Vertical Shore Research Articles

Accessing the Time-Series Two-Dimensional Displacements around a Reservoir Using Multi-Orbit SAR Datasets: A Case Study of Xiluodu Hydropower Station

The construction of large-scale hydropower stations could solve the problem of China’s power and energy shortages. However, the construction of hydropower stations requires reservoir water storage. Artificially raising the water level by several tens of meters or even hundreds of meters will undoubtedly change the hydrogeological conditions of an area, which will lead to surface deformation near the reservoir. In this paper, we first used SBAS-InSAR technology to monitor the surface deformation near the Xiluodu reservoir area for various data and analyzed the surface deformation of the Xiluodu reservoir area from 2014 to 2019. By using the 12 ALOS2 ascending data, the 100 Sentinel-1 ascending data, and the 97 Sentinel-1 descending data, the horizontal and vertical deformations of the Xiluodu reservoir area were obtained. We found that the Xiluodu reservoir area is mainly deformed along the vertical shore, with a maximum deformation rate of 250 mm/a, accompanied by vertical deformation, and the maximum deformation rate is 60 mm/a. Furthermore, by analyzing the relationship between the horizontal deformation sequence, the vertical deformation sequence, and the impoundment, we found the following: (1) Since the commencement of Xiluodu water storage, the vertical shore direction displacement has continued to increase, indicating that the deformation caused by the water storage is not due to the elastic displacement caused by the load, but by irreversible shaping displacement. According to its development trend, we speculate that the vertical shore direction displacement will continue to increase until it eventually stabilizes; (2) Vertical displacement increases rapidly in the initial stage of water storage; after two water-storage cycles, absolute settlement begins to slow down in the vertical direction, but its deformation still changes with the change in the storage period.

Comparative Analysis of the Erosion Mechanism of Different Profiles in the Arcuate Foreshore under Typhoon Action

The comparison results of three beach profile data repeatedly measured before and after the typhoon in Shuidong Bay, west Guangdong province which show that there are significant differences in beach profile erosion and response process. And the changes of beach profile can be divided into: strong downward overall low shoreline regressive type and overall slight erosion shoreline regressive type. Application of the modified mild-slope equation along three beach profile are simulated wave high reflection to the sea side, to the section vertical shore pressure gradient and including water roll force and radiation stress, the vertical shore forces one dimensional profile along the momentum conservation equation (radiation stress and water roll force) bottom friction and lateral mixing reaction between numerical solution, the momentum conservation equations of the wave increases the water flow velocity and section along the profile distribution of wave height and related forces. The analysis shows that the extent and difference of coastal erosion depend on the shoreline erosion mode stimulated by the maximum surge water of the coastal current and the maximum velocity of the coastal current and the dynamic state of the profile topography under the action of the profile location, morphology and incident wave elements.

EXPERIMENTAL RESEARCH OF THE CLIFFS AND BANKS WASHAWAY

Vertical and inclined shores washout processes were simulated in the small-scaled water tunnel with curved bed and in the rectangular-sectioned hydraulic flume. Intensity of the washout of lithologically homogeneous material of vertical shore is in direct correlation with the attack angle of flow on the coast: Wa = 349.8(1 + + 3.21sin3 a), where Wa is the intensity of washout at the attack angle a. The power-low relation (Wb = 82 + 1.72b0.71) of underwater river bank washout intensity (Wb) from its incline (b) to the flow surface is fixed. Mathematic simulation results show that the ratio of side erosion to bottom erosion shifts to bottom erosion if flow velocity was increased. Due to their morphometric, timing and hydraulic parameters these models are closest to the processes parameters and morphology of the beds of slope drainage network of shallow waterflows. Sharp river bed curves, high flow velocities and flow turbulence on the top of high water are typical for them. All these features occur in the river drainage networks as well, especially on the mountainous rivers. On the plain rivers the most adequate are the high water processes analogues as long as high water passes in the berm edges of flood-plain coasts.

