NORFOLK BIODIVERSITY ACTION PLAN SPECIES DATA AUDIT ...

TERRESTRIAL AND
FRESHWATER
MOLLUSCS
Spp.
Considered
Extinct
Species Present
or
absent
in
Norfolk
Little Whirlpool Ram’s-horn
snail
Anisus vorticulus
Thames Ram’s-horn Snail
Gyraulus acronicus
Lagoon Spire Snail
Heleobia stagnorum
Freshwater Pearl Mussel
Margaritifera margaritifera
Spp. New
to National
BAP List
No. of
records in
database
No. of
1km
squares
recorded
since
1980
Possible other
sources
of data sets
56
Other survey
work
completed or
in progress
Comments
P 37 12 Current UK Species Action Plan
Occurs in unpolluted, calcareous waters in
well-vegetated marsh drains.
Internationally threatened - Over-frequent
ditch clearance, nutrient enrichment due to
fertiliser applications, and conversion of
grazing levels to arable farming with
associated water table lowering.
Norfolk Action Plan published December
1998, revised January 2003.
A - - Not recorded in Norfolk
Preferred habitat is cold water lakes and
ponds.
Marked decline in UK – Habitat loss
New to national list of BAP priority
species 2007
A - - Not recorded in Norfolk
Found in saline lagoons.
Declining – Habitat loss and degradation.
New to national list of BAP priority
species 2007.
A - - Not recorded in Norfolk
Vulnerable. Current UK Species Action Plan.
The species is dependent on the presence of
salmonid fish as hosts for its larvae.
Internationally threatened - Poor water
quality, habitat removal and alteration
through development, drainage schemes,
decline in populations of host fish, conifer
planting, amateur pearl fishing and poor land
management in the catchment.