Nemo travel distance a signpost for reef management

Tracking wayward youth seems crucial for the preservation of coral reef fish populations, writes Tim Wallace.

A clownfish that has found its anemone.
Nick Hobgood

Baby clownfish might be closely guarded by their fathers as eggs, but once hatched their experience diverges dramatically from that of the coddled eponymous character of Finding Nemo.

In real life clownfish youngsters immediately stray – or to be precise float – far from the nest, dispersing over distances of 10 to 13 kilometres, according to the latest research, drifting on their own through open waters for nearly two weeks as transparent larvae before their colours develop and they swim to the shelter of a coral reef to settle down with an accommodating anemone.

Butterfly fish have an even more wayward youth, dispersing over distances of 43 to 64 kilometres,

Yet these impressive distances are, in fact, much less than previously assumed, note the international team of marine scientists who tracked the dispersal of thousands of clown and butterfly fish larvae on coral reefs off New Britain Island in Papua New Guinea.

This is something that has implications for human management strategies to conserve coral reef environments.

“Patches of reef habitat are frequently isolated from each other by deeper water that forms a barrier to adult movement,” the researchers write in Nature Ecology and Evolution, “and so larval dispersal is likely to be a critical process in the persistence of many reef fish populations over demographic and evolutionary timescales.”

The upshot is that marine conservation areas need to be designed, both in terms of the size of individual areas and the distances between those sanctuaries, to ensure reserve networks “maximize the probability of population persistence in the face of rapid environmental change”.

The research involved extensive field sampling at eight sites in Kempe Bay on the north coast of New Britain Island in 2009 and 2014, collecting thousands of fish and then using their DNA fingerprints to match juveniles with potential parents (and thus point of origin). An estimated 90% of

Clownfish juveniles settled within 43 km of their parents in 2009, compared with 31 km in 2011.

The research team included scientists from Australia’s Great Barrier Reef Marine Park Authority, James Cook University, University of Queensland and University of Melbourne, as well as the Woods Hole Oceanographic Institution in Massachusetts, the King Abdullah University of Science and Technology in Saudi Arabia and the Insular Research Centre and Environment Observatory in French Polynesia.

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