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BIOLOGICAL INSTRUMENTS 

 Elbert H. Ahlstrom 



GENERAL 



Of prime importance in the study of plants and animals in the sea are 

 instruments designed for their collection. Whether we are interested in mere- 

 ly determining the kind of organisms present and their geographic and bathymet- 

 ric distribution, or in the more complex problems of population dynamics as re- 

 lated to the physical, chemical and biological factors of the environment, we 

 need gear that will provide representative samples of plants and animals. 



Obtaining adequate samples of marine organisms is not a simple prob- 

 lem. This is equally true whether we are interested in determining the distri- 

 bution and abundance of a single species, or in samipling a biological community 

 such as the phytoplankton or the organisms making up the deep scattering layer. 

 Even our best collecting gear can obtain only a smiall and often inadequate samp- 

 ling of a population whose distribution may be both very widespread and irregu- 

 lar. 



We are all aware of the diversity of plant and animal life in the sea: a 

 range in size from bacteria to whales; a diversity of habitat from the shoreline 

 to the benthic deeps, from the surface film through all levels of the oceanic pro- 

 vince; a range in motility from sessile forms attached to the bottom or organ- 

 isms passively carried by currents, to such powerful swimmers as whales and 

 sharks. Of necessity, there must be a great variety of biological instruments, 

 for locating, observing, collecting or culturing organisms so diverse in size, 

 habitat and motility. 



The biologists use a convenient classification of marine organisms based 

 upon their ecological distribution and habits. They divide the population of the 

 sea into three large groups - the benthos, nekton and plankton. Benthic organ- 

 isms are found on the bottom of the sea. The nekton is composed of actively 

 swimming animals such as fish, whales and squid that inhabit the pelagic zone. 

 The plankton include plant and aninmal organisnis, usually microscopic in size, 

 that drift more or less passively with the currents. The floating plants, princi- 

 pally composed of diatoms and dinoflagellates, are collectively known as phyto- 

 plankton. The animal plankton, known as zooplankton, include not only a multi- 

 tude of species that pass their whole life in a floating state, but also countless 

 larvae and eggs of the animals composing the benthos and nekton. Much of bio- 

 logical instrumentation is concerned with the sampling of organisms in the one 

 or the other of these large groups. 



Recent advances in instrumentation in the biological field are neither as 

 spectacular nor as. novel as in some of the other fields which will be treated in 



