dorsal
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dorsal situated at, or relatively nearer to, the back, i.e., the side of a bilateral animal which is normally turned away from the ground or substratum; opposite of ventral.
doubling time the time needed for a population to double in size.
downwelling the downward movement of surface water under influence of the
wind, because of Ekman transport; opposite of upwelling.
drag coefficient a nondimensional factor in the relation between the square of
the flow velocity at a given distance from a boundary and the surface stress.
It depends on the turbulent character of the boundary layer and is, under certain conditions, considered constant.
dredge sampling gear for collecting materials from the seabed as benthic flora and
fauna, stones or minerals etc. The two types most commonly used are the pipe
dredge and the frame dredge. The pipe dredge is a metal cylinder of about
2 m with a diameter of about 50 cm. The sharpened front edge eventually cuts
the rock and the rear has a grating with enough space to allow fine sediment
to pass through. The frame dredge has a bag attached to a metal frame. The
Dredge