Shore Exposure Research Articles

Influence of algal architecture and shore exposure on population dynamics of marine amphipods at Ras Mohamed Protectorate, Egypt.

Amphipods are one of the major invertebrate groups and spreading among marine macro-algae in the intertidal zone at Ras Mohamed Protectorate. But, very scarce information is available about amphipod species presence, their abundance and the factors affecting their distribution. So the present work aimed to study the effect of some physical factors on the abundance and diversity of amphipod species inhabited macro-algal hosts. Through the present work, samples were collected seasonally from three sites inside this protectorate. Results indicated that 2 macro-algal species of red algae were collected from these three sites. The algal species fluctuated in different sites. 16 of the amphipod species were recorded inhabiting them. The highest abundance and diversity of amphipod species were recorded at Yollanda beach. Some amphipod species were found at the site and not recorded at other sites. The diversity and abundance of these amphipod species were fluctuated between sites depending on many physical factors such as wave exposure, the shape of algal hosts, surrounding habitats and environments

Epi- and endobiont faunal communities on an Egyptian Mediterranean rocky shore: species composition and their competition for space

The exposed calcareous rocky area of the Abu Qir Headland, east of Alexandria, Egypt which range from coarse grains, through pebbles, cobbles, and boulders to rocky platforms, was significantly colonized by sclerobionts (epibionts and endobionts). The epibiont species diversity was comparatively higher than that of endobionts. Epibiont communities included bryozoans (the anascan-grade cheilostome Biflustra savartii), serpulid (Hydroides elegans, Spirobranchus cf. tetraceros, Vermiliopsis striaticeps and Protula or Apomatus) and spirorbid (Spirorbis) wormtubes, and balanoid barnacles (Amphibalanus amphitrite, Balanus trigonus, and Perforatus perforatus). The cheilostome bryozoan colonies, which developed extensive sheets, proliferated on the study rocky shore either encrusting the bioeroded basement directly, or encrusting other epilithic taxa, particularly balanoid barnacles and serpulid worms. Encrusters displayed a remarkable marginal competitive interaction (overgrowth and stand-off) for space on the study rocky shore. On the other hand, endobionts were not well represented on the studied rocky shore exposure. It was possible to identify three ichnotaxa: Gastrochaenolites, Maeandropolydora, and Finichnus. The findings documented represent a significant contribution to our knowledge of sclerobionts composition, sequence of their colonization and/or bioerosion, and their mutual relationships on the intertidal rocky shore of the Abu Qir Headland.

Occurrence and characterization of surface sediment microplastics and litter from North African coasts of Mediterranean Sea: Preliminary research and first evidence

The aim of this research work is to investigate the abundance of macroplastics and microplastics from North African coasts of Mediterranean Sea in the Gulf of Annaba (Algeria). The study areas are well known for the high population and high industrial activities that can contribute to the plastic pollution. In this case, microplastics were sampled from the surface sediments at four different stations representing different local activities. The microplastics were extracted by the density separation method from collected samples. Each particle was identified using Fourier transform infrared spectroscopy (ATR-FTIR). Furthermore, beach litters were obtained according to the adopted methodology - guidance on monitoring of marine litter in European seas.The obtained mean concentrations are 182.66 ± 27.32 and 649.33 ± 184.02 kg−1 sediment (DW), respectively. A detailed spatial and quantitative analysis revealed that their distribution was a function of proximity to populated areas and associated with wastewater effluents, industrial installations, degree of shore exposure and complex tidal flow patterns. Five types of microplastics were identified; the most common were fibers (70%), fragments (21%), pellets (5%), films (2%) and foams (2%). Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis showed that the main polymers detected in the studied microplastics were polyethylene (48%), polypropylene (16%), polyethylene terephthalate (14%), polystyrene (9%), butyl branham (7%), ethylene propylene (3%) and cellulose tri acetate (3%).The obtained results provided a holistic view of the abundance, distribution, and characteristics of microplastics in the Gulf of Annaba. This study confirmed the presence of microplastics in the Gulf of Annaba, albeit further studies remain necessary for better understanding of sources and fate.

