!_>,, The Outline of Science 



relatively easygoing conditions of the open sea (pelagic area), 

 which im-an.s the well-lighted surface waters quite away from 

 land. Many small organisms have their maximum abundance at 

 about fifty fathoms, so that the word "surface" is to be taken 

 generously. The light becomes very dim at 250 fathoms, and the 

 open sea, as a zoological haunt, stops with the light. It is hardly 

 necessary to say that the pelagic plants are more abundant near 

 the surface, and that below a certain depth the population con- 

 Msts almost exclusively of animals. Not a few of the animals 

 sink and rise in the water periodically; there are some that come 

 near the surface by day, and others that come near the surface by 

 night. Of great interest is the habit of the extremely delicate 

 Ctenophores or "sea-gooseberries," which the splash of a wave 

 would tear into shreds. Whenever there is any hint of a storm 

 they sink beyond its reach, and "the ocean's surface must have 

 remained flat as a mirror for many hours before they can be lured 

 upwards from the calm of their deep retreat. 



The Floating Sea-meadows 



To understand the vital economy of the open sea, we must 

 recognise the incalculable abundance of minute unicellular plants, 

 for they form the fundamental food-supply. Along with these 

 must also be included numerous microscopic animals which have 

 got possession of chlorophyll, or have entered into internal 

 partnership with unicellular Alga? (symbiosis). These green or 

 greenish plants and animals are the producers, using the energy 

 of the sunlight to help them in building up carbon compounds out 

 of air, water, and salts. The animals which feed on the producers, 

 or on other animals, are the consumers. Between the two come 

 those open-sea bacteria that convert nitrogenous material, e.g. 

 from dead plants or animals that other bacteria have rotted, into 

 forms, e.g. nitrates, which plants can re-utilise. The importance 

 of these middlemen is great in keeping "the cirulation of matter" 

 agoing. 



