152 



Life 



niferans, of which the genera Globigerina, 

 Globigerinoides, Globigerinella, Globorotalia, 

 Globotruncana, Orbulina, and six others are 

 pelagic (Cushman, 1940, p. 45). Many sam- 

 ples of sediments from basins and banktops 

 consist of 20 per cent or more foraminiferal 

 tests, of which the majority are commonly 

 of pelagic forms. More complex than the 

 protozoans are copepods, tiny planktonic 

 crustaceans having elaborate appendages to 

 aid their flotation and permit a limited 

 amount of swimming. Their most interest- 

 ing movement is a diurnal vertical one in 

 response to intensity of light (Esterly, 1912, 

 1928). Because of their large numbers, they 

 probably complement the diatoms in form- 

 ing a balanced oxygen-carbon dioxide sys- 

 tem in the water. Copopods are the primary 

 grazers on phytoplankton; their importance 

 in the food chain of the ocean is illustrated 

 by the parallelism in abundance of copepods, 

 notably Calanus, with fish caught (Sverdrup, 

 Johnson, and Fleming, 1942, pp. 906-907). 

 Also grazing on the phytoplankton are 

 larval stages of Emerita, the sand crab whose 

 adult life is spent on beaches. Johnson and 

 Lewis (1942) showed that the area of greatest 

 abundance of the larvae in plankton catches 

 corresponds closely to the off'shore belt of 

 cold water that is rich in nutrients and 

 diatoms. 



In addition to minute forms, zooplankton 

 also includes large ones. Perhaps most 

 common of these in southern California is 

 Velella lata, a 8-cm siphonophore carrying a 

 triangular sail and trailing short tentacles. 

 It is related to the larger Portuguese man- 

 of-war which occurs in tropical waters. 

 Jellyfish are also fairly common and are 

 frequently seen at or just beneath the water 

 surface or stranded on sandy beaches. Pul- 

 sations of their mantles give them a high 

 degree of mobility for plankton. Perhaps 

 most common is the white and purple radi- 

 ally striped Pelagia. Another coelenterate, 

 the transparent ctenophore Pleurobrachia, 

 is less often seen. It consists of a 1- to 2-cm 

 sphere, or cat's eye, trailing tentacles and 

 swimming slowly through the water by 

 rhythmic movements of combs of cilia. 

 Tunicates, belonging to the phylum Chordata, 



are also common members of the larger 

 zooplankton. One, the salp Pyrosoma gi- 

 ganteum, sometimes occurs at the surface in 

 a density as great as one per square meter. 

 It is a tubular colony, commonly of 4-cm 

 diameter and 15-cm length, which has 

 orange transluscent walls and a cavity along 

 the whole length, except that one end is 

 closed. Slow jet propulsion is provided by 

 contractions of the cavity walls. Its ex- 

 ceptionally high bioluminescence is recog- 

 nized by the name Pyrosoma, which means 

 fire body. 



A discussion of the composition of plank- 

 ton must include mention of bacteria. 

 These organisms, usually referred to the 

 plant kingdom, are not abundant in a truly 

 planktonic form but instead become estab- 

 lished chiefly on the surfaces of plankton 

 that has died and is sinking down through 

 the water. As a result, bacteria of many 

 kinds are most abundant in areas of greatest 

 abundance of plankton and at depths shghtly 

 greater than the depth of maximum plankton 

 concentration (ZoBeU, 1946c, pp. 67, 77). 

 Bacteria thus begin the regeneration of 

 organic materials soon after death of the 

 plankton (Fig. 131) and continue their activ- 

 ities after the debris reaches the bottom and 

 is buried under later sediments. 



The nekton, or swimmers, consists only 

 of animals. Some of the zooplankton, such 

 as prawns, have some swimming ability, and 

 so they lie astride the boundary between 

 plankton and nekton. Aside from these 

 doubtful members, the nekton consists of 

 cephalopods, fishes, and mammals — aU 

 characterized by fairly high intelligence. 

 The only invertebrates, the cephalopods, 

 are represented ofl" southern California by 

 squids. The chief past source of informa- 

 tion about them is a volume by Berry (1912), 

 but a new book by Lane (1958) contains 

 much new general data. As pointed out by 

 Hardy, (1956, pp. 278-291), squids are so 

 mobile that they are rarely caught in nets, 

 but yet they must be present in the ocean in 

 large numbers because they appear to be a 

 chief food component of mammals, particu- 

 larly in the Antarctic. They are able to 

 move so fast that they frequently fly out of 



