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Cerithidea cingulata and Littoraria scabra are type of snail that use mangrove ecosystems as one of their habitat. Dumai is one of the industrial cities in the province of Riau, where various kinds of human activities can disrupt the ecosystem of mangroves and its associated biota. This research was conducted in October 2018 in the Mangrove Forest Area (PAB) of Pangkalan Sesai village of Dumai City, aiming to determine population densities and length-weight relationship of C. cingulata and L. scabra. The method used in this study is a survey method. Sampling was conducted by using the line transect method, where each station consists of 3 transects and each transect consists of 3 sampling points as replications. The results showed the population density of C. cingulata and L. scabra snails was higher than at stations near the Dumai river estuary compared with the population near by mangrove forest and length-weight relationship showed that the growth patterns of both C. cingulata and L. scabra were allometric negative and have strong correlation value.

Microplastic has been known to contaminate our marine environment. This research aim was to determine the abundance of microplastic in mangrove periwinkle snail Littoraria scabra and mangrove crab Metopograpsus quadridentata in Pramuka Island, Jakarta Bay, Indonesia. Pramuka Island was chosen as the research site because this island is densely populated and received waste from Jakarta Bay. Samples of mangrove snails were taken by purposive random sampling method of 10 individuals with shell lengths ranging from 1.5 to 2.7 cm, and 9 individuals crab with circa 6 cm carapace wide were collected. Analysis of microplastic abundance was done by isolating microplastic in each sample. Isolation in the sample was done by dissolving tissue of animals in a 65% nitric acid (HNO3 ) solution for 24 h and sodium chloride (NaCl) was added to increase density of solution. Sample was observed under microscope. The results obtained 3 types of microplastic found in the body of snail (fiber, film, and fragment) and 4 types in crab (fiber, film, fragment, and granula). Fiber has the highest percentage in snail (66.89%) and crab (68.72%). The average of microplastic abundance were 86.88 particles/individual in snail and 327.56 particles/individual in crab, respectively. This result indicated that the coastal area of Pramuka Island has been polluted by the microplastics. There was positive correlation between microplastic abundance and the body weight of snail (r=0.9778), and body weight of crab (r=0.9193).

Mangrove forests are one of the natural ecosystems that make a large contribution to the population as a food source, one of which is gastropods. The purpose of this study was to determine the density of mangroves, the abundance of gastropods and the discussion between the density of mangroves and the abundance of gastropods. This research was carried out in September - November 2018 in the area of 12 ha KKMB. The research method used was a survey method by conducting direct research on 12 plot points with a plot size of 10 x 10 meters were in each plot there were 3 sub-plots made 1 x 1 meter randomly carried out in the plot to take gastropod samples. The collected data are grouped by type variable, mangrove density as a variable (X) and gastropod abundance as a variable (Y). The results showed that the mangrove yields in the area obtained by KKMB belonged to the very solid (good) category with a value of 11.700 ind / ha. The highest gastropod abundance is dominated by the type of Cassidula aurisfelis with the number of 79 individuals and the lowest abundance of the type Littoraria scabra with the number of 14 individuals . The low level of gastropod abundance is reduced due to the low density of mangrove species and the low food source in the mangrove area. The relationship of mangrove density with gastropod abundance using simple linear regression analysis obtained the value of determination coefficient (R2) of 0.227, while the coefficient value was 0.4766 which means that it is positively correlated.

The study assessed the structure, natural regeneration capacity and Biotic agents of Avicennia marina and Bruguiera gymnorrhiza species in Mida creek, Kilifi County. The study used both cross section and descriptive research design. Avicennia marina species was more dominant with a greater complexity index (A2.7, B0.4), basal area (A588cm2, B484cm2) and mean height (A26m, B10m) compared to Bruguiera gymnorrhiza species with both having an aggregate dispersion pattern. During dry season, Height, and diameter of Avicennia marina had a correlation of 0.56 while Bruguiera gymnorrhiza species had 0.78. During rainy season both had a correlation of 0.67. B. gymnorrhiza species had more straight poles than A. marina species, 75.3% of B. gymnorrhiza trees assessed had straight pole compared to 1.7% of Avicennia marina trees. Both Avicennia marina and Bruguiera gymnorrhiza species had fair regeneration capacity where the number of seedlings was greater than saplings and number of saplings was less than mature trees. Littoraria scabra fed mostly on micro-organisms and algae, Littoraria Glabrata fed mostly on mud surface, Sesarma guttata and Sesarma leptosoma fed on mangrove leaves, Cerithidea decollata fed on deposits and organic matter, Terebralia palustris and Selatium elongatium fed more on algae and leaves, Sesasrmi ortmanni, Metopograpsus oceanicus and Neosarmatium meinerti fed on leaves and young propagules, Barnacles and Oyster bunch on the roots and stems of B. gymnorrhiza species. Biotic agents were insignificant in affecting regeneration capacity of A. marina and B. gymnorrhiza species however combinations with climatic and anthropogenic factors affected Regeneration capacity of the two species.

