Northern hatchet shell (Thyasira gouldii)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help

Summary

Description

A small, rather globular, white burrowing bivalve. The two halves of the shell are the same shape and the shell itself is thin and fragile. This species is very similar to Thyasira flexuosa, the wavy hatchet shell.

Recorded distribution in Britain and Ireland

At the head of Loch Etive, west coast of Scotland. Formerly also found in Lochs Linnhe, Eil and Sunart. Recorded also from Shetland (further detail lacking). Presence in Scottish waters forms the extreme southern end of the geographic range.

Global distribution

A pan-arctic distribution from waters of the Commonwealth of Independent States along the north coast of Norway, around the coast of Greenland. On American coasts as far south as Cape Cod on the east and California on the west coast.

Habitat

Inhabits a small chamber in the top few centimetres of soft mud or sand-mud sediments at the head of some sea lochs. Habitat generally characterized by the presence of organic matter.

Depth range

15-25

Identifying features

  • A small, white, globular bivalve.
  • The shell is equivalved but thin and fragile.
  • The hinge line is without teeth.
  • The inside of the shell is white and muscle scars indistinct.
  • The gills are thick, fleshy and dark brown in colour.

Additional information

The larger eggs and characteristic sperm are useful features for separating Thyasira gouldii from Thyasira flexuosa.

Biology review

Taxonomy

LevelScientific nameCommon name
PhylumMollusca
ClassBivalvia
OrderLucinida
FamilyThyasiridae
GenusThyasira
Authority(Philippi, 1845)
Recent Synonyms

Biology

ParameterData
Typical abundanceModerate density
Male size rangeup to 8mm
Male size at maturity4mm
Female size range4mm
Female size at maturity
Growth formBivalved
Growth rate1mm/year
Body flexibilityNone (less than 10 degrees)
Mobility
Characteristic feeding methodActive suspension feeder, Non-feeding
Diet/food source
Typically feeds onsuspended organic matter and digestion of mutualistic bacteria.
Sociability
Environmental positionInfaunal
DependencyMutualist (Mutualism).
a bacterium.
SupportsHost

the parasitic copepod Axinophylus thyasirae and a mutualistic bacterium.

Is the species harmful?No

Biology information

Thyasira gouldii has been found up to 1,500 individuals per square metre but typically below 500. Such abundances may no longer exist in Scottish waters. It is difficult to define an adult size range as there appears no specific point where juveniles become adult. Values provided are roughly maximum size where size refers to shell length. Large numbers of a mutualistic bacterium live sub-cuticularly in the gills of Thyasira gouldii (and several other thyasirids). The bacteria are chemoautotrophic and oxidise sulphur in order to assimilate carbon dioxide. Carbon isotope ratios indicate that digestion of these bacteria contributes considerably to the nutrition of this species. Although the bacteria utilise sulphur the bivalves inhabit sediment with very little free sulphide. The relationship is not thought to be obligate but the presence of the bacterium is very beneficial to the brachiopod. Eleven percent of a population of Thyasira gouldii in Loch Etive was infected with the parasitic copepod Axinophylus thyasirae Blacknell & Ansell, 1975). This parasite inhabits the mantle cavity and causes lower body weights and indirect castration. The female parasites reach sizes of 4.5 mm and there can be up to five parasites per host causing massive restriction of the cavity and interfering with feeding currents.

Habitat preferences

ParameterData
Physiographic preferencesSea loch or Sea lough
Biological zone preferencesLower circalittoral, Lower infralittoral, Upper circalittoral
Substratum / habitat preferencesMud, Muddy sand, Sandy mud
Tidal strength preferences
Wave exposure preferences
Salinity preferencesReduced (18-30 psu)
Depth range15-25
Other preferencesNo text entered
Migration PatternNon-migratory or resident

