tional regulations have now been set up to limit the 

 take of both groups of species. 



The applied ecologist is also concerned in the 

 fouling of ship bottoms by growth of organisms, par- 

 ticularly those belonging to the balanoid-gastropod- 

 thallophyte biome. This is of major economic im- 

 portance because of reduction of speed and the greater 

 fuel consumption imposed on fouled ships. The prob- 

 lem has stimulated intensive studies of the behavior 

 of the organisms concerned and the searching for 

 chemicals or methods of treatment of ship bottoms to 

 prevent their setting (Iselin 1952). 



SUMMARY 



Geographic distribution of marine organ- 

 isms depends on their responses to current, temper- 

 ature, and physical barriers; their local distribution 

 is affected by waves and tides, type of bottom, salin- 

 ity, and depth. Major divisions of the marine bio- 

 cycle are pelagic (open water) and benthic (bottom). 

 Major communities recognized are the oceanic plank- 

 ton and nekton biome in the open sea, the balanoid- 

 gastropod-thallophyte biome on rocky shores, the 

 pelecypod-annelid biome on sand and mud bottoms, 

 and the coral reef biome. 



Organisms making up the oceanic biome are 

 widely distributed around the world but may be di- 

 vided into warm-water and Arctic and Antarctic 

 faunas. Coral reefs are found only in the Tropics. 

 The two biomes on the continental shelf subdivide 

 into warm-water, temperate, Arctic, and Antarctic 

 faunas and into more restricted regions and subre- 

 gions. The warm-water faunas are richest in species, 

 especially in the Indo-Malayan and West Indian sub- 

 regions. 



Marine plankton include a greater variety of 

 forms than does fresh-water plankton, although roti- 

 fers are nearly absent ; cladocerans, less important. 

 They possess various unique mechanisms for flota- 

 tion. Although abundance varies greatly from place 



to place and from season to season, plankton is gen- 

 erally much more numerous in neritic coastal waters 

 than in the open sea. Diel movements between the 

 surface at night and greater depths during the day 

 are pronounced. 



Mollusks (squids), fishes, birds, and mammals 

 constitute the nekton. The taxonomic composition of 

 the fish fauna varies with depth. Bioluminescence is 

 exceptionally well developed among deep-sea nekton 

 and benthos. 



Benthos includes a great variety of sessile, creep- 

 ing, and burrowing forms. It is very abundant in the 

 littoral zone, and decreases in numbers with depth 

 until only scattered individuals are found in the deep 

 ocean trenches. There is considerable difTerence in 

 the life-form and species composition of benthos oc- 

 curring on rocky shores and on sand and muddy 

 ones. Zonation of species is more prominent on rocky 

 than on depositing shores. Succession and dominance 

 occurs in some situations, but is less important than 

 in terrestrial communities. Coral reefs have many 

 special features. 



Food chains in the sea are similar to those in 

 fresh water but different species make up the various 

 links in the different communities. Productivity is 

 especially high in regions where upwelling and tur- 

 bulence bring nutrients from deeper levels up to the 

 surface. 



The three great biocycles of ocean, fresh-water, 

 and land come into contact around the margins of the 

 seas. The succession from the ocean to land is abrupt 

 and from the ocean to fresh water only slightly less 

 so. 



Because of its high productivity and occurrence 

 over 71 per cent of the earth's surface, the plankton 

 of the sea represents an important potential food 

 supply for man. However, the energy value of this 

 plankton is used by man at the present time only as 

 it is transferred with considerable loss into the higher 

 food-chain links of mollusks, larger arthropods, 

 fishes, and to a certain extent, sea turtles. The con- 

 servation and development of marine resources repre- 

 sent a major challenge to the applied ecologist. 



372 Geographic distribution of communities 



