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Nemo’s Journey Really Is an Epic

Clownfish larvae can swim up to 400 km in search of a home, making them better able to cope with environmental change, according to new research published in PLOS ONE.

Clownfish spend their entire adult lives under the protection of their host anemone, but as babies they must wander the open ocean. “In the past we haven’t known where they go, but now we’ve been given a rare glimpse into how far they can swim, crossing large tracts of ocean to find new homes,” says co-author Dr Hugo Harrison of the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

“Knowing how far larvae disperse helps us understand how fish populations can adapt to environmental changes,” Harrison says. “The further they can swim, the better they can cope.”

An international team led by Dr Stephen Simpson of the University of Exeter travelled to southern Oman to collect samples of the only two known populations of the Omani clownfish, Amphiprion omanensis.

“There are only two coral reef systems along this coast, and they are separated by 400 km of ocean water,” Simpson says. “In order to persist, fish must be migrating between these two populations.”

The research team collected tissue samples from almost 400 clownfish and used DNA fingerprinting to identify fish that had migrated between the two populations.

“We can look at the signature of each fish and tell whether it belongs there or not,” Harrison says. It’s like finding an Englishman in New York. They stand out.”

The study found the fish were making regular migrations from one population to another, and in doing so were travelling across 400 km of open ocean, mostly from north to south. This corresponds with the dominant ocean currents in the region, which are driven by the winter monsoon.

Second-generation migrants were also present in both populations, which suggests that after completing their dispersal phase, migrants are settling into anemones and surviving long enough to reproduce.

Simpson says it’s the furthest they’ve been able to track the dispersal of any coral reef fish, and the findings show how connected the marine environment can be. “The findings change our understanding of marine populations. They’re not small and separate as we often assume. Rather, this research shows they’re often vast and inter-connected,” he says.