Spatial and temporal patterns of subtidal and intertidal crabs excursions

Highly mobile predators such as fish and crabs are known to migrate from the subtidal zone to forage in the intertidal zone at high-tide. The extent and variation of these habitat linking movements along the vertical shore gradient have not been examined before for several species simultaneously, hence not accounting for species interactions. Here, the foraging excursions of Carcinus maenas (L.), Necora puber (Linnaeus, 1767) and Cancer pagurus (Linnaeus, 1758) were assessed in a one-year mark-recapture study on two replicated rocky shores in southwest U.K. A comparison between the abundance of individuals present on the shore at high-tide with those present in refuges exposed at low-tide indicated considerable intertidal migration by all species, showing strong linkage between subtidal and intertidal habitats. Estimates of population size based on recapture of marked individuals indicated that an average of ~4000 individuals combined for the three crab species, can be present on the shore during one tidal cycle. There was also a high fidelity of individuals and species to particular shore levels. Underlying mechanisms for these spatial patterns such as prey availability and agonistic interactions are discussed. Survival rates were estimated using the Cormack-Jolly-Seber model from multi-recapture analysis and found to be considerably high with a minimum of 30% for all species. Growth rates were found to vary intraspecifically with size and between seasons. Understanding the temporal and spatial variations in predation pressure by crabs on rocky shores is dependent on knowing who, when and how many of these commercially important crab species depend on intertidal foraging. Previous studies have shown that the diet of these species is strongly based on intertidal prey including key species such as limpets; hence intertidal crab migration could be associated with considerable impacts on intertidal assemblages.

한국 태안군 진산리 저서미세조류의 계절별 종조성 및 생물량 변화

Seasonal species composition and biomass of microphytobenthos were examined at the intertidal flats of Jinsanri, Taean, Korea, from April to December 2011. In total, 121 species were identified, including 109 diatoms, 5 blue-green algae, and 5 dinoflagellates. Seasonal variation in species number ranged from 49 to 56 species (minimum in October and maximal in April), while vertical variation across three different shore levels ranged from 64 to 77 species with maximum at high and minimum at low shore. Species diversity ranged from 3.22 to 3.42 seasonally and from 3.50 to 3.17 across vertical shore levels. Seasonal average values of the normalized difference vegetation index and the vegetation index were 0.06 and 1.14, respectively. Chlorophyll a concentrations were <TEX>$66.00-120.73mg/m^2$</TEX>, with a seasonal minimum and maximum in July and October, respectively, and a vertical shore maximum of <TEX>$137.35mg/m^2$</TEX> at mid shore. Phaeopigment concentrations peaked in October (<TEX>$50.78mg/m^2$</TEX>) and at high shore (<TEX>$61.58mg/m^2$</TEX>) and were lowest in December (<TEX>$22.53mg/m^2$</TEX>) and at low shore (<TEX>$15.28mg/m^2$</TEX>). The number of microphytobenthos ranged from 78,556 to 287,898 cells/<TEX>$cm^2$</TEX>, reaching a maximum in April and a minimum in July. The diatoms Paralia sulcata, Navicula sp., and Delphines surirella were dominant at all tidal levels over the study period. Dinoflagellates were dominant in July at low shore, and blue-green algae were abundant between July and October at mid shore. In conclusion, species composition and primary production of microphytobenthos exhibited clear seasonal and vertical patterns.

Aerial and underwater metabolism of Patella vulgata L.: comparison of three intertidal levels

Intertidal molluscs are known to possess specific respiratory organs that permit aerial breathing during emersion. Patella vulgata is a widely distributed intertidal species found from low-water spring tide to high-water neap tidal level. In order to determine metabolic adaptations to habitat, carbon fluxes associated with respiration and calcification of P. vulgata living at high-shore, middle-shore and low-shore levels were compared. Seasonal aerial respiration was measured using an infrared gas analyser; seasonal underwater respiration and calcification were calculated from dissolved inorganic carbon and total alkalinity. P. vulgata showed net CaCO3 deposition at all seasons, although the high-shore level limpet annual calcification rate was relatively low due to longer air exposure. Both aerial and underwater respiration rates were highly correlated with seasonal temperature variations and followed the vertical shore gradient, with stronger fluxes for low-shore tidal level limpets and lower fluxes for high-shore level limpets that must limit energy expenditure. P. vulgata appears to be well adapted to aerial exposure, with average hourly respiration fluxes stronger in air than in water. This study demonstrates that P. vulgata calcification and respiration are reduced in upper shore levels and are important factors determining the upper distribution limit of the species.