Morphometric methods for the analysis and classification of gastropods: a comparison using Littorina littorea

The study of morphology is a common means of biological grouping and classification. In recent years, morphometric studies have been dominated by quantitative geometric-morphometric methods of data extraction such as outline or landmark-based analysis. These methods are often used in conjunction with various classification methods such as linear discriminant analysis (LDA) and random forests (RF) in order to achieve inter- and intraspecific grouping based on environmental factors. Despite numerous studies incorporating these data-extraction and classification methods, comparisons of the effectiveness of these methods are largely lacking, especially for species which display low morphological variation. The aim of this study was to compare the effectiveness of two data-extraction methods, elliptic Fourier analysis (EFA) and generalized Procrustes analysis, and two classification methods, LDA and RF, using Littorina littorea as the study organism. The results show that the principal component scores derived from EFA, provided the optimal data input for classification while the greatest percentage of successfully classified individuals was achieved using LDA. However, based on this study RF is the recommended classification method as it is resistant to overfitting, makes no assumptions about the data, is well suited to morphometric data and produces similar rates of classification to LDA. The results are discussed in a biological context for L. littorea, based on the environmental factors of zonation and shore exposure.

Microplastic contamination of intertidal sediments of Scapa Flow, Orkney: A first assessment

The concentration of microplastic particles and fibres was determined in the intertidal sediments at selected sites in Scapa Flow, Orkney, using a super-saturated NaCl flotation technique to extract the plastic and FT-IR spectroscopy to determine the polymer types. Mean concentrations were 730 and 2300kg−1 sediment (DW), respectively. Detailed spatial and quantitative analysis revealed that their distribution was a function of proximity to populated areas and associated wastewater effluent, industrial installations, degree of shore exposure and complex tidal flow patterns. Sediment samples from Orkney showed similar levels of microplastic contamination as in two highly populate industrialized mainland UK areas, The Clyde and the Firth of Forth. It was concluded that relative remoteness and a comparative small island population are not predictors of lower microplastic pollution. Furthermore, a larger concerted effort across Scotland and the UK is required to establish a baseline microplastic database for the evaluation of future policy measures.

Determinants of sediment properties and organic matter in beach and dune environments based on boosted regression trees

AbstractGrain size properties and the variation of organic matter in coastal beach and dune environments are assumed to be controlled by the intensity of aeolian processes, time and the sediment source. However, assumptions are based on relatively limited empirical studies. In this study, we examined which environmental variables are the main predictors of multiple topsoil properties. To achieve this, we analysed an extensive dataset systematically collected across all beach zones and a large geographical area at the Finnish Baltic Sea coast characterized by post‐glacial land uplift. We included a comprehensive set of predictors in the analysis and applied boosted regression trees, a modern modelling technique particularly suited for analysis without prior assumptions of the data model. The results suggest that mean grain size and sorting are mainly determined by northing and fetch. Northing, disturbance and fetch predicted the variation of soil organic matter while litter cover was strongly related to disturbance. Based on the analyses, we were able to identify the main drivers of multiple topsoil properties on land uplift beaches. Parent material is suggested to determine sediment textural properties, which largely masks the effects of transient processes. Mean grain size and sorting are highly interdependent: grains become finer and sorting improves with increasing shore exposure. The intensity of momentary geomorphic processes controls the accumulation of litter whereas the slower accumulation of organic matter in the soil is influenced also by the static exposure setting. Skewness and kurtosis of the grain size distribution are mainly influenced by unmeasured processes, potentially relating to the geomorphological origin of the sediment. Copyright © 2014 John Wiley & Sons, Ltd.

Sex on the Shore: Wishful Identification and Parasocial Relationships as Mediators in the Relationship Between Jersey Shore Exposure and Emerging Adults' Sexual Attitudes and Behaviors

Exposure to highly sexualized television programs has been correlated with emerging adults' sexual attitudes and behaviors. However, little is known about the variables that may mediate these relationships. The studies presented here investigated wishful identification and parasocial relationships withJersey Shore cast members as mediators in the relationship between exposure to Jersey Shore and permissive sexual attitudes. In Study 1, a secondary examination of content analysis data suggested that sex was pervasive on Jersey Shore. Analyses revealed that, on average, one sexual instance occurred every minute on Jersey Shore. The frequency of sexual instances on Jersey Shore was significantly higher than the frequency of sexual instances in other popular primetime television programs. In Study 2, data collected from a sample of emerging adults revealed a positive relationship between Jersey Shore exposure and permissive sexual attitudes mediated by participants' wishful identification and parasocial relationships with Jersey Shore cast members. Permissive sexual attitudes were positively correlated with sexual activity. Results are consistent with predictions made by cultivation and social cognitive theory. The relationships between television exposure, wishful identification, parasocial relationships, and emerging adults' sexual attitudes and behaviors are the focus of the discussion.

