November 26, 1909] 



SCIENCE 



141 



are influenced by the amount of sunlight, 

 quite apart from any temperature effect. 



Bullen" 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 sho^vn 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 [curves shown] , thus es- 

 tablishing the following connection between 

 the food of man and the weather: Mack- 

 erel— Copepoda— diatoms— sunshine. One 

 more example of the influence of light may 

 be given. Kofoid has shown that the 

 plankton of the Illinois River has certain 

 twenty-nine day pulses, which are appar- 

 ently 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 ai'e told, to appreci- 

 ably affect photosynthesis in the phyto- 

 plankton. The eft'ectiveness of the moon 

 in this photosynthesis is said to be to that 

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

 Kofoid is probably justified in his conten- 

 tion that at the time of full moon the addi- 

 tional light available has a marked effect 

 upon the development of the phyto-plank- 

 ton. 



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 Mur- 

 ray 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 



" il. B. A. Journ., VIII., 269. 

 'Ibid., VTl., 394. 



the young fry are hatched when the spring 

 diatoms abound, and the phyto-plankton is 

 followed in summer by the zoo-plankton 

 (such as Copepoda), upon which the 

 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 present of the 

 substance — carbon, nitrogen, silica, or 

 whatever it may be— that is first used up 

 determines the quantity of the phyto-plank- 

 ton. Nathansohn in a recent paper* con- 

 tends that what Brandt supposes never 

 really happens; that the phyto-plankton 

 never uses up any food constituent, and 

 that it develops just such a rate of repro- 

 duction as will compensate for the destruc- 

 tion to which it is subjected. This de- 

 struction he holds is due to two causes: 

 currents carrying the diatoms to unfavor- 

 able zones or localities, and the animals of 

 the plankton which feed on them. The 

 quantity of phyto-plankton present in a 

 sea will then depend upon the balancing of 

 the two antagonistic processes— the repro- 

 duction of the diatoms and their destruc- 

 tion. We still require to know their rate 

 of reproduction and the amount of the de- 

 struction. 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 Any, would at the 

 end of a month form a mass of living mat- 



' Monaco Bulletin, No. 140. 



