Crepidula fornicata (Linnaeus, 1758)

COMPILED BY: Anastasija Zaiko
CITATION OF THIS ENTRY: Zaiko A. 2005. Crepidula fornicata. In: Baltic Sea Alien Species Database. S. Olenin, E. Leppakoski and D. Daunys (eds.).
INTERNET: http://www.corpi.ku.lt/nemo/mainnemo.html

TAXONOMY

Crepidula fornicata (Photo by Sergej Olenin)	Crepidula fornicata shells (Photo by Sergej Olenin)

IDENTIFICATION

• Diagnosis:

The shell is oval, up to 5 cm in length, with a much reduced spire. The large aperture has a shelf, or septum, extending half its length. The shell is smooth with irregular growth lines and white, cream, yellow or pinkish in colour with streaks or blotches of red or brown. Slipper limpets are commonly found in curved chains of up to 12 animals. Large shells are found at the bottom of the chain, with the shells becoming progressively smaller towards the top (Rayment 2003).

Life Style:

Stacks of adult Crepidula fornicata live attached to the substratum and are incapable of moving. They are active suspension feeders, generating a water current through the mantle cavity by ciliary action and trapping food particles on a mucous sheet lying across the front surface of the gill filament. Smothering with a 5cm layer of sediment would be expected to clog the feeding and respiration structures. However, it has been demonstrated that Crepidula fornicata is capable of clearing its feeding structures at some energetic cost. Furthermore, areas with large Crepidula fornicata populations do tend to become silted up through deposition of pseudofaeces, apparently with little effect on the species and the fact that Crepidula fornicata lives in chains of up to 12 individuals means that at least some of the chain would avoid the effects of smothering. Therefore, although there may be some energetic cost as a result of smothering, probably resulting in decreased growth and reproductive output, there is unlikely to be mortality and an intolerance result of low is recorded. Following the smothering event, growth and reproduction should quickly return to normal and hence a recoverability of very high is recorded (Rayment 2003).

INTRODUCTION AND DISTRIBUTION

• First record from the Baltic Sea (year, area, reference):

Year ­ 1940
Area - Kattegat and Belt Sea
Reference - Nikolaev 1951

• Established:

in the entire Baltic Sea ­ ?
in the area of primary introduction ­ Yes

• Origin of the species:

North America

• General characteristics:

