A paper entitled "An experimental evalua- 

 tion of the C^"^ method for measuring phyto- 

 plankton production, using cultures of Ouna/ieZia 

 •primolecta Butcher" was completed to a first 

 draft and circulated for comment. 



Improved Methods of Measuring Chlorophyll A 



{R . IV. Holmes and R. J. Linn) 



Standing crop of chlorophyll a is determined 

 routinely at noon stations on STOR cruises, 

 by measuring optical densities of acetone 

 extracts of material filtered from sea water. 

 To facilitate the optical density nneasurements 

 a number of modifications have been made in 

 the Beckm.an Model DU spectrophotometer. 

 They expedite the detern^ination of chlorophyll 

 a and simplify the maintenance of the spectro- 

 photometer aboard ship. To hasten the meas- 

 urement of the optical density of the chlorophyll 

 extracts the conventional 10-cm. cell com- 

 partment cell holder has been replaced with 

 one which acconnnnodates four rather than two 

 1 0-cm. semimicro cells (volume about 5.2 ml.). 



Maintenance of the DU has been simplified 

 by the construction of new desiccant holders 

 which may be easily inspected and changed; 

 by the transference of the C batteries to a 

 box located next to the cell compartment 

 which also contains an external switch for 

 the adjustnnent of screen voltage and plugs 

 for the rapid determination of battery condi- 

 tion with a special test meter; and by the 

 location of the 6-volt storage battery chargers 

 adjacent to the transmittance dial on the DU. 

 The DU is covered with a wooden lid when not 

 in use and the heat generated by the chargers 

 helps to reduce difficulties caused by salt air. 



The need for a more sensitive method of 

 estimating chlorophyll a has been evident for 

 some time. A fluorimeter was constructed to 

 increase the sensitivity about eightfold over 

 the optical density method and this instrunnent 

 performed well m the laboratory. It failed to 

 operate on the first sea trial, possibly because 

 of moist conditions in the vessel's laboratory, 

 and awaits modification. 



A paper entitled "A modified Beckn-ian 

 Model DU spectrophotometer for seagoing 

 use" has been submitted for publication as a 

 Special Scientific Report- -Fisheries of the 

 Fish and Wildlife Service. 



Enumeration of Phytoplankton (R.w. Holmes) 



The use of the molecular filter in the 

 preparation of marine phytoplankton for mi- 

 croscopic examination and enumeration has 

 received attention, and certain modifications 

 in the method of Goldberg, Baker, and Fox 

 (1952) are recommended. 



The proposed method involves the micro- 

 filtration of a fixed and preserved sea-water 

 sample. The organisms are retained on the 

 upper surface of the filter where they are 

 washed with successively diluted volumes of 

 sea water, dehydrated with ethanol, stained 

 with alcoholic Fast Green, and finally rinsed 

 with absolute thanol. The filter disc is then 

 cleared with beechwood-creosote, xylene, or 

 anisole, and mounted directly on a microscope 

 slide with xylene or toluene balsam under a 

 thin cover glass. 



Many nannoplankton species may be readily 

 identified and counted on the filter disc. The 

 keeping properties of the preparations appear 

 to be excellent; no signs of deterioration are 

 visible in preparations over 5 years old. 



Using this technique half of the Expedition 

 SCOT fine net (32|j, mesh) samples have been 

 identified and counted. This work, when com- 

 pleted, will forin the basis of a floristic study 

 of the larger species of phytoplankton in the 

 area. 



Electron microscope technique for identifi- 

 cation of phytoplankton (especially coccolitho- 

 phorids) has been improved. 



A paper entitled "The preparation ofmarine 

 phytoplankton for microscopic examination 

 and enumeration on molecular filters" has 

 been completed. 



The work was supported in part (about 50 

 percent) by the California Marine Research 

 Connmittee. 



Standing Crop Measurements of Major 

 Zooplankton Components fff. c. Griffiths) 



The standard measurements of zooplankton 

 standing crop in eastern tropical Pacific in- 

 vestigations have been the displacement vol- 

 ume, per 1,000 m.-' of water strained, of 

 (a) the total catch and (b) the total catch minus 

 any organisms longer than 5 cm. The latter 

 volume has been used in quantitative studies 

 such as those reported below, e.g., in investi- 

 gating statistical relationships with standing 

 crops of other biota, but there was some 

 inconsistency in these results for which it 

 was thought the varying composition of the 

 zooplankton nnight be responsible. Therefore, 

 the problem of measuring the volumes of the 

 major components of plankton catches was 

 attacked. 



The displacement volume is obtained by 

 separating plankton from its preserving fluid 

 by filtration and placing the drained plankton 

 in a graduated cylinder with a known volume 

 of fluid. Another method of measuring the 

 volunne of the plankton is to nnake the original 



29 