동해안 남부 하정 연안의 조하대 해조류 군집구조의 계절적 변화

Subtidal benthic macroalgal flora and community structure on barren grounds were examined seasonally along vertical shore gradients on the rocky shore of Hajung, Pohang, on the southeast coast of Korea, from February 2005 to November 2006. Twenty-six seaweed species were identified, including 5 green, 7 brown, and 14 red algae. The number of seaweed species ranged between 7 and 17 among seasons and between 13 and 20 species were found in vertical gradients along the shore. Over the study period, average seaweed biomass (g wet wt/<TEX>$m^2$</TEX>) was 299.88 g and it ranged seasonally from 120.99 to 620.00 g. Seaweed biomass declined with increasing seawater depth and ranged between 323.06 and 593.68 g. The dominant seaweed species, in terms of biomass, were Desmarestia ligulata and Sargassum honeri, which grew at depths between 5 and 10 m. The red alga Delisea pulchra was also abundant at a depth of 15 m. No seasonal patterns were found in community indices. Along vertical shore gradients, community indices showed different patterns; the dominance index increased and the richness, evenness, and diversity indices decreased with seawater depth.

Seasonal Variability of Seaweed Biomass along the Vertical Shore Gradients of Nachido and Odo Islands, the Yellow Sea, Korea

Seasonal variation in seaweed biomass was examined along vertical shore gradients on the rocky shores of Nachido and Odo Islands, the Yellow Sea, Korea, from August 2007 to April 2008. The average annual biomass of seaweed was 404.07 g wet wt/<TEX>$m^2$</TEX>, with seasonal variation from 232.61 g in the spring to 754.90 g wet wt/<TEX>$m^2$</TEX> in the summer at Nachido Island. At Odo Island, average biomass was 270.82 g wet wt/<TEX>$m^2$</TEX> and ranged from 48.35 g in the winter to 451.66 g wet wt/<TEX>$m^2$</TEX> in the spring. Seaweed biomass exhibited an even distribution across the shore gradient from the high intertidal zone to -5 m depth at Nachido Island, whereas seaweed biomass was concentrated from the mid intertidal zone to -1 m depth in the subtidal zone at Odo Island. Sargassum thunbergii was the most dominant species, occupying 28.24% (114.12 g wet wt/<TEX>$m^2$</TEX>) and 36.57% (99.05 g wet wt/<TEX>$m^2$</TEX>) of total biomass at Nachido and Odo Islands, respectively. Subdominant seaweed species was Gelidium amansii, comprising 15.23% (61.52 g wet wt/<TEX>$m^2$</TEX>) and 14.70% (39.82 g wet wt/<TEX>$m^2$</TEX>) of total biomass at Nachido and Odo Islands, respectively. Dominant functional group was the coarsely branched-form group, which grows under moderate environmental conditions and comprised 93.34% (377.15 g wet wt/<TEX>$m^2$</TEX>) and 66.96% (181.35-g wet wt/<TEX>$m^2$</TEX>) of total biomass at Nachido and Odo Islands, respectively. Percentage biomass of sheet-form seaweeds growing at relatively disturbed and polluted areas was approximately 20.83% (56.40 g wet wt/<TEX>$m^2$</TEX>) of total biomass along the Odo rocky shore. Based on the biomass and functional-form composition of seaweeds, we concluded that Nachido Island provides better environmental conditions than does Odo Island. In addition, the vertical distribution and dominant species of seaweeds on the two islands were very similar, but the functional-form composition of seaweeds at Nachido Island differed slightly from that at Odo Island.

