308 THE ESSEX NATURALIST
Angle of Slope and Disturbance
It has been suggested by Spooner and Moore (1940) that C.
volutator is exceptionally sensitive to disturbances of the ground
by tidal currents. In Benfleet Creek C. volutator is found only on
the flat-topped bank of area G. C. arenarium, however, was found
in part of area B on a bank with an average gradient of 1 in 7.
It was on this bank, therefore, that I investigated this pheno-
menon of disturbance. A number of transects had been surveyed
and the Corophium zone marked on them. The angle of slope
between each station has been calculated and the results for the
first 12 stations on four of the transects are shown in figure 6.
The arrows denote the beginning of the C. arenarium zone.
Figure 6. The occurrence of C. arenarium in relation to the angle of
slope on four transects in area B. Arrows indicate the commence-
ment of the C. arenarium zone.
Figure 6 shows that C. arenarium does not appear until the
steepest gradient has been passed. In transect 1 the steepest
slope is 13° 17' at station 6 and the Corophium appears at station
8. On transect 2 the steepest gradient is 11° 46' at station 7 and
Corophium appears at station 10. A similar situation holds for
the other transects. This suggests that, all other factors being