6. Deep-Water Communities . 

 (M. E. Vinogradov) 



Communities of the meso-, bathy- and abyssopelagic zones live below 

 the producing surface zone of the ocean and inhabit basically the inter- 

 mediate, deep and benthic waters. 



E nergy dependence . Communities inhabiting waters below the euphotic 

 zone have practically no producers of their own. In a few regions, 

 chemosynthesizinq bacteria act as producers, but the organic matter 

 which they form plays a clearly subordinate and local role in the overall 

 balance of organic matter in the ocean. Thus, all communities of the 

 meso-, bathy- and abyssopelagic zones are energetically dependent on 

 communities in the producing zone and cannot be looked upon as viable 

 biocenoses in the meaning of Yu. Odum (see I.l). 



However, there is a permanent, and at times very intensive exchange 

 of population between the communities of the various vertical zones. For 

 example, the population of interzonal herbivores in the cold-water regions 

 of the ocean feeding in the surface zone, descends to depths of 

 1000-2000 m. They make up almost half of the mass of the population of 

 the meso- and bathypelagic zones, and are the most important components 

 of both the surface and the deep-water communities. From this standpoint, 

 the surface and dependent deep-water communities can be considered as 

 a part of a single, larger community, encompassing all or almost all of 

 the depths of the oceanic waters, and this mass with its population can 

 be looked upon as a single ecosystem. Nevertheless, the population of the 

 mass of water is stratified, which allows us to speak of communities 

 characteristic for various depths, and to study their specific features. 



Energy enters the communities of the ocean depths with organic 

 matter formed in the surface layers, in the euphotic zone. By whatever 

 path this matter reaches the depths of the ocean, in the form of products 

 of metabolism of the animals living in the higher levels or in the form of 

 their dead remains, in the bodies of animals performing vertical migrations, 

 carried down from the coast and shelf by benthic currents, in any case 

 the quantity of this organic matter decreases as it descends into the 

 deeper layers due to consumption by the population of the intermediate 

 depths and mineralization. Therefore, as depths increase, the population 

 of the pelagic zone finds itself living in conditions of ever-increasing 

 food shortage. The concentration of plankton decreases with depth 

 roughly exponentially. 



In those regions of the ocean where the productivity of the plankton 

 of the euphotic zone is higher, the quantity of deep-water plankton is 

 also higher, and the change in the structure of its communities with depth 

 is slower than in oligotrophic regions. 



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