Intertidal Limpet Research Articles

Bioactive Metabolites from the South African Marine Mollusk Trimusculus costatus

A reinvestigation of extracts of the endemic South African intertidal limpet Trimusculus costatus yielded the known labdane diterpenes 6beta,7alpha-diacetoxylabda-8,13 E-dien-15-ol ( 1) and 2alpha,6beta,7alpha-triacetoxylabda-8,13 E-dien-15-ol ( 2) and three new metabolites, 6beta,7alpha,15-triacetoxylabda-8,13 E-diene ( 3), 3alpha,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione ( 4), and cholest-7-en-3,5,7-triol ( 5). Chiral derivatization and X-ray analysis were used to confirm the labdane absolute configuration of 2. Compounds 1, 2 and 4 exhibited moderate activity (3-25 microM) against the WHCO1 human esophageal cancer cell line.

Low heat shock thresholds in wild Antarctic inter-tidal limpets (Nacella concinna)

Heat shock proteins (HSPs) are a family of genes classically used to measure levels of organism stress. We have previously identified two HSP70 genes (HSP70A and HSP70B) in sub-tidal populations of the Antarctic limpet (Nacella concinna). These genes are up-regulated in response to increased seawater temperatures of 15 degrees C or more during acute heat shock experiments, temperatures that have very little basis when considering the current Antarctic ecology of these animals. Therefore, the question was posed as to whether these animals could express HSP70 genes when subjected to more complex environmental conditions, such as those that occur in the inter-tidal. Inter-tidal limpets were collected on three occasions in different weather conditions at South Cove, Rothera Point, over a complete tidal cycle, and the expression levels of the HSP70 genes were measured. Both genes showed relative up-regulation of gene expression over the period of the tidal cycle. The average foot temperature of these animals was 3.3 degrees C, far below that of the acute heat shock experiments. These experiments demonstrate that the temperature and expression levels of HSP production in wild animals cannot be accurately extrapolated from experimentally induced treatments, especially when considering the complexity of stressors in the natural environment. However, experimental manipulation can provide molecular markers for identifying stress in Antarctic molluscs, provided it is accompanied by environmental validation, as demonstrated here.

Evidence of Plasticity in the Reproduction of a Trematode Parasite: The Effect of Host Removal

The parasitic trematode Proctoeces lintoni requires 3 hosts (intertidal mussels, keyhole limpets, and clingfish) to complete its life cycle. The densities and size structure of host communities are modified by selective human harvesting. This study examined clutch and egg size of P. lintoni in 3 adjacent sites in rocky intertidal areas of central Chile presenting differences in the levels of human disturbance (i.e., from a fully protected marine reserve to free open-access areas). We found significant differences in parasite fecundity among sites. An increase in number of eggs was observed inside protected marine areas compared with open-access areas, suggesting a plastic response of the parasite reproductive strategies to the host community modification. These results show that host removal by humans in coastal ecosystems can strongly influence parasite life history traits.

Small spatial scale population genetic structure in two limpet species endemic to the Kermadec Islands, New Zealand

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 349:159-170 (2007) - DOI: https://doi.org/10.3354/meps07110 Small spatial scale population genetic structure in two limpet species endemic to the Kermadec Islands, New Zealand Ann R. Wood*, Jonathan P. A. Gardner Centre for Marine Environmental and Economic Research, School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand *Email: ann.wood@vuw.ac.nz ABSTRACT: Persistence of marine species in isolated habitats requires either continuing recruitment from distant sources or self-recruitment from the local population. Species endemic to small isolated oceanic islands such as the SW Pacific Kermadec Islands (New Zealand) are reliant on self-recruitment for continued existence. Population genetic studies in such isolated habitats can provide data on the extent to which dispersal limits the occurrence of organisms and determines their genetic structure. We used randomly amplified polymorphic DNA markers (RAPDs) to examine genetic structuring and connectivity among populations of 2 intertidal limpets endemic to the Kermadec Islands. Significant genetic differentiation and limited connectivity were observed among populations of these limpets separated by less than 1 km, suggesting that a large proportion of successfully recruiting larvae do not disperse far from their population of origin. Patterns of connectivity may be explained partly by the geographic distance among populations, but the data suggest that other barriers to gene flow, most likely associated with local hydrographic features, contribute to the observed patterns of small-scale population genetic structuring. KEY WORDS: Population genetic variation · Gene flow · Self-recruitment · Scutellastra kermadecensis · Siphonaria raoulensis · RAPDs · Kermadec Islands Marine Reserve · SW Pacific Full text in pdf format PreviousNextCite this article as: Wood AR, Gardner JPA (2007) Small spatial scale population genetic structure in two limpet species endemic to the Kermadec Islands, New Zealand. Mar Ecol Prog Ser 349:159-170. https://doi.org/10.3354/meps07110 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 349. Online publication date: November 08, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Responses of the limpet, Cellana grata (Gould 1859) , to hypo-osmotic stress during simulated tropical, monsoon rains