Salinity range. C. fornicata lives mainly in marine conditions. Can tolerate brackish water for short periods (Minchin 1999).
Temperature. Normally found in bays and estuaries where they may be exposed to frosts and high summer temperatures exceeding 25°C (Minchin 1999). Larvae are found to tolerate daily temperature cycles of 5°C between 15°C and 30°C with little mortality. Adults are able to tolerate chronic change over time and larvae are able to tolerate acute change in the short term. The ability of larvae to tolerate acute change also contributes to the species' very high recoverability (Rayment 2003).
Tolerance to pollution. No evidence was found on the effects of synthetic compounds specifically on Crepidula fornicata. Limpets are extremely intolerant of aromatic solvent based dispersants used in oil spill clean-up. During the clean-up response to the Torrey Canyon oil spill nearly all the limpets were killed in areas close to dispersant spraying. Viscous oil will not be readily drawn in under the edge of the shell by ciliary currents in the mantle cavity, whereas detergent, alone or diluted in sea water, would creep in much more readily and be liable to kill the limpet. For example, a concentration of 5ppm of dispersant killed half the limpets tested in 24 hours. Thus, although no evidence has been found specifically relating to Crepidula fornicata, the intolerance of species in the same class to synthetic chemicals suggests an intolerance of high with moderate confidence. Due to its high reproductive potential, recoverability is recorded as high. It is suggested that gastropods are rather tolerant of heavy metals. Crepidula fornicata does occur in an area where water polluted with heavy metals mixes with the open ocean. In this area, concentrations of silver, cadmium, copper, lead and zinc were found to be higher than in 'control' estuaries. This suggests that Crepidula fornicata is at least partially tolerant to heavy metal contamination. Laboratory trials have revealed specific responses to heavy metals. Thain (1984) investigated the effects of exposure to mercury. The adult and larval 96 hour LC50s (concentrations at which half the organisms die after 96 hours) were 330 and 60 µg l-1 respectively. As a reference, levels of mercury in UK waters at the time of these experiments were 104 to 105 below the 96 hour LC50 for adult Crepidula fornicata. Furthermore, sub-lethal concentrations of mercury were shown to impair growth and condition of young adult Crepidula fornicata and impair reproductive capacity at 0.25µg l-1. Nelson et al. (1983) investigated the effects of exposure to silver. Reproductive output was found to be impaired following exposure to the highest concentration of silver nitrate (10µg l-1) for 24 months. The evidence suggests that high concentrations of heavy metals will cause mortality in Crepidula fornicata and therefore intolerance is recorded as intermediate. Lower concentrations, which could realistically occur in situ impair growth, condition and reproductive output and will therefore affect the long term health of the population. Due to its high reproductive potential, recoverability is recorded as high. No evidence could be found for the effect of hydrocarbons on Crepidula fornicata specifically. However, inferences can be drawn from closely related groups (Rayment 2003).
Preferable substrate. Sand or gravel bottoms in low energy environments, in which the accumulation of shells may lead to the formation of a biogenic hard substrate (CIESM 2005) .
Vulnarable (invasible) habitats. Present almost everywhere and very abundant, offshore as well as in littoral areas, in fully marine conditions as well as in brackish conditions, on groins, as fouling on buoys, ships, harbour installations, also benthic ( WGITMO 2001). Occurs from the lower shore and known to depths of 60m (Minchin 1999). However, the species is rarely found in abundance below 30 m depth (Hopkins 2002). Survives out of water under cool damp conditions for several days. Able to colonise areas with turbid water (Minchin 1999).
Reproduction. Crepidula fornicata is a protandrous hermaphrodite. This means that the animals start their lives as males and then subsequently may change sex and develop into females. Although breeding can occur between February and October, peak activity occurs in May and June when 80-90% of females spawn. Most females spawn twice in a year, apparently after neap tides. Females can lay around 11,000 eggs at a time contained in up to 50 egg capsules. Laboratory experiments by Thain (1984) revealed that, following incubation, approximately 4000 larvae were released per female. Incubation of the eggs takes 2-4 weeks followed by a planktotrophic larval phase lasting 4-5 week. Due to the length of the planktonic phase, the potential for dispersal is high. Recruitment will be determined by the local hydrographic regime. For example, in sheltered bays the larvae may be entrapped and small scale eddies (e.g. over obstacles and inconsistencies in the surface of the substratum) may result in the concentration of larvae. The ability of Crepidula fornicata to disperse widely and colonize new areas is demonstrated by its spread through Europe following introduction from North America at the end of the 19th century. The spat settle in isolation or on top of an established chain of Crepidula fornicata. Crepidula fornicata needs to be part of a chain in order to breed and therefore would be expected to settle preferentially where high densities of conspecifics already exist. High densities of suspension feeders and surface deposit feeders together with epibenthic predators and physical disturbance may result in high post settlement mortality rate of larvae and juveniles. Males reach sexual maturity 2 months after settlement. If a male develops directly into a female, sexual maturity may be reached in 10 months (MarLin 2001).

THE ROLE IN THE BALTIC SEA ECOSYSTEM

Competition for food and/or space. The environmental requirements of C. fornicata and oysters seem to be similar and as C. fornicata breed they attach to oyster shells and thereby compete with oysters for food (Weidema 2000; Wolff, Reise 2002; Dyrynda 2003). It also can compete for food with other filter-feeding invertebrates (Jarvekiulg 1979; Eno et al. 1997).
Habitat change. It was often suggested that Crepidula fornicata causes deposition of mud in turbid waters of sheltered and estuarine bays, thus rending the beds unsuitable for oyster culture, modifies benthic faunal assemblages and creates a new community with low diversity and competes for food with other filter-feeders. The influence on the diversity of benthic fauna assemblages may be quitecontroversial: a moderate colonisation of C. fornicata may increase point diversity (a species richness); on the contrary, when colonies spread over large areas of a given ecosystem, decrease of species richness and modifications in trophic structures are likely to occur. (Goulletquer et al. 2002; Dyrynda 2003).
Transfer of parasites. It may introduce new pests and parasites which can affect native species (Eno et al. 1997).
Community dominance . In suitable conditions, Crepidula fornicata can reach very high densities; up to 4770 individuals per m² (MarLin 2001). The extensive spreading of C. fornicata onto bottoms changed the trophic structure of the benthic communities with an increase of the suspension feeders biomass within large areas all over the ecosystem (Chauvaud et al. 2003).
Benthic-pelagic interaction . Crepidula encourages deposition of mud (Eno et al. 1997).

