Services · Specialist

Mollusc Surveys

Mollusc surveys are among the rarest specialisms in UK ecological consultancy. We deliver freshwater and terrestrial mollusc assessments with on-site laboratory identification — particularly for legally protected species such as freshwater pearl mussel and Desmoulin's whorl snail.

Freshwater seasonMay – September
Terrestrial seasonApril – October
Key speciesFreshwater pearl mussel
ID methodOn-site laboratory

Overview

Mollusc surveys assess the presence, distribution and conservation status of freshwater and terrestrial snails and mussels on or near development sites. Several UK mollusc species are legally protected or of significant conservation concern, and their presence can be a material consideration in planning decisions.

Freshwater pearl mussel (Margaritifera margaritifera) is one of the UK's most endangered species and is protected under the Habitats Regulations and the Wildlife and Countryside Act. Surveys for this species involve snorkel-based or bankside searches in rivers and streams with suitable substrate and water quality. Desmoulin's whorl snail (Vertigo moulinsiana) — another Habitats Directive Annex II species — is found in tall-herb fen, marsh and ditch-edge vegetation and is surveyed by systematic hand searching.

We have particular strength in mollusc identification, including on-site microscopy for species that cannot be reliably identified in the field. This is genuinely unusual in the UK consultancy market — most ecological practices subcontract mollusc work to a handful of national specialists.

When you need this

  • Development is proposed on or near rivers known to support freshwater pearl mussel populations
  • Your site includes fen, marsh, ditch or wet grassland habitats that could support Desmoulin's whorl snail
  • The Habitats Regulations Assessment for your project identifies potential impacts on Annex II mollusc species
  • An Environmental Impact Assessment requires invertebrate survey including molluscs
  • Your PEA identifies aquatic or wetland habitats where protected molluscs could be present

Our approach

  1. 01
    Habitat assessment

    A walkover to assess substrate, water quality, flow conditions and bankside vegetation to determine suitability for target mollusc species.

  2. 02
    Field survey

    Snorkel surveys or bankside searches for freshwater species. Systematic hand searching through vegetation and leaf litter for terrestrial species. Timed searches with standardised effort.

  3. 03
    Laboratory identification

    Specimens are identified on-site using microscopy where field identification is insufficient. Shell morphology, soft-body features and habitat context are all used in determination.

  4. 04
    Assessment and reporting

    Species lists, distribution maps and conservation assessments are compiled into a planning-grade report with clear mitigation recommendations where protected or notable species are present.

Frequently asked questions

01Why are mollusc surveys so specialist?+
Many mollusc species can only be reliably identified under a microscope using features of the shell or soft body. This requires specialist training and equipment that most ecological consultancies don't hold. We maintain on-site laboratory capability for mollusc identification.
02Is freshwater pearl mussel likely to be on my site?+
Freshwater pearl mussel is now extremely rare in England and confined to a small number of clean, fast-flowing rivers and streams with salmonid fish populations. If your site is on or near one of these watercourses, survey may be required. Your PEA will flag this.
03What is Desmoulin's whorl snail?+
Vertigo moulinsiana is a tiny (2 mm) terrestrial snail found in tall, dense vegetation at the margins of ditches, fens and marshes. It is protected under the Habitats Regulations as an Annex II species. Its presence has been a decisive factor in several planning decisions in southern England.
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