Habitat Information

Geographic distribution was probably more general during the last glaciation and remaining populations are relicts. The populations in Lochs Linnhe and Eil have been killed by the discharge of pulp-mill effluent. The population in Loch Etive has also decreased massively between 1984 and 1989. It is possible that this decrease has been brought about by a viral infection of the mutualistic bacteria living on the gills of Thyasira gouldii. Digestion of the bacteria provides considerable nutrient input. This species can burrow up to ten times its shell length (max. 8cm) and uses its vermiform foot to create channels deeper into the sediment. A mucus lined inhalant tube is made up to the surface from the living chamber. Little information is available about preferred water flow rates but are probably quite low being at the head of a sea loch. Wave exposure preferences are also likely to be sheltered. Typical depths in Scottish waters are 15-25 metres but the species has been found down to a few hundred metres depth. Optimal salinity levels are 25-30 psu. Thyasira gouldii appears to be restricted to locations where bottom waters remain cool throughout the year as a result of salinity stratification.

Life history

Adult characteristics

ParameterData
Reproductive typeGonochoristic (dioecious)
Reproductive frequency Annual protracted
Fecundity (number of eggs)100-1,000
Generation timeInsufficient information
Age at maturityInsufficient information
SeasonJanuary - December
Life spanInsufficient information

Larval characteristics

ParameterData
Larval/propagule type-
Larval/juvenile development Direct development
Duration of larval stageNot relevant
Larval dispersal potential <10 m
Larval settlement periodNot relevant

Life history information

The sexes are separate and fertilization probably occurs in the mantle or suprabranchial cavity. Egg development is temperature dependent being (in the laboratory) around 50 days at 10 degrees C and 37 days at 16 degrees C. There is no synchronisation of reproduction and spawning occurs throughout the year. Eggs are white, oval and about 260 microns long. Up to 750 eggs are produced with each spawning. No information is available on the mechanism of spawning or the number of spawnings per year. Fertilised eggs are 'pumped' out of the inhalant tube and being quite dense, sink down onto and stick to the sediment about 1 cm from the opening. Consequently eggs are rarely dispersed by water currents. No information is available about lifespan but given the known growth rate and maximum size achieved it must be at least 5-10 years.

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

Use / to open/close text displayed

 IntoleranceRecoverabilitySensitivityEvidence / Confidence
Substratum loss [Show more]

Substratum loss

Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details

Evidence

The adults bury in the sediment so sediment loss would result in death. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very low / none Very High Low
Smothering [Show more]

Smothering

Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details.

Evidence

The species is an active burrower down to 8cm. Smothering with a further 5 cm sediment should not cause mortality. The bivalve would be able use its vermiform foot to burrow back up towards the surface. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal.
Low Very high Very Low Low
Increase in suspended sediment [Show more]

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Changes in siltation would probably not have a great effect on Thyasira gouldi. Feeding depends on the presence of suspended organic matter - decreases in siltation may reduce the food available, increases may facilitate feeding. Large increases in siltation may block up the inhalant tube which would require energetic expenditure to clear. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal.
Low Very high Very Low Low
Decrease in suspended sediment [Show more]

Decrease in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

No information
Desiccation [Show more]

Desiccation

  1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
  2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

The species in entirely subtidal and breathes using gills. It is likely to be highly intolerant of desiccating influences. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very low / none Very High Low
Increase in emergence regime [Show more]

Increase in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

The species in entirely subtidal and breathes using gills. It is likely to be highly intolerant of emergence. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very High Low
Decrease in emergence regime [Show more]

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

No information
Increase in water flow rate [Show more]

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Increases in water flow may cause sediment movement, blocking the inhalant tube requiring energetic expenditure to clear. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal.
Low Very high Very Low Low
Decrease in water flow rate [Show more]

Decrease in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

No information
Increase in temperature [Show more]

Increase in temperature

  1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
  2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

The populations in the British Isles are at the southern extreme of the geographical distribution. The surviving relict populations are restricted to areas where the bottom waters remain cool all year round. Any increases in temperature are likely to cause death. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very High Moderate
Decrease in temperature [Show more]

