Distribution and Development of Limulus Egg Clusters on Intertidal Beaches in Delaware Bay



Accurate knowledge of where spawning Limulus females place their egg clusters in beaches is important for sampling egg cluster density, which in turn is important in studies of habitat use, monitoring Limulus egg production, determining potential shorebird forage, and for investigating the effects of beach erosion or replenishment. We examined Limulus egg cluster placement on seven western shore Delaware Bay beaches. Depth to center of recently laid clusters ranged from 3.5–25.5 cm, with an average depth to center of 15.5 ± 3.5 cm (n=533). Centers of 88.0% (469) of all clusters were within 20 cm of the undisturbed beach surface, and 98.1% of all clusters (523) extended 1 cm or more into the 20 cm horizon. Clusters were found only in the upper 85% of the foreshore, beginning at the spring tide high-water mark, even though beach widths varied (n = 6,132 clusters in 80 transects). Intact, recently laid clusters contained from 2,524 to 16,835 eggs, with an average size of 5,786 ± 2,834 eggs (n =26). Beach sediment temperatures in early May ranged from 13.7°C to 24.2°C (mean = 17.0° ± 3.0°C SD); in early June from 16.4 to 29.7°C (mean = 21.6° ± 3.3°C SD); and in early July from 22.4 to 30.4°C (mean = 26.8° ± 1.9°C SD). Under these conditions, the first trilobite larvae (<25 larvae per beach sampled) normally began to appear in our sediment samples during the first week in June, suggesting that about 35 days are required for development of the earliest eggs in a normal spring. Because egg clusters on all beaches were confined to 85% of the upper foreshore, and most clusters were within reach of a 20 cm deep sample, future studies to assess cluster densities should be designed to sample within that portion of a beach.


Tidal Flat Horseshoe Crab Cluster Distribution Beach Sediment Beach Width 
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We thank Katy O’Connell, manager of the St. Jones Center, Delaware National Estuarine Research Reserve, and previous manager Mark Del Vecchio, for making workspace available at the Center and for their attention to various research needs as they arose. Robert Scarborough, St. Jones Center Research Coordinator, worked to assure availability of special equipment. It is a pleasure to acknowledge the careful assistance of several Delaware Coastal Programs staff in this series of projects: T. Arndt, W. Conley, M. Fox, S. Love, M. Mensinger, and J. Reid. Seasonal employees H. Hudson, S. Midcap, D. Ostroff, and W. Ross provided additional support. We also thank David Smith, USGS, for providing critical insights during the course of these projects. All work on beaches, and sampling for egg clusters and eggs, was done under a series of annual permits from the Division of Fish and Wildlife, Delaware Department of Natural Resources and Environmental Control. This project was funded, in part, by a grant from the Delaware Coastal Programs with funding from the Office of Ocean and Coastal Resource Management, National Oceanic and Atmospheric Administration under award number NA05NOS4191169. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA, or of any of its subagencies.


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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.Delaware National Estuarine Research ReserveDoverUSA
  2. 2.Delaware Department of Natural Resources, Division of Soil and Water ConservationDoverUSA

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