Trochus
Encyclopedia
Trochus is a genus
of medium-sized to very large sea snail
s. They are marine
gastropod molluscs in the family
Trochidae
, the top snails.
Trochus niloticus, for example, is a very large (up to 13 cm) Indo-Pacific
top shell, which has a very thick inner layer of nacre
. This species is commercially exploited to make mother of pearl buttons, mother of pearl beads, pendants and so on. In 2006, for example, the sole commercial export of the Wallis and Futuna
Islands was 19 ton
s of Trochus shells valued at US$122,000.
and a flat base.
The interior of the shell is pearl
y and iridescent because of the nacre.
Hatchery-reared individuals are usually lab-spawned and raised. Broodstock can be collected from local wild populations and from sites which juveniles are to be released . Spawning is usually induced by heat shock under laboratory conditions ; . Larvae are grown on coral rubble and shell grit and fed with benthic diatoms . (Nitzschia spp. and Navicula spp.) . Juveniles used in cage experiments may have an initial size of 8mm shell diameter . Other experiments may start at 15mm basal shell width .
The release size of cultured juveniles is important to ensure its survival or response to predators where the larger the individual the less vulnerable it is to predation . A release size of 35mm (basal shell width, BSW) is recommended . The period of growth to this suitable size is about 6 months under optimum conditions . However producing large individuals is costly. Alternatives such as high density releases of small juveniles and over large areas are less expensive and solutions to reduce predation pressure from fish species such as Choerodon cyanodus and Diodontidae and crustaceans such as Mancinella tubercosa and Calappa hepatica . Hatchery and transit conditions are also factors that may affect the vulnerability of juveniles to predators . It is recommended animals are reared on natural substrata before release .
The growth of the cultured individuals can depend on the density of juveniles in the cages and the likely causes are competition for food and space . An initial density of 100 trochus m-2 achieves a basal diameter of 10-20mm which can then be reduced to 50 trochus m-2 to yield basal diameters 25-40mm. Beyond this range a density of less than 10 trochus m-2 is recommended .
Seaweed and algae are the main food and these grow on the dead corals and rocks which may occur naturally at the cultured sites or collected from adjacent areas and placed at the bottom of the cages . It is recommended that for cages with juveniles sized >30mm, these seaweed-covered rocks should be replaced 2 to 3 times a month and cover over 50% of the area .
Cage design is important in preventing escape of juveniles and entry of predators and also shading of algal and seaweed on rocks. Recommended designs include cages with 8x8mm plastic mesh and an aluminium frame . Steel reef, plastic reef and plastic floating cages have proven ineffective as steel reef cages allowed high mortality from predator entry and plastic cages induced shading of the rocks algae and seaweed are attached to which results in low productivity . Suitable locations for reef cages are sand and rubble bottom reef bases exposed to less wave action or fore-flat zones which are 10m behind the reef crest with water depths of 0 to 2.5m during spring-tides . Shifting sand and sediment deposition areas may smother foraging surfaces and need to be avoided when allocating cages ; . Wind-ward sections of the reef flat are considered suitable sites. Floating cages require frequent cleaning to remove fouling species and allow high water flow and/ or nutrient flux for high algal biomass and quality . Other environmental factors such as water temperature and salinity can have seasonal and episodic effects on the growth of the juveniles .
Suitable release sites of trochus juveniles into the wild include unconsolidated coral rubble and areas where predators are absent . It is common that juveniles are placed upright inside a cover such as a reef crevice ; or under macroalgae as a means of predator protection .
The success of released individuals in contributing to wild populations can be measured by the mark and recapture method. However the validity of this method may be limited by factors such as detection methods, predation, escape of juveniles, translocation of juveniles by strong currents or detection may simply be not carried out .
The following species are also mentioned :
Species brought into synonymy :
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of medium-sized to very large sea snail
Sea snail
Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....
s. They are marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
gastropod molluscs in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Trochidae
Trochidae
The Trochidae, common name top snails, are a taxonomic family of very small to large sea snails, marine gastropod molluscs in the clade Vetigastropoda ....
, the top snails.
Trochus niloticus, for example, is a very large (up to 13 cm) Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
top shell, which has a very thick inner layer of nacre
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....