Decrease in temperature

  1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
  2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

No information
Increase in turbidity [Show more]

Increase in turbidity

  1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
  2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

This species is infaunal and as such will be tolerant of changes in turbidity.
Tolerant Not relevant Not sensitive Low
Decrease in turbidity [Show more]

Decrease in turbidity

  1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
  2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

No information
Increase in wave exposure [Show more]

Increase in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Thyasira gouldi lives in rather wave sheltered areas at the heads of sealochs. Increases in wave exposure may disrupt the sediment in which they live, cause continual displacement and physical damage to the shells which are thin and fragile. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very High Low
Decrease in wave exposure [Show more]

Decrease in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

No information
Noise [Show more]

Noise

  1. Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods.
  2. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details

Evidence

This species probably has very limited facility for detection of vibrations.
Tolerant Not relevant Not sensitive Very low
Visual presence [Show more]

Visual presence

Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details

Evidence

This species is infaunal and probably has very limited facility for visual perception.
Tolerant Not relevant Not sensitive Low
Abrasion & physical disturbance [Show more]

Abrasion & physical disturbance

Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details.

Evidence

Thyasira gouldi is a small species and the shell is thin and fragile. They occupy the top few centimetres of the sediment and physical disturbance by a passing scallop dredge is likely to cause death Therefore, an intolerance of high has been recorded.
Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very High Low
Displacement [Show more]

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Thyasira gouldi are active burrowers, displacement will probably result in the bivalve burrowing back down into the sediment and creating a new living chamber and mucous lined inhalant siphon. There would be an energetic cost to this and feeding would be impaired. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal.
Low Very high Very Low Low

Chemical pressures

Use [show more] / [show less] to open/close text displayed

 IntoleranceRecoverabilitySensitivityEvidence / Confidence
Synthetic compound contamination [Show more]

Synthetic compound contamination

Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:

  • evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity;
  • evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity;
  • evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity.

The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details.

Evidence

Insufficient
information
No information No information No information Not relevant
Heavy metal contamination [Show more]

Heavy metal contamination

Evidence

Insufficient
information
No information No information No information Not relevant
Hydrocarbon contamination [Show more]

Hydrocarbon contamination

Evidence

Insufficient
information
No information No information No information Not relevant
Radionuclide contamination [Show more]

Radionuclide contamination

Evidence

Insufficient
information
No information No information No information Very low
Changes in nutrient levels [Show more]

Changes in nutrient levels

Evidence

Organic enrichment from pulp mills is believed to have been the cause of the death of two populations in west Scotland sealochs. Similar species such as Thyasira flexuosa may be considerably more tolerant of nutrient enrichment (densities of up to 4000 per square metre have been recorded in areas or organic enrichment). Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible.
High Very High Moderate
Increase in salinity [Show more]

Increase in salinity

  1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
  2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

The species inhabits waters of reduced salinity with 25-30 psu being optimal. Adults exposed to lower than optimal salinities produced non viable or slow developing eggs. There is insufficient information regarding the effects of salinity on adults. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. Immigration from other populations is highly unlikely. Reproduction occurs throughout the year, development is direct with quite high fecundity (750 eggs / spawning) High densities of the species are known to occur (up to 1500 per square metre). Growth however is rather slow (1mm/yr) and maturity is only reached at around 4 mm. Recruitment from this population would allow the population to recover in five to ten years.
Intermediate Moderate Moderate Moderate
Decrease in salinity [Show more]

Decrease in salinity

  1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
  2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

No information
Changes in oxygenation [Show more]

Changes in oxygenation

Benchmark.  Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details.

