132 NIELSEN [CHAP. 7 



sediment. The mineral oil, which at present is utilized to such a high degree, in 

 all probability originates from the primary production in super-eutrophic, in- 

 harmonious marine, shallow areas during ancient geological periods. 



Of course planktonic algae also sink in the open ocean. However, the vertical 

 distribution of the algae, as shown in Table I, according to the reports from 

 the Meteor Expedition, clearly indicates that ordinarily nearly all of the algae 

 are eaten either within the photic zone or during the sinking through the 

 water-masses just below the photic zone. However, exceptions exist (see 

 Bernard, 1958). We may characterize the ocean in general as a harmonious bio- 

 type. Most of the organic matter from the primary production is utilized by 

 the next trophic level, the herbivores. Presumably the transfer again to the 

 subsequent trophic level, the carnivores, is harmonious too. 



With regard to the primary production, it is of extreme importance whether 

 the conditions for the production are stable or unstable. If the develop- 

 ment in the sea is to be harmonious it is necessary that the conditions for 

 growth are stable at least to some extent. Catastrophes like the red tide (see 

 page 188) occur presumably because the planktonic algae for some reason or 

 other "grow wild". The normal "brakes", ordinarily regulating the growth of 

 the algae, do not function. A normal "brake" of primary importance is grazing 

 by the zooplankton. Nathansohn (1910) first called attention to the importance 

 of zooplankton as the regulators of algal production. This early and out- 

 standing contribution to biological oceanography has received surprisingly 

 little attention from plankton scientists. 



A provisional lack of zooplankton regulating algal production may sometimes 

 be a perfectly normal phenomenon in the ocean. At higher latitudes, during a 

 quiet period in spring, the production of phytoplankton often starts in an 

 explosive way because a surface layer has been established due to heating by 

 the sun (North Atlantic). Only a few grazing zooplankton organisms will be 

 present provisionally. The ordinary brake for algal production is thus lacking. 

 After a while, when a stock of zooplankton has been produced, an equilibrium 

 will be established between zooplankton and phytoplankton. The grazing of 

 the zooplankton can usually keep the stock of phytoplankton at just the 

 appropriate level corresponding to the external growth conditions, such as the 

 supply of nutrient salts. The size of the production at a higher trophic level 

 cannot be considered to be merely a simple and uncomplicated product of 

 the size of the production at the lower level. Production at all trophic levels 

 must be considered as an interrelated whole. 



During recent years there has been some disagreement concerning the con- 

 cept of the size of the primary production in the big anticyclonic eddies in the 

 oceans, such as the Sargasso Sea. In contrast to earlier investigations on the 

 standing stock of plankton (see Lohmann, 1920 and Hentschel, 1933-1936), 

 Riley et at. (1949) considered these ocean areas to be in fact very productive. 

 This view was refuted by Steemann Nielsen (1952) by means of the measure- 

 ments with the carbon- 14 technique made during the Galathea Expedition 

 in such areas — not only in the Sargasso Sea. Sverdrup (1955) did the same 



