Marine Biology

Description of nylon filtering materials

Owing to the fineness of the filtering materials used in plankton nets, there is every possibility for choking which depends on many factors such as, (i) ratio of the opening of the net to the filtering surface, (ii) quality of fineness, i.e no. of nylon net cloth or no. of meshes/cm² or mesh width (porosity) and (iii) density of plankton in the environment. As coarser net is less likely to be choked up, it can filter only larger zooplankton and not micro (net) phytoplankton. Invariably for coarser net, a ratio of 1:4 between the opening of the net and the filtering surface is maintained. On the other hand, for nets of smaller mesh widths and for collecting quantitative microphytoplankton, the ratio has to be altered and the filtering surface should be increased in relation to the net opening.

Depending on the fineness of the filtering portions, a number of monofilament nylon materials are available. The number of the net material increases with  increase in fineness of the net and the decrease in the sifting area which is nothing but the sum of mesh area per unit.

Observed values of mesh widths of the various monofilament nylon net materials

No. of the net	Av. mesh width (µm)
0 3 4 8 12 13 14 15 16 17 18 19 20 21 25 30	508 306 288 184 130 115 101 93 88 78 72 70 60 62 55 41

are of the filtering portion. A two net pieces (nos. 3 and 30) with different mesh widths are diagrammatically shown in figs .