LIKELY IMPACT ON USES/RESOURCES AND HUMAN HEALTH

Aquaculture. It can become a pest on commercial oyster beds, competing for space and food, while depositing mud on them so that the substrate is unsuitable for spat settlement (Eno 1997; Hopkins 2002).
Tourism. Crepidula clumps may change the recreational environment (Minchin 1999).
Water Quality. Reduces food in water by filtering activity (Minchin 1999)

REFERENCES

1. Chauvaud L.L., Jean F.L., Ragueneau O.O., Thouzeau G.G. 2003. Do benthic suspension feeders modify Si cycle? (http://www.aslo.org/santafe99/abstracts/SS13FR0245S.html) Accessed 02/11/2005
2. CIESM 2002. Ciesm Atlas of Exotic Species in the Mediterranean (http://www.ciesm.org/atlas/) Accessed 02/11/2005
3. Dyrynda P. 2003. Slipper limpet beds. In: School of Biological Sciences, University of Wales Swansea server (http://www.swansea.ac.uk/biodiv/poole/Slipper~limpet.htm) Accessed 07/03/2004
4. Eno N.C., Clark R.A., Sanderson W.G. 1997. Non-native marine species in British waters: a review and directory. Published by JNCC, Peterborough: 152pp.
5. Goulletquer Ph., Bachelet G., Sauriau P.G., Noel P. 2002. Open Atlantic coast of Europe - a century of introduced species into french waters. In: Leppakoski E., Gollasch S. and Olenin S.(eds), Invasive Aquatic species of Europe - distribution impacts and management. Kluwer Academic Publishers, Dordrecht, Boston, London: 276-290.
6. Hopkins C.C.E., 2002. Introduced marine organisms in Norwegian waters, including Svalbard. In: Invasive aquatic species of Europe - distribution, impacts and management. Kluwer Academic Publishers, Dordrecht, Boston, London: 240-252.
7. Jarvekiulg A. 1979. The bottom fauna of the Eastern part of the Baltic Sea. Tallinn, “Valgus”: 382pp. (in Russian).
8. MarLin 2001. Additional ecology of Crepidula fornicata and Aphelochaeta marioni in variable salinity infralittoral mixed sediment (http://www.marlin.ac.uk/Bio_pages/Bio_DetEco_IMX.CreAph.htm) Accessed 12/12/2005
9. Minchin D. 1999. Crepidula fornicata (Linneaus, 1758), Calyptraeidae, Gastropoda. In: Exotics across the ocean. Case histories on introduced species: their general biology, distribution, range expansion and impact. Published by University of Kiel, Germany, Department of Fishery Biology, Institute for Marine Science: 43-48.
10. Rayment W.J. 2003. Crepidula fornicata. Slipper limpet. In: Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme (on-line). Plymouth: Marine Biological Association of the United Kingdom. (http://www.marlin.ac.uk/species/Crepidulafornicata.htm) Accessed 07/12/2003
11. Weidema I.R. 2000. Introduced species in the nordic countries, Nord, 13: 242pp.
12. WGITMO. Report. 2001. International Council for the Exploration of the Sea. Barcelona, Spain. 100 pp.
13. Wolff W.J., Reise K. 2002. Oyster imports as a vector for the introduction of alien species into Northern and Western European coastal waters. In: Leppakoski E., Gollasch S. and Olenin S.(eds), Invasive Aquatic species of Europe - distribution impacts and management. Kluwer Academic Publishers, Dordrecht, Boston, London: 193-205.