. This species is commercially exploited to make mother of pearl buttons, mother of pearl beads, pendants and so on. In 2006, for example, the sole commercial export of the Wallis and Futuna
Wallis and Futuna
Wallis and Futuna, officially the Territory of the Wallis and Futuna Islands , is a Polynesian French island territory in the South Pacific between Tuvalu to the northwest, Rotuma of Fiji to the west, the main part of Fiji to the southwest, Tonga to the southeast,...
Islands was 19 ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...
s of Trochus shells valued at US$122,000.
Shell description
Sea snails in the genus Trochus have shells that have a conical spireSpire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
and a flat base.
The interior of the shell is pearl
Pearl
A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...
y and iridescent because of the nacre.
Aquaculture
Trochus niloticus is a highly sought after resource in the Pacific and Indo-Pacific regions which has resulted in the species being over-harvested. By 2007 the Solomon Islands, Fiji and Papua New Guinea have the most depleted stocks with four surveyed sites in the Solomon Islands in 2006 averaging a density of 11 trochus ha^-1 . Releasing hatchery-reared juveniles is an option to replenish reduced wild stocks. Methods of culture are still under assessment and development where experiments have been conducted in Vanuatu ; , Australia , Indonesia and Vietnam . Cage-based cultures have proven effective because they allow control of food and predators which contribute greatly to the growth and survival of juveniles ; . Other benefits of sea cages include lower cost, easy to construct and transport, manageability and the advantage of using existing water bodies .Hatchery-reared individuals are usually lab-spawned and raised. Broodstock can be collected from local wild populations and from sites which juveniles are to be released . Spawning is usually induced by heat shock under laboratory conditions ; . Larvae are grown on coral rubble and shell grit and fed with benthic diatoms . (Nitzschia spp. and Navicula spp.) . Juveniles used in cage experiments may have an initial size of 8mm shell diameter . Other experiments may start at 15mm basal shell width .
The release size of cultured juveniles is important to ensure its survival or response to predators where the larger the individual the less vulnerable it is to predation . A release size of 35mm (basal shell width, BSW) is recommended . The period of growth to this suitable size is about 6 months under optimum conditions . However producing large individuals is costly. Alternatives such as high density releases of small juveniles and over large areas are less expensive and solutions to reduce predation pressure from fish species such as Choerodon cyanodus and Diodontidae and crustaceans such as Mancinella tubercosa and Calappa hepatica . Hatchery and transit conditions are also factors that may affect the vulnerability of juveniles to predators . It is recommended animals are reared on natural substrata before release .
The growth of the cultured individuals can depend on the density of juveniles in the cages and the likely causes are competition for food and space . An initial density of 100 trochus m-2 achieves a basal diameter of 10-20mm which can then be reduced to 50 trochus m-2 to yield basal diameters 25-40mm. Beyond this range a density of less than 10 trochus m-2 is recommended .
Seaweed and algae are the main food and these grow on the dead corals and rocks which may occur naturally at the cultured sites or collected from adjacent areas and placed at the bottom of the cages . It is recommended that for cages with juveniles sized >30mm, these seaweed-covered rocks should be replaced 2 to 3 times a month and cover over 50% of the area .
Cage design is important in preventing escape of juveniles and entry of predators and also shading of algal and seaweed on rocks. Recommended designs include cages with 8x8mm plastic mesh and an aluminium frame . Steel reef, plastic reef and plastic floating cages have proven ineffective as steel reef cages allowed high mortality from predator entry and plastic cages induced shading of the rocks algae and seaweed are attached to which results in low productivity . Suitable locations for reef cages are sand and rubble bottom reef bases exposed to less wave action or fore-flat zones which are 10m behind the reef crest with water depths of 0 to 2.5m during spring-tides . Shifting sand and sediment deposition areas may smother foraging surfaces and need to be avoided when allocating cages ; . Wind-ward sections of the reef flat are considered suitable sites. Floating cages require frequent cleaning to remove fouling species and allow high water flow and/ or nutrient flux for high algal biomass and quality . Other environmental factors such as water temperature and salinity can have seasonal and episodic effects on the growth of the juveniles .
