Shell bank in the River Avon at Nafford, Worcestershire

Gary & Nicki Farmer

On the 6^th of May 2013 we were walking along the banks of the River Avon at Nafford when we noticed what we first thought was a shingle bank with some mollusc shells mixed in (01, 02). We walked on to the bank to look for shells and realised that it was not a shingle bank at all, but the entire thing was made of empty mollusc shells. We spent just a few minutes picking through the shells and found several species including land snails Dark-lipped Banded Cepaea nemoralis and Copse Snails Arianta arbustoum which must have been washed into the river further upstream. Of the water snails present the most abundant was the River Snail Viviparus viviparus (03) along with other gastropods including many small Bithynia tentaculata (04). These two species are typical of relatively slow-flowing, well-oxygenated water courses. Along with these were just a few small shells of the Wandering Pond Snail Lymnaea peregra (Radix balthica) (05), a ubiquitous species.

Bivalves were also present, represented by the Nut Orb Mussel Sphaerium rivicola (06), larger Duck Mussel Anodonta anatina (07)and a much less common species, the Depressed River Mussel Pseudanodonta complanata (08).

However the most striking species of the day was the invasive Zebra Snail Dreissena polymorpha. (08) This attractive species was first recorded in Britain in the 1820's and it spread rapidly throughout the canals and rivers of lowland England. Killeen et al 2004 note that the species has increased in abundance since 1999 and has become a pest of water facilities.

Later in the year while editing some of my photographs I 'zoomed-in' on one of the shell bank pictures and noticed what appeared to be small black shells with white spots. I knew that these must be River Nerites Theodoxus fluviatilis a species of lime-rich water courses, preferring hard surfacing to graze on including the masonry of bridges (Kerney 1999). As I had never seen this species (or its shells) we made a return visit to Nafford on a Nerite hunt on 1^st September 2013. When we arrived we found that the shell bank was actually the main route onto the river for canoeists and so the continuous trampling through the summer had turned the pile of shells into grit! Luckily the Nerites have very hard shells and after several minutes of careful searching we were rewarded with a few shells of this most attractive little water snail (07).

Many thanks to Rosemary Hill for helping with the identification of the shells.