THE MARINE FAUNA OF THE BLACKWATER ESTUARY 13
experienced before and erosion on the exposed shores has been
extensive ever since. Also, the methods of oyster cultivation
practised in the Blackwater, where generally oysters are removed
and pests such as Crepidula left alone, would allow the muddy
Crepidula shell bottom to increase. The abundance of Crepidula
on derelict oyster grounds in the River Crouch has been shown by
Mistakidis (1951), and it is probable that the practice of harrow-
ing to clean the beds before a potential spat-fall does more to
encourage the settlement of Crepidula.
These factors, acting individually and in combination, have
in the past, and perhaps are still changing the fauna of the Black-
water. The decline of species such as Aphrodite aculeata and
Psammechinus miliaris might well have started as a result of
severe winters but their failure to re-establish themselves seems
most likely related to the changes in conditions on the bottom. It
would be interesting to know what the bottom sediments of the
Blackwater were like before 1900, perhaps clean shell 'culch', sand
and 'ross', as now persist in the places offshore where Aphrodite
and Psammechinus are still to be found.
ACKNOWLEDGMENTS
The completion of an extensive faunistic survey and compila-
tion of a fauna list is necessarily a task which could not be accom-
plished without the help of many colleagues. Much of the initial
collecting and sorting of specimens was carried out by the Staff
of the Central Electricity Research Laboratories, particularly Dr.
E. J. Perkins, Messrs B. R. H. Williams, T. E. Howard, B. G. A.
Carrie, J. R. Burdett and G. B. Penny, with the assistance of
students from Brunei College, London, and Bristol College of
Technology. Some records are also drawn from work carried out
by Messrs G. D. Waugh and D. Key of the Ministry of Agriculture,
Fisheries and Pood. Mr. P. R. French of West Mersea gave con-
siderable assistance in the detailed exploration of the area.
Staff of the British Museum (Natural History) have confirmed
the identifications or identified the majority of the species re-
corded, and I would like to thank particularly Messrs W. A. Smith,
R. Sims, R. W. Ingle, N. Tebble, W. J. Rees, D. Heppel and A.
Wheeler, and Miss P. L. Cook, for work in their particular field of
interest.
The work was carried out at the Central Electricity Research
Laboratories and this paper is published by permission of the
Central Electricity Generating Board.
References
Chipperfield, P. (1951). Breeding of Crepidula fornicata in the River
Blackwater. J. Mar. Biol. Ass., 30: 49-71.
Clark, P. (1898). The encroaching sea on the East Coast. Essex Nat.,
10: 297-299.
Cole, W. (Edit.) (1888). The Essex Field Club meeting to Maldon and the
Blackwater Estuary. Essex Nat, 2: 246-250.