September i6, 1909] 



NATURE 



357 



organisms (both animals and plants) in the sea, is uniformly 

 distributed over an area where the physical conditions 

 are approximately the same, and that by taking a com- 

 paratively small number of samples it would be possible 

 to calculate the quantity of plankton contained at the time 

 of observation in a given sea area, and to trace the changes 

 of this plankton both in space and time. This was a 

 sufficiently grand conception, and it has been of great 

 service to science by stimulating many workers to further 

 research. In order to obtain answers to the problems 

 before him, Hensen devised nets of the finest silk of about 

 6000 meshes in the square centimetre, to be hauled up 

 from the bottom to the surface, and having their constants 

 determined so that it is known what volume of water 

 passes through the net under certain conditions, and 

 yields a ceitain quantity of plankton. 



Now if this constancy of distribution postulated by 

 Hensen could be relied upon over considerable areas of the 

 sea, far-reaching conclusions, having important bearings 

 upon fisheries questions, might be arrived at ; and such 

 have, in fact, been put forward by the Kiel planktologists 

 and their followers — such as the calculation by Hensen 

 and Apstein that the North Sea in the spring of 1895 con- 

 tained at least 157 billions of the eggs and larvae of certain 

 edible fisli ; and from this figure and the average numbers 

 of eggs produced by the fish, their further computation 

 of the total number of the mature fish population which 

 produced the eggs — a grand conclusion, but one based upon 

 only 15S samples, taken in the proportion of one square 

 metre sampled for each 3,465,968 square metres of sea. 

 Or, again, Hensen 's estimation, from 120 samples, of the 

 number of certain kinds of fish eggs in a part of the West 

 Baltic, from which, by comparing with the number ' of 

 such eggs that would normally be produced by the fish 

 captured in that area, he arrived at the conclusion that 

 the fisherman catches about one-fourth of the total fish 

 population — possibly a correct appro.\imation, though differ- 

 ing considerably from estimates that have been made for 

 the North Sea. 



Such generalisations are most attractive, and if it can 

 be established that they are based upon sufficiently trust- 

 worthy data, their practical utility to man in connection 

 with sea-fishery legislation may be very great. But the 

 comparatively small number of the samples, and the 

 observed irregularity in the distribution of the plankton 

 (containing, for example, the fish eggs) over wide areas, 

 such as the North Sea, leave the impression that further 

 observations are required before such conclusions can be 

 accepted as established. 



Of the criticisms that have appeared in Germany, in the 

 United States and elsewhere, the two most fundamental 

 are : — (i) that the samples are inadequate ; and (2) that 

 there is no such constancy and regularity in distribution 

 as Hensen and some others have supposed. It has been 

 shown by I^ofoid, by Lohmann, and by others that there 

 are imperfections in the methods which were not at first 

 realised, and that in some circumstances anything from 

 50 to 98 per cent, of the more minute organisms of the 

 plankton may escape capture by the finest silk quantitative 

 nets. The mesh of the silk is 1 /200th inch across, but 

 many of the organisms are only i/3oooth inch in diameter, 

 and so can readily escape. 



Other methods have been devised to supplement the 

 Hensen nets, such as the filtering of water pumped up 

 through hose-pipes let down to known depths, and also 

 the microscopic examination in the laboratory of the centri- 

 fuged contents of comparati%'ely small samples of water 

 obtained by means of closing water-bottles from various 

 zones in the ocean. But even if deficiencies in the nets 

 be thus made good by supplementary methods, and be 

 allowed for in the calculations, there still remains the 

 second and more fundamental source of error, namely, un- 

 equal distribution of the organisms in the water ; and in 

 regard to this a large amount of evidence has now been 

 accumulated, since the time when Darwin, during the 

 voyage of the Beagle on March 18, 1832, noticed off the 

 coast of South America vast tracts of water discoloured by 

 the minute floating alga Tyichodesmium erythraeum, 

 which is said to have given its name to the Red Sea, and 

 which Captain Cook's sailors in the previous century 

 ^ It is probable that too high a figure was taken for thi--, 

 NO. 2081, VOL. 81] 



called " sea-sawdust." Many other naturalists since have 

 seen the same phenomenon, caused both by this and by 

 other organisms. It must be of common occurrence, and 

 is widespread in the oceans, and it will be admitted that a 

 quantitative net hauled vertically through such a tricho- 

 desmium bank would give entirely different results from 

 a haul taken, it might be, only a mile or two away, in 

 water under, so far as can be determined, the same physical 

 conditions, but free from Trichodesmium. 



