Wednesday, July 8, 2015

Topotaxis: geomagnetically driven orientation and navigation above the ocean floor

The composed noun topotaxis is built from the Greek words topos, meaning place, and taxis, meaning order or responsive movement. The word topotaxis refers to the movement of an animal  from place to place (migration) in response to geographical features the animal is able to sense. The term was coined by the marine biologist and sensory physiologist A. Peter Klimley, who wants to find out if sharks and rays can detect changes in local magnetic underwater topography and use these magnetic-field features as their guiding map—instead of the globally-caused, compass-oriented vector of  Earth's magnetic field, as typically hypothesized [1,2].

Islands, seamounts and subsurface ridges are examples of  geographic formations causing distinct local geomagnetic underwater-landmarks. By diving with the sharks and tagging & tracking them to follow their ocean floor navigation, Klimley explains how is idea of geomagnetic topotaxis has surfaced [3]: 

Our survey of the magnetic field surrounding El Bajo [an volcanic underwater mountain in Mexico's Sea of Cortez rising from the depths of the ocean floor to just 20 meters from the surface] revealed that the outbound and return path of the sharks we were studying coincided with these magnetic ridges and valleys, I hypothesized, therefore, that the magnetic variations in the ocean floor presented the sharks with the equivalent of a route map, and in a 1993 paper in Marine Biology [4], I coined the term topotaxis for an animal's orientation to these magnetic-topographic features.

Understanding navigation and resting behavior of sharks and other marine life—driven by topotactic guidance or other means—will help to design marine sanctuaries, which may protect dwindling shark populations and at the same time provide sites for educational and recreational shark ecotourism.

Keywords: magnetic topography, magnetoreception, travel pattern, migration, Baha California.

References and more to explore
[1] A. Peter Klimley, Director of the Biotelemetry Laboratory, University of California, Davis:
[2] A. Peter Klimley: Experimental Study of Geomagnetic Topotaxis With Elasmobranchs. Grantome:
[3] A. Peter Klimley: Shark Trails of the Eastern Pacific. American Scientist July-August 2015, 103 (4), pp. 276-287 [].
[4] A. P. Klimley: Highly directional swimming by scalloped hammerhead sharks, Sphyrna lewini, and subsurface irradiance, temperature, bathymetry, and geomagnetic field. Marine Biology 1993, 117, pp. 1-22 [].

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