As the month of May comes to the shores of Delaware Bay, birders, marine biologists, and all naturalists think of the same thing: Horseshoe Crabs. The Horseshoe Crab breeding season typically begins this month, and huge flocks of northbound shorebirds rely on Horseshoe Crab eggs to fuel their migratory flights. The populations of both have declined precipitously in recent years and the conservation of Horseshoe Crab populations has become a major issue for NJ Audubon and other conservation organizations. More horseshoe crabs breed along the shores of Delaware Bay than anywhere else in the world.
So the time seems right for revisiting a book that was released in early 2004. The American Horseshoe Crab, edited by Carl. N. Shuster, Jr., Robert B. Barlow, and H. Jane Brockmann, is the encyclopedia of all things horseshoe crab, and there’s no denying that this animal, Limulus polyphemus, is a fascinating creature. Its biology and natural history are of interest to an unusually wide variety of people. The lineage of this arthropod is ancient, with close relatives dating back at least 450 million years. Ecologically it is a keystone species, with shorebirds and many other species dependant on Horseshoe Crabs at one life stage or another. Extensive basic research into this animal has had wide-reaching implications, especially the study of vision; for their studies of the visual systems of Horseshoe Crabs, H. Keffer Hartline and George Wald received a share of the Nobel Prize in Medicine in 1967. Horseshoe Crabs have been harvested for fertilizer and bait, and blood extracted from these creatures is the basis for Limulus amebocyte lysate, an extremely valuable agent for testing pharmaceuticals for contamination.
Unregulated harvest of Horseshoe Crabs was permitted until just a few years ago. There is much controversy as to the efficacy of harvest limits that are now in place. “Horseshoe crabs are the most researched of all marine arthropods,” state the authors in the preface to this book. “Writing a treatise on Limulus was clearly a worthwhile goal; but everyone agreed that an even more useful pursuit, though perhaps a greater challenge, would be to write a book that would introduce horseshoe crabs to a wide audience.” While the ensuing book is more the former than the latter, it is an impressively detailed look into many aspects of Horseshoe Crab biology and a summary of much important research that has been conducted about its ecology, physiology, anatomy, evolutionary history, and the past and present uses of the species by humans.
For those with some science background, especially those with an interest in marine biology, this book is filled with treasures. There can’t be much about the lives of Horseshoe Crabs that isn’t included, from embryonic development to responses to pathogens. Two particular lines of research about Horseshoe Crabs have led to discoveries with value far beyond the realm of marine biology: the study of vision and the development of Limulus amebocyte lysate as a tool for monitoring endotoxin contamination. The authors document the long trail of research studies that led to these major discoveries; in both cases it’s a fascinating read. A final chapter on Horseshoe Crab conservation sounds a persuasive alarm for the need to reduce harvests and protect habitats if Limulus polyphemus is to continue in its role as an organism of great ecological significance through much of its range. The American Horseshoe Crab is a serious book about a serious topic. It’s seriously good.
Shuster, Jr., Carl N., Robert B. Barlow, and H. Jane Brockmann, Eds. The American Horseshoe Crab. Cambridge, Massachusetts, and London, England, Harvard University Press, 2004. 427 pages hardcover, $102.00. ISBN-13: 978-0-674-01159-5; ISBN-10: 0-674-011569-7.