so the individuals inside a colony will be genetically identical (not counting the inevitable mutations).

When the tide is out, the polyps are contracted and do not fight. When the tide comes in, the conflicts begin. The wars rage for about 20 to 30 minutes and then settle down, at least until the beginning of the next high tide. The study, according to Grosberg and Ayre, shows that complex organization can occur in animal species, even though the brainpower is almost completely absent.

Despite all the warfare, borders between colonies can remain stable for years.