SiS 



NATURE 



[August 26, 1920 



agreement as to the cause thereof. Brandt first 

 attributed the poverty of the plankton in the tropics 

 to the destruction ot nitrates in the sea as a result 

 of the greater intensity of the metabolism of de- 

 nitrifying bacteria in the w-armer water; and various 

 writers since then have more or less agreed that 

 4:he presence of these denitrifying bacteria, by 

 keeping down to a minimum the nitrogen concentra- 

 tion in tropical waters, may account tor the relative 

 scarcity of the phyto-plankton, and, consequently, of 

 -the zoo-plankton, that has been observed. But Gran, 

 Nathansohn, Murray, Hjort, and others have shown 

 that such bacteria are rare or absent in the open 

 sea, that their action must be negligible, and that 

 Brandt's hypothesis is untenable. It seems clear, 

 moreover, that the plankton does not vary directly 

 with the temperature of the water. Furthermore, 

 Nathansohn has shown the influence of the vertical 

 circulation in the water upon the nourishment of the 

 phyto-plankton — by rising currents bringing up neces- 

 sary nutrient materials, and especially carbon dioxide, 

 from the bottom layers; and also possibly by convey- 

 ing the products of the drainage of tropical lands to 

 more polar seas so as to maintain the more abundant 

 life in the colder water. 



Putter's view is that the increased metabolism in 

 the warmer water causes all the available food 

 materials to be used up rapidly, and so puts a check 

 to the reproduction of the plankton. 



According to van't Hofl's law in chemistry, the 

 rate at which a reaction takes place is increased by 

 raising the temperature, and this probably holds good 

 for all biochemical phenomena, and therefore for the 

 metabolism of animals and plants in the sea. This 

 has been verified experimentally in some cases by 

 J. Loeb. The contrast between the plankton of Arctic 

 and Antarctic zones, consisting of large numbers of 

 small crustaceans belonging to comparatively few 

 species, and that of tropical waters, containing a great 

 many more species generally of smaller size and fewer 

 in number of individuals, is to be accounted for, 

 according to Sir John Murray and others, by the rate 

 of metabolism in the organisms. The assemblages 

 captured in cold polar waters are of different ages and 

 stages, young and adults of several generations oc- 

 curring together in profusion,* and it is supposed that 

 the adults "may be ten, twenty, or more years of 

 age." At the low temperature the action of putre- 

 factive bacteria and of enzymes is very slow or in 

 abeyance, and the vital actions of the Crustacea take 

 place more slowly and the individual lives are longer. 

 On the other hand, in the warmer waters of the 

 tropics the action of the bacteria is more rapid, meta- 

 bolism in general is more active, and the various 

 stages in the life-history are passed through more 

 rapidly, so that the smaller organisms of equatorial 

 seas probably live only for days or weeks in place of 

 years. 



This explanation may account also for the much 

 g^reater quantity of living organisms which has been 

 found so often on the sea-floor in polar waters. It 

 is a curious fact that the development of the polar 

 marine animals Is, in general, "direct" without 

 larval pelagic stages, the result being that the young 

 settle down on the floor of the ocean in the neigh- 

 bourhood of the parent forms, so that there come to 

 be enormous congregations of the same kind of animal 

 within a limited area, and the dredge will in a par- 

 ticular haul come up filled with hundreds, it may be, 

 of an Echinoderm, a Sponge, a Crustaoean, a 

 Brachiopod, or an Ascidian ; whereas in warmer seas 

 the young {lass through a pelagic stage and so become 



_8 Wiiether, however, the low temperature may not .also xatarjd reproduc- 

 tion is worthy of consideration. 



NO. 2652, VCfL. 105] 



more widely distributed over the floor ot tlie ocean. 

 The Challenger Expedition found in the Antarctic 

 certain Echinoderms, for example, which had young 

 in various stages of development attached to some 

 part of the body of the parents, whereas in temperate 

 or tropical regions the same class of animals set free 

 their eggs and the development proceeds in the open 

 water quite independently of, and it may be far distant 

 from, the parent. 



Another characteristic result of the difference in 

 temperature is that the secretion of carbonate of lime 

 in the form of shells and skeletons proceeds more 

 rapidly in warm than in cold water. The massive 

 shells of molluscs, the. vast deposits of carbonate of 

 lime formed by corals and by calcareous seaweeds, are 

 characteristic of the tropics ; whereas in polar seas, 

 while the animals may be large, they are for the most 

 part soft-bodied and destitute of calcareous secretions. 

 The calcareous pelagic Foraminifera are characteristic 

 of tropical and sub-tropical plankton, and few, if 

 any, are found in polar waters. Globigerina ooze, a 

 calcareous deposit, is abundant in equatorial seas, 

 while in the Antarctic the characteristic deposit is 

 siliceous Diatomaoeous ooze. 



The part played by bacteria in the metabolism of 

 the sea is very important and probably of wide- 

 reaching effect, but we still., know very little about it. 

 A most promising young Cambridge biologist, the 

 late Mr. G. Harold Drew, now unfortunately lost to 

 science, had already done notable work at Jamaica 

 and at Tortugas, Florida, on the effects produced by 

 a bacillus which is found in the surface waters of 

 these shallow tropical seas and in the mud at the 

 bottom ; and which denitrifies nitrates and nitrites, 

 giving off free nitrogen. He found that this Bacillus 

 calcis also caused the precipitation of soluble calcium 

 salts in the form of calcium carbonate ("drewite") 

 on a large scale in the warm shallow waters. Drew's 

 observations tend to show that the great calcareous 

 deposits of Florida and the Bahamas previously known 

 as "coral muds " are not, as was supposed by Murray 

 and others, derived from broken-up corals, shells, 

 nullipores, etc., but are minute particles of carbonate 

 of lime which have been precipitated by the action of 

 these bacteria.' 



The bearing of these observations upon the forma- 

 tion of oolitic limestones and the fine-grained un- 

 fossiliferous Lower Palaeozoic limestones of .New 

 York State, recently studied in this connection by 

 R. M. Field,'" must be of peculiar interest to geo- 

 logists, and forms a notable instance of the annectant 

 character of oceanography, bringing the metabolism 

 of living organisms in the modern sea into relation 

 with palaeozoic rocks. 



The work of marine biologists on the plankton has 

 been in the main qualitative, the identification of 

 species, the observation of structure, and the tracing 

 of life-histories. The oceanographer adds to that the 

 quantitative aspect when he attempts to estimate 

 numbers and masses per unit-volume of water or of 

 area. Let me lay before you a few thoughts in regard 

 to some such attempts, malnlv for the purpose of 

 showing the difficulties of the investigation. Modern 

 quantitative methods owe their origfin to the ingenious 

 and Inborious work of Victor Hensen, followed by 

 Brandt, Apsteln, Lohmann, and others of the Kiel 

 school of quantitative planktologists. We mav take 

 their well-known estimations of fish-eggs in the 

 North Sea as an example of the method. 



The floating egtfs and embryos of our more important 

 food-fishes may occur in quantities in the plankton 

 during certain months In spring, and Hensen and 



9 Journ. Mar. Biol. Assoc. October, 191 1. 

 10 Carnegie institution .of Washington. "Year Book for z^ig," ■p. .197. 