Although heat stress is often cited as the dominant physical stress on tropical shores, intertidal organisms in regions with monsoonal climates are also regularly exposed to prolonged periods of heavy rainfall. Such events are predicted to have adverse physiological effects on individuals and may result in mortality. In a series of laboratory experiments, the impact of simulated monsoonal rains was investigated on the patellid limpet, Cellana grata. Sub-lethal responses in terms of body water content, body fluid osmolality and heart rate were measured in two different size cohorts maintained on horizontal and vertical substrata. Limpets were unable to achieve any effective behavioural isolation, and exposure to either simulated rainfall or diluted seawater resulted in both large and small C. grata gaining water with subsequent dilution of mantle water and haemolymph osmolalities. With increased duration of rainfall, dilution of body fluids increased with little difference between individuals on horizontal and vertical surfaces. Body fluids generally showed proportional dilution during prolonged rain, but in some individuals there was evidence for regulation of the haemolymph relative to the mantle fluid. Overall, smaller limpets were more susceptible to prolonged rainfall than large animals in terms of swelling of soft tissues and detachment and also had higher heart rates than large limpets. Both cohorts reduced heart rates with prolonged rainfall, suggesting a degree of metabolic depression, especially on horizontal surfaces. In small limpets, no difference in heart rate was found with substratum orientation, whereas large limpets had elevated heart rates on vertical as compared to horizontal substrata, when exposed to either simulated rainfall or washed with dilute seawater. This may reflect the increased energetic costs required to maintain a relatively larger body on a vertical surface under stressful conditions. Monsoonal rainfall during emersion, and subsequent dilution of seawater, therefore, have sub-lethal physiological and possible lethal effects on intertidal limpets. This influence has been largely overlooked, but coupled with the possible synergistic effects of thermal stress, monsoon rains are likely to play an important role in community dynamics on tropical shores.

Simultaneous polyphenism and cryptic species in an intertidal limpet from New Zealand

The small intertidal limpets known under the name Notoacmea helmsi occupy a wide variety of habitats in New Zealand and exhibit a variety of shell forms. Phylogenetic analyses of DNA sequences from two genes, mitochondrial COI and nuclear ITS1, reveal that this taxon comprises at least five morphologically cryptic species, with at least one of these species, N. scapha, consisting of individuals with two obviously different shell types. One of these forms is an ecophenotypic response to living on eelgrass (Zostera) fronds. Unlike its extinct relative, Lottia alveus, N. scapha is not restricted to this substrate, but individuals living elsewhere are larger and have a different shell shape. Although there is significant overlap in shell form among the different cryptic species, there is some habitat differentiation, with two species predominantly found on exposed shores and three confined to mudflats. One species exhibits distinctive light-avoiding behaviour, the first known case in which behaviour can be used to separate cryptic species in molluscs.

Lack of genetic differentiation among four sympatric southeast African intertidal limpets (Siphonariidae): phenotypic plasticity in a single species?

Specimens of four sympatric intertidal limpet species (Siphonaria dayi, S. tenuicostulata, S. anneae and S. nigerrima ) were collected from four localities on the east coast of South Africa and southern Mozambique. Their phylogenetic relationships were investigated using sequences of the mitochondrial COI gene and the intron-containing nuclear ATPSb gene. Two closely related lineages were recovered, which grouped specimens on the basis of geography rather than morphology. One lineage was associated with the subtropical coastline of South Africa’s east coast and the other with the tropical coastline of northeastern South Africa and southern Mozambique. This genetic discontinuity coincides with a biogeographic boundary located in the vicinity of Cape St Lucia. Combined genetic diversity of the four species was lower than that of three other southern African congeners, and fell within the range determined for single southern African marine mollusc species. We suggest that the four limpet species are in fact different morphotypes of a single species.