Using ice‐scars as indicators of exposure to physical lakeshore disturbances, Corvette Lake, northern Québec, Canada

ABSTRACTThe hypothesis tested in this study is that ice‐scars recorded by lakeshore tree stands can be used as an integrative proxy indicator of the overall hydrodynamic disturbance regimes affecting northern lakeshores. A 2‐km‐long shore segment was divided into 21 sections according to shore orientation and slope. An ice‐scar chronology and a wave exposure index value were obtained for each shore section. A significant relationship was found between ice‐scar chronology and wave exposure index, which indicates that the mechanical action and physical force of ice activity mainly depend on the same environmental factors determining exposure to wave action (i.e. fetch, wind direction and velocity, and shore slope). The spatial and temporal variability of ice‐scar chronology features also corresponded to the distribution of geomorphological features associated with ice activity along the shoreline. Analysis of the hydrological signal associated with these ice‐scar chronology features indicated that an increase in ice‐push frequency observed in the 1930s can be associated to an increase in wave action related to more frequent spring floods maintaining high lake levels during the ice‐free period. This study demonstrates that ice‐scars have strong potential as proxy indicators of shore exposure and provide a temporal frame to reconstruct the history of lakeshore disturbance regimes at a local scale. Together, ice‐scars and wave exposure index provide essential information to interpret the evolution of lakeshore vegetation mosaics in time and space. Copyright © 2012 John Wiley & Sons, Ltd.

Importance of consumers on exposed and sheltered rocky shores

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 443:65-75 (2011) - DOI: https://doi.org/10.3354/meps09412 Importance of consumers on exposed and sheltered rocky shores N. E. O’Connor1,2,*, I. Donohue3, T. P. Crowe4, M. C. Emmerson1,2,5 1Environmental Research Institute, University College Cork, Lee Road, Cork, Ireland 2School of Biological Sciences, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK 3School of Natural Sciences, Department of Zoology, Trinity College Dublin, Dublin 2, Ireland 4School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland 5School of Biology, Earth and Environmental Sciences, University College Cork, North Mall, Cork, Ireland *Email: n.oconnor@qub.ac.uk ABSTRACT: It is often suggested that the relative importance of biotic processes, such as recruitment, competition and predation of marine benthic species, varies predictably along a gradient of exposure to wave action. Several established models of community dynamics on rocky shores predict that top-down processes are more important for structuring communities on sheltered than on exposed shores. To test the relative dominance of top-down processes, we first measured the establishment of key benthic species (mussels, barnacles and algae) on 3 sheltered and 3 exposed rocky shores in southwest Ireland over two 6 mo periods. We then manipulated the presence of consumers (e.g. grazing gastropods, crabs, whelks), using caged exclosures, on 2 sheltered and 2 exposed shores to test for an interaction between effects of consumers and shore exposure on the establishment of benthic species. In contrast to predictions, we found that consumers strongly affected establishment of all species regardless of shore exposure. We also found that shore exposure was not a reliable predictor for spatial and temporal variation in rates of establishment of sessile benthic species. Our findings provide experimental evidence which demonstrates the importance of consumers in early post-settlement stages of benthic species—essential for the development of benthic−pelagic models. KEY WORDS: Algae · Barnacles · Consumers · Grazers · Mussels · Intertidal · Rocky shore Full text in pdf format PreviousNextCite this article as: O’Connor NE, Donohue I, Crowe TP, Emmerson MC (2011) Importance of consumers on exposed and sheltered rocky shores. Mar Ecol Prog Ser 443:65-75. https://doi.org/10.3354/meps09412 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 443. Online publication date: December 20, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Amphipods (Crustacea: Amphipoda) associated with red algae (Rhodophyta) in Kandalaksha Bay (the White Sea, Russia)

