in the substratum and the interstitial fauna which live between the sand par- 

 ticles of the porous sediment (the middle region) . 



1. Epif auna . 



The epif auna live on or above the sand surface. Considering species diver- 

 sity, this group represents the smallest number of animals associated with the 

 beaches, but it is the major group linking the marine and terrestrial species. 

 Reduced species diversity of epifauna on the high-energy beaches is probable 

 because: (a) shifting sand is inhospitable to many animals that need stable 

 conditions or protection; and (b) only the larger animals that are strong and 

 fast enough to keep up with the waves and currents are able to compete with 

 the dynamic conditions. Consequently, these larger forms establish the 

 highest level in the food chain in the surf and beach zones and are generally 

 relatively few. 



2. Endo fauna . 



The endofauna include those species whose biological activities are re- 

 stricted within the sand. Based on size, animals of this group are divided 

 into macrofauna (animals retained by a 0.5-millimeter mesh screen) and 

 meiofauna (animals that pass through a 0.5-millimeter mesh screen and are 

 retained by a 0.062-millimeter mesh screen). In areas of heavy wave activity, 

 the endofauna are generally limited to the robust and quickly moving species. 

 Therefore, on high-energy beaches, stationary or semisedentary forms are 

 generally scarce. The endofauna on most sandy beaches are dominated by crus- 

 taceans, mollusks (clams) and polychaetes (worms). 



3. Interstitial Fauna . 



This group includes the meiofauna and microfauna (animals smaller than 

 0.062 millimeter) that have the ability to live within the interstitial space 

 of sand grains. They include a greater diversity of species than the epifauna 

 and endofauna. These organisms are known to be highly sensitive to the 

 slightest changes in edaphic conditions, which correspond to differences in the 

 hydrodynamic forces. The dominant interstitial fauna found in the intertidal 

 environment are protozoans (ciliates and foraminif erans) , turbellarians (flat- 

 worms), nematode (roundworms), gastrotrichs, and harpacticoid copepods 

 (crustaceans) . The vertical distribution of many of these organisms in a sandy 

 beach varies with season of the year; a migration toward greater depths occurs 

 during the cooler seasons. Fenchel (1969) described the distribution of inter- 

 stitial fauna as related to oxidation-reduction properties of the sediment and 

 its mechanical composition. 



IV. ADAPTATION OF BEACH AND NEARSHORE FAUNA 



Animals that live in shifting sands on marine beaches are well adapted to 

 the unusual conditions of their existence and tolerate various environmental 

 factors in order to feed, burrow, and reproduce. Many sand dwellers endure 

 periods of low oxygen levels, and large animals that live deep in burrows have 

 the capability to create respiratory currents. These animals are adapted to 

 withstand the beating and pulling actions of waves and currents. Some are 

 skillful burrowers that dig in quickly when exposed by the waves. Many of the 

 beach animals withstand desiccation and do not die when left exposed on the 



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