The northern geographic range limit of the intertidal limpetCollisella scabra: a test of performance, recruitment, and temperature hypotheses

A decline in abundance towards a species' range boundary is often interpreted as evidence of a decline in individual success, and is usually assumed to reflect a decline in suitable environmental conditions. Gradual declines towards high latitude range boundaries are frequently attributed to limitations on organismal tolerance of cold temperature. Rarely have these two assumptions been empirically tested. The intertidal gastropodCollisella scabradeclines monotonically in abundance from 435 to <1 m−2over the northern 300 km of its geographic distribution. I examined temperature, adult performance (survival, growth, reproduction), and recruitment at five locations in this region of decline. Mortality ranged from 4.9 to 11.2% per month, but was highest at the lowest latitude study site. Growth rates ranged from 0 to 5.2 mm yr−1, but were generally lower at lower latitude sites. Gonad development was high in the three populations examined, but the possibility of infrequent spawning at high latitude sites could not be excluded. Finally, a comparison of performance differences among populations with temperature revealed clear effects of temperature on both growth and mortality; however, the patterns were not consistent with a hypothesis of cold stress at the range boundary. Overall there was little evidence for either reduced performance or increasing cold stress in low density high latitude populations. Over the same 300 km, recruitment declined monotonically from a mean of six recruits per 625 cm2to less than one; suggesting that limitations on recruitment, rather that adult performance, are responsible for low abundance in marginal populations. Several hypotheses for the decline in recruitment are discussed in the paper and the most likely explanation appears to be an increase in the distance between populations at the range margin, reducing the chances that dispersing larvae find suitable habitat for settlement.

Comparative phylogeography of coastal limpets across a marine disjunction in New Zealand

Cook Strait, which separates the North and South Island of New Zealand, has been a transient, but re-occurring feature of the New Zealand land mass throughout the Pleistocene, maintaining its current width and depth for the past 5000 years. Historic land fragmentation coupled with the complex hydrography of the Greater Cook Strait region has created both biogeographic and phylogeographic disjunctions between the North and South Island in several marine species. Here we use mitochondrial cytochrome b DNA sequences of three endemic intertidal limpets, Cellana ornata, Cellana radians and Cellana flava to assess intraspecific phylogeographic patterns across Cook Strait and to look for interspecific concordance of ecological and evolutionary processes among closely related taxa. We sequenced 328-359 bp in 85-321 individuals from 8-31 populations spanning the biogeographic range of the three species. Intraspecific phylogeographic analyses show moderate to strong genetic discontinuity among North and South Island populations due to allopatric fragmentation. This pattern was broadly concordant across the three species and the observed divergence among this group of intertidal limpets (0.3-2.0%) is similar to that of previously studied subtidal organisms. For each species, divergence time calculations suggest contemporary North and South Island lineages diverged from their respective most recent common ancestor approximately 200 000 to 300 000 years before present (bp), significantly earlier than previous estimates in other coastal marine taxa that arose from a miscalculation of divergence time.

Ecological impacts on the limpet Lottia gigantea populations: human pressure over a broad scale on island and mainland intertidal zones

Here long-term monitoring data taken at 33 sites in southern and central California coast and islands were used to evaluate the size structure of the large intertidal limpet, Lottia gigantea in restricted-access and in easily accessible intertidal zones that encompass a wide range of ecological variables. Using multi-dimensional analysis of population size structures, we found that sites on islands and strictly protected mainland sites have significantly larger median limpet sizes and a greater range of limpet sizes than unprotected mainland sites, while no pattern occurs in latitudinal or regional comparison of sites. Although intertidal predators such as oystercatchers were not the primary focus of the monitoring efforts, extensive natural history notes taken during sampling visits support the argument that predation was not a primary cause for the size structure differences. Finally, substratum differences were determined not to have biased the observation of larger limpets in protected sites. In regard to human interactions with limpets, we conclude that the degree of enforcement against poaching is the better predictor of limpet size structure than proximity to population centers or visitation to intertidal sites.

