Marine Biology (2+1)

PUMP AND HOSE

This method is used to collect water samples for quantitative plankton analysis from the desired depth for filtering the plankton. An electrically operated rotary pump or centrifugal pump having flexible inlet and outlet rubber or plastic hose pipes are suitable. The inlet hose is marked off in metres in order to read off the depth. Further a weight is attached near the open end of the inlet hose to make sure that the hose descends vertically when sent down. The diameter of the inlet hose pipe is about 5-10 cm depending on the suction power of the pump. The pump may be used to constantly suck seawater samples with their plankton contents onto the vessel. The cross section of the tube must be sufficient to permit a volume of water at the rate of about 1001/min. The water taken onto the vessel from the specified depth is either transferred to sedimentation chamber or poured through one or several hand nets (vide chapter 2) of various mesh sizes suspended one above the other if fractional study of phytoplankton is contemplated. The plankton collected from the different bag nets is fixed for further qualitative or standing crop analysis. There are several advantages in the use of plankton pump. They are:

1. It can be used to collect the plankton of a desired depth.
2. It is possible to encounter the organisms at different depths in a particular stretch of the water column; and
3. Pumps may be used for continuous sampling from the moving ship itself unlike the water samplers.

However, the only disadvantage of the pump method is that, owing to the coiling of the tube, the plankton pump could only be used to a limited depth of the upper 100m.