THE BOTTOM FAUNA OF THE BLACKWATER ESTUARY 15
The Bottom Fauna of the Blackwater Estuary :
The Macrofauna of the Area Adjacent to Bradwell
Nuclear Generating Station
R. S. K. Barnes* & J. Coughlan
C.E.R.L. Marine Biological Laboratory, Fawley, Hampshire,
S04 1TW
SUMMARY
The distribution of animal species in the general vicinity of
the Barrier Wall separating the cooling water intakes and out-
falls of Bradwell Power Station appears to be related to the two
major substrate types present in that area. The "shell on mud"
present to the north of the wall (intake side) supports a diverse
fauna of sedentary and sessile species, of which Alcyonidium
gelatinosum, Sabellaria spinulosa ("ross"), scale worms and
colonial hydroids are particularly characteristic. The "mud on
clay" to the south of the wall (outfall side) supports a fauna
characterised by fewer species, although some of them are pre-
sent in large numbers, including errant polychaetes and (especi-
ally) Phoronis ?mulleri which can be regarded as the indicator
of this type of bottom. The more abundant fauna to the north
of the wall is a reflection of the variety of niches provided for
epifaunal organisms by the whole-shell remains overlying the
mud: the temperature differences on the two sides of the wall do
not seem to affect or effect the distribution of the local fauna
except within the immediate vicinity of the outfall culverts.
The areas immediately adjacent to the intake and outfall cul-
verts are typified by modified substrates and both bear specialised
faunas: the former notable for its paucity as a result of scouring
action and the latter for the large number of predators and
scavengers feeding mainly on organic debris washed out of the
culverts. Two warm-water species, Pilumnus hirtellus and
Cereus pedunculatus, with predominantly south-western distri-
butions and rare or absent respectively in the North Sea area,
were recorded from the immediate vicinity of the thermal dis-
charge.
Some 50% of the fauna recorded from the Blackwater as a
whole in 1970 and 1971 is known from the Barrier Wall area and
there is no evidence for faunal impoverishment. Psammechinus,
*Present address: Department of Zoology, University of Cambridge,
Downing Street, Cambridge CB2 3EJ.