39.2 Thursday, Jan. 5 Magnetic orientation for larval release migration by the land crab Metasesarma aubryi in Kenting National Park, southern Taiwan HUANG, H.-D.*; WU, C.-H.; LIU, H. C.; National Museum of Natural Science, Taiwan; National Chung-Hsing University, Taiwan; Providence University, Taiwan email@example.com
The terrestrial sesarmid crab Metasesarma aubryi inhabit in burrows under maritime forest of Hengchun Peninsula, southern Taiwan. Ovigerous females migrate to surf for larval release during the last quarter of lunar cycle from May to November. Preliminary study showed that ovigerous crabs orient seawards when no visual and chemical cue presented. This study aims to test the hypothesis that ovigerous M. aubryi utilize geomagnetic signals for orientation in larval release migration. Animal collection and experiments were conducted in Sitzkou area, Kenting National Park. Crabs were tested with magnetic treatments in a circular arena; their responses and orientation in the arena were examined. In natural geomagnetic field, crabs oriented toward the seaward direction. When attached a magnet on crab carapace, or placed an isometric rubber magnetic plate under the arena, ovigerous females performed random movement. In artificial magnetic fields with designated directions, crabs oriented to the “seaward directions” corresponding to the new magnetic fields. We conclude that M. aubryi may equip biological compasses inside the body; geomagnetic signals may be employed as primary orientation cues for larval release migration.