This article explores the world of the African periwinkle, focusing on its biology, culinary uses, and significance as a seafood resource.
Biology of the Common Periwinkle (Littorina littorea)
The common periwinkle, scientifically known as Littorina littorea, is a robust intertidal species characterized by a dark, sometimes banded shell. The shell is broadly ovate, thick, and sharply pointed except when eroded. It contains six to seven whorls with some fine threads and wrinkles. The color varies from grayish to gray-brown, often with dark spiral bands. The base of the columella is white, and the shell lacks an umbilicus.
The white outer lip is sometimes checkered with brown patches. The width of the shell ranges from 10 to 12 millimeters (3⁄8 to 1⁄2 in) at maturity, with an average length of 16 to 38 mm (5⁄8 to 1+1⁄2 in). Shell height can reach up to 30 to 52 mm (1+1⁄8 to 2 in). The length is measured from the end of the aperture to the apex.
L. littorea can be highly variable in phenotype, with several different morphs known. Its phenotypic variations may be indicative of speciation, as opposed to phenotypic plasticity.
Reproduction and Growth
L. littorea is oviparous, reproducing annually with internal fertilization of egg capsules that are then shed directly into the sea, leading to a planktotrophic larval development time of four to seven weeks. Females lay 10,000 to 100,000 eggs contained in a corneous capsule from which pelagic larvae escape and eventually settle to the bottom. This species can breed year round depending on the local climate. Female specimens have been observed to be ripe from February until end of May, when most are spawning. Male specimens are mainly ripe from January until the end of May and lose weight after copulation.
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A study in Plymouth Sound suggests an initial growth reaching up to 14 mm (1⁄2 in) in height December the first year, and 17.4 mm (5⁄8 in) by the end of the second year.
Periwinkle CATCH CLEAN COOK!!! Simple but delicious survival food
Habitat and Distribution
The common periwinkle is mainly found on rocky shores in the higher and middle intertidal zone. It sometimes lives in small tide pools. Common periwinkles were introduced to the Atlantic coast of North America, possibly by rock ballast in the mid-19th century. The first recorded sighting in the East was in 1840 in the Gulf of St. Lawrence. This species is also found on the west coast of the United States, from Washington to California. L. littorea is now the most common marine snail along the North Atlantic coast.
Global distribution of Littorina littorea (Common periwinkle). Source: ResearchGate
Diet and Predators
L. littorea is an omnivorous, grazing intertidal gastropod. It is primarily an algae grazer, but it will feed on small invertebrates such as barnacle larvae. It uses its radula to scrape algae from rocks and, in the salt marsh community, pick up algae from cord grass or from the biofilm that covers the surface of mud in estuaries or bays. The radula is taenioglossate, consisting of seven teeth per row: one middle tooth, flanked on each side by one lateral and two marginal teeth. Phlorotannins in the brown algae Fucus vesiculosus and Ascophyllum nodosum act as chemical defenses against L. littorea.
Parasites and Shell Burrowers
The common periwinkle can act as a host for various parasites, including Renicola roscovita, Cryptocotyle lingua, Microphallus pygmaeus and Himasthla sp. More studies are needed before any conclusions regarding the effect of parasites on growth can be reached. Polydora ciliata has also been found to excavate burrows in the shell of the common periwinkle when the snail is mature (above 10 mm long). The reason why this happens only to mature snails is not yet known, but one hypothesis is that a mature snail will excrete a signal substance which attracts the P. ciliata larvae. Another hypothesis is that a mature snail has a change in the shell surface that makes it suitable for P. ciliata larvae to settle. Older individuals above 15 months old seem to have a mortality of only 23% per annum.
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Periwinkles as a Food Source
This species appears in prehistoric shellfish middens throughout Europe and is believed to have been an important source of food since at least 7500 B.C.E. in Scotland. It is still collected in quantity in Scotland, mostly for export to the Continent and also for local consumption. The official landings figures for Scotland indicate over 2,000 tonnes of winkles are exported annually. This makes winkles the sixth most important shellfish harvested in Scotland in terms of tonnage, and seventh most important in terms of value.
Periwinkles are usually picked off the rocks by hand or caught in a drag from a boat. They are mostly eaten in the coastal areas of Scotland, England, Wales and Ireland, where they are commonly referred to as winkles or in some areas buckies, willicks, or wilks. Periwinkles are considered a delicacy in African and Asian cuisines. Periwinkles are also used as bait for catching small fish.
Seafood Supply Chain and Processing
As for seafood supply chains in general, the supply chain consists of a collector, processor, distributor and finally the retailer. If fresh seawater is readily available, the periwinkles are first graded if possible, using a machine custom built for the purpose. The method used for grading differs, but two proven methods include a Trommel screen with horizontal bars instead of a mesh, and a circle-throw vibrating machine also using bars. Periwinkles are graded by number of snails per kilogram.
After grading, the periwinkles are "climbed" close to the consumer, which involves checking whether they are still alive. This can take anywhere from a few hours to several days, depending on how healthy the periwinkles are and the temperature of the water they climb in. Any periwinkles left immobile at the bottom are considered dead and are discarded. Hereafter, the winkles are commonly packed in smaller quantities before being distributed to customers.
To sell large quantities, distributors are commonly used to move the periwinkles to the retailer. These have networks of transport available both internationally, regionally and locally inside a city. The common periwinkle is sold by fishmongers at seafood markets in large cities around the world, and is also commonly found in seafood restaurants as an appetizer or as a part of a seafood platter. Ongrowing has been investigated as a potential way of increasing commercial value, but no documented pilot facilities have been established.
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Commonly packed in 3 kg boxes by the processor, the box is usually polystyrene foam or thin wood, depending on the market demands. Holes in the box ensures that any water lost by the snails drains out, so that they remain in better condition for longer. In a refrigerator, the common periwinkle can usually be stored for up to a week, but this may vary depending on how long they have been stored prior to sale, and how they have been kept since the moment they are fished. As long as they are kept moist and cold, they can survive well for a longer period of time.
Grading of Periwinkles in France
The following table displays some common grades in France. The actual value depends upon supply and demand, with seasonal variations.
| Grade | Snails per Kilogram |
|---|---|
| Extra Large | Less than 80 |
| Large | 80-120 |
| Medium | 120-180 |
| Small | More than 180 |
Hand-gathering of periwinkles on the Atlantic coast of France. Source: FAO
Sustainable Circular Utilization
As the world’s population is expected to hit ~10 billion by 2050, the importance of circular utilization for a sustainable approach to the use of available resources becomes critical. Through circular economy the life cycle of resources is extended. In West Africa, periwinkles have been the most dominant species among aquatic molluscs and have successfully invaded several parts of aquatic ecosystems. They are known to be a relatively cheap source of protein, and their nutritional composition, accessibility, and cost is the major reason for high market demand.
Therefore, the authors set out to analyze the proximate composition, nutritionally significant minerals, trypsin inhibitors, and carotenoids of Tympanotonus fuscatus, Pachymelania aurita, and Thais coronata shells. The high percentage of CaCO3 makes them a probable source used in the production of slurry for chromatography. The author’s findings suggest that periwinkle shells contain specific minerals that can be applied in numerous industries.
