Spatial and Temporal Characteristics of Entrainment and Transport of Horseshoe Crab (Limulus polyphemus) Eggs in the Swash Zone of Estuarine Beaches

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The location and timing of entrainment, dispersal and deposition of eggs of fish and invertebrates have important implications for the feeding behavior and life cycles of many organisms. A key example is found in the significance of horseshoe crab eggs as a nutritional source for western hemisphere shorebirds that migrate thousands of kilometers from South America to the Arctic. This project will examine the role of swash (wave uprush and backwash) processes in mediating the relationship between horseshoe crabs and migratory shorebirds that are both under stress due to horseshoe crab harvesting and alteration of estuarine beach habitat. These stresses place increased importance on understanding the physical processes that maintain the link between horseshoe crabs and shorebirds. The mechanics of egg transport in the swash are not known, and existing models of sediment transport are designed for beaches in exposed ocean environments, not in estuaries. This study will identify key processes in the swash that explain sediment and egg entrainment and transport and test the applicability of swash transport models using field data from two sites in Delaware Bay, New Jersey. Data will be gathered on: 1) flow velocity, depth, width and duration of the swash, 2) entrainment of sediment and eggs using tracer injected in the foreshore in locations where exhumation and transport is due to both the swash and breakers and swash alone, and 3) amount of sediment and eggs transported in the swash using total load sediment traps. Statistically significant relationships between swash parameters and total load for sediment and eggs will be determined, and data on cross-shore flow velocities and sediment load will be used to test and calibrate a transport model.The results of this study will fill the gap in our understanding of swash processes on estuarine beaches in high micro-tidal environments. The swash zone is where the highest rates of transport occur in response to storms on these beaches and study results will provide better a better process explanation for cycles of erosion and accretion. As more sandy shores in estuaries are artificially nourished to provide protection to human settlements, there is an increasing need for beach nourishment design criteria that enhance biological productivity and ecosystem function in addition to the traditional purposes of providing shore protection and recreation space. Population fitness of migratory bird populations and models of potential endangerment based on nutritional sources will be enhanced from increased knowledge of egg transport in the swash zone. The project also provides an intensive field and laboratory experience for two undergraduate students who will have the opportunity to work on a field experiment with faculty from both physical geography and biology and thus have a unique learning experience that will integrate these two fields of knowledge to the study of a critical resource problem.