Imamsyah A, Arthana IW, Astarini IA. 2020. The influence of physicochemical environment on the distribution and abundance of mangrove gastropods in Ngurah Rai Forest Park Bali, Indonesia. Biodiversitas 21: 3178-3188. Ngurah Rai Forest Park is the widest mangrove ecosystem in Bali that close to the business center and tourism area. The strategic location of the Ngurah Rai Forest Park is estimated to produce anthropogenic waste that can disrupt the gastropod population and stability of the mangrove ecosystems. This study aims to analyze the mangrove density, distribution, and abundance of gastropods based on the quality of the biophysical environment. Mangrove data collection was carried out using a plot transect of 10 m x 10 m, 5 m x 5 m, and 1 m x 1 m. Meanwhile, samples gastropods were collected on a plot transect of 0.5 m x 0.5 m in plot transect of 5 m x 5 m. A total of 11 gastropods species and 6 mangrove species were recorded in this study. The dominant gastropods species found were Assiminea brevicula (28 ind/m2). Species mangrove of Sonneratia alba and Rhizophora apiculata found were in all study sites with tree density values of 1000 ind/ha. Subsequently, the ecological index calculation results show that the diversity index (H’) (2.89-3.2), evenness index (E) (0.87-0.93), and dominance index (C) (0.12-0.17). Based on the Principal Component Analysis (PCA) found was Assiminea brevicula spread on sand and silt substrates and adaptive to the temperature condition, salinity, pH, and dissolved oxygen. Furthermore, other analysis results showed that Cerithidea cingulata, Cerithidea quadrata, Littoraria articulata, and Littoraria scabra were found on clay substrate with high C-organic content. In conclusion, gastropods are evenly distributed and no species dominate the ecosystems.

The Saudi Arabian Gulf coast is witnessing many industrial, recreational and other developmental activities. Impact of these activities on the intertidal macrofaunal communities of this region has not been documented well. Thirty four stations falling under four zones along this coast were sampled to study the benthic macrofaunal community. A total of 81 taxa were recorded and the species richness varied between the zones. Among the 48 polychaetespecies found, Exogone heterosetosa, Dialychone collaris, Ophelina longicaudata, Paraprionospio pinnata, Perinereis falsovariegata and Scololepis squamata were dominant. Species such as Littoraria scabra, Bullia vittata, Incatella cingulata, Meretrix meretrix, Donax sp. and Maoricardium setosum were dominant among the twelve gastropod species. The thirteen species of macrofauna identified to occur in all the zones comprised eight species of gastropods besides two species each of amphipods and isopods and one species of cumacean. ANOSIM showed significant differences in assemblage overall among the four zones and in pairwise comparison. Distance based linear modeling (DISTLM) showed the environmental parameters to explain 55.67% of the variability in macrofauna with variables such as pH, salinity, temperature, pebble and gravel showing significant relationship with macrofauna and explained higher variability. The alpha diversity values were comparatively lower in zone 3 which had high anthropogenic pressure. Shannon–Wiener​ diversity, Margalef richness and more importantly the M-AMBI showed the healthy nature of the study area. The findings of the present study are helpful in tracing the future changes in the intertidal habitat due to anthropogenic activities in this fast developing geographical area.