Amphipods' assemblages living in the red algae communities were studied in Velikaya Salma Strait (Kandalaksha Bay, north-western White Sea) in the depth range of 3–11 m. Sampling sites were located along the depth and shore exposure gradients in the areas with a significant number of rhodophytes. In total 12 species of amphipods were found withAmpithoe rubricataandCrassicorophium bonelliibeing most common and abundant.Gammaropsis melanopsandPleusymtes glaberwere revealed as subdominant species. As an algal grazerA. rubricataappeared to be the species most closely associated with various algal assemblages.Crassicorophium bonelliiwere found on substrates being a deposit feeder predominantly inhabiting mixed assemblages of red algae where deposition and accumulation of seston most likely took place.Gammaropsis melanopsandP. glaberare known as grazers but they preferred the habitats with both red algae and sponges. None of the species can be considered as obligate inhabitants of red algae hosts.Ampithoe rubricataandC. bonelliioccurred in red algae communities in the shallow area (about 4 m). The most diverse and quantitatively rich amphipod assemblages were found at depths of 8–9 m in the area protected from waves and surf by the islands. Three of the most common and abundant speciesA. rubricata, C. bonelliiandP. glaberare considered as amphiboreal while most of the species associated with rhodophytes belong to the Arctic-boreal ones. Amphiboreal species are presumably adapted to a broader temperature-range, in particular to higher summer temperature, than the Arctic-boreal species; they most likely have an advantage when occupying biotopes at shallow subtidal depth with local conditions in the White Sea.

Nutrient availability modifies species abundance and community structure of Fucus-associated littoral benthic fauna

The brown alga Fucus vesiculosus is a foundation species in the Baltic Sea littoral, hosting a rich faunal community. We compared the species composition and diversity of invertebrate macrofauna living on F. vesiculosus between sites differing in their eutrophication status and exposure to waves at three different times during a season. We determined the size, nitrogen and phlorotannin content of the alga. The invertebrate community differed substantially between sites near fish farms and those in more pristine environment. Snails and bivalves were more abundant on the Fucus stands near fish farms than on control stands, where crustaceans were more abundant. The abundance of molluscs decreased with the increasing shore exposure, while gammaridean amphipods dominated on the exposed shores. Abundance of several taxa increased during the proceeding growing season. The density of the most important herbivore of F. vesiculosus, Idotea balthica, varied 100-fold during the season being the lowest in June and the highest in August when the generation born in the summer started to feed on Fucus. Thus, the diversity and composition of Fucus-associated invertebrate fauna varies both with environmental conditions of the stand and seasonally. Although the negative effects of eutrophication on distribution and abundance of Fucus stands are well documented, a moderate increase of nutrients was found to increase the species richness of Fucus-associated fauna in early summer.

Shore exposure affects mussel population structure and mediates the effect of epibiotic algae on mussel survival in SW Ireland

On rocky shores, the relative importance of abiotic and biotic processes that regulate community structure are thought to vary with levels of shore exposure. This can lead to characteristic features found on sheltered and exposed shores. This study identified differences in the population structure of mussels on exposed and sheltered rocky shores on Atlantic coasts of south-west Ireland. Direct interactions between epibiotic algae and their host mussels were also examined to test if potential effects varied with shore exposure. Mussel beds on sheltered shores were less dense and comprised larger mussels with greater rates of individual survival and growth than those on exposed shores. The results of a field experiment showed that algal epibionts had a negative effect on mussel survival on sheltered shores but not on exposed shores. Surprisingly, the presence of algal epibionts had no effect on mussel growth on either shore type. These findings contrast with those of previous studies. The effects of shore exposure and algal epibionts on mussels may be species-specific and may interact with other factors across different regions. This study shows that predictions of effects of exposure on mussel populations and their epibionts should only be based on specific experimental evidence and cannot be generalised across regions.

