10 The Animal Ecology of the Cold Spring Sand Spit 



at a distance of ten meters or more, and moving hither and thither upon the surface. 

 We conclude then that the rising tide has caught up with certain of the little insects. 

 They rest upon the surface of the water by virtue of numberless fine hairs with which 

 they are covered, in which the air is entangled so that the bodies of the insects are 

 prevented from getting wet These are chiefly Anurida. 



A second species that occurs on the middle beach in great numbers during the 

 latter part of June is the horseshoe crab, Limulus polyphemus. This occurs here 

 because it lays its eggs in the sand of the beach, thereby reaping the advantage of the 

 superior oxygenation afforded by this situation over sand constantly submerged. The 

 eggs are laid in nests containing several hundred each. The eggs are oval and about 

 two millimeters in diameter. Each is enveloped in a tough membrane so that the sand 

 cannot injure it. The position of the nest may be detected by a slight depression in 

 the surface over it, and by the absence of pebbles. Not all the middle beach is 

 occupied by these nests, but only those regions where the sand is coarse enough to let 

 water through readily, but not so gravelly as to make hard digging. The east end of 

 the sand spit where the current flows swiftest affords the best conditions, and here the 

 nests are crowded together. In June also one finds many carcasses of female horse- 

 shoe crabs that have died in consequence of oviposition ; for, as in many other species, 

 oviposition is accompanied by a great mortality. Most of these carcasses are even- 

 tually thrown up to the high-tide line, and their fate will be considered in connection 

 with the fauna of the upper beach. 



Finally, mention should be made of the great annelid, Nereis limbata, that 

 occurs burrowing in the sand above low-water mark. This again is confined to the tip 

 of the sand spit where oxygenation is best carried on. 



III. THE FAUNA OF THE UPPER BEACH 



The upper beach I shall define as the zone including the high-tide line and above 

 to the storm bluff (Fig. 3 left, Fig. 5). This region is inhabited by a very few annual 

 plants ; its main characteristic, however, is the debris cast up by the sea (Fig. 5). All over 

 the world the upper beach is the graveyard of the shallow sea. In this graveyard two 

 sorts of remains are found: first, such as have been floating on the surface of the sea; 

 and, second, such as have fallen to or were lying on the bottom of the shallow sea. 

 The floating remains are carried in toward the shore by winds from the sea. If 

 the sea is quiet, they are merely dropped at the time the tide begins to fall ; conse- 

 quently they mark the high-water line (Fig. 5). If the sea is heavy, the floating or 

 drowned debris may be thrown against the upper part of the upper beach and even 

 against the storm bluff. This flotsam and jetsam consists, in the first place, of such 

 things as lumber and articles of wood and cork ; fruits and seeds ; bits of eel grass ; 

 stems of last year's marsh grass, Spartina; fronds of Ulva torn from the mud flats; 

 jelly fishes; drowned insects, especially heavy-bodied beetles, which have probably 

 been blown out to sea and been drowned or have fallen in during migration. The 



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