Marine Biology (2+1)

Counting of cells in Utermohl’s chambers

The tubular chamber along with the sedimented plankton is put on to the inverted microscope and is examined from below through the coverglass bottom. If the phytoplankton is abundant then the counting of the entire bottom area of the tubular chamber could not be possible. Under these circumstance, one can restrict the counting to a portion of the bottom area of the chamber making use of the provisions available inside the ocular eye piece of the microscope. The ocular eye piece is marked inside with two vertical threads and a horizontal thread and the space (counting area) between the vertical threads can be adjusted according to one’s need and phytoplankton density on the bottom plate using the provision available on the ocular eye piece. During the counting, if the organisms are found abundant in the counting area between the vertical threads, then the area may be reduced or vice-versa. At the beginning of the enumeration, the left vertical thread should be brought to one end of the field left vision and by adjusting the concerned movable screws, the threads are passed through the field of vision and the organisms between the threads are counted from the top to bottom. As soon as the counting of this segment is over, keeping an organism bordering the right vertical thread as a mark, with the help of the other screw, the left thread is moved, so that, the left thread will lie now on the marked organism. The counting between the two threads is then continued as above. Thus the organisms present in the entire field of vision are counted. If any plankter lies on one of the two threads or half inside and half outside the thread, one should consider only either the left hand or the right hand thread. Depending on the concentration of the organisms in the bottom plate, either half (first half) or the entire area of the bottom plate may be counted. For counting the organisms in the first hall of the bottom area, the centre of the field of vision is first determined by finding out the approximate number of vertical segments in the field of vision in between vertical threads, with the help of planktonic organisms marked at each vertical thread. Depending on the nature of analysis, the planktonic organisms should be identified either to species or generic level.