Life at the edge: an experimental study of a poleward range boundary

Experimental studies of biogeographic processes are important, but rarely attempted because of the logistical challenges of research at large spatial scales. I used a series of large-scale transplant experiments to investigate the mechanisms controlling species abundance near a poleward range boundary. The intertidal limpet Collisella scabra experiences a 100-fold decline in abundance over the northernmost 300 km of its range. Temperature and food supply both strongly influenced individual survival, growth, and maturation. Regression analysis also revealed significant interactions among these conditions: the effect of one could not be predicted without knowing the level of the other. But these relationships could not explain geographic abundance patterns. Instead, individual limpets were highly successful at sites with relatively low abundance. These results suggest that, even though temperature is important to the success of individual C. scabra populations, the primary effect of warming temperatures under climate change may not be a shift in geographic distribution.

Morphological and habitat divergence in the intertidal limpet Patelloida pygmaea

In the intertidal limpet Patelloida pygmaea, two distinctive morphs, the forms pygmaea and conulus, have been recorded. The former possesses a flat elongated shell, and the latter has an extremely high round shell. It has been observed in the field that pygmaea is found on oyster shells Crassostrea gigas. The form conulus uses an unusual substrate for attachment. It is found on the living shells of the intertidal gastropod Batillaria cumingi. Although conulus is normally found only on shells of Batillaria, it can also be found on oyster shells when pygmaea and Batillaria shells are not present in nature. An electrophoretic analysis of allozymes showed that these two forms are reproductively isolated from each other and coexist without gene exchange on the same mudflat. Laboratory experiments showed that pygmaea prefers oyster shells and conulus prefers Batillaria shells as substrates for attachment when both oyster and Batillaria shells are present. The form pygmaea did not attach to Batillaria shells, even when only Batillaria shells were available. However, conulus also attached to oyster shells when Batillaria shells were not available. The proportion of individuals of conulus that attached to oyster shells decreased significantly when pygmaea was attaching to the oyster shells. These results suggest that pygmaea is ecologically more specialized to living on oyster shells than conulus.

Thermal stress on intertidal limpets: long-term hindcasts and lethal limits

When coupled with long-term meteorological records, a heat-budget model for the limpet, Lottia gigantea, provides a wealth of information regarding environmental and topographic controls of body temperature in this ecologically important species. (1) The maximum body temperature predicted for any site (37.5 degrees C) is insufficient to kill all limpets, suggesting that acute thermal stress does not set an absolute upper limit to the elevation of L. gigantea on the shore. Therefore, the upper limit must be set by behavioral responses, sublethal effects or ecological interactions. (2) Temperatures sufficient to kill limpets are reached at only a small fraction of substratum orientations and elevations and on only three occasions in 5 years. These rare predicted lethal temperatures could easily be missed in field measurements, thereby influencing the interpretation of thermal stress. (3) Body temperature is typically higher than air temperature, but maximum air temperature can nonetheless be used as an accurate predictor of maximum body temperature. Warmer air temperatures in the future may thus cause increased mortality in this intertidal species. Interpretation of the ecological effects of elevated body temperature depends strongly on laboratory measurements of thermal stress, highlighting the need for additional research on the temporal and spatial variability of thermal limits and sublethal stress. The lengthy time series of body temperatures calculated from the heat-budget model provides insight into how these physiological measurements should be conducted.

Size-assortative mating and non-reciprocal copulation in a hermaphroditic intertidal limpet: test of the mate availability hypothesis

Mating behaviour and mating patterns are affected to a large extent by body size in both hermaphrodites and gonochorists. Detailed research on mating patterns, mate choice, pre- and post-copulatory sexual selection in marine pulmonates is wanting, thus warranting more attention as a study system in the future. The simultaneous hermaphroditic limpet Siphonaria capensis (Pulmonata: Basommatophora) shows size-dependent fecundity, and acts as a suitable organism to test the effects of body size on mating patterns, mating success, gender expression and reciprocity in hermaphroditic marine gastropods. We mainly used bootstrap resampling techniques to estimate the effects of different factors on mating patterns. In the populations studied, a strong size-assortative mating pattern was observed, where small-scale spatial distribution of potential mating partners (the mate availability hypothesis) could explain 65% of this pattern, while mate choice and mating constraints explaining the rest. No significant difference in mating success between limpets with different body size was found, even though in one population, the sperm recipients were larger than the non-copulating limpets. Interestingly, we found that intromission was non-reciprocal during copulations. This may mean that this species does not conform to the common rule of reciprocity predicted for hermaphrodites, unless there is sex-role alternation between individuals in a mating pair. The mating partners consisted of similar sized, acting males and females, thus without any indication of the body size determining the gender expression. The matings took place in early mornings only at spring tides and the animals were observed laying egg masses only during neap tides. Since siphonariid limpets possess both a spermatheca and a seminal vesicle, which may have either a sperm storing and/or digestive function, post-copulatory sexual selection (e.g., sperm competition) cannot be dismissed.

