41 



The filters can be used for concentrating and then culturing marine bac- 

 teria. The bacteria retained on the upper surface of the thin membrane can uti- 

 lize a nutrient which diffuses through the pores if it is brought into wetting con- 

 tact with the opposite side of the film. For culturing bacteria, a blotter the 

 size of a filter membrane can be saturated with a basic culture medium, placed 

 under the membrane in a petri dish and then inverted over a moist towel to pre- 

 vent dehydration and contamination. This use of the membranes has proven 

 very satisfactory in assessing the abundance of bacteria at various levels in 

 oceanic waters. 



Several features of the membranes make them peculiarly useful in as- 

 sessing phytoplankton abundance. The organisms can be quantitatively separat- 

 ed from the water, and then studied without removal from the membrane. Dr. 

 Goldberg of Scripps has developed techniques for staining the specimens on the 

 membrane, then clearing both membrane and organisms so that they may be ex- 

 amined directly on the filter membranes. He uses a membrane that retains all 

 particles greater than approximately 0.5 u (Type HA, available from the Lovell 

 Chemical Company, Watertown, Massachusetts). The membrane are ruled into 

 squares, which facilitates the estimation of the numbers of organisms present. 



Carbon- 14 - In studying productivity, more is needed than the static picture 

 obtained from standing crop estimates. The production of organic matter by a 

 given standing crop has usually been investigated by the increase in oxygen of a 

 collected sample of water. Recently, E.S. Nielsen (1951), has reported on a 

 technique used during the recent cruise of the GALATHEA, whereby the rate of 

 productivity is estimated from the fixation of radioactive tracer carbon-14. This 

 new technique appears to be very nnuch more satisfactory than the older method 

 for determining photo-synthetic fixation in water where the planktonic popula- 

 tions are low. Of course, a Geiger counter is necessary for assaying radio- 

 metrically the fixation of carbon-14. 



This is but one use of a radioactive tracer compound in biological re- 

 search. Radioactive tracers are being used in so many ways already, and of- 

 fer such potentialities for further advances, that this is certainly one of the 

 most promising fields in research. 



NEW METHODS OF SAMPLING THE NEKTON 



Midwater trawl - The most persevering collectors of the larger marine organ- 

 isms are fishernnen and sportsmen. Biologists, particularly fishery biologists, 

 are quick to take advantage of the collecting skill of cominnercial fishermen for 

 obtaining material needed in many of their research problems. They are also 

 likely to adopt the collecting gear and methods of the fishermen, as well. 

 Hence, until recently, the gear mostly ennployed in collecting bathpelagic spec- 

 ies at mid-depths was the otter trawl, a widely used fishing trawl. However, 

 the otter trawl in its role as a midwater trawl is not particularly satisfactory, 

 and the need has long been felt for efficient collecting devices specifically de- 

 signed to sample the bathypelagic fauna. There is little need to point out that 

 the fish and other animals that inhabit the mid-depths of the ocean are very im- 

 perfectly known. 



The Isaacs-Kidd (1951) midwater trawl, developed at Scripps, breaks 

 away from traditional trawl design. The heart of the new trawl is a wide, V- 

 shaped, rigid diving vane that has sufficient depressing force to get the net down 

 to considerable depths (the new trawl has been successfully tested to depths of 

 approximately IZ.OOO feet), and sufficient stability to maintain the net at a pre- 

 determined depth at comparatively high ship speeds (up to about six knots). 



