Orientation and Navigation
When hit by a wave, a human swimmer may easily lose direction and swim the wrong way. Besides the well-known biosonar used by wales and dolphins, marine organisms have developed many different strategies of orientation in open waters. The glass eel, for example, was found to use the position of the moon for orientation. Interestingly, the moon does not need to be visible to serve the eel as a reference point. This mechanism is not yet fully understood. Glass eels are also guided by the Earth’s magnetic field and by their sensitive olfactory system. Sea turtles also use several elaborate concepts of orientation, including visual cues, sensing the orbital movement of waves, and magnetic field detection. Adult Florida Loggerhead turtles can find their way back to the beaches where they hatched, even after spending years in the North Atlantic gyre. For many other species, especially their larvae, sound plays an important role in finding a suitable habitat. Marine soundscapes are largely of biological origin, and therefore carry a lot of information about a potential habitat. A 2016 study found that this type of orientation might be at risk, when results suggested that ocean acidification has negative effects on soundscape orientation.The gif was composed of about 80 images and captures the moment of disorientation when being hit by a crushing wave.
Sources: Cresci, Alessandro et al., “The relationship between the moon cycle and the orientation of glass eels (Anguilla anguilla) at sea”, Royal Society, (2019).
Lohmann, Kenneth and Catherine Lohmann, “Orientation and open-sea naviagation in sea turtles”, The Journal of Experimental Biology, vol. 199, (1996): 73-81.
Rossi, Tullio et al., “Lost at sea: ocean acidification undermines larval fish orientation via altered hearing and marine soundscape modification”, Royal Society, (2016).