Nine nations bordering the north-west seas of Europe, 

 some seven or eight years ago, engaged in a joint scheme 

 of biological and hydrographical investigation, mainly in 

 the North Sea, with the declared object of throwing light 

 upon fundamental facts bearing on the economic problems 

 of the fisheries. One important part of their programme 

 was to test the quantity, distribution, and variation of the 

 plankton by means of periodic observations undertaken four 

 times in the year (February, May, August, and November) 

 at certain fixed points in the sea. Many biologists con- 

 sidered that these periods were too few and the chosen 

 stations too far apart to give trustworthy results. It is 

 possible that even the original promoters of the scheme 

 would now share that view, and the opinion has recently 

 been published by the American planktologist, C. .'\. 

 Kofoid — than whom no one is better entitled, from his 

 own detailed and exact work, to express an authoritative 

 verdict — that certain recent observations " can but reveal 

 the futility of the plankton programme of the International 

 Commission for the investigation of the sea. The quarterly 

 examin.ations of this programme will, doubtless, yield some 

 facts of value, but they are truly inadequate to give any 

 trustworthy view of the amount and course of plankton 

 production in the sea.'" That is the latest pronounce- 

 ment on the subject, made by a neighbour of yours to the 

 south, who has probably devoted more time and care to 

 detailed plankton studies than anyone else on this 

 continent. 



It is evident that before we can base far-reaching 

 generalisations upon our plankton samples, a minute study 

 of the distribution of life in both marine and fresh waters 

 at very frequent intervals throughout the year should be 

 undertaken. Kofoid has made such a minute study of the 

 lakes and streams of Illinois, and similar intensive work 

 is now being carried out at several localities in Europe. 



Too little attention has been paid in the past to the 

 distribution of many animals in sivarms, some parts (5f 

 the sea being crowded and neighbouring parts being desti- 

 tute of such forms, and this not merely round coasts and 

 in the narrow seas, but also in the open ocean. For 

 example, some species of Copcpoda and other small 

 Crustacea occur notably in dense crowds, and are not 

 universally distributed. This is true also of some of the 

 diatoms, and also of larger organisms. Many naturalists 

 have remarked upon the banks of Trichodesmium, of 

 Medusae and Siphonophora, of Salpae. of Pteropods. of 

 Peridinians, and of other common constituents of the 

 plankton. Cleve's classification .into Tricho-Plankton 

 (Arctic), Stvli-Plankton (temperate), and Desmo-Plankton 

 (tropical) depends upon the existence of such vast swarms 

 of particular organisms in masses of water coming into the 

 North .Atlantic from different sources. 



It is possible that in some parts of the ocean, far from 

 land, the plankton may be distributed with the uniformity 

 supposed by Hensen. It is important to recognise that at 

 least three classes of locality exist in the sea in relation 

 to distribution of plankton : — 



(i) There are estuaries and coastal waters where there 

 are usually strong tidal and other local currents, with 

 rapid changes of conditions, and where the plankton is 

 largely influenced by its proximity to land. 



(2) There are considerable sea areas, such as the centre 

 of the North Sea and the centre of the Irish Sea, where 

 the plankton is removed from coastal conditions, but is 

 influenced bv various factors which cause great irregularity 

 in its distribution. These are the localities" of the greatest 

 economic importance to man, and to which attention should 

 especially be directed. 



(3) There are large oceanic areas in which there may 



1 " Internationale Revue der H ydrobiologie und Hyc'rografhie," vol. i. 

 p. 846. Dec**mher, Tgo8. 



- See Dakin, Trans. Biol. Soc. Liverpool, xxii , p. SK- 



