MICROSCOPIC FAUNA OF SANDY BEACHES 



95 



1. During the course of an average sum- 

 mer day tlie temperature of tlie surface of 

 the damp sand may vary as much as 10° C ; 

 frequently the range is jirobably greater, 

 especially during other seasons of the year. 



2. The surface layers, where most of the 

 organisms are found, lieat up and eool off 

 more rapidly than the deeper layers. 



3. Near the edge of the water the sand 



the i)articnlate organic matter deposited on 

 shore by waves, wind, and rain. Determin- 

 ations of total organic matter in 18 differ- 

 ent beaches gave means for the individual 

 locations which ranged from 0.4 to 6.5 mg 

 per 10 ce of sand. Single samples some- 

 times contained as much as 80 mg. The 

 particulate organic material is of two types : 

 a finely divided organic debris present in 



V 



^#r-^*»& 



.>. .*; 



Fig. 1. Beacli on the north sliorc of Trout Lake, Vilas County, Wisconsin. 



temperature is governed largely by the lake 

 water temperature. 



4. Even under a hot sun a small amount 

 of water in the sand, 25 per cent saturation 

 for example, is sufficient to keep the tem- 

 perature low enough to be tolerated by the 

 organisms. Sand containing this amount 

 of moisture was never found to rise above 

 32° C. Of the rate of evaporation from the 

 surface of the sand very little is known. 



In addition to bacteria and algae, an im- 

 portant food source for the organisms is 



all beaches and a coarser material, less 

 generally distributed, composed of bits of 

 leaves, aquatic vegetation, and insect re- 

 mains. In the majority of cases the sand 

 within 100 cm of the lake averaged less 

 than 3 mg of particulate organic matter per 

 sample. This low organic content is due to 

 wave action which serves to keep the inner 

 beach washed comparatively clean. Of 

 course, the amount of particulate material 

 in any one beach may vary over a wide 

 range, but the data thus far gathered show 



