6
THE ESSEX NATURALIST
The subsidence of the Essex coast has been reported in the
Essex Naturalist by Clark (1898), Dalton and Laver (1910), and
others, while actual physical changes are dealt with by Rudler
(1905) and Robinson (1953). There is also much historical evidence
documented in the Essex Naturalist to show continued subsidence
and erosion of the coast since Roman times.
The Zooplankton: The records of zooplankton that have been
included in the Fauna List were made largely by the late Mr. B.
G. A. Carrie and Mr. T. E. Howard, who carried out a sampling
programme from 1960 through to 1964. Qualitative samples
were taken with 80 mesh/inch and 140 mesh/inch net tows and
vertical hauls, and quantitative samples with volume calibrated
motor pump and 140 mesh/inch net. Early investigations
showed the presence of a Copepod crustacean fauna, established
as characteristic of European estuaries and inshore waters. The
species composing this fauna are: —Acartia clausi, Acontia
discaudata, Centropages hamatus, Temora longicornis, Paracalanus
parvus, Pseudocalanus elongatus, Eurytemora hirundoides,
Oithona similis, and Euterpina acutifrons.
A limited amount of work in the brackish waters of the Black-
water and Colne in 1963 and 1964 produced some records of
euryhaline species of Copepod, particularly Acartia grani, while
there are also records of open sea species such as Calanus
finmarchicus and the chaetognath Sagitta setosa.
Some attention was also paid to the planktonic larvae of
bottom-living animals, particularly of barnacles and oysters.
These larval forms constitute a significant part of the plankton at
some times during the summer. The highest densities of zooplank-
ton occur in July and late September (the actual time varying
from year to year) when the harpacticoid Copepods are in great
abundance. In September 1962 the total number of animals in
a plankton sample from the Blackwater exceeded 96,000 per cubic
metre of water, the largest proportion being harpacticoid Copepods.
The Littoral and Benthic Fauna: A considerable part of the effort
in the recent investigations has been devoted to the study of the
littoral and benthic fauna. Qualitative samples were taken by
hand collection on the shore and from the bottom with a hand
dredge, beam trawl and otter trawl. Quantitative samples and
samples for micro-benthos were taken on the shores with a
1/16 nr quadrat frame and from the bottom with a 1/10 m2 Van
Veen type grab. For counts of larger animals, these samples were
sorted by washing through sieves of 1/4 inch and 1/8 inch mesh.
The distribution of different sediments on the shores and
bottom of the Blackwater are most important in determining the
animal communities. There is very little zonation of fauna as is
found to occur on rocky shores and many of the species of
crustaceans, molluscs and echinoderms usually found at low tide
level, are only found sublittorally. The main reason for this would