September i6, 1909J 



NA TURE 



359 



reduces the rate of all metabolic processes, and increases 

 the length of life, that we have in the more abundant 

 pla[il^ton of the colder waters several generations living on 

 side by side, whereas in the tropics with more rapid meta- 

 bolism they would have died and disappeared. The 

 temperature of the sea-water, however, appears to have 

 little or no effect in determining the great vernal maximum 

 of Phyto-Plankton. 



Considering the facts of photosynthesis, there is much to 

 be said in favour of the view that the development, and 

 possibly also the larger movements of the plankton, are 

 influenced by the amount of sunlight, quite apart from any 

 temperature effect. 



BuUen ' showed the correlation in 1903-7 between the 

 mackerel catches in May and the amount of Copepod 

 plankton in the same sea. The food of these Copepoda 

 has been shown by Dakin to be largely Phyto-Plankton, 

 and Allen has lately " correlated the average mackerel 

 catch per boat in May with the hours of sunshine in 

 the previous quarter of the year, thus establishing 

 the following connection between the food of man and 

 the weather : — Mackerel — Copepoda — Diatoms — Sunshine. 

 One more example of the influence of liglit may be given. 

 Kofoid has shown that the plankton of the Illinois River 

 has certain twenty-nine-day pulses, which are apparently 

 related to the lunar phases, the plankton maxima lagging 

 about six days behind the times of full moon. The light 

 from the sun is said to be 618,000 times as bright as that 

 from the full moon ; but the amount of solar energy 

 derived from the moon is sufficient, we are told, appreci- 

 ably to affect photosynthesis in the Phyto-Plankton. The 

 effectiveness of the moon in this photosynthesis to that of 

 the sun is said to be as two to nine, and if that is so 

 Kofoid is probably justified in his contention that at the 

 time of full moon the additional light available has a 

 marked effect upon the development of the Phyto- 

 Plankton. 



As on land, so in the sea, all animals ultimately depend 

 upon plants for their food. The plants are the producers 

 and the animals the consumers in nature, and the pastures 

 of the sea, as Sir John Murray pointed out long ago, are 

 no less real and no less necessary than those of the land. 

 Most of the fish which man uses as food spawn in the 

 sea at such a time that the young fry are hatched when 

 the spring Diatoms abound, and the Phyto-Plankton is 

 followed in summer by the Zoo-Plankton (such as Cope- 

 poda), upon which tlie rather larger but still immature 

 food fishes subsist. Consequently, the cause of the great 

 vernal maximum of Diatoms is one of the most practical 

 of world problems, and many investigators have dealt with 

 it in recent years. Murray first suggested that the meadows 

 of the sea, like the meadows of the land, start to grow 

 in spring simply as a result of the longer days and the 

 notable increase in sunlight. Brandt has put forward the 

 view that the quantity of Phyto-Plankton in a given layer 

 of surface water is in direct relation to the quantity of 

 nutritive matters dissolved in that layer. Thus the actual 

 quantity pi'esent of the substance — carbon, nitrogen, silica, 

 or whatever it may be — that is first used up determines 

 the quantity of the Phyto-Plankton. Nathansohn in a 

 recent paper ' contends that what Brandt supposes never 

 really happens ; that the Phyto-Plankton never exhausts any 

 food constituent, and that it develops just such a rate of 

 reproduction as will compensate for the destruction to 

 which it is subjected. This destruction he holds is due 

 to two causes : currents carrying the Diatoms to unfavour- 

 able zones or localities, and the animals of the plankton 

 which feed on them. The quantity of Phyto-Plankton pre- 

 sent in a sea will then depend upon the balancing of the 

 two antagonistic processes — the reproduction of the Diatoms 

 and their destruction. We still require to know their rate 

 of reproduction and the amount of the destruction. It 

 has been calculated that one of these minute forms, less 

 than the head of a pin, dividing into two at its normal 

 rate of five times in the day, would at the end of a month 

 form a mass of living matter a million times as big as the 

 sun. The destruction that keeps such a rate of reproduc- 



1 M. B. A. Journ., viii.. 26q. - Ibiii., v!i., 39,). 



s Monaco Bulletin, No. 140. 



