94 LIFE IN THE SEA [PART I 



indeed shews that this is the case. Even the permanent plankton 

 varies with the season. In the sea, as on the land, there is seed- 

 time and harvest, and with the spring a multitude of life comes 

 into existence to pass away in the autumn and winter. I leave 

 aside in the meantime a consideration of the causes of the variation 

 in abundance and nature of the plankton. We shall see later that 

 enquiry into this carries us away from the traditional province of 

 the biologist into that of the physicist and astronomer. Very 

 probably many of the larger variations in the plankton are caused 

 by cosmical events. 



It is possible to construct a "calendar of the plankton \" If we 

 make periodical hauls with a tow-net in any small sea area once a 

 week or oftener throughout the year it is easy to see that the fauna 

 and flora of the plankton do not vary fortuitously, but there is a 

 very definite order of succession in the nature and abundance of the 

 organisms found throughout the year. Fishes, molluscs, Crustacea, 

 echinoderms and other creatures which live in the sea all have 

 their spawning seasons. The nature of the seasons may delay or 

 hasten these spawning times ; exceptional gales or unusual periods 

 of fine weather may have great influence and produce changes 

 in the abundance of the permanent plankton, confusing the order 

 of appearance of the transitorily occurring organisms, but when the 

 observations of a number of years have been accumulated one knows 

 roughly when to expect the appearance of the usually occurring 

 things. I will consider here the main changes in the order of the 

 plankton which may be observed in the sea off the west coast of 

 England. 



There is never absolute sterility in the sea. Wherever and 

 whenever one fishes with the tow-net life is to be found. But at the 

 beginning of the year the plankton is not abundant, that is with 

 relation to the other seasons. The permanent constituents are 

 generally scarce and the great outburst of life, which is due to the 

 spawning of the fishes and other bottom-living or nektic creatures, 

 has not yet taken place. But very soon, as the intensity of sun- 

 light increases and the amount of food matter in solution in the 

 sea begins to accumulate, the diatoms multiply at an increased rate. 



1 Mcintosh, Ann. Rep. Scottish Fishery Board for 1889. See also Garstang, 

 Joiirn. Mar. Biol. Ass. Vol. iii., 1893-5. 



