98 



PROBLEMS OF LAKE BIOLOGY 



tion and interchange of ions between beach 

 sands and lake. 



Fig. 4 shows some typical chemical condi- 

 tions in the capillary waters of a beach in 

 relation to the adjacent lake water. 



Fig. 4. Typical chemical conditions in capillary 

 water. Values to the left of em are for the lake- 

 water within 50 em of the water's edge. Cm'ves 

 beyond the 100 cm station are theoretical. 



The Organisms 



The psammolittoral Metazoa were col- 

 lected by means of brass tnbes 14 cm in 

 length, and having cross-sectional areas of 

 10 sq cm. At various distances from the 

 edge of the water the tubes were thrust 

 vertically into the sand. Then, with the 

 contained cores of sand, they were removed 

 and corked at both ends. In the laboratory 

 the corks were removed and each core of 

 sand was pushed out of the top of its tube 

 by means of a plunger inserted at the lower 

 end. In this way successive one-centimeter 

 slices of the damp sand could be removed 

 at the upper end. By a series of Avashing 

 and concentration processes, the organisms 

 were removed from these 10 cc sand samples 

 and preserved for later examination. 



BACTERIA 



During the past summer investigations 

 at the Trout Lake Limnological Laboratory 

 in northeastern Wisconsin have shown that 

 beaches contain unusually large numbers of 

 bacteria. These studies justify the follow- 

 ing generalizations : 



1. 80 to 90 per cent of the bacteria were 

 found in the top 3 cm of sand. 



2. Horizontally, they were most numer- 

 ous between 75 and 150 cm from the edge of 

 the water, being 10 to 20 times as abundant 

 there as in the rest of the beach. 



3. The numbers varied between 33,000 

 and 8,000,000 per cc of sand. 



4. In contrast to the situation in lake 

 waters, the sand was found to contain large 

 numbers of anaerobes, sometimes as many 

 as 19,000 per cc of sand. A common maxi- 

 mum was 5,000. 



PROTOZOA 



Like the bacteria, the Protozoa were most 

 abundant in the top 3' cm of sand between 

 75 and 150 cm from the edge of the water. 

 The numbers found there ranged from 300 

 to 50,000 per cc of sand. Frequently there 

 were found between 7,000 and 12,000 per cc. 

 Among the 30 genera found, some were 

 Sarcodina and Ciliata, but the small flagel- 

 lates, both green and colorless, were by far 

 the dominant group. Often great crops of 

 euglenoids, in sufficient numbers to give the 

 sand a distinct greenish color, were en- 

 countered in the beaches of soft-water lakes. 

 We believe that the Protozoa of beaches pre- 

 sent a wide opportunity for the protozo- 

 ologist from the points of view of physiol- 

 ogy and ecology as well as taxonomy. 



Vigorous wave action served to lower 

 bacterial and protozoan populations mark- 

 edly, but in a few days the numbers re- 

 turned to normal. 



TARDIGRADA 



A group which has been almost entirely 

 neglected in this country are the Tardi- 

 grada, or "water-bears." These organisms 

 form a large part of the psanunolittoral 

 population in the Wisconsin beaches. All 

 of the specimens which were closely ex- 

 amined were found to belong to the genus 

 Macrohiotus (Schultze), but only a small 

 percentage were examined. Their food 

 habits in beaches are unknown, but pre- 

 sumably they subsist on desmids and fila- 

 mentous algae and perhaps occasionally on 

 the body fluids of rotifers and nematodes. 

 From data gathered at 18 beaches it is evi- 

 dent that the tardigrade populations in 

 the sand cannot be ascribed to simple eco- 

 logical relationships. Table I shows the 