Suitable release sites of trochus juveniles into the wild include unconsolidated coral rubble and areas where predators are absent . It is common that juveniles are placed upright inside a cover such as a reef crevice ; or under macroalgae as a means of predator protection .
The success of released individuals in contributing to wild populations can be measured by the mark and recapture method. However the validity of this method may be limited by factors such as detection methods, predation, escape of juveniles, translocation of juveniles by strong currents or detection may simply be not carried out .
Species
Species within the genus Trochus include :- Trochus bellardiiTrochus bellardiiTrochus bellardii is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Issel, 1869 - Trochus flammulatusTrochus flammulatusTrochus flammulatus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Lamarck, 1822 - Trochus incrassatusTrochus incrassatusTrochus incrassatus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
J. B. Lamarck, 1822 - Trochus maculatusTrochus maculatusTrochus maculatus, common name the maculated top shell, is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Linnaeus, 1758- Trochus maculatus verrucosus J. F. Gmelin, 1791
- Trochus nigropunctatusTrochus nigropunctatusTrochus nigropunctatus, common name the black-spotted topshell, is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Reeve, 1848 - Trochus noduliferusTrochus noduliferusTrochus noduliferus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Lamarck, 1822 - Trochus ochroleurcusTrochus ochroleurcusTrochus ochroleucus, common name : the Yellow-mouth Top Shell, is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.-Description:The size of an adult shell varies between 15 mm and 35 mm.-Distribution:...
Gmelin, 1791 - Trochus radiatusTrochus radiatusTrochus radiatus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Gmelin, 1791 - Trochus squarrosusTrochus squarrosusTrochus squarrosus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Lamarck, 1822 - Trochus subincarnatusTrochus subincarnatusTrochus subincarnatus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
P. Fisher, 1879 - Trochus sublaevisTrochus sublaevisTrochus sublaevis is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Geinitz, 1842 - Trochus tentoriumTrochus tentoriumTrochus tentorium is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Gmelin, 1791 - Trochus tubiferTrochus tubiferTrochus tubifer is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Kiener, 1850 - Trochus virgatusTrochus virgatusTrochus virgatus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Gmelin, 1791 - Trochus zhangiTrochus zhangiTrochus zhangi is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Dong, 2002
The following species are also mentioned :
- Trochus aemulans A. Adams, 1855
- Trochus akoya T. Kuroda, 1942
- Trochus calcaratus Souverbie, 1875
- Trochus californicum A. Adams, 1853
- Trochus camelophorusTrochus camelophorusTrochus camelophorus is a species of small sea snail, a marine gastropod mollusc in the family Trochidae, the top snails.-References:...
Webster, 1906 - Trochus chloromphalus A. Adams
- Trochus coerulescens Lamarck, 1822
- Trochus crassicosta A. W. B. Powell, 1937
- Trochus creniferus Kiener, 1880
- Trochus cumingi A. Adams, 1853
- Trochus elegantulus Wood, 1828
- Trochus fasciatus
- Trochus fastigiatus A. Adams, 1853
- Trochus ferreirai Bozzetti, 1996
- Trochus firmus Philippi, 1850
- Trochus flammulatusTrochus flammulatusTrochus flammulatus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
J. B. Lamarck, 1822 - Trochus fultoni Melvill, 1898
- Trochus granosus J. B. Lamarck, 1822
- Trochus granularis Röding, 1798
- Trochus hanleyanus Reeve, 1842
- Trochus histrio Reeve, 1848
- Trochus huttoni E. A. Smith, 1876
- Trochus intextus Kiener, 1850
- Trochus laciniatus Reeve
- Trochus lamprus Watson, 1881
- Trochus murreus L. A. Reeve, 1865
- Trochus nardinii Selli, 1973
- Trochus neptuni (A. Adams, 1855)
- Trochus obeliscus J. F. Gmelin, 1791
- Trochus oppressa F. W. Hutton, 1878
- Trochus optatus Sowerby,
- Trochus pachychiles Watson, 1879
- Trochus pallidulus A. Adams, 1853
- Trochus pustulosus Philippi, 1849
- Trochus radiatus fultoni J. C. Melvill
- Trochus rota R. W. Dunker, 1860
- Trochus rubicatus R. A. Philippi, 1848
- Trochus sacellum R. A. Philippi, 1854
- Trochus sacellum rota R. W. Dunker, 1862
- Trochus sandwichensis F. L. A. Souleyet, 1852
- Trochus satrapius Maltzan
- Trochus scabrosus R. A. Philippi
- Trochus schlueteri Sowerby, 1894
- Trochus shinayaka T. Habe, 1961
- Trochus smaragdus L. A. Reeve, 1861
- Trochus stellatus Gmelin, 1791
- Trochus submorum (Abrard, 1942)
- Trochus tiaratusTrochus tiaratusTrochus tiaratus is a species of small sea snail, a marine gastropod mollusc in the family Trochidae, the top snails.thumb|left|Trochus tiaratus underside view-References:...
