Vol. XXVII—Part IX. April, 1944—Sept, 1944.
THE
Essex Naturalist:
BEING THE
Journal of the Essex Field Club.
THE NANNOPLANKTON OF BOMB-CRATER POOLS IN
EPPING FOREST.
By D. J. SCOURFIELD, I.S.O., F.L.S., F.R.M.S.
[Read 27th November, 1943.]
PLANKTON AND NANNOPLANKTON.
BY way of introduction to this subject, a few words about
"plankton" and "nannoplankton" will probably not be
out of place, in spite of the fact that the word plankton at any
rate is often to be seen nowadays even in newspaper articles.
The word plankton (from Greek "plagktos" = drifting) was
proposed by Hensen (1887) as a collective term for the small
organisms which occur suspended or free-swimming in water
and whose powers of movement, if any, are relatively so small
that they drift about at the mercy of the currents which are
constantly taking place in all kinds of waters.
For the collection and concentration of such organisms, nets
of silk gauze (silk "bolting cloth" of the millers) are generally
used. The finest grade of such gauze has a mesh of about two
hundred threads to the inch each way, but as the threads occupy
rather more than half the total space, the clear openings between
them are only 1/500th of an inch across or even slightly less. It
had, of course, long been known that there were many organisms
smaller than this, but for some time they were not thought to
be of much importance, and it was not until Lohmann (1908)
issued his paper on the absolute amount of plankton in sea
water that the abundance and significance of these very small
organisms was fully realised. Later Lohmann (1909 and 1911)
introduced the term nannoplankton (from Greek "nannos" =