Horseshoe Crab Aquaculture

Horseshoe Crab Breeding

Horseshoe crabs come ashore at night to breed starting in late Spring along the Northeastern coastline of the United States. This breeding ritual, usually under the light of a full moon, has been occurring for millenia. A female horseshoe crab , with a male firmly grasped to her, will ride the high tide onto the beach where she will lay up to 6000 eggs in one nest. After the female deposits her eggs in the nest, she continues to move forward and her male companion will then release sperm, fertilizing the eggs. When done, the horseshoe crabs leave their nest behind and return to the water. A female horseshoe crab may repeat this process numerous times, often laying in excess of 80,000 eggs in a season!

If horseshoe crabs lay so many eggs, why are the oceans not overrun with horseshoe crabs? The answer is pretty simple. The majority of horseshoe crab eggs and larvae are eaten - by migrating shorebirds and filter-feeding organisms, including many bivalves and fish. Juvenile horseshoe crabs are often eaten by larger wading shorebirds and other predators that live in the same coastal environments as they do. For every adult horseshoe crab that is alive, there are hundreds of thousands of eggs, larvae, and juveniles that never made it!

In 1998, Dr. Carmela Cuomo, a marine geochemical ecologist, accepted a dare from a colleague and began researching whether or not she could get horseshoe crabs to successfully mate and nest in captivity, something that had not been previously done except by accident. Ideally, if one cold successfully breed and raise horseshoe crabs in captivity, it might be possible to preserve and increase the wild populations of horseshoe crabs which are so important to ecosystem function and human health. It took Dr. Cuomo and her team a few years but she succeeded - and has been successfully breeding horseshoe crabs in captivity ever since.

The majority of the eggs and larvae produced by the crabs that Dr. Cuomo breeds are allowed to simply return to the wild. Some of the eggs and larvae, however, have been used in studies to determine the optimal diet and conditions necessary to rear horseshoe crabs to young adult stages. Over the years, Dr. Cuomo and her lab assistants, have been able to develop sustainable methods of horseshoe crab culture, allowing them to successfully rear healthy horseshoe crabs in captive settings to young adult size (4 years).

Dr. Cuomo is excited to partner with RIO and the University of Rhode Island GSO to bring horseshoe crab breeding to Rhode Island as part of the HCRI!

Rearing Horseshoe Crabs

Horseshoe crab eggs start out a grayish-green color but as the fertilized eggs mature, their color changes to a darker green. The horseshoe crab embryo undergoes four molts while inside the egg, case, its appearance becoming more horseshoe crab-like with each molt. As this process occurs, the embryo inside the egg case becomes more visible and can be frequently seen moving around within the egg case. A horseshoe crab that has undergone its 4th pre-hatch molt is ready to hatch and, in appearance, resembles and adult crab without a telson.

Horseshoe crab embryonic development is very dependent on temperature and other environmental conditions. On average, the majority of eggs hatch within two to four weeks of fertilization. The hatchling - called a Trilobite larva - because it slightly resembles a fossil trilobite.

A large number of newly hatched trilobite larvae leave the nest on the next high tide after hatching, usually in the evening during a full moon. They will remain in the plankton for ~ 7-10 days, until they undergo their first post-hatch molt and settle onto nearshore sandy habitats where they will graze on bacteria and other food in the sediments.

Horseshoe crabs will molt at least 6more times in their first year of life and a minimum of 2-3 times in their second year of life. Molting is dependent on a number of factors, both environmental and hormonal. Horseshoe crabs continue to molt, although not that frequently, until they reach sexual maturity which may take 7-10 years.

Dr. Cuomo and her team have reared horseshoe crabs successfully from egg to four years of age and have developed specific dietary regimes and conditions for the horseshoe crabs at each stage of their growth. In partnership with RIO, these diets and conditions will be used to rear eggs from horseshoe crabs bred at RIO’s facility at the University of Rhode Island’s Graduate School of Oceanogaphy to young adulthood.