Rare predation by the intertidal crab Pachygrapsus marmoratus on the limpet Patella depressa

The predatory effects of Pachygrapsus marmoratus on populations of the intertidal limpet Patella depressa were analysed on rocky shores located on the central coast of Portugal. Nocturnal observations on crab feeding behaviour were conducted and experimental exclusion cages were set in the substratum to assess density effects on limpets. The results indicated that although crabs feed on adult limpets the predatory level was minimal. Crabs used consistent tactics to detach limpets from the substratum but the majority of the attacks were unsuccessful, possibly due to morphological and behavioural adaptations of limpets. An alternative recruitment hypothesis is advanced to explain non-significant differences between experimental treatments and a possible predatory role on shaping levels of recruitment on lower levels of the shore is considered.

Demography, competitive interactions and grazing effects of intertidal limpets in southern New Zealand

Population dynamics and the effects of intraspecific competition on limpet growth and maintenance of bare patches were investigated for the intertidal limpet Cellana ornata (Dillwyn) at a boulder-dominated site and on a rocky platform near Kaikoura (South Island), New Zealand. Distribution and abundance patterns of C. ornata were described in relation to other biota and tidal height. C. ornata occurred almost exclusively in patches devoid of macroalgae, particularly in the mid-tidal zone. Both adult and juvenile limpets were most abundant on the tops of boulders, where their numbers were positively correlated with barnacle cover, which averaged 77%. The size structure and growth patterns of C. ornata were different between populations. Mark-recapture studies showed that the slopes of annual growth increments regressed on initial sizes were similar at both sites but that the annual increments on the platform were about 6 mm greater than on boulders. Growth virtually ceased at 27 mm for limpets at the barnacle-dominated boulder site and at 40 mm at the platform site. Recruiting cohorts had 20% survival on boulders and 37% on the platform during their first year. The largest size classes at both sites had around 57% annual survival. To test the effects of varying limpet densities on the growth and mortality of limpets and the maintenance of bare patches, densities of C. ornata were experimentally increased at both sites. Beyond a density of 4 per 0.25 m 2, sizes and survival of limpets were reduced at both sites, but the effect was more pronounced at the boulder site. Limpets at the boulder site were more effective at maintaining bare space than those on the reef platform. Enclosing limpets in plots with and without barnacles showed that C. ornata and a co-occurring species ( Cellana denticulata (Martyn)) grazed more effectively and had greater growth in cleared plots. Overall, there was considerable variation in the demographics of C. ornata between populations driven by site-specific characteristics.

Recruitment in the intertidal limpet Lottia digitalis (Patellogastropoda: Lottiidae) may be driven by settlement cues associated with adult habitat

The ribbed limpet, Lottia digitalis, is found high in rocky intertidal habitat throughout its geographic range. In order to identify likely natural settlement locations for larvae of this species, laboratory-reared larvae were settled onto substrata collected from within and near an adult L. digitalis habitat. Of larvae exposed to rock chiseled from within high-intertidal adult habitat, 31.0% and 23.3% underwent metamorphosis during two separate experiments. Similarly, an unidentified filamentous green alga that was isolated from this rock induced metamorphosis in 26.6% and 8.7% of larvae during additional experiments. In contrast, larvae did not metamorphose upon bare rocks or upon rocks encrusted with a crustose corraline alga (CCA) that were collected from lower intertidal zones, nor did they metamorphose upon the macroalgae Ulva sp., Enteromorpha contorta, Alaria marginata, or Polysiphonia sp. The presence of mucus from adult conspecifics during these experiments did not enhance metamorphosis onto rock taken from adult habitat, but it did induce metamorphosis in an average of 13.5% and 7.0% of larvae introduced to the mid-intertidal bare rock and CCA substrata, respectively. Finally, 38.0% and 34.4% of larvae from two experiments underwent metamorphosis when exposed to the high-intertidal barnacle Pollicipes polymerus. These results suggest that larval settlement, rather than differential post-settlement mortality and/or migration, drives recruitment of L. digitalis in high-intertidal habitats.

