of the food and also shelter for many species. Bacterial decomposition of stranded fishes 

 and algae takes place here, and provides most of the nutrients required for the production 

 cycle. Animal activity cycles can be well traced by observing the marks left in the loose 

 sand (Bider, 1968), providing an excellent way to study behavior and predator-prey 

 relationships. The substratum sand in this zone is usually finer than that in the zone of 

 uprush, but coarser than that of the dunes. 



The middle zone is characterized by annelid worms, the small coquina clam, Donax, the 

 mole crab Emerita, and various other crustaceans and mollusks. Most are found where the 

 spent waves wash the sand; they alternately burrow and are uncovered by wave action. 

 Most are excellent and rapid burrowers, an adaptation necessary to preserve their position 

 where food is carried to them by the water. A number of interstitial animals are also found 

 here, feeding among the sand grains on bacteria and unicellular algae. The zone contains an 

 admixture of herbivores, primary carnivores, and some high-order carnivores such as the 

 mole crab. Flora consists mainly of bacteria and unicellular algae; these play a large role in 

 beach production. Humm, in Pearse, et al., (1942), discusses bacterial roles at some length. 

 Habits and action of coquina and the mole crab have been thoroughly studied and 

 reported. The annelid worms in this zone, are mostly tube dwellers, and are partly or 

 wholly buried in the sands except when feeding. This zone is particularly harsh due to 

 environmental fluctuations, and often is oxygen-poor. Thus, here is found a paucity of 

 species, though large numbers of individuals, and species that are often curiously modified 

 to meet the particular environmental requirements. As in the upper zone, the animals of 

 this zone are not only agile and mobile, but are also capable of resisting long periods of 

 environmental stress. 



The lower zone, the zone under water all or most of the time, contains a relatively rich 

 and varied fauna. Burrowing Crustacea, such as the mud shrimps Callionassa or Eupogebia 

 are often found here as are the sand dollars, Mellita, and many snails. In the water column, 

 are small fish and crabs of the genera Callinectes, Arenius, and Ovalipes. A number of kinds 

 of tube-dwelling annelid worms are also present. Most of the worms and carnivores rely on 

 food washed in from the sea or off the beaches by waves. Though bacteria and unicellular 

 algae contribute some primary productivity, it is probable that most of the production 

 takes place in the sea, and the producers are swept in with the waves. 



This then is a broad picture of the normal fauna and flora of a typical sand beach, with 

 a nutrient and energy cycle not unlike that of submerged seabeds of nearshore waters, 

 except that it is dependent to a greater extent on adjoining areas for products of primary 

 production. The beach is also more difficult to study because the faunistic and topographic 

 borders are less well defined. 



b. Beach Stabilization. The beach is constantly changing. It is changed by waves, 

 tides, longshore currents, wind, and man's activities. There are, however, stabilizing factors. 

 The sum of all the interstitial (between-grain) fauna, such as the worms and crustaceans 

 may provide a cementing action that is an efficient factor in holding beach sands together. 



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