Sample collection
22 ditch water samples were collected from ditch surface water by
Natural England staff at Stodmarsh NNR between the
16th and 27th November 2020 (Figure
2). 10 ditch water samples outside the known range of S. nitida were
collected by ADAS staff between the 10th January and
the 4th February (sample information can be found in
supplemental file 1, table S1 and S2). 20x 30 mL water samples were
collected along the length of each of the ditch and pooled into sterile
sampling bag. Up to 500 mLs of this water was filtered through a 0.22 µM
PES sterivex filter (Millipore) using a 50 mL luer-lock syringe (Table
1). After filtration of water, 95% ethanol was added as a preservative.
Snail specimens were collected during an invertebrate survey carried out
at the same 22 ditches at Stodmarsh NNR by Dan Bennett of The Ecology
Co-op, contracted by Natural England between December and January
2020/2021 (specimen information and detailed sampling methodology can be
found in supplemental file 1, table S3). Manual surveys of the 22
ditches were performed using an adapted invertebrate sampling protocol
from Drake (2007). The emphasis was on the free-style netting of
suitable looking micro-habitats (e.g. emergent vegetation stands) that
are likely to be most productive for this assemblage. Effort was
deliberately not divided in proportion to the extent of features nor
length of ditch, since species are not distributed in this fashion.
Snail specimens from S.nitida and nine other similar ram’s-horn
shaped species, from the 16 species of snail ) found during invertebrate
survey were identified and preserved in 95% ethanol prior to shipment
to the laboratory: Anisus vortex, Bathyomphalus contortus,
Gyraulus crista, Gyraulus albus, Hippeutis complanatus, Planorbarius
corneus, Planorbis carinatus, Planorbis planorbis, Segmentina nitida,
Valvata cristata.