marine populations occur, as compared with other parts of the ocean. 

 In deep water, such areas can be identified by their color, for water 

 rich in life is greenish, whereas "desert" water is blue. 



c. Marine Life 



The sea's inhabitants range from a multitude of microscopic 

 one-celled organisms to the 100-ton blue whale. Smaller forms, 

 especially plants, are extremely prolific under proper conditions and 

 furnish the food supply for successively larger forms of animals. In 

 describing the population of the sea, three major groups are 

 distinguished depending upon habitat: nekton, benthos, and plankton. 

 Nekton is the name given to swimming animals that can move freely over 

 large distances. The term benthos refers to the sessile animals such 

 as sponges, creeping forms such as crabs, and burrowing forms such as 

 worms found at and in the sea bottom. The plankton includes all 

 floating plants (phytoplankton) , animals that live permanently in a 

 floating state (zooplankton) , and also larvae and eggs of animal 

 benthos and nekton (meroplankton) . The plant plankton (e.g., diatoms, 

 dinof lagellates, and coccolithophores) and animal plankton 

 (e.g., globigerina and radiolaria) are so numerous that extensive 

 areas of the ocean floor are covered with oozes (fig. 2-7) containing 

 their skeletons. There is some question regarding the grouping of 

 motile dinof lagellates as plants even though they carry on photosynthesis. 

 Figure 3-3 shows a zooplankton sample, including meroplankton. 



In the sea, as on land, plants are capable of developing com- 

 plex organic substances from the simple compounds dissolved in water. 

 Without these plants animal life would be restricted to a small region 

 near the shore where organic material of terrestrial origin exists. 

 Nearly all marine plants are thallophytes, primitive plants with no 

 true root, stem, or leaf. They include marine algae and fungi, and 

 bacteria are frequently included with them. Brown algae vary greatly 

 in size, and plants of this class form the "kelp beds" commonly 

 harvested for commercial purposes. Yellow-green algae are mainly 

 floating forms and include diatoms, which are unicelluar in structure, 

 and dinof lagellates, again typically unicelluar, but possessing two 

 flagella for locomotion. The latter are second only to diatoms as 

 producers in the marine plankton. Some of the latter have the capacity 

 to luminesce when disturbed. Mosses (bryophytes) and ferns (pteridophytes) , 

 two major divisions of the plant kingdom, are not represented in the 

 sea. The highest plants, the spermatophytes , are represented, however, 

 by some 30 species of flowering plants. They have invaded the sea by way 

 of fresh water. 



Of more than 50 animal classes, only four are exclusively 

 nonmarine. In contrast to plant life, all major groups (phyla) of 

 animal life are represented in the sea. Each phylum is subdivided 

 successively into class, order, family, genus, and species. When 

 thinking of animal life in the sea, one tends to emphasize the higher 