Macrobenthic fauna is often used as a bioindicator of environmental quality. However, information about the environmental characteristics and the existence of macrobenthic fauna in the mangrove reforestation area is still very limited. The study of the profile of the Seribu Island mangrove reforestation area based on the characteristics of the macrobenthic environment and fauna was carried out in March 2014. The aim of this study is to determine the ecological conditions of the waters around the Seribu Island mangrove reforestation area. To find out the relationship between environmental characteristics and macrobenthic fauna with observation stations carried out by statistics on Correspondence Analysis (CA), while the environmental characteristics that determine macrobenthic fauna and their relationships are carried out with Principal Component Analysis (PCA) statistics and simple linear regression. The results of the study show that the concentration of measured environmental characteristics is not very different between stations and does not exceed the quality standard threshold for marine life. Then the macrobenthic fauna found consisted of 6 species with the highest density at Station 3 (05.00 ind/m2) and the lowest at Station 1 (02.00 ind/m2). At Station 1 the pH and temperature concentration is very high, while Station 2 and 3 have high salinity concentrations. Macrobenthic fauna Atilia (Columbella) scripta, Metopograpsus latifrons, Littoraria scabra, Saccostrea cucculata, and Cardisoma carnifex can be associated with mangroves at all stations. In addition, the environmental characteristics that determine the presence of C. carnifex macrobenthic fauna are pH parameters, where the higher the pH concentration, the lower the density of C. carnifex. Then the environmental characteristics that determine the presence of the macrobenthic fauna of S. cucculata, M. latifrons and A. scripta are determined by DO (Dissolved Oxygen) and salinity parameters namely the lower DO (Dissolved Oxygen) concentration and salinity, the higher the density of S. cucculata, M. latifrons and A. scripta.

This research was found novelty of reproduction strategy uniqueness of L. scabra that very rare in nature, reverse male function fertilized eggs are sucked for brooding in mantle of male up to hatching as veligers, and thus, the males are capable of releasing the larvae in full and new moon at spring tide during the research. The second finding in reproduction strategy uniqueness of L. scabra that mating individuals, both males and females, released their larvae during research period. Key Words : Littoraria scabra, uniqueness, releasing, veliger, male and female ABSTRAK Penelitian yang amat langka di alam ini menemukan kebaharuan keunikan strategi reproduksi Littoraria. scabra , di waktu kopulasi jantan berperan seks terbalik menyedot sebagian telur yang dibuahi dan dierami telur-telur yang dibuahi dalam tubuhnya sampai menetas menjadi larva-larva serta melepaskan larva-larva tersebut di bulan penuh dan baru yang mengikuti siklus pasang selama penelitian. Temuan amat langka kedua keunikan strategi reproduksi L. scabra , yang amat langka di alam dengan pasangan jantan-betina lagi kawin melepaskan larva-larva baik jantan maupun betina pada siklus bi-lunar bersamaan dengan siklus pasang selama penelitian. Kata Kunci : Littoraria scabra, keunikan,pelepasan, veliger, jantan dan betina

Littoraria scabra (Linnaeus, 1758) Figs 6 Q–R Helix scabra Linnaeus, 1758: 770. Littoraria (Littorinopsis) scabra: Reid 1986: 94 –103, figs 3, 5, 27–30 (full synonymy); Okutani 2000: 138 –139, pl. 69, fig. 15; Thach 2005: 53. Littoraria scabra: Lozouet & Plaziat 2008: 116 –117, pl. 22, figs 1–2; Zvonareva et al. 2015: 8. Material examined. Nha Phu Bay, Dam Bay, mangrove plantation, about 15 specimens. Abundance. Common. Measurements. Up to 35 mm (Reid 1986). Ecological notes. Ovoviviparous species (Reid 1986). An oceanic species, typically on trunks and roots of Rhizophora and less frequently on trunks of Avicennia near seaward edge of mangrove forest and on isolated trees, 0.5 to 2 m above the ground. Rarely found on driftwood on sandy shores where mangroves are absent and on sheltered rocks (Reid 1986). In studied sites it was found on trunks and roots of young and old Rhizophora trees. Relation to mangroves. Predominantly mangrove-associated. Distribution in Vietnam. From northern-east coast to southern delta (Thach 2005). General distribution. Throughout the tropical and subtropical Indo-Pacific (Reid 1986)., Published as part of Zvonareva, Sofya & Kantor, Yuri, 2016, Cheсklist of gastropod molluscs in mangroves of Khanh Hoa province, Vietnam, pp. 401-437 in Zootaxa 4162 (3) on page 420, DOI: 10.11646/zootaxa.4162.3.1, http://zenodo.org/record/254973, {"references":["Linnaeus, C. (1758) Systema Naturae per Regna tria Naturae. Vol. 1. 10 th Edition. Salvius, Stockholm, 823 pp.","Reid, D. G. (1986) The littorinid molluscs of mangrove forests in the Indo-Pacific region: the genus Littoraria. British Museum (Natural History), London, 227 pp.","Okutani, T. (2000) Marine Mollusks in Japan. Tokai University Press, Tokyo, 1173 pp.","Thach, N. N. (2005) Shells of Vietnam. Conchbooks, Hackenheim, 338 pp.","Lozouet, P. & Plaziat, J. - C. (2008) Mangrove environments and mollusks. Abatan River, Bohol and Panglao Islands, Central Philippines. ConchBooks, Hackenheim, 166 pp.","Zvonareva, S., Kantor Yu., Xinzheng, L. & Britayev, T. (2015) Long-term monitoring of Gastropoda (Mollusca) fauna in planted mangroves in central Vietnam. Zoological studies, 54, 1 - 39."]}

