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amphipods, mysids, and euphausiids, as well as the larvae of shrimps, crabs, 
and lobsters. ‘Although most abundant in the surface and near-surface wa- 
ters, the zooplankton is found at all depths of the sea. From the stand- 
point of vertical zonation the zooplankton may be classified as epipelagic 
(0-200m), mesopelagic (200-700m), or bathypelagic (700m and more), as shown 
in Figure 3.- Many of the epipelagic species exhibit regular patterns of 
daily vertical migration in the water column, being nearer the surface at 
hight and deeper during the daylight hours. 
Nekton. Nekton includes those free-swimming animals of the sea that 
are larger than plankton and that have more powerful swimming abilities. 
They are able to move independently and may roam from one water mass to 
another. Included are all marine mammals and most fishes, cephalopod mol- 
lusks (especially the squids), and certain larger swimming crustaceans 
(Figure 4). As in the case of the plankton, the nekton is most abundant in 
the near-surface waters, but it may be encountered at any depth. Nekton 
organisms display a variety of feeding types. For example, the great blue 
whale (the largest mammal) and the whale shark (the largest fish) feed on 
zooplankton, the menhaden and sardine feed on phytoplankton, others prey 
upon nektonic species, and still others consume organic detritus (the dead 
and decaying organic matter that constantly rains down from the surface 
layers of the sea). 
Some of the most important commercial and recreational finfish belong to the 
nekton. Among these are tunas of all kinds, salmon, menhaden, herring, an- 
chovies, sailfish, marlin and many others. 
Benthos. Benthos includes all the organisms intimately asociated with 
the bottom. Some species live within the bottom sediments (infauna). 
Others live upon the bottom surface or in the near-bottom portion of the 
water column (epifauna). Finfish that swim in the water column but are 
wholly dependent upon bottom material for food (called demersal fish) are 
also included in the benthos. Some benthos burrow (e.g. worms), others are 
attached to the substrate (barnacles), still others crawl upon the surface 
(dungeness crab). 
