104
A BRACKISH WATER COMMUNITY NEAR
SOUTHEND.
By N. H. HOWES
(Department of Zoology and Comparative Anatomy,
University College, London).
(With One Plate).
IN 1933 Mr. F. J. Lambert introduced me to an artificial
lagoon which had been made by the damming of a creek
(New England Creek) running from the Yokefleet, a tributary of
the River Roach, to the Maplin Sands. Preliminary investiga-
tion showed that the chlorinity of the water isolated in this
lagoon was already considerably less than that of sea-water,
and it seemed well worth while to investigate the chemical and
physical nature of the environment and to correlate results so
obtained with the fauna and flora. The particular interest lay
in the fact that, unlike most brackish water communities, which
are generally estuarine and hence directly open to invasion by
fresh-water and marine organisms, this was a closed system and,
apart from insects, would contain only animals which could
breed in the new environment.
The lagoon is situated to the north-east of Southend between
Great Wakering and Foulness Island. It lies between Haven-
gore, which is still open, and Shelford Creek, which is dammed by
the Wakering-Foulness Island road. In 1924 the War Office
dammed the seaward approach of New England Creek, and in
July, 1925, the Yokefleet end, thereby enclosing a strip of water
about two miles long and from 50 to 80 yards wide. The road
divides this into a north-west portion about 11/2 mile long and
a small south-east portion, connected by a narrow culvert.
This work deals exclusively with the north-west portion, which
has a maximum depth of 12 feet, a surface area of from 172,400
to 203,000 square yards and contains 301,000 to 392,000 cubic
yards of water. All these values fluctuate, since the level of the
water varies under different climatic conditions, e.g., between
January and October, 1934, the level fell 20 inches but recovered
14 inches by March, 1935. The sources of the salts in the water are
primarily the water originally enclosed and secondly, the drainage