270 THE ESSEX NATURALIST
regions (Fig. 3). A maximum of 28 species was recorded from
station C.3, whilst a minimum of 0 was obtained from 7.4% of
the Blackwater stations (2A.2, 2A.3, S.14 and HB.l). The average
value was 11.5 species per station within the Blackwater, and
10.3 species per station was obtained for the offshore stations.
Distribution and Abundance of Key Species
Davis (unpublished) maintained records of the frequency of
occurrence of a number of benthic species during the years
1960, 1961, 1962, 1963 and 1965. The 1970 survey endeavoured
to obtain comparable data in order to ascertain the extent to
which these species had recovered from the severe winter of
1962-1963. The earlier data are in the form of percentage of
Blackwater and offshore stations in which the various species
were found, changes in abundance at individual stations were
not noted on a yearly basis. The present survey also attempted
to obtain abundance figures for the relevant species, but in view
of the small number of samples taken, etc., these are probably
unreliable. Some simplified abundance maps are, however, pre-
sented in Fig. 6; broad abundance bands have been drawn in an