Coral reef fish larvae show no evidence for map-based navigation after physical displacement

Millions of minute, newly hatched coral reef fish larvae get carried into the open ocean by highly complex and variable currents. To survive, they must return to a suitable reef habitat within a species-specific time. Strikingly, previous studies have demonstrated that return to home reefs is much more frequent than would be expected by chance. It has been shown that magnetic and sun compass orientation can help cardinalfish maintain their innate swimming direction but do they also have a navigational map to cope with unexpected displacements? If displaced settling-stage cardinalfish Ostorhinchus doederleini use positional information during their pelagic dispersal, we would expect them to re-orient toward their home reef. However, after physical displacement by 180 km, the fish showed a swimming direction indistinguishable from original directions near the capture site. This suggests that the tested fish rely on innate or learned compass directions and show no evidence for map-based navigation.