PLANKTONIC DISTRIBUTION 



Roland T. von Hentig 



Biologische Anstalt Helgoland 



Hamburg, West Germany 



ABSTRACT 



An attempt was made to gather information about the 

 distribution, stability, and diurnal periodicity of the 

 zooplankton population in relation to different sub- 

 strates and to the habitat. By means of a swimmer 

 operated net quantitative samples were taken at 

 various stations at 0900, 1300, and 2200 hours over a 

 ten day period. In spite of the relatively small 

 number of samples, some patterns emerged, populations 

 differed characteristically according to location. A 

 pilot experiment was conducted to test the varying 

 response of zooplankters to different wavelengths of 

 light. 



OBJECTIVE 



Qualitative sampling at specific locations in the vicinity of the 

 fringing reef of St. John island was expected to yield information 

 concerning the size and composition of the permanent plankton popu- 

 lation and conversely the degree of exchange of zooplankton near the 

 various substrates in the course of a 24 hour period, as well as over 

 the entire time of investigation. Possible effects of pollution 

 caused by the habitat were to be considered. 



Collections made at night in front of the habitat lights permitted 

 comparison of frequency distributions made at the regular collecting 

 stations at about the same time. Considering the importance of zoo- 

 plankton as being the main first- order consumers in the community, 

 investigations of vagility and distribution are basic to considera- 

 tions of the energetics of such a system. 



A study concerned with the preference of various plankters for dif- 

 ferent wavelengths of light was intended to test the possibility of 

 differential attraction of such organisms. 



EQUIPMENT 



The plankton net was designed to be operated by a swimmer. This 

 limited the size of the mouth; a diameter of 35.7 cm was chosen to 

 give a swept area of 0.1 m . The bias caused by avoidance reactions 

 was to be balanced against the bias inherent in the slow movements 



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