ECOLOGICAL STUDIES IN SOUTH BENFLEET CREEK 293
illustrated in Area G (see fig. lb.) where the steeper slope up from
the stream appears to be of a sandy nature and much firmer as
compared with the flat top of the region, which is of a decidedly
muddier consistency, Moore and Spooner (1940), Percival (1929),
Rees (1940).
The preliminary investigations of the lower reaches of the
creek in June revealed the presence of a large population of the
amphipod crustacean Corophium. An investigation of the whole
creek, however, revealed that there were two species of Corophium
present, each species having a different distribution. The aim of
this paper, therefore, is to discover reasons for the differing
distribution of these two species—Corophium volutator (Pallas)
and Corophium arenarium (Crawford)—in Benfleet Creek.
Position of the sampling stations
Sampling stations were set up in each type of substratum in
the Creek.
On the sand banks A, B and E—C. arenarium areas—random
samples were taken. Their position is shown on figure 2 by
small circles. In addition, a transect was put down on bank B
and sampling stations were set up at 1 yard intervals from Low
Water Mark on August 7th, 1959 (see figure la). The position
of this transect is shown in figure 2 by a line across area B. Nine
other transects 20 feet apart were also surveyed and the positions
of the C. arenarium zone marked. Some of these transects are
used in figure 6.
Another transect was put across area G, the C. volutator
zone, about 1/4 mile below Benfleet Bridge. The transect was
surveyed (figure lb) and four sampling stations established 8,
50, 115 and 125 yards from H.W.M.M.T. The position of the
transect is shown by the line across area G in figure 2.
Three sampling stations (shown by crosses in figure 2) which
have been called the Long Transect were set up outside the
estimated Corophium zones. It was important that this should
be done in order to complete the ecological picture and to discover
factors limiting the distribution of Corophium.
Animal communities are subject to rapid changes, caused by
the yearly life cycle of the species, Watkins (1941), and possible
changes in the location of the community at different seasons of
the year. Thus the time at which any investigation of an animal
community is made is of some importance. Two preliminary
investigations of the area were carried out, one at the end of
June and the other at the end of July. The detailed work was
done during the period of August 1st to August 29th, 1959.
Final details, mainly concerned with collecting water and some
soil samples were completed up to September 7th and some soil
samples had to be recovered and the pH of the water determined
early in December. Thus the details of distribution of the species,
and the conclusions arrived at as to the factors determining their
distribution, can only be related to the month of August 1959,