Lagoon Spire Snail (Heleobia stagnorum)
Key Details
| Taxonomic Groups: | Invertebrate > mollusc > Mollusc (non-marine) |
| Red List Status: | Critically Endangered (Not Relevant) [CR(nr)] |
| D5 Status: | Included in the baseline Red List Index for England (Wilkins, Wilson & Brown, 2022) |
| Section 41 Status: | (not listed) |
| Taxa Included Synonym: | (none) |
| UKSI Recommended Name: | Semisalsa stagnorum |
| UKSI Recommended Authority: | (Gmelin, 1791) |
| UKSI Recommended Qualifier: | (none specified) |
| Red List Citation: | Seddon et al., 2014 |
| Notes on taxonomy/listing: | (none) |
Criteria
| Question 1: | Does species need conservation or recovery in England? |
| Response: | Yes |
| Justification: | The snail is only known living at a single site on Thorney Island, West Sussex, which is at risk in a number of ways. Last surveyed in autumn 2019. |
| Question 2: | Does recovery/ conservation depend on species-specific actions? |
| Response: | Yes |
| Justification: | The very slightly brackish lagoon that it lives in is vulnerable due to a number of factors including (1) encroachment of marginal Phragmites beds reducing water area, (2) an influx of salt water to raise salinity level to negatively affect snail, (3) sewage effluent from an adjacent water treatment works. |
| Question 3: | At a landscape scale, would the species benefit from untargeted habitat management to increase habitat mosaics, structural diversity, or particular successional stages? |
| Response: | No |
| Justification: | This species would not benefit from untargeted management |
Species Assessment
| Current step on the Species Recovery Curve (SRC): | 5. Remedial action identified |
| Recovery potential/expectation: | Low - Relict or natural rarity |
| National Monitoring Resource: | Structured - insufficient |
| Species Comments: | Conservation action will require specific collaboration with the Chichester Harbour Conservancy who manage the area. |
Key Actions
Key Action 1
Proposed Action: Undertake targeted habitat management to reduce the encroachment of phragmites into the open water that is required by this species.
Action targets: 5. Remedial action identified
Action type: Habitat management
Duration: 6-10 years
Scale of Implementation: 1 site
High priority sites: Little Deep, Thorney Island, Chichester Harbour, West Sussex.
Comments:
Key Action 2
Proposed Action: Undertake further surveys of other, as yet unsurveyed non-tidal, very low salinity lagoons in the vicinity of Portsmouth, Langstone and Chichester Harbours is recommended to try to locate further populations of this snail. Clearly further populations would increase resilience to extinction of this snail in England.
Action targets: 3. National Monitoring Plan agreed and implemented
Action type: Status survey/review
Duration: 2 years
Scale of Implementation: ≤ 20 sites
High priority sites: Portsmouth, Langstone and Chichester harbours
Comments:
Key Action 3
Proposed Action: Explore creation of a managed retreat lagoon system into which it might retreat in the face of continued sea level rise. This would need to model likely sea levels, degree of saline incursion and security to stand a chance of working. Scope out plans with Harbour trust and others.
Action targets: 4. Autecology and pressures understood
Action type: Scientific research
Duration: 3-5 years
Scale of Implementation: ≤ 20 sites
High priority sites:
Comments:
Acknowledgment:
Data used on this website are adapted from Threatened species recovery actions 2025 baseline (JP065): Technical report and spreadsheet user guide (Natural England, 2025). Available here.