Mating American Horseshoe Crabs (Limulus polyphemus) in Delaware Bay, south New Jersey, U.S.A. Photograph by Asturnut (talk) - I (Asturnut (talk)) created this work entirely by myself., CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=27534108 Worldwide there are four living species of horseshoe crabs and all exhibit reproductive habits unique set of reproductive habits unlike other arthropods; they exhibit amplexus (see above - males attach to females) broadcast spawning, and do not brood the eggs. Mating horseshoe crabs primarily form pairs with the smaller males using specialized appendages to attach to the larger females. These pairs migrate to shallow water or onto beaches during high tides where females scoop out shallow nests in the sand before injecting tens of thousands of eggs into the sediment in clusters. Males release their free-swimming gametes and eggs are fertilized either within the water or the sediment. Horseshoe crab eggs in hand. Mispillion Harbor, Delaware. Credit: Gregory Breese/USFWS Public Domain Photograph downloaded from https://www.flickr.com/photos/usfwsnortheast/4035580656 The young horseshoe crabs develop 7 to 20 cm (≈ 3 – 8 in.) within the sediment over a period of three to four weeks and emerge during periods of high tides or heavy wave action. While the primary spawning season is The larvae’s lack of a “tail” or telson gives them the appearance of the extinct arthropod group by that name. The trilobite larvae are semi-plankton for several days before molting and assuming the role of a benthic juvenile horseshoe crabs. The juveniles inhabit shallow water in the vicinity of their birth beaches and feed on smaller benthic organisms and organic detritus. As they grow larger they move into deeper water and only return to shallower estuaries for spawning. Horseshoe crabs spawn primarily during the spring and early summer, although late season spawning can produce larvae that hatch and spend within the beach sediment. American horseshoe crabs are important members of the ecological communities of the Atlantic and Gulf coasts. Their eggs are eaten by invertebrates and fish and they are a key food source for migrating shorebirds stopping off in the Delaware Bay region during the spring. Newly hatched trilobites are also eaten in large numbers by both fish and invertebrates. Adults horseshoe crabs are reported prey of American alligators (Alligator mississippiensis) in Florida’s Indian River Lagoon and by loggerhead turtles (Caretta caretta) in lower Chesapeake Bay. The adults horseshoe crabs have a strong influence on benthic communities by both their feeding on various bivalve species and through the disturbance of sediment during feeding. The exoskeletons of adults also serve as habitat for organisms needing a hard surface in a soft sediment habitat. Epibionts gain both a firm and mobile attachment surface. Once a Spawn a Time: Horseshoe Crabs Mob the Beach
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