Harlequin Ducks in Iceland

In Iceland, the Harlequin Duck (Histrionicus histrionicus) is generally distributed as a breeder on rapid clear-water streams, from sea level to about 700 m. Densities are generally low, except at the headwaters of streams draining productive lakes where blackflies (Simulium vittatum) are abundant. In northwest, north and east Iceland, molting Harlequin Ducks are found in similar localities as the wintering birds, but molting birds are largely absent from the southwest coast. During the molt, the birds often stay close to cliffs or rocks and are hard to find. Harlequin Ducks winter on exposed rocky coasts and densities are correlated with substrate as indicated by shore exposure. In 1998-2001, the total wintering population of Harlequin Ducks in Iceland was estimated at 14,000, with 95% confidence limits of 12,000 to 16,000. Assuming that migration in and out of Iceland is insignificant, the total Icelandic breeding population is 3,000-5,000 females, or three to five females (pairs) 100 km-2. A decline in wintering numbers was found in southwest Iceland in 1961-2002, but numbers in the northeast have increased. This may be related to increased temperatures, but changes in exploitation may also have affected the population. The conservation of the Icelandic population of the Harlequin Duck is largely a matter of wise use of the coast and streams which should include preemptive measures, such as minimizing pollution and development. Small-scale river development for power production and salmon fishing pose potential threats to Harlequin Ducks, but direct exploitation of this population is not likely.

Gonad development and fatty acid composition of Patella depressa Pennant (Gastropoda: Prosobranchia) populations with different patterns of spatial distribution, in exposed and sheltered sites

The present study examines the effect of shore exposure on the feeding performance (assessed by fatty acid analyses of the whole body) and gonad condition (stage of development and gonad somatic index, GSI) of Patella depressa populations. Male and female limpets were collected at exposed and sheltered sites, during winter and summer. The population at the exposed site was at a more advanced stage of gonad development, with a higher dispersion of gonad stages, both in winter and summer. Additionally, limpets from the exposed site, particularly the males, presented a higher GSI than the corresponding stage in the sheltered site. The quantitatively most important fatty acids were the saturated fatty acids (SFA) 16:0, 14:0, and 18:0, the monounsaturated fatty acids (MUFA) 18:1( n−7), 18:1( n−9), 16:1( n−7) and 20:1( n−9) and the polyunsaturated fatty acids (PUFA) 20:5( n−3) and 20:4( n−6). Females had a significantly higher fatty acid methyl esters (FAME) content (in summer and winter) and higher amounts of SFA and MUFA (in summer), which points to a higher degree of storage of neutral lipids in this sex. Male and female limpets at the exposed site had a significantly higher FAME, SFA, MUFA, PUFA and highly unsaturated fatty acids (HUFA) content than the corresponding sex in the sheltered site in summer. In addition, an inversion in the eicosapentaenoic acid (EPA)/arachidonic acid (ARA) and ( n−3)/( n−6) ratios was observed in the sheltered site, as a result of the significantly higher levels of ARA and ( n−6) fatty acids and lower amounts of EPA and ( n−3) fatty acids found in the sheltered limpets. A high variability among patches in the fatty acid composition in the exposed site was found in winter, possibly related to the aggregation of limpets at this time. The differences found between limpets from the exposed and sheltered sites suggest qualitative and quantitative differences in their diets. Additionally, the results show that the spatial aggregation strategy adopted by limpets in sites of great wave and wind exposure does not affect their feeding and reproductive success, at least in the site examined here. In fact, more developed gonads, a higher GSI and an elevated FAME content was found in the exposed population. Possible factors are suggested and discussed to explain these observations.

Small-particle concentration fluctuations at a coastal site

Aerosol size spectra ( d=10 nm–10 μm) were measured with an electrical aerosol spectrometer (EAS) at Mace Head on the west coast of Ireland. Several small aerosol particle (diameter 10–32 nm) concentration bursts were observed during the measurement period. Relationships between the events, air mass trajectories, tide height, and meteorological parameters are examined. Series of bursts were observed when a spectral transformation due to subsequent particle growth from 10 to 56–100 nm can be identified in an Eulerian experiment. Particle growth rates of between 1 and 3 nm/h were determined. These bursts appear in cold and comparatively clean arctic or polar air masses with temperature and relative humidity fluctuations, and do not correlate with low tide in some cases. These episodes, similar to those frequently found in the continental boundary layer, are thought to occur over a wide area and, for clear detection, require stable airflow for a few days. Elevated small-particle concentration events are more common during low tide or shortly after, and are typically associated with low wind speeds. Here, the increased shore exposure during low tide is thought to influence the nucleation and the subsequent growth of these aerosol particles. The occurrences of the bursts are found to depend on local wind direction. The highest d=10–32 nm particle concentrations appeared for wind sectors furthest from the tidal regions when the wind direction was 150–160°(south-easterly). Most of the events occurred during daytime when solar irradiation is most intense.