Evidence

The bivalve burrows in often black, anoxic sediment but the area surrounding the mollusc is oxygenated through water movement down the inhalant tube. If the water inhaled becomes de-oxygenated (for instance because of isolation of water masses ) some mortality is likely.. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. Immigration from other populations is highly unlikely. Reproduction occurs throughout the year, development is direct with quite high fecundity (750 eggs / spawning) High densities of the species are known to occur (up to 1500 per square metre). Growth however is rather slow (1mm/yr) and maturity is only reached at around 4 mm. Recruitment from the local population would allow the population to recover in five to ten years.
Intermediate Moderate Moderate Low

Biological pressures

Use [show more] / [show less] to open/close text displayed

 IntoleranceRecoverabilitySensitivityEvidence / Confidence
Introduction of microbial pathogens/parasites [Show more]

Introduction of microbial pathogens/parasites

Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details.

Evidence

Viral infection of the mutualist bacterium living on the bivalve's gills has been suggested as the reason for a major decline in the Loch Etive population. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. Immigration from other populations is highly unlikely. Reproduction occurs throughout the year, development is direct with quite high fecundity (750 eggs / spawning) High densities of the species are known to occur (up to 1500 per square metre). Growth however is rather slow (1mm/yr) and maturity is only reached at around 4 mm. Recruitment from this population would allow the population to recover in five to ten years.
Intermediate Moderate Moderate Moderate
Introduction of non-native species [Show more]

Introduction of non-native species

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

Insufficient
information
No information No information No information Not relevant
Extraction of this species [Show more]

Extraction of this species

Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

It is extremely unlikely that this species will be extracted - it has no economic or interest value and is protected by the Wildlife and Countryside Act and is covered by a UK Biodiversity Action Plan.
Not relevant Not relevant Not relevant Moderate
Extraction of other species [Show more]

Extraction of other species

Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

The larva has no known obligate partner species that are likely to be extracted. Benthic trawls or dredges for other species may damage or destroy the shells but the species is protected by the Wildlife and Countryside Act and is covered by a UK Biodiversity Action Plan.
Not relevant Not relevant Not relevant Moderate

Additional information

Importance review

Policy/legislation

DesignationSupport
Wildlife & Countryside ActSchedule 5, section 9

Status

Non-native

ParameterData
Native-
Origin-
Date Arrived-

Importance information

-none-

Bibliography

  1. Anonymous, 1999g. Northern hatchet shell (Thyasira gouldi). Species Action Plan. In UK Biodiversity Group. Tranche 2 Action Plans. English Nature for the UK Biodiversity Group, Peterborough., English Nature for the UK Biodiversity Group, Peterborough.

  2. Blacknell, W. M. & Ansell, A. D., 1974. The direct development of bivalve Thyasira gouldi (Philippi). Thalassia Jugoslavica, 10, 23-43.

  3. Blacknell, W. M. & Ansell, A. D., 1975. Features of the reproductive cycle of an arctic bivalve from a Scottish sea loch. Marine Ecology, Pubblicazioni Della Stazione Zoologica Di Napoli I, 39, Suppl., 26-52.

  4. Bowden, J. & Heppel, D., 1973. Revised list of British Mollusca. 2. Unionacea - Cardiacea. Journal of Conchology, 26, 237-272.

  5. Dando, P.R. & Southward, A.J., 1986. Chemoautotrophy in bivalve molluscs of the Genus Thyasira. Journal of the Marine Biological Association of the United Kingdom, 60, 915-929.

  6. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  7. Southward, E.C. & Southward, A.J., 1991. Virus-like particles in the bacteria symbiotic in bivalve gills. Journal of the Marine Biological Association of the United Kingdom, 71, 37-45.

  8. Southward, E.C., 1986. Gill symbionts in the Thyasirids and other bivalve molluscs. Journal of the Marine Biological Association of the United Kingdom, 66, 889-914.

  9. Tebble, N., 1966. British Bivalve Seashells. A Handbook for Identification. Edinburgh: British Museum (Natural History), Her Majesty's Stationary Office.

Datasets

  1. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  2. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-07-21

Citation

This review can be cited as:

Jackson, A. 2007. Thyasira gouldii Northern hatchet shell. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21-07-2024]. Available from: https://marlin.ac.uk/species/detail/1149

Last Updated: 30/08/2007