Championing the Survival of a Living Fossil
About the Research

by Dr. Jennifer Mattei, Associate Professor of Biology
Sacred Heart University

Limulus polyphemus is a "living fossil" unique to the Atlantic Coast of North America. For over 350 million years horseshoe crabs have populated Earth's waters, yet in recent years its numbers have begun to decline throughout its range. Causes for decline include harvesting as bait for the fishing industry, collection for biomedical research and the pharmaceutical industry, and habitat degradation. The collection and sale of Limulus Amoebocyte Lysate (LAL) from the horseshoe crab's blood is used to test vaccines and other products for bacterial contamination, and has become a multi-million dollar industry.

Limulus has a unique ecological role in Long Island Sound (LIS) partially because of the critical importance of its eggs as a food source for migratory shorebird populations. Most of what is known about the ecology of the species is based upon studies conducted in the southern portions of its range.

The status of the LIS population is largely unknown but may be declining. Because the adult breeding population is harvested in large numbers, a management plan needs to be enacted. However, a solid management plan is based on population data, and long-term population data is nonexistent for the horseshoe crabs residing in LIS. Also, once a management plan is in place, a monitoring program must be continued to learn if conservation measures are helping the population to remain stable or increase.

My research sets out to examine breeding site fidelity, home range, sex ratio and general population health of horseshoe crabs in LIS. In other words, it is important to know which beaches are particularly important for horseshoe crab spawning if the states involved want to create a plan to protect the beaches to increase breeding success.

My long-term research goals include: estimating how many breeding adult horseshoe crabs reside in LIS, discovering if they utilize the same beach every year or if they range broadly, selecting different beaches on which to lay eggs. Because egg production is so costly (energetically), I am investigating if female horseshoe crabs spawn every year or if they skip some years.

These long-term, far-reaching goals cannot be completed by studying a sample population on a single beach. Therefore in 2000, I initiated a tagging program entitled "Project Limulus " at Milford Point, CT, that involved not only scientists but also teachers, students and concerned citizens. We quickly expanded the project with the help of Sacred Heart University undergraduate research assistants and environmental educators at the Connecticut Audubon Coastal Center. "Project Limulus" now includes collaborations with The Maritime Aquarium (Norwalk Harbor), The Sound School (New Haven Harbor), SoundWaters (Stamford Harbor) and The New York Aquarium (Coney Island).

The intent of this study is to tag and measure as many breeding horseshoe crabs as possible between mid-May and early July on the beaches of the LIS region. I have also sonar tagged 20 horseshoe crabs and have been following their movement patterns for the past two years with the assistance of the Northeast Fisheries Science Center, Milford Lab.

With support from the CTDEP Long Island Sound License Plate Program, the National Fish and Wildlife Foundation, Wildlife Trust and The Maritime Aquarium , "Project Limulus " workshops are held every spring to train science educators on how to involve their students in this community research project. The study area is vast, but with the help of volunteers, teachers and students monitoring beaches in Connecticut and New York, the project will simultaneously train future conservationists and provide data required for proper management and conservation of Limulus .

My goal for the students is to learn about the biology and ecology of horseshoe crabs, and to actually experience hands-on 'science.' My plan is for students to collect data, learn to analyze the data, understand how their data is part of a larger project, and most importantly, how their health and daily activities are connected to the LIS ecosystem. A tall order, I know, but I have worked with students from Harding High School (in Bridgeport, CT) who initially considered Limulus an ugly, disgusting creature. Gradually, their attitude changed to caring about them and volunteering to tag and collect data for a second year.

THE DATA

Initial results, from four years of tagging, show that the Limulus population of LIS ranges extensively throughout the Sound. The population has a skewed sex ratio with more males than females present on breeding beaches. Horseshoe crabs infrequently come back to the same beach to spawn in consecutive years. Less than 1% of the crabs tagged at Milford Pt. have returned to spawn again. However, 9% of the horseshoe crabs tagged return to breed on the same beach more than once in a season. Preliminary data from both the sonar and cinch tagging efforts show that the horseshoe crabs in Long Island Sound are capable of moving great distances over several years time. One individual was tagged in Brooklyn, NY, and recaptured 16 months later in Narragansett Bay, RI. However, 75% of the recaptures occur in the Milford area beaches from animals that were tagged on Milford Point.

Movement patterns of 4 tagged and recaptured horseshoe crabs in Long Island Sound          (Map from LISS website)

These results are preliminary; more information is needed. In the future, I plan to expand this project along the coasts of Connecticut and New York.