1 86 BRITISH FISHERIES 



other animals are beginning to spawn, and by the 

 end of March the eggs of the former and the 

 larvas of other marine animals, like crabs, are 

 abundant. At this time, as on the land, there is 

 a great development of vegetation in the sea ; 

 diatoms have become very abundant, so that, since 

 these constitute the bulk of the catch, the 

 maximum bulk of plankton in the sea occurs about 

 this time. Other groups of marine microscopic 

 animals, like copepods, also now become abundant. 

 With the onset of summer this luxuriance of 

 plankton passes away, diatoms are not so abundant, 

 while larvas of fishes and other marine animals 

 have entered their nektonic or benthotic phases. 

 Towards the middle of the summer and for some 

 time later "jelly-fishes" become abundant. Such 

 animals are Noctiluca (one of the causes of phos- 

 phorescence in the sea), ctenophores, medusas, etc. 

 There may also be a second maximum of diatoms 

 during the autumn, again augmenting the bulk of 

 the plankton. Finally, in the last two or three 

 months a general scarcity in all forms of life again 

 occurs. 



This is only a very general scheme, and all 

 plankton studies have shown that the nature and 

 amount of microscopic life in the sea are greatly 

 affected by a number of conditions. Inshore, in 

 shallow waters subject to the influence of the 

 land, of fresh water, and consequent changes of 

 salinity and temperature, and under the influence 



