Loggerhead turtles and spiny lobsters ability to use the Earth’s magnetic field

Loggerhead turtles and spiny lobsters ability to use the Earth’s magnetic field

Varying marine vertebrates and invertebrates have gained the adaptation to use the Earth’s magnetic field to their advantage.  For both loggerhead turtles and spiny lobster they are able to use it for navigation purposes.  

For the loggerhead turtle they use the Earth’s magnetic field for directionality during their migration period.  Hatchlings begin on the Florida beaches and then make their way into the Atlantic.  Once they have begun their migration they swim to the North Atlantic gyre for food rich water, but in order to make it there they must use the Earth’s magnetic field.  Turtles are able to distinguish different fields depending on their location, which helps them stay away from northern waters in Great Britain as well as the currents of South Africa.  This was tested by introducing turtles to certain magnetic fields that mimic certain areas in the Atlantic Ocean, such as the magnetic field near Great Britain and the magnetic field around South Africa.  In both situations the turtles were able to orient themselves in such a way that they would swim in the opposite direction and back towards their migration path. 

           This use of navigation has also been seen in spiny lobsters.  They are nocturnal animals and travel shorter distances than the loggerhead turtle but still use the Earth’s magnetic field to find their way from a food source back to their original habitat.  This use of navigation is referred to as “true navigation” because they have the ability to travel out a given distance and then still be able to travel back to a determined area. 

            As far as the neurology behind the ability to sense magnetic fields, scientists are still doing research to better understand it.  Currently, the nudibranch mollusk has shown promise for researchers because of its simple circuitry.  They have found that there are three neurons that have been shown to react to the Earth’s magnetic field.  The first two are Pd5 and Pd6 which are excited by changes in direction to a magnetic field.  The third neuron is Pd7 which has been shown to be inhibited when introduced to a magnetic field. 

            The use of these three neurons is still fuzzy as to their abilities and responsibilities within brain of marine life, but what is known is that loggerhead turtles and spiny lobsters both have the ability to use their environment to the best of their abilities in order to navigate murky and sometimes life threatening water. 

Reference: http://icb.oxfordjournals.org/content/45/3/539.full