Saparua Island is one of the islands in the Central Moluccas that has a complete ecosystem, unfortunately records on mollusk research is very limited. The aim of this research is to know the composition, diversity and utilization of mollusk. The objectives of the study are to determine the composition, diversity and utilization of mollusks using square transect and free collection method which conducted on April and September 2016. Water analysis is also done to determine the environmental hydrographic condition. Temperature and salinity indicate the presence of freshwater input through rivers, especially in St-2 2 (Waisisil). Concentrations of nutrients show a fairly high value, ranging from 0.001 to 0.114 mg L-1 for phosphate; 0.012 - 0.023 mg L -1 for nitrate and 0.140 - 0.443 mg L -1 for silicate. There are 641 individual mollusks of 107 species consisting of 85 species of Gastropoda and 22 species of Bivalves. Species found mostly by Littoraria scabra (Littorinidae), Cypraea annulus (Cypreidae), Terebralia sulcata (Potamididae); Clypeomorus battilariaeformis (Cerithiidae); and Nerita chamaeleon (Neritidae). The existing mollusk community has moderate and uniform diversity with low species dominance. There are at least 35 species of mollusks that can be utilized into various commodities such as food products, accessories/decorations and raw materials of drugs.

This research was found the ecological adaptive significance for their survivorship in mangrove microhabitat was as follow resting place, avoiding high tide, finding food, lying larvae, avoid sunshine, and hiding from predators. Significance of clumped distribution was taken to reduce drying stress, temperature, fallen from substrate against wave strikes, feeding and reproduction activity, suitable habitat. Significance of population abundance to balance strong predation and response to pressure of nature selection for their survivorship. Key Words : Littoraria scabra, significance, ecology, survival, and mangrove ABSTRAK Penelitian ini menemukan bahwa signifikansi ekologi Littoraria scabra untuk survival di mikrohabitat mangrove Tombariri yang ekstrim adalah sebagai berikut berfungsi sebagai tempat istirahat, menghindari perendaman air, mencari makanan, meletakkan larva, menghindar cahaya dan bersembunyi dari predator-predator. Signifikansi L. scabra distribusi spasial mengelompok untuk mereduksi stres kekeringan, suhu, terlepas di substrat akibat gelombang, aktivitas makan, reproduksi, kecocokan habitat. Signifikansi distibusi mengelompok dengan populasi tinggi untuk mengimbangi kuatnya predasi serta merespons tekanan seleksi alam yang kuat demi kelangsungan hidupnya. Kata Kunci : Littoraria scabra, signifikansi, ekologi, survival dan mangrove

Gastropod was one of the class from mollusca in mangrove ecosystem. Lubuk Kertang Village's mangrove forest was been converted into tourist areas, agricultural land and settlements. The purpose of this study was to analyze the structure of gastropods at Avicennia lanata, Rhizophora apiculata and Sonneratia alba. This research was conducted at Lubuk Kertang Village in February-March 2017. Gastropod were collected in 1 m × 1 m transect in mangrove. Examples of biota were taken by using shovel, then the biota was inserted into a plastic bag sample, wrote date of sampling and identified. The results showed there were 15 species Gastropods, namely Achatina fulica, Cerithidea alata, Cerithidea cingulata, Cerithidea obtusa, Chicoreus capucinus, Cymatium pileare, Ellobium aurimisdae, Ellobium aurisjudae, Littoraria melanostoma, Littoraria scabra, Murex tribulus, Nerita balteata, Nerita planospira, Pugilina cochlidium, Stramonita gradata, Telescopium telescopium and Terebralia sulcata. Diversity index ranged 1.702 to 2.165 was in medium category, Similarity index ranged 0.676 to 0.799 was in low category and Dominance index ranged 0.142 to 0.282 that categorized was low. The highest gastropod density was 31 individuals/m2 in the Sonneratia alba. The conclusion of the research is the existing mangrove ecosystem in Lubuk Kertang Village in a stable state.