Investigating Vertical Load Distribution and Shoring Systems of Reinforced Concrete Buildings during Construction

The loads of reinforced concrete buildings are bore by shores and early age concrete members during construction. In order to analysis the distribution of vertical load between concrete members and shores, the approximate method was developed based on the finite element method and simplified method. According to the process of construction, seven primary structures were brought forward in the approximate method. The coefficients of vertical load distribution between concrete members and shores are confirmed through the finite element method. The loads of concrete members and shores could be obtained conveniently through the distribution coefficients. Three shoring systems (2S, 2S1R and 3S) could be calculated by the approximate method, so the suitable shoring systems for reinforced concrete buildings would be confirmed.

Adaptive responses of independent traits to the same environmental gradient in the intertidal snail Bembicium vittatum

The snail Bembicium vittatum occupies a wide range of intertidal habitats in the Houtman Abrolhos Islands, Western Australia. Allozyme variation reflects patterns of connectivity, which are independent of local habitat. In contrast, heritable differences in shell shape among 83 shore sites vary with habitat, indicating local adaptation. Here we examine dimorphisms of colour and spotting of the shell in the same populations, as a test of consistency and complexity of patterns of local adaptation. Within populations, the frequency of spotted shells is higher in dark shells. Despite this association, spatial variations of colour and spotting are only weakly correlated. As predicted for traits associated with local adaptation, subdivision is greater for colour, spotting and shape than for allozymes. Colour and shape are associated with local habitat, such that populations on vertical shores have higher frequencies of dark and relatively flatter shells than those on gently sloping shores. These associations are repeatable between three separate groups of islands. Spotting shows a weaker, but significant association with the same gradient. Although shape does not differ between colour morphs within populations, the proportion of dark shells is strongly associated with shape. Thus, the independent shell traits are apparently adapted to a common, biologically significant gradient, even though the adaptive mechanisms probably differ for colour and shape. The parallel variations of independent traits highlight both the complexity of local adaptation and the potential to reveal evolutionarily significant environmental contrasts by examining adaptively relevant traits.

Intertidal seawalls as habitats for molluscs

Coastal urbanization changes intertidal shorelines, by alteration and destruction of natural habitat and addition of new built habitat. In Sydney Harbour, New South Wales, Australia, up to 50% of the shoreline is composed of constructed habitat, particularly seawalls. Research has shown that many components of intertidal assemblages live on seawalls, but patterns of abundance and diversity are very variable. Seawalls differ physically from natural shores in a number of ways that are likely to influence distribution and abundances of intertidal molluscs, which are very important determinants of structure of intertidal assemblages. This study examined diversity, abundances and frequencies of occurrence of intertidal molluscs on seawalls and on natural horizontal and vertical shores in numerous locations in Sydney Harbour and in natural boulder-fields and artificial boulder-fields created from rubble of seawalls. On seawalls, assemblages varied between tidal heights and among locations, but when data were combined across locations, there were some general patterns. Sessile bivalves (oysters and mussels) and many limpets were found in similar numbers on both habitats, or patterns varied inconsistently. Many coiled snails, in contrast, including whelks and grazing gastropods, plus opisthobranchs, which were either common or relatively sparse on horizontal shores, were not found on seawalls and found in intermediate frequencies on vertical shores. Similarly, common species of molluscs were found in natural and artificial boulder-fields in similar numbers, or patterns were not consistent, although rarer species were not found in these boulder-fields. Because molluscs are such important contributors to intertidal dynamics, these results have important implications for management of intertidal biodiversity in urbanized and altered environments.

Validation of Shoring Made of HDPE Pipe or CGS Pipe Normally Used for Culverts and Sewers

Considering the diversity of excavation work, municipalities are always trying to find new methods of shoring. This is how the idea grew up about using a high density polyethylene (HDPE) sewer pipe or a corrugated galvanized steel (CGS) pipe as shoring on the water supply and sewer network for small-dimension excavations of short duration where proven shoring and shielding systems cannot be used and/or a backhoe cannot be used for excavating. HDPE and CGS pipes have been designed according to the requirements for water and sewer pipes. However, when they are used for vertical shoring and subjected to earth pressure, their behavior has never been the subject of quantifications or tests. This study describes the validation by calculations and tests of the use of HPDE and CGS pipes as shoring for small-dimension excavations of short duration on the water supply and sewer network.

