BOTTOM FAUNA OF BLACKWATER ESTUARY: 1970 273
Macropodia, however, was decimated by the winter, so much
so that it "declined to an undetectable level" (Davis, 1967). In
1965, only two specimens of it were obtained "during dredging in
mid river between stations C.3 and line 1, Stn. 3" (Davis, 1967);
the 1970 survey failed to record it. Ophiothrix also declined
markedly, but had started to effect a recovery by 1965 (Fig. 4d).
Solaster (Fig. 5a) declined somewhat and continued declining, so
that by 1965 its frequency within the Blackwater stood at half
the 1960 level, whilst Eupagurus (Fig. 5b), Carcinus (Fig. 5c) and
Asterias (Fig. 5d) continued declines which commenced in 1961-
62. Davis did not keep records of the frequencies of Urosalpinx
and Ostrea within the Blackwater during the years 1961, 1962
and 1963, although in both cases their 1965 frequency was lower
than that of 1960. Conversely, their frequencies at the offshore
collecting ground were the same in 1965 as in 1962. Urosalpinx
has always been comparatively rare in the main part of the
Blackwater (at least in recent years): it was only recorded from
two stations in 1965; the 1970 survey failed to find it.
The 1970 survey, then, failed to find Porcellana, Macropodia
or Urosalpinx, but recorded the other ten species at varying
frequencies. The 1970 values for eight of these are compared
with the values from 1960 to 1965 in Figs. 5 and 6. From these
graphs it will be apparent that (a) Eupagurus and Ophiura are
more widespread now, both in the Blackwater and offshore, than
at any time in the 1960s; (b) Carcinus, Buccinum and Ophiothrix
are more widespread within the Blackwater than they were
during 1960-65, although the two former may be on the decrease
offshore, and the latter has not yet attained its 1962 level outside
the Blackwater, it is, however, on the increase there; (c) Hyas
and Asterias were more widespread offshore in 1970 than in
either 1962 or 1965 (the two previous records), but although
they both appear to be on the increase within the Blackwater,
their frequencies have not yet risen to their 1963 levels; and (d)
Solaster was as abundant in 1970 as at any time from 1960 to
1965, its frequency having increased markedly since 1965;
offshore it has also increased since 1965, but has not yet attained
its 1962 level. Ostrea has also increased its frequency since 1965,
particularly in the offshore regions (from 7% to 19%). Only
Crepidula may possibly be on the decline, it being found in
about 12% less stations within the Blackwater in 1970 than in
1965, and in about 4% less offshore. It still remains, however,
the most widespread macroscopic species (Table 2), and also
the most abundant of the larger species in number of individuals
(Fig. 6a).
In summary of the above, it can be stated that the evidence,
such as it is, appears to indicate that (a) Porcellana and Macro-
podia have not recolonised the Blackwater, (b) Urosalpinx
remains infrequent, if present, within the survey area, and (c)
that all species, with the exception of Crepidula, were more