Maintenance of small horseshoe crabs
Horseshoe crabs are hard animals to keep if you have limited space. However, you can obtain small specimens to keep in a 20 gallon aquarium. If you are near a beach where the horseshoe crabs are mating, you can mark the area where a mating pair (the male clings to the female to fertilize her eggs as she digs a shallow nest on the beach) has come ashore. Come back to this area after several hours and you should be able to collect some fertilized eggs that you can take back to your classroom. Eggs can be placed into an aquarium or glass container that is gently aerated. Keep in mind that it will take 5-6 weeks for the eggs to hatch. Students can sample the eggs regularly to see the development of the larvae within the egg by using a microscope. Once hatched, the larvae should be transferred to an aquarium and fed brine shrimp larvae or rotifers. Generally, the larvae are hardy and can be viewed by the students readily with the naked eye. You should release those animals that you do not need for your observations.
For the aquarium, there should be at least 5 cm of substrate on the bottom as these animals will bury periodically, especially if the container is too cold or if it is time for them to molt. They are carnivores, feeding on worms and bivalves in the field. In the laboratory, they will accept cut fresh or frozen fish, shrimp or clam. Fresh oysters are readily consumed. They will also eat shrimp pellets, but do not generally do well on these pellets over a long period of time. If you are feeding them fresh foods, you must keep a watch on the nitrate level of the aquarium to make sure that it is not increasing rapidly.
It takes nearly 15 years for the animals to reach sexual maturity. After they reach this age, they typically no longer molt. Males are generally smaller than females.
Background Readings for horseshoe crab projects
Brockmann, HJ; Penn, D. 1992. Male mating tactics in the horseshoe crab, Limulus polyphemus. Animal Behaviour 44 (4): 653-665.
Chabot, CC; Kent, J; Watson, WH III. 2004. Circatidal and Circadian Rhythms of Locomotion in Limulus polyphemus.Biological Bulletin, Marine Biological Laboratory, Woods Hole 207 (1): 72-75.
James-Pirri, MJ; Tuxbury, K; Marino, S; Koch, S. 2005. Spawning Densities, Egg Densities, Size Structure, and Movement Patterns of Spawning Horseshoe Crabs, Limulus polyphemus, within Four Coastal Embaymnts on Cape Cod, Massachusetts. Estuaries 28 (2): 296-213.
Swan, B. 2005. Migrations of Adult Horseshoe Crabs, Limulus polyphemus, in the Middle Atlantic Bight: a 17-Year Tagging Study. Estuaries 28 (1): 28-40.
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