Intertidal assemblages on seawalls and vertical rocky shores in Sydney Harbour, Australia

Abstract Understanding the ecological role of artificial structures, such as seawalls, in shallow coastal waters is necessary in order to plan sound strategies of conservation and management of natural habitats. In Sydney Harbour (NSW, Australia), about 50% of the foreshore is made of retaining seawalls This study evaluates the changes caused to natural assemblages of organisms by these structures, by comparing intertidal assemblages between seawalls and vertical rocky shores. The following hypotheses were tested: that assemblages on seawalls would differ from those on rocky shores at mid‐, but not at low‐shore levels; where assemblages differ between habitats, there would be differences in cover/abundances of widespread species; patterns would be consistent among locations and through time; the variability of assemblages at the scales of 10s of cm and metres would differ between seawalls and rocky shores at mid‐ and low‐shore levels. To test these hypotheses, assemblages on seawalls and rocky shores were sampled at three locations, at roughly 4‐monthly intervals, over a period of about 18 months. Results indicated that mid‐shore assemblages on seawalls were different from those on rocky shores, but this was not the case at low‐shore levels. Few taxa were unique to either habitat. Cover of common species of algae and sessile animals and abundances of mobile grazers were variable with few consistent patterns. Variability at the scales sampled differed between habitats and heights on the shore. Seawalls and rocky shores, in general, supported a similar suite of species, but patterns of abundance and variation differed among locations and from height to height in each habitat. The implications of these findings for the future management of seawalls are briefly considered.

Structural Modeling and Design Considerations for Double-Layer Shoring Systems

This paper presents structural modeling and design considerations for a double-layer shoring system made of wood posts based on analytical derivation, numerical computation, and the LeMessurier formula. Simplified two-dimensional models of double-layer shoring systems are developed. The analysis shows that system critical loads do not increase with the addition of individual pinned-ended shores, i.e., leaning columns, in the system during construction. If these individual pinned-ended shores are widely used, more cases of falsework failure may occur. The effects of lengths of horizontal stringers and vertical shores, stiffnesses of stringers, and positions of strong shores are investigated in the paper. The reinforcement by addition of bracing to the shoring systems can improve the system buckling strength. The study concludes that appropriately fastening a group of pinned-ended shores with horizontal bracings, i.e., strong shores, can increase the load-carrying capacity of a double-layer shoring system.

Patterns of movement of the limpet Cellana tramoserica on rocky shores and retaining seawalls

Artificial structures are becoming common features of the landscape in shallow waters of urban areas, but very little is known about their ecology. In Sydney Harbour (NSW, Australia), intertidal seawalls replace considerable portions of natural habitats, including rocky shores. Previous studies have shown that seawalls and rocky shores generally support similar assemblages of plants and animals, with important differences in relative abundances of some species. The behaviour of key consumers can have a fundamental role in structuring benthic assemblages, and it is, therefore, necessary to assess whether it is changed by the replacement of natural habitats with artificial structures. This study compares patterns of movement of the common patellid limpet Cellana tramoserica between seawalls and vertical rocky shores. The distances displaced, the orientation of movement and the homing behaviour of marked individuals were recorded from day to day, over a period of several tidal cycles (14 d) and for a longer period (ca. 3 mo), on several seawalls and rocky shores. Short-term patterns of movement (1 to 14 d) did not differ between structures. In contrast, after 3 mo, although the orientation of the movement remained random on both kinds of structures, limpets on seawalls had dispersed longer distances and tended not to retain their original positions. These results suggest that long-term dispersal of C. tramoserica, rather than foraging bouts, could be altered by the replacement of rocky shores with artificial structures. Differences in use of habitat by key consumers should be incorporated in models aimed at identifying the mechanisms responsible for the occurrence of different assemblages on natural and artificial structures.