Research on the diversity of invertebrate epifaunas associating with mangroves in the Balangdatu village of Tanakeke regency, Takalar district, South Sulawesi, has been conducted from September to December 2016. The objective of this research was to know the diversity of invertebrate epifaunas associating with mangrove in Balangdatu Village of Tanakeke Islands. Sample collection was done by using explorative quantitatively plot methods with size 2 x 2 m, applied at three different stations. Data analysis includes calculation of Absolute density, Uniformity Index (Shannon-wiener), Dominance Index, and Distribution Index. The results showed that there were 13 species of epi fauna of 9 tribes, namely Littoraria sp 1, Cerithidea cingulata , Littoraria sp 2, Littoraria pallescens , Episesarma sp , Saccostrea cucullata , Pagurus sp, Terebralia sulcata , Cerithidea sp , Nerita planospira , Nisto histrio , Littoraria scabra , and Cassidula vespertilionis . The highest density was found in Littoraria scabra with a density of 0.72 ind/m 2 . Diversity indices are low which indicate depressed environmental conditions. Distribution Index values across stations

Heavy metals were determined in the soft tissue and shells of the littorinid, Littoraria scabra, and in the sediments of four mangrove areas along the Dar es Salaam coastline where L. scabra was collected. Several metals accumulate, preferentially in the animals' soft body parts, but do not seem to affect the shell morphology of this species. Sediment-metal levels, measured in the direct vicinity of Dar es Salaam have increased dramatically over the last decade. Nonetheless, these levels are still lower compared to metal-sediment levels reported in polluted European and American estuaries. Soft-tissue metal levels detected in L. scabra are, nevertheless, with the exception of Cr and Zn, comparable to metal levels reported in other gastropod species. Keywords: Heavy metals, Mangrove, Littoraria Scabra, Dar es Salaam

The mangrove forest is a transitional ecosystem between land and sea. As a transition area between land and sea, mangrove forest ecosystems have environmental properties of a sharp gradient. Tides can result in changes in several environmental factors, mainly temperature and salinity. One type of animal that can tolerate these environmental changes are of a group of mollusks. The purpose of this study was to identify the types of mollusks (Gastropoda) found on the floor of Mangrove Forest, using transects squares drawn perpendicular from the shoreline mangrove cutting edge. From this research activity gastropods found in the floor of mangrove forest-Rap Rap village consists of five phyla, and nine species, namely: Family Cerithiidae, namely Cerithium cobelty and Clypeomorus coralium. Family Littorinidae are Littoraria scabra, family Muricidae are Chicoreus capucinus, and morula margariticola Drupella rugosa, from the family of Nassarius Nassariidae Potamididae margaritifer and family, namely Telescopium telescopium and Terebralia sulcata.

Mangroves function as important shelter and feeding habitats for marine fauna, but the degree to which mangrove-derived carbon contributes to local food webs has long been debated. In this study, stable isotope analysis was used as a technique to elucidate the role of mangrove carbon in the diets of the macroinvertebrate and fish fauna of an intertidal fringing mangrove forest and adjacent intertidal/subtidal mudflats in a macrotidal Tanzanian estuary. The expectation was that sessile species and those with low motility depend to a larger extent on local carbon sources than highly motile species. A clear distinction in δ13C was present between primary producers from mangrove and mudflat habitats. Macroinvertebrates revealed a gradient in their δ13C where Sesarma crabs were the only species that directly utilised mangrove carbon by feeding on mangrove leaves/detritus. Uca crabs and the gastropod Littoraria scabra showed a higher dependence on microphytobenthos from the mangrove substratum. Among the fish fauna, the amphibious mudskipper was the only species to which the mangroves were accessible during low tide. Consequently this was the only fish species for which it was clear that it fed in the mangrove habitat, most commonly on mangrove-associated Uca crabs. All other species of sessile as well as motile macroinvertebrates and fish from the mangrove and mudflat habitat showed a high degree of utilisation of mudflat carbon. Overall, mangrove carbon thus contributed little to the mangrove and mudflat food webs, despite the high tidal amplitude and the resulting potential for exchange of carbon and fauna in the estuary studied here. Utilisation of mangrove carbon appears to depend more on the ecology of the species in consideration (e.g., species-specific use of zones within the mangrove habitat) than on their potential motility or tolerance to exposure during low tide.

