Fish are fond of gardening too

Damselfish maintain algae gardens and they weed, harvest and defend them, a new study reveals.

The research, to be published in the journal BMC Evolutionary Biology, also found that this arrangement benefits both damselfish and the algae.

According to lead author Hiroki Hata, a researcher in the Graduate School of Science and Engineering at Ehime University, damselfishes defended territories where certain algae grew by chasing off sea urchins and other fish.

"Additionally, an intensive farmer, Stegastes nigricans does weeding on less digestible algae, and it results in a monoculture of a specific algal species," Discovery News quoted Hata, as saying.

Hata and colleagues Katsutoshi Watanabe and Makoto Kato watched with amazement as the damselfish picked up this unwanted algae and dumped it outside of their farm-like gardens.

The researchers also conducted an experiment to see how the fish-preferred algae would grow without the arduous maintenance.

They found that the "weeds" would quickly overcome the other algae.

For the study, the scientists surveyed 320 territories of 18 damselfish species from coral reefs in Egypt, Kenya, Mauritius, the Maldives, Thailand, Borneo, the Okinawa Islands and the Great Barrier Reef.

Although the algae garden crop shifted in the West Indian Ocean, "the intensive farming by damselfish was seen throughout this geographic range," said Hata.

He explained that damselfishes can only eat certain types of algae like the red Polysiphonia, because damselfishes do not have organs and digestive enzymes that would allow them to stomach more fibrous algal species - the "weeds."

These fish gardeners enjoy their harvests, however, pulling up and ingesting the red algae with such gusto that some marine turf is still attached.

Hata said: "The (damselfish) stomach is filled with the algae but we think... animals harbored by the turf are also important food resources."

Fish also compete for land that's suitable for their algae plots.

Some damselfishes grow a mixture of algae crops. "Others maintain small monocultures with higher yield per unit area," said Hata.

The damselfish/algae relationship, "cultivation mutualism," is not usually seen in marine habitats.

Gavin Maneveldt and Derek Keats, botanists at the University of the Western Cape, previously discovered that a certain species of limpet, Patella cochlear, gardens algae along the South and southern West coasts of South Africa.