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- Permanent Link:
- http://dpanther.fiu.edu/dpService/dpPurlService/purl/FI14090839/00001
Notes
- Scope and Content:
- Source: Horseshoe Crabs 1
Length of Segment: 00:01:15
Hi, I'm Dr. Jerry Jackson, out with the wild things. A walk on the beach in Florida may well give you a view of one of nature's relics, a creature that has remained essentially unchanged in appearance for more than 300 million years. An armored creature that can sometimes be a foot in diameter and have a long pointed tail that looks, well, dangerous, but it isn't. I'm speaking of the horseshoe crab. This brown to bronze creature has a hard outside covering that is smoothly curved in front in the shape of a horseshoe, and seemingly armed in back with spikes. It's a somewhat flattened animal whose legs are largely hidden beneath the flattened dome of its body. Horseshoe crabs move slowly on land and when seen, are usually in shallow water or right at the waters edge. Most often, what the beach-comber finds is the empty skin of one of these creatures. As the horseshoe crab grows, it must periodically shed its outgrown, rigid covering. It emerges as a soft-covered creature and quickly swells to its new size before its new skin hardens. During its lifetime, which scientists suspect can be as long as twenty years, a horseshoe crab undergoes sixteen molts, each time increasing its size by about 25%. ( English )
- Scope and Content:
- Source: Horseshoe Crabs 2
Length of Segment: 00:01:15
Hi, I'm Dr. Jerry Jackson, out with the wild things. Although the shed skin of the large bronze horseshoe crab is often found on Florida beaches, this animal lives its life in the shallow water nearby, coming to the water's edge only to breed. Most breeding is in spring during the high tides of the new and full moons. At these times, males and females find one another and the much smaller males literally latch on to their chosen mate. Males have special hook-like claws that grasp the female's shell. The female swims to the water's edge with her male or males in toe, digs a hole in the wet sand, and lays her eggs. The male then releases sperm over the eggs and the horseshoe crabs leave, allowing wave action to bury the pale-green eggs. While the eggs are only about one-sixteenth of an inch in diameter, each female will lay five to seven clusters of 2,000- 4,000 eggs each during each breeding cycle and as many as 90,000 eggs each year. As the fertilized eggs develop, the tiny larvae inside undergoes four molts within as little as two weeks before the eggs hatch and the young make their way into the muck at the bottom to feed and grow. ( English )
- Scope and Content:
- Source: Horseshoe Crabs 3
Length of Segment: 00:01:15
Hi, I'm Dr. Jerry Jackson, out with the wild things. The large bronzed somewhat tank-like horseshoe crab can be seen at almost anytime of year along Florida beaches. It's a creature of shallow waters and estuaries where it uses the front of its horseshoe-shaped hard shell to plow through the sand and muck at the bottom in search of food. The favorite foods of horseshoe crabs are small clams and worms and it burrows in search of them, feeding as it moves. Most of the horseshoe crab's feeding is done at night under cover of darkness, but they sometimes feed at any time of day. Horseshoe crabs have no jaws, but literally tear their prey into tiny pieces with leg-like appendages, passing the pieces back as the animal moves into a forest of bristles that trap the pieces and funnel them into the crab's mouth. Feeding requires movement of the legs, thus giving new meaning to the old phrase '”Eat and run”. Once inside the horseshoe crab's digestive system, muscle action and bits of sand in its gizzard further reduce the food to digestible size. Although horseshoe crabs will eat larval clams and oysters, their numbers are not sufficient to cause problems. ( English )
- Scope and Content:
- Source: Horseshoe Crabs 4
Length of Segment: 00:01:15
Hi, I'm Dr. Jerry Jackson, out with the wild things. The brown to bronze-colored horseshoe crab is rounded in front, giving rise to the name 'horseshoe' crab, but it's not a crab; indeed our horseshoe crab and three similar species found in Asia have no close living relatives. They are what we call ‘relics’: creatures left behind while all their close relatives have disappeared. Horseshoe crabs very similar in appearance to those living today swam in coastal waters more than 300 million years ago. The animals living today that are the closest, but still distant, relatives of the horseshoe crab are the spiders and their kin. The adaptations of the horseshoe crab to its environment have served it well. Its legs are protected, hidden underneath a somewhat upturned bowl-shaped body, the hard covering of its body protects it from above and its shape is such that it's difficult to flip over. That long sword-like tail on a horseshoe crab may look menacing, but the horseshoe crab is harmless to people. The tail serves as a rudder as it swims and is a convenient tool that allows the animal to flip itself right side up if the waves or a predator do happen to get it upturned. ( English )
- Scope and Content:
- Source: Horseshoe Crabs 5
Length of Segment: 00:01:15
Hi, I'm Dr. Jerry Jackson, out with the wild things. Around Chesapeake Bay, horseshoe crabs come ashore each spring in massive numbers and their eggs are now known to be essential food for a shore bird known as the red knot. The red knot is only a visitor to Chesapeake Bay, stopping there in route from its wintering area in South America to its nesting area on the Artic tundra. As horseshoe crab numbers have declined due to pollution and human exploitation, red knot members have also declined. In Florida, the eggs of horseshoe crabs are also likely an important food for migrant birds and a diversity of other creatures. Although a single female horseshoe crab may lay 90,000 eggs in a season, one estimate suggests that only ten of those will survive to produce an adult horseshoe crab. Nature’s seeming extravagance is matched by the rigors of the world in which the horseshoe crab lives. Horseshoe crabs play important roles in our own world, too. For example, an enzyme in horseshoe crab blood has proven very important to the detection of impurities in medicines that are injected into the human circulatory system. ( English )
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- Resource Identifier:
- FI00900172
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