LOCOMOTOR AND LIGHT RESPONSES OF LARVAE OF THE HORSESHOE CRAB, LIMULUS POLYPHEMUS (L.).

The horseshoe crab Limulus polyphemus lays its eggs on sandy beaches at the level of the highest high tide in the northeastern Gulf of Mexico, buried approximately 18 cm below the surface. When they hatch, the larvae must move from the buried nest site into the marine environment. In the field, nests of larvae move to the sand surface and emerge at the spring high tide on the night of full moon. They may also be released by heavy surf associated with storms. No release occurs on the spring high tides associated with new moon. In the laboratory, larvae are seen to be nocturnally active, both under ambient and DD photoperiods. Activity peaks at times of full and new moons, and larvae are positively phototatic at all lunar phases except new moon. A model to account for observed field behavior in light of laboratory activity and light responses is presented.