Quoy & Gaimard, 1834 - Trochus tomlini Fulton, 1930
- Trochus transenna Watson, 1879
- Trochus tricatenatus Reeve, 1861
- Trochus tubiferus Kiener, 1880
- Trochus venetus L. A. Reeve, 1862
- Trochus viridisTrochus viridisTrochus viridis is a species of small sea snail, a marine gastropod mollusc in the family Trochidae, the top snails.-References:* Powell A W B, New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1...
GmelinJohann Friedrich GmelinJohann Friedrich Gmelin was a German naturalist, botanist, entomologist, herpetologist and malacologist.- Education :Johann Friedrich Gmelin was born as the eldest son of Philipp Friedrich Gmelin in 1748 in Tübingen...
, 1791 - Trochus zhangii Zhengzhi, 2002
Species brought into synonymy :
- Trochus cariniferus Reeve, 1842 : synonym of Infundibulops cariniferusInfundibulops cariniferusInfundibulops cariniferus is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
(Beck in Reeve, 1842) - Trochus conoidalis Pease, 1867 : synonym of Peasiella conoidalisPeasiella conoidalisPeasiella conoidalis is a species of sea snail, a marine gastropod mollusk in the family Littorinidae, the winkles or periwinkles....
(Pease, 1868) - Trochus erithreus Brocchi, 1821 : synonym of Infundibulum erythraeum (Brocchi, 1821)
- Trochus kochii Philippi, 1844 : synonym of Infundibulops kochii (Philippi, 1844)
- Trochus lineatus J. F. Gmelin, 1791 : synonym of Gibbula cinerariaGibbula cinerariaGibbula cineraria is a species of small sea snail, a marine gastropod mollusc in the family Trochidae, the top snails....
(Linnaeus, 1758) - Trochus niloticus : synonym of Tectus niloticusTectus niloticusTectus niloticus is a species of sea snail, a marine gastropod mollusk in the family Turbinidae, the turban snails....
(Linnaeus, 1767) - Trochus verrucosus J. F. Gmelin, 1791 : synonym of Trochus maculatusTrochus maculatusTrochus maculatus, common name the maculated top shell, is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails....
Linnaeus, 1758
Further reading
- NZ Mollusca
- Powell A. W. B.Arthur William Baden PowellDr Arthur William Baden Powell CBE was a New Zealand malacologist, naturalist and palaeontologist, a major influence in the study and classification of New Zealand molluscs through much of the twentieth century. He was known to his friends and family by his third name, "Baden".Powell was born at...
, New Zealand Mollusca, William Collins Publishers LtdHarperCollinsHarperCollins is a publishing company owned by News Corporation. It is the combination of the publishers William Collins, Sons and Co Ltd, a British company, and Harper & Row, an American company, itself the result of an earlier merger of Harper & Brothers and Row, Peterson & Company. The worldwide...
, Auckland, New Zealand 1979 ISBN 0-00-216906-1 - Miller M & Batt G, Reef and Beach Life of New Zealand, William Collins (New Zealand) LtdHarperCollinsHarperCollins is a publishing company owned by News Corporation. It is the combination of the publishers William Collins, Sons and Co Ltd, a British company, and Harper & Row, an American company, itself the result of an earlier merger of Harper & Brothers and Row, Peterson & Company. The worldwide...
, Auckland, New Zealand 1973