OVERWINTERING BY TRILOBITE LARVAE OF THE HORSESHOE-CRAB LIMULUS-POLYPHEMUS ON A SANDY BEACH OF DELAWARE BAY (NEW-JERSEY, USA)

Trilobite larvae of the horseshoe crab Limulus polyphemus L. develop from eggs deposited within intertidal sediments. Most of these larvae emerge from sediments during the summer. We have found that a smaller component of the larval population on a Delaware Bay (New Jersey, USA) beach can delay emergence, and remain alive within the sediments until the following spring. Overwintering trilobites were distributed in a 3 m wide band in the mid-tide region, at sediment depths > 15 cm. 10(3) to 10(4) live trilobites m-2 have been found throughout winter and into early spring. This phenomenon may be ecologically significant, since emergence of overwintering larvae in early spring occurs dt a time when predation by birds is minimal. Sediment disturbance by winter storms may be the major factor limiting the survivorship of overwintering cohorts.