Aquatic ecology and Biodiversity

Unit 12- Biodiversity and conservation

Practicals 1- Study of collection and analysis of plankton
Experiment No. 1
Phytoplankton
The phytoplankton is collated using bottle samplers and Pump and hose. Bottle samplers are ideal for small quantitative phytoplankton collections in coastal waters,estuaries and mangroves etc. Surface water can be obtained by gently scooping water into a container of a suitable size from the leeward side of the vessel. Subsurface water can be obtained by using sampler like Mayer’s water sampler, Friedenger’s water sampler, Nansen Reversing water Sampler. Van Dorn Water Bottle, Niskin Water Bottle, NIO Water Bottle, Universal Water Sampler etc.
Zooplankton
Zooplankton of more than 50µm size can be collected by ordinary net sampling. This method could preferably used for qualitative plankton collections, as large quantity of water is filtered. A net is towed vertically, horizontally or obliquely. Shape of nets commonly used are-conical, conico-cylindrical (conical net with a collar) and conical with a mouth reducing cone. Rectangular shaped nets have also been designed. The net is attached to the wire directly with a bridle. At the cod-end of plankton net, a sampling bucket is attached.
Micronekton:
Issacs-Kidd Midwater Trawl (IKMT) is a midwater trawl used to sample larger plankton having considerable swimming ability and net avoidance. It has a horizontal bar in the upper part and a depressor in the lower part of the net. Net is obliquely towed at a speed of over 2.5m.sec^-1.
Neuston
Pleuston and Neuston are the zooplankton community organisms associated with the surface layer, between the water’s surface and a few centimeters below. The ORI neuston net, has a rectangular mouth opening, attached to a frame which holds float on both sides and the net is towed from its sides.
Epibenthic Plankton:
Some zooplankton occur in midwater during the night and aggregate close to the area floor during the day often form assemblage in benthic layers. Bayer’s epipenthic closing net is designed primarily to collect epibenthic plankton.
Preservation of plankton
Preservation is the maintenance of the fixed condition for extended periods of time. After collection of plankton, the sample should be preserved immediately. For determination of chemical composition, specimens should be fixed within 10min after collection. Samples should be norcotised, fixed and preserved in the order. Use Lugol’s solution for phytoplankton and Buffered formalin for zooplankton.
Storage of samples
Containers such as glass bottles with wide mouth, Polypropylene with plastic screw-on lid are commonly used. Store the samples in a dust free dark and cool place. Maintain the pH between 6.5 and 7.5. Periodic checking for colour and pH is required. The preservative should be changed if necessary.
Analysis of plankton
Transfer one ml of well mixed plankton sample using stempel pipette into the Sedgwick Rafter cell (50x20x1mm) with 1ml. Spread evenly in the form of a thin layer. Allow the chamber undisturbed for half an hour under microcope. Count the organisms in the cell by moving horizontally or vertically.
Calculation

N = nxv/V

Where: N=Total number phytoplankton cells/l
n= Average number of phytoplankton cells in 1ml of sample
v=Volume of plankton concentrate
V=Volume of total water filtered in litre.