[Chap. XLVI 



UNDER-WATER ENVIRONMENTS 



601 



below the freezing point, such for example as the marine algae of arctic 

 and antarctic regions. The destructive effects of temperature, however, 

 are much less in the ocean than on land because of the absence of 

 extremes and rapid changes. Indirectly temperature is important in 

 another way since carbon dioxide is much more soluble in cold than 

 in warm water; in the tropics the warm water may become almost 

 depleted of this gas. Likewise the production of plant and animal plank- 

 ton is less in the warmer water of tropical oceans than in the cooler 

 water of temperate regions. Other factors that reduce plankton produc- 

 tion in the tropics are the increased rate of respiration, and deficiency 

 in compounds of nitrogen and phosphorus. 



PLANTS AND ANIMALS IN THE OCEAN 



Water environments, both fresh and marine, are populated with great 

 numbers and many kinds of plants and animals. The largest as well as 

 the smallest known organisms live in the ocean. In the sea are whales, 

 large fishes, crustaceans, and squids, as well as myriads of microscopic 

 species. The largest plants in the sea are the brown kelps (Fig. 271) 



Fig. 271. One of the brown algae (Nereoci/stis) along the western coast of 

 North America. Only a part of the plant is visible at the surface of the water at 

 low tide. See Fig. 287 F. Photo from Lois Lampe. 