Microscale genetic differentiation along the vertical shore gradient in White Sea snails Littorina saxatilis (Olivi) assessed by microsatellite markers

probably due to supercoiling phenomena of the DNA doublehelix.We conclude that for samples critical for DNA extraction,drowning must not be used as a method of relaxation and thatcooling the samples during drowning does not improve the con-ditions. For studies that require material for both histological/dissection and molecular purposes, we suggest that a tiny pieceof tissue is cut from the animals prior to the drowning andplaced in 10–20 vols of alcohol or is frozen. For molecular studies only very little tissue is usually needed (1–3 mm

Intertidal seawalls—new features of landscape in intertidal environments

Artificial structures, such as pier pilings, floating pontoons, breakwaters and seawalls are becoming common features of landscape in shallow coastal waters of urbanised areas, in some areas, replacing considerable portions of natural habitats. In Sydney Harbour (NSW, Australia), approximately 50% of the shore is composed of retaining seawalls or other built habitats. Intertidal seawalls and other similar structures provide new surfaces for colonisation by benthic organisms and therefore provide new intertidal habitats for estuarine animals and plants. They have the potential to supplement natural habitat by supporting natural assemblages, in terms of species composition and relative abundances. Alternatively, artificial structures may support only a subset of natural assemblages, provide habitat for additional species not found on nearby rocky shores, or provide habitat in which some species are consistently missing and additional species found (a combination of the previous two models). Understanding the ecological role that seawalls and other intertidal structures have in urbanised estuaries is important in planning of developments along foreshores. This study compared intertidal assemblages, at each of three different heights among seawalls and nearby horizontal and vertical rocky shores to specifically test the model that seawalls support the same assemblages of animals and plants as are found on natural rocky reefs. Hypotheses from this model were tested at three study locations by measuring abundances of animals and plants in quadrats in replicate sites on each structure. Results indicated that, at mid- and highshore levels, there were frequent differences between assemblages on natural shores and seawalls. In contrast, at lower levels, differences between assemblages on seawalls and vertical rocky reefs were small compared to differences between sites on each structure. Nevertheless, it appeared that the seawalls and rocky shores examined supported a similar suite of species and most differences were due to relative abundances and frequencies of occurrence of the species present. It is, however, premature to conclude that seawalls support similar assemblages to rocky shores until more intensive sampling has been done, specifically to search for rare species. In addition, until we have more knowledge on ecological processes in these assemblages, seawalls should not be considered as surrogates for natural shores.

The complexity of phenotypic plasticity in the intertidal snail Nodilittorina australis

The intertidal snail Nodilittorina australis has distinct nodulose and striate morphs, which are plastic, developmental responses to sloped and vertical rocky shores, respectively. The nodulose morph cools more quickly, which should be advantageous on the sunnier, sloped shores. In contrast, the striate morph responds more quickly to submersion, which should be advantageous on the more wave-intense vertical shores. Transplant experiments revealed that even large snails can alter development of new shell. The developmental transitions indicate partial dissociation of colour and sculpture. However, the incomplete association of component traits is seen in very few natural populations, indicating that canalization of nodulose and striate pathways has evolved to the extent that is adaptively relevant. There is a distinct asymmetry of the lability of development, whereby nodulose snails are much more likely to switch to development of striate shell than the reverse; this directionality occurs naturally as well as in transplant experiments. Rather than representing an underlying constraint, the asymmetry probably reflects a greater advantage of nodules in smaller snails. The only clear developmental constraint affecting this dimorphism is the association of the production of nodules with slower growth, an expected consequence of the rate-limiting process of shell deposition.

The complexity of phenotypic plasticity in the intertidal snail Nodilittorina australis

The intertidal snail Nodilittorina australis has distinct nodulose and striate morphs, which are plastic, developmental responses to sloped and vertical rocky shores, respectively. The nodulose morph cools more quickly, which should be advantageous on the sunnier, sloped shores. In contrast, the striate morph responds more quickly to submersion, which should be advantageous on the more wave-intense vertical shores. Transplant experiments revealed that even large snails can alter development of new shell. The developmental transitions indicate partial dissociation of colour and sculpture. However, the incomplete association of component traits is seen in very few natural populations, indicating that canalization of nodulose and striate