Gardening Fish "Domesticate" Crops of Algae

Helen Scales
for National Geographic News
July 23, 2007

Damselfish can appear quite contrary to species that wander into their gardens of algae by aggressively chasing off larger fish and even nipping at human divers.

But for some damselfish species, protecting their "crop" is a matter of survival for both the fish and the algae, according to recent research.

The dusky farmerfish has developed a co-dependent relationship with a species of the red algae Polysiphonia.

Both creatures are found on coral reefs in the Ryukyu archipelago, a scattering of islands that stretches between southern Japan and Taiwan (map of Asia).

"Not only do the fish rely on the algae as a source of food, but the algae only survive well if they are farmed," said Hiroki Hata, a marine biologist from Kyoto University in Japan.

"We saw dusky farmerfish feeding exclusively inside their farms, which are dominated by a single type of algae that we called 'Polysiphonia species one,'" Hata said.

Scouring the reefs also revealed that Polysiphonia species one grows only inside the gardens of dusky farmerfish.

In total, Hata and colleagues identified four new Polysiphonia species that have adapted to rely on particular types of damselfish.

"Life inside the damselfish gardens is so good for the algae that they seem to have come to depend on being farmed," Hata said.

Guarding and Weeding

Damselfish are among the handful of animals—including humans, ants, and salt-marsh snails—that are known to cultivate beneficial crops.

Although they are relatively tiny—on average about 6 inches (15 centimeters) long—damselfish seem to tend their gardens with zeal.

Continued on Next Page >>




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