NO. 2081, VOL. 81] 



tion in check must be equally astonishing. It is claimed 

 that the Valdivia results, and observations made since, 

 show that the most abundant plankton is where the surface 

 water is mixed with deeper layers by rising currents. 

 Nathansohn, while finding that the hour of the day has 

 no effect on his results, considers that the development of 

 the Phyto-Plankton corresponds closely with evidence of 

 vertical circulation. Like some other workers, he 

 emphasises the necessity of continuous intensive work in 

 one locality : such work might well be carried on both at 

 some point on your great lakes and also on your Atlantic 

 coast. The Challenger and other great exploring expedi- 

 tions forty years ago opened up problems of oceanography, 

 but such work from vessels passing rapidly from place to 

 place could not solve our present problems — the future lies 

 with the naturalists at biological stations working con- 

 tinuously in the same locality the year round. 



The problems are most complex, and may vary in 

 different localities — for example, there seem to be two kinds 

 of Diatom maxima found by Nathansohn in the Mediter- 

 ranean, one of ChjEtoceros due to the afflux of water from 

 the coast, and one of Rhizosolenia calcaravis, due to a 

 vertical circulation bringing up deeper layers of water. As 

 a local example of the importance of the Diatoms in the 

 plankton to man, let me remind you that they form the 

 main food of your very estimable American clam. The 

 figures I now show, and some of the examples I am taking, 

 are from the excellent work done on your own coasts in 

 connection with fisheries and plankton by Prof. Edward 

 Prince and Prof. Ramsay Wright and their fellow-workers 

 at the Canadian biological station, on your eastern sea- 

 board. 



The same principles and series of facts could be illus- 

 trated from the inland waters. Your great lakes periodic- 

 ally show plankton maxima, which must be of vast import- 

 ance in nourishing animals and eventually the fishes used 

 by man. Your geologists have shown that Manitoba was 

 in post-Glacial fimes occupied by the vast lake Agassiz, 

 with an estimated area of 1 10,000 square miles ; and while 

 the sediments of the extinct lake form your celebrated 

 wheat fields, supplying food to the nations, the shrunken 

 remains of the water" still yield, it is said, the greatest 

 fresh-water fisheries in the world. See to it that nothing 

 is done to reduce further this valu.able source of food ! 

 Quoting from vour neighbours to the south, we find that 

 t"he Illinois fisheries yield at the rate of a pound a day 

 throughout the year of cheap and desirable food to about 

 80,000 people — equivalent to one meal of fish a day for a 

 quarter of a million people. 



Your excellent " whitefish " alone has yielded, I see, 

 in recent vears more than 5,000,000 lb. in a year ; and all 

 scientific men who have considered fishery questions will 

 note with approval that all your fishing operations are now 

 carried on under regulations of the Dominion Government, 

 i and that fish hatcheries have been established on several 

 of your great lakes, which will, along with the necessary 

 restrictions, form, it may be hoped, an effective safeguard 

 against depiction. Much still remains to be done,^ how- 

 ever, in the way of detailed investigation and scientific 

 exploitation. The German institutes for pond-culture show 

 what can be done by scientific methods to increase the 

 supplv of food-fishes from fresh waters. It _ has been 

 shown in European seas that the mass of living food 

 matters produced from the uncultivated water may equal 

 that yielded bv cultivated land. When aquiculture is as 

 scientific as agriculture, your regulated and cultivated 

 waters, both inland and marine, may prove to be 

 more productive even than the great wheat lands of 

 Manitoba. 



Inland waters may be put to many uses : sometimes they 

 are utilised as sewage outlets for great cities, sometimes 

 thev are converted in'to commercial highways, or they may 

 become restricted because of the reclamation of fertile 

 bottom lands. All these may be good and necessary 

 developments, or any one of them may be obviously best 

 in the circumstances; but, in promoting any such 

 schemes, due regard should always be paid to the import- 

 ance and promise of natural waters as a perpetual 

 source of cheap and healthful food for the people of the 

 country. 