The periwinkle Littoraria scabra was collected at polluted and pristine mangrove sites along the Tanzanian coastline, including Msimbazi, Mbweni (i.e. Dar es Salaam) and Kisakasaka, Nyamanzi and Maruhubi (i.e. Zanzibar). Periwinkles were morphologically characterized, sexed and their heavy metal content was determined using ICP-MS. Analysis revealed that L. scabra from polluted areas contained higher soft tissue heavy metal levels, were significantly smaller and weighed less compared to their conspecifics from the unpolluted mangroves. The current morphological observations may be explained in terms of growth and/or mortality rate differences between the polluted and non-polluted sites. Although a variety of stressors may account for these adverse morphological patterns, our data suggest a close relationship with the soft tissue heavy metal content. Compared to soft tissue heavy metal levels that were measured in L. scabra along the same area in 1998, most metals, except for arsenic, chromium and iron have decreased dramatically.

Since October 1994, a long-term program of Asia/Pacific Mussel Watch: Taiwan Regional Studies has been carried out. The results indicate that trace metal contents in mollusca varied among 30 different species and the environments (water and sediments) along the Taiwan coast. The orders of bioaccumulation of trace metals in mollusca were: Cu (over 200 μg/g), Thais clavigera > Isognomon legumen > Clibanarius rivescens > Crassostrea gigas ; Zn (over 700 μg/g), Moruta granulata > C. gigas > Asiatica cypraea arabica > T. clavigera ; Cd (over 5 μg/g), Trochus hanleyanus > Acanthopleura japonica > Nerita albicilla > Patella flexuosa ; Pb (over 2 μg/g), P. flexuosa > C. gigas > T. hanleyanus > T. clavigera > C. gigas > Capiyulum mitella ; Ni (over 10 μg/g), Meretrix lusoria > Philine sp. > Littoraria scabra > Tridacna squamosa > T. hanleyanus ; Cr (over 30 μg/g), Littoraria undulata > T. hanleyanus > N. albicilla > Nerita chamaelor > M. granulata ; As (over 20 μg/g), Perna viridis > L. scabra ; and Sn (over 5 μg/g), P. viridis > L. undulata > C. mitella > C. gigas . Their seasonal and regional variations as well as their correlation are evaluated and discussed.

The zonation of 15 species of Littoraria in the scabra group is described, using a transect method, at 13 mangrove localities in Australia, Thailand, Malaysia and Hawaii. At these localities the littorinids occurred only on trees, and showed both vertical and horizontal patterns of zonation, with broad overlaps between co-occurring species. It is suggested that vertical distribution is determined mainly by behavioural responses, while the landward limits of horizontal distribution may be set by physiological tolerance. Several species occurred predominantly on either leaf or bark substrates, but no consistent associations with tree species were found. On the basis of local distribution patterns, Littoraria species can be classified as continental or oceanic in character. Oceanic species may be less tolerant of sediment in the water or on the substrate.

Littoraria filosa (Sowerby) is a member of the L. scabra group, found amongst the foliage of mangrove trees in northern Australia. The colour of the shell is polymorphic, showing two discrete ground colours, either yellow or orange-pink, with a variable degree of superimposed brown patterning. At a site on Magnetic Island, northern Queensland, colour frequencies of small snails were similar on different backgrounds. Amongst larger shells yellows were more frequent on Avicennia trees with abundant foliage, and browns on relatively bare trees, suggesting that visual selection for crypsis occurred. There was no evidence of substrate selection by the morphs. Yellow shells were cooler than brown shells, but differences in colour frequencies on sunny and shaded trees, and at different seasons, did not suggest climatic selection. By manipulating the colour frequencies of subpopulations of small snails isolated on individual trees, it was shown that the disappearance of yellow and brown shells was frequency-dependent. This result is consistent with hypotheses of mimicry of background elements by the morphs and of apostatic selection by unknown predators. Only the latter can account for the persistence of the highly conspicuous pink morph at a low frequency.