Phenotypic variation in Fucus spiralis (Phaeophyceae): morphology, chemical phenotype and their relationship to the environment

Phenotypic variation of Fucus spiralis was examined in terms of morphology and chemical composition, as determined by pyrolysis mass spectrometry (PyMS). After discriminant analysis both techniques revealed the existence of two morphotypes which were subsequently designated as F. spiralis and F. spiralis forma nanus. The nanus plants differed from the nominate spiralis in that they were shorter, narrower and had fewer branches, but had more units of growth from a single holdfast. F. spiralis f. nanus was consistently higher on the shore than F. spiralis, but the two morphotypes overlapped in terms of shore exposure level. We suggest that the formae exist within a mosaic of stable phenotypes representing populations specifically adapted to the local environment. PyMS data were in agreement with morphological descriptions showing that gross morphology can be correlated with chemical composition.

Phenotypic variation in Fucus spiralis (Phaeophyceae): morphology, chemical phenotype and their relationship to the environment

Phenotypic variation of Fucus spiralis was examined in terms of morphology and chemical composition, as determined by pyrolysis mass spectrometry (PyMS). After discriminant analysis both techniques revealed the existence of two morphotypes which were subsequently designated as F. spiralis and F. spiralis forma nanus. The nanus plants differed from the nominate spiralis in that they were shorter, narrower and had fewer branches, but had more units of growth from a single holdfast. F. spiralis f. nanus was consistently higher on the shore than F. spiralis, but the two morphotypes overlapped in terms of shore exposure level. We suggest that the formae exist within a mosaic of stable phenotypes representing populations specifically adapted to the local environment. PyMS data were in agreement with morphological descriptions showing that gross morphology can be correlated with chemical composition.

A biological index to predict pulp mill pollution levels

The species diversity of mid to low rocky intertidal beaches along the protected coast of British Columbia, Canada, increases significantly as exposure to pulp mill effluent decreases. Species were categorized according to hardiness and ranked as either pollution tolerant, sensitive, or intolerant. Indicator species whose presence or abundance is highly correlated to exposure to mill effluent were discovered. A biological index (Bioindex) was developed to predict a rocky shore's exposure to mill effluent by analyzing the hardiness of the resident biota. The Bioindex is useful to evaluate the environmental stress from pulp mills, to pinpoint depleted beaches for cleanup, and to evaluate pristine areas to be protected. The Howe Sound mills were found to have the most detrimental and widespread effect on rocky shore beaches of all regions surveyed, followed, in order of decreasing severity, by the Crofton mill, the Prince Rupert mill, and the Powell River mill.

Phenotypic variation along a cline in allozyme and karyotype frequencies, and its relationship with habitat, in the dog-whelk Nucella lapillus, L.

The dog-whelk Nucella lapillus exhibits a number of phenotypic variations and genetic polymorphisms which correlate with habitat-specific environmental pressures, especially those associated with wave action and temperature. This study investigates the relationship between genetic composition (karyotypic and electrophoretic variation) and phenotypic differentiation in N. lapillus sampled at 15 points along an 8 km stretch of coastline. Coincident clinal variation in gene frequencies and shell shape is described; they covary with differences in karyotype and also with growth. Laboratory-reared young show that differences in phenotype (shell shape and growth) are inherited. Experimental evidence is presented that specific shell shapes are adaptive under conditions of thermal stress. Together with the well-established correlations between shell shape and shore exposure, this association provides an argument for a relationship between genetic composition, phenotype and habitat in this species.

Phenotypic variation along a cline in allozyme and karyotype frequencies, and its relationship with habitat, in the dog-whelk Nucella lapillus, L.

The dog-whelk Nucella lapillus exhibits a number of phenotypic variations and genetic polymorphisms which correlate with habitat-specific environmental pressures, especially those associated with wave action and temperature. This study investigates the relationship between genetic composition (karyotypic and electrophoretic variation) and phenotypic differentiation in N. lapillus sampled at 15 points along an 8 km stretch of coastline. Coincident clinal variation in gene frequencies and shell shape is described; they covary with differences in karyotype and also with growth. Laboratory-reared young show that differences in phenotype (shell shape and growth) are inherited. Experimental evidence is presented that specific shell shapes are adaptive under conditions of thermal stress. Together with the well-established correlations between shell shape and shore exposure, this association provides an argument for a relationship between genetic composition, phenotype and habitat in this species.