32 FISHERIES OF THE NORTH SEA 



Necton. The other form -of marine life 

 which is grouped under the name of Plank- 

 ton, includes those forms of live substances 

 most of which drift passively on the cur- 

 rents. It includes starfish, jellyfish, fish 

 -eggs, plants, as well as those transparent, 

 delicate animals so small that millions 

 can be contained* in a pint of water. The 

 latter are of varying sizes, shapes, and 

 colours. Some, although invisible indi- 

 vidually, collectively supply the phos- 

 phorescent light which is so often a fea- 

 ture of sea travel. It is the quantity and 

 colour of the plankton which gives different 

 seas their tinge. The Red Sea owes its 

 name to the presence of reddish plankton ; 

 other waters are of other colours chiefly 

 through plankton of different hue being 

 present on the surface. Sunlight pene- 

 trates the shallow 'depths and. reaches the 

 seabed of the submarine plateau surround- 

 ing the British Isles, and, in conjunction 

 with incoming currents of suitable tern-, 

 perature and salinity, is favourable to 

 constant accumulations of plankton. As 

 small fish fatten on these foods and supply 

 themselves in turn food for bigger fishes, 



