For many coral reef fish, life in the sea begins by drifting in the vast oceans as larvae, till they find a suitable place to settle down. Some find their way back to where their journey began. For others, welcoming homes with high chances of survival are hundreds of kilometres away from their place of birth. What is intriguing is how these larvae, who do not have maps to guide them, find their way around. In a study conducted in Papua New Guinea and published in 2008, authors Danielle Dixson and colleagues found that clown-fish use the smell of leaves and anemones to find suitable homes.

Clownfish usually live in coral reefs close to rainforest-inhabited islands. Dixson and colleagues decided to find out whether odours of the islands and their surroundings might serve as cues for the clownfish. They chose anemones- the mutualistic partners of clownfish, and rainforest leaves from the island as potential cues. They put young clownfish in the middle of an experimental chamber which had plain sea water on one side and sea water treated with the scent of either anemones or rainforest leaves, on the other. The treated sea water had been allowed to stand with anemones or rainforest leaves before they were removed, so that it was their smell that the fish would respond to. Spending a large chunk of time on one side of the chamber indicated that the clownfish preferred the water on that side.

The clownfish’s choices were clear: it preferred water laced with the smell of sea anemones and rainforest leaves. Given that leaves are likely to float fairly large distances away from the reef, clownfish larvae might be using use their smell to orient towards islands; once they get close they might be using the smell of anemones to home in. More importantly, these smells allow the clownfish to distinguish between reefs without islands and reefs near rainforest-inhabited islands, as it is only in the latter that they will find other clownfish and their mutualistic partners, the anemones.

I wonder, if the makers of Finding Nemo were aware of this, would the movie have turned out differently?

Further reading:

Dixson DL, GP Jones, PL Munday, S Planes, MS Pratchett, M Srinivasan and SR Thorrold. 2008. Coral reef fish smell leaves to find island homes. Proceedings of the Royal Society of London B: Biological Sciences, 275(1653), 2831-2839.