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Fig. 1. Migrating horseshoe crabs
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Each year during the late Spring and early Summer, horseshoe crabs ( Males patrol the water a few meters off the beach in search of the arriving females. Females of this species are generally the larger of the two sexes and approach the beach perpendicularly and the males use these traits to select a possible mate. When a male sights a relatively large animal approaching the beach, he maneuvers behind it and graps the back of its shell with specially modified walking legs. If the animal does not proceed onto the beach within a short time, the male will release its grasp (it may have grasped another male) and continue searching. If, however, the animal continues onto the beach, the two have begun mating ritual (Fig 2). The two connected animals then ascend the beach to near the coming high water mark. The female burrows forward and down into the sand using the from edge of her shell as a plow. When she is nearly covered with sand she deposits her eggs (Fig. 3).Tens of thousand of the small round green eggs (1.6-1.9mm) are deposited at once (Fig 4). When she has finished, she pushes forward and out of the sand dragging the still-attached male across the pile of eggs where he deposits his sperm to fertilize them. Many animals attempt to deposit their eggs at a point too low on the beach and are already being covered by waves when the tide is not yet at its highest point (Fig 5). The eggs from these nests are quickly washed from the sand and are scattered across the sand where thousands of migrating shore birds await them (Fig 6). The successful mating pair, after burying its eggs, returns to the sea leaving only its trail in the sand behind (Fig 7). You can click on any of the images for the full-screen picture |
Fig. 2. A mating pair
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