Shell-size variation of Notoacmea biradiata (Archaeogastropoda: Acmaeidae) as a response to gastropod density and height in shore in the Colombian Pacific coast

Notoacmea biradiata (Reeve, 1855) is an abundant intertidal limpet on the rocky shore of the Colombian Pacific coast. This paper reports a field factorial experiment on shell-size variation of N. biradiata as a response to two independent factors: intertidal gastropod density and shore height above sea level. Four rocky shores were selected on the Colombian Pacific coast, two in Gorgona Island and two in Utr?Cove. The intertidal gastropods density was determined in each rocky shore using the transect-quadrant technique. Significant differences were observed in the gastropod densities between study sites: low density in the rocky shores of Utr?Cove and high density in the rocky shores of Gorgona Island (P < 0.009). A factorial sampling was conducted to determine the effect of the density and height on the shore over shell-length, shell-height and shell-thickness. A twoway ANOVA and a least-squared regression was used to determine whether the shell-sizes differ between varying densities and shore heights. Intertidal gastropod density was found to be the dominant factor in determining basal shell length (ANOVA, P < 0.001) and shell height (ANOVA P < 0.05) changes. Thus, at low population densities the shells are larger and taller. The height on the shore did not influence the shell-size of N. biradiata (ANOVA, P > 0.30).

Effects of a complex archipelago on genetic subdivision of the intertidal limpet Siphonaria kurracheensis

Allozyme variation in the intertidal limpet Siphonaria kurracheensis was examined in 11 populations from the Houtman Abrolhos Islands, Western Australia, and four from the adjacent mainland, to test if the effects of these islands on genetic subdivision should include species with high dispersal. Consistent with extensive planktonic dispersal, genetic subdivision was low, with an average standardized variance in allelic frequencies (FST) of 0.010 over 400 km along the mainland, and 0.009 over 70 km in the Abrolhos Islands. Nevertheless, subdivision was statistically significant at the smallest scale examined (about 10 km), showing a pattern of local heterogeneity and large-scale homogeneity, which is common in planktonic dispersers. Among the island populations, heterozygosity was positively correlated with a multivariate index of exposure. The level of heterozygosity at the most exposed island sites is equivalent to that at the (also exposed) mainland sites, whereas it is lower in the most sheltered island sites. Although this indicates that some island populations are less well connected to the major pool of larvae, the overall effect of the archipelago on genetic subdivision is no greater than occurs on the mainland coast. This is contrary to findings in previously studied species with less potential for dispersal, suggesting that the local impediments to dispersal are selective in their effects, and are unlikely to be broadly important for genetic divergence in widely dispersing species.

Meltwater effects on intertidal Antarctic limpets, Nacella concinna

Responses of the Antarctic limpet Nacella concinna (Mollusca: Gastropoda) to meltwater exposure were studied at Adelaide Island (67°34′S 68°08′W). Limpets in crevices could be bathed in pure meltwater, though animals in large pools often avoided significant exposure to lowered salinity because of marked halocline formation. Small pools containing limpets showed extremely demanding osmotic environments with fluctuations between salinities of 3 and 30 psu being recorded within 1–2 min because of alternating meltwater and wave action. Analysis of haemolymph osmolarities in animals taken from the field demonstrated significant falls in osmolality (to 600–800 mOsm kg−1) compared with control animals living in seawater (1000 mOsm kg−1). A few moribund animals had osmolarities <600 mOsm kg−1. Nacella concinna are stenohaline osmoconformers with a median lower lethal salinity (96 h) of 20·9 psu and a median lethal time for freshwater exposure of 2 h 18 min. A 1 h exposure to freshwater caused a 14% increase in body volume and a 27% loss of body fluid ions. Nacella concinna responds behaviourally to meltwater by short-term, ineffective, clamp down of the shell, retraction of the head, cephalic tentacles and mantle margin tentacles. On vertical surfaces limpets respond actively to freshwater exposure by rapid detachment; 50% of animals lose adhesion within 5 min. Consideration of tidal regimes at Adelaide Island suggests that an individual intertidal limpet has a risk of being exposed to severe meltwater exposure about once per year.