lislies feed on these invertebrates or are carnivorous 

 on otlier fish. Many of them have very wide mouths, 

 distensible stomachs, and formidable teeth. In addi- 

 tion to tliese food coactions, it is also likely that many 

 deei)-sea fish and larger invertebrates undergo ver- 

 tical migrations so that they obtain food by preying 

 on living organisms at more moderate depths. Much 

 that is known about the life histories of these deep 

 benthic species has been summarized by Marshall 

 (1954). 



I".s|)ccially fertile regions of the open ocean occur 

 when there is deep mi.xing of waters by turbulence 

 and itf'Ti.'t'lling. \'ertical water currents bring nutri- 

 ents up to the surface from intermediate dejiths where 

 they had accumulated. Prominent regions of upwell- 

 ing occur around the Antarctic continent, off the 

 coasts of California, Peru, and Somali, and off the 

 west coasts of both north and south Africa. 



The net zooplankton feed predominantly on the 

 nannoplankton, probably including bacteria, and on 

 the i^hytoplankton (Clarke 1934). Particulate or- 

 ganic matter, only partially decomposed, may also be 

 important. Most animals depending on these small 

 organisms and organic detritus have various filter- 

 feeding mechanisms for straining food out of the 

 water. They do not actively search and catch indi- 

 vidual items through directed actions. Invertebrate 

 animals may also be able to absorb some essential salts 

 and dissolved organic compounds to build their skele- 

 tal structures and for general metabolism, but there is 

 considerable controversy on this point (Collier 1933). 



The baleen or whalebone whales (Mysticeti) are 

 toothless but possess large plates in their mouths 

 that strain out the plankton (especially copepods, 

 euphausiaceans, mysidaceans) that they use as food. 

 Only occasionally are small fish or other invertebrates 

 ingested. Some whales reach tremendous propor- 

 tions, and the differential in size between these ani- 

 mals and their food is one of the most remarkable 

 in the animal kingdom. Much more common is the 

 feeding on plankton by squids, the young stages of 

 most fishes and such adult fishes as sardine, anchovy, 

 menhaden, herring, and mackerel. The menhaden is 

 unique in having such fine-mesh gill-rakers that it 

 can feed extensively on diatoms, which because of 

 their smaller size cannot be readily secured by other 

 large marine animals (Clarke 1954). 



Small nektonic species are in turn preyed on by 

 larger species. Sharks commonly hold the last link 

 in the food chain. The pelagic birds are also fish- 

 eaters or depend on floating carrion for their food. 



Productivity 



Most studies of plankton productivity have 

 been conducted in the neritic zone. In the English 



FIG 28 5 The filter feeding apparatus of the California sardine: 

 a) gill cover and gills removed to show one side of branchial 

 sieve fornned by gill rakers; b| enlarged drawing of a section 

 of the branchial sieve; c) a small copepod, Oifhona plumilera. 

 drawn to the same scale as b); d) a medium-sized copepod. 

 Colanui iinmarchicui. drawn to the same scale as b) (Sverdrup 

 ef al. 1942). 



Channel, the mean annual standing crops of phyto- 

 plankton, zooplankton, and pelagic fish in dry weight 

 of organic matter are 0.4, 1.5, and 1.8 g/m-. This is 

 unusual in giving a larger biomass of herbivores and 

 carnivores than of photosynthetic plant material. 

 However, the daily productivity of phytoplankton 

 makes up for this because it is over 100 per cent, 

 while that of zooplankton is only 10 per cent and 

 that of fish 0.09 per cent. The productivity ratio of 

 phytoplankton : zooplankton : fish is appro.xiniately 

 280:100:1 (Harvey 1950). 



The daily net productivity of phytoplankton in the 

 upper 20 m of Block Island Sound near the eastern 

 end of Long Island has been estimated at 26 per cent 

 of the standing crop in excess of that consumed by 

 zooplankton and bacteria in the surface layer. The 

 zooplankton consumes not more than 4 per cent of 

 the phytoplankton per day. Most of the excess daily 

 production ( 19 per cent) in the surface waters settles 

 downward and is used by animals and bacteria on 

 or near the bottom, with the rest (7 per cent) becom- 

 ing laterally dispersed into adjacent areas (Riley 

 1952). The daily productivity of zooplankton in this 

 same area was calculated at 17 per cent of the stand- 

 ing crop (Deevey 1952). 



Phytoplankton productivity varies with the time 

 of the year. Near Kiel, Germany, in August there is 

 a surplus of phytoplankton production over the 

 amount consumed by animals ; the productivity 

 amounts to 350 mnr'/m^/day while animal consump- 

 tion is 60 mm^/m^/day. During February, the pro- 

 ductivity of plankton is only 10 mm'Ym^/day while 

 the food requirements of animals is 18 mnr''/m^/day. 

 This deficiency in food production is correlated with 

 the decrease at that time in the standing crop of 

 both plants and animals (Sverdrup et a!. 1942). 



The average net phytoplankton of the Sargasso 

 Sea is only one-quarter to one-third what it is in 

 the more productive temperate waters (Riley 1957). 

 Productivity is especially high in those parts of the 

 ocean where there is upwelling. It is in these areas 



Marine biomes 361 



