OCEANIC i HON 



Figure VIII— 4 — SOME PHYTOPLANKTON 







(Copyright 1965, Houghton Mitflin Company, Boston, Mass) 



The illustration shows drawings of some phytoplankton, enlarged about 400 times. 

 Diatoms: 



10. Chaetoceros decipiens 



11. Ditylium brightwellii 



12. Guinardia flaccida 



13. Eucampia zoodiacus 



14. Thalassiothrix longissima 

 Dinoflagellates: 



15. Peridinium depressum 



16. Ceratium tripos 



17. Ceratium furca 



1. 

 2. 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 



Asterionella japonica 

 Rhizosolenia stolterfothii 

 Rhizosolenia alata 

 Grammatophora serpentina 

 Coscinodiscus excentricus 

 Biddulphia regia 

 Biddulphia sinenis 

 Lauderia borealis 

 Skeletonema costatum 



as many oceanographic programs as 

 possible, with particular a\.l : , 

 paid to the usefulness of such data 

 as a basis for evaluating the relative 

 potentials of food production in dif- 

 ferent parts of the world ocean. 



Zooplankton 



Since most oceanic plants are ex- 

 tremely small, the typical forms of 

 marine herbivores are also very small 

 and planktonic, again making a sharp 

 contrast to grazing animals on land. 

 An enormous variety of small crus- 

 taceans and other invertebrates, 

 mixed with the young of larger an- 

 imals including fish, form a commu- 

 nity of herbivores and little carnivores 

 collectively called the zooplankton. 

 Although some species of larger an- 

 imals, such as bivalves, anchovies, 

 and sardines, also utilize phytoplank- 

 ton to varying degrees, the herbivores 

 of the zooplankton, particularly such 

 crustaceans as copepods and euphau- 

 sids, play an overwhelmingly im- 

 portant role in converting plant 

 material into animal material. The 

 size of planktonic herbivores in adult 

 stages ranges from less than one mil- 

 limeter to over five centimeters. They 

 have efficient filtering apparatus to 

 collect phytoplankton. Figure VIII— 5 

 illustrates some of the zooplankton. 



Potential Use by Man — Aside 

 from their ecological role as the 

 main grazers in the sea, plankton 

 animals give some promise of being 

 harvested directly by man. Before 

 going into the detail of this aspect, 

 we must explain why man should 

 want to take the trouble of harvest- 

 ing these little animals. As organic 

 matter is transferred from plants to 

 herbivores, from herbivores to first- 

 stage carnivores, and from first-stage 

 carnivores to those of higher stages, 

 there are large losses of energy or 

 materials from respiration and de- 

 composition. The food web in the 

 sea is so complex that we have no 

 simple methods of estimating an 

 average loss at each stage of transfer. 

 For the sake of simplified discus- 

 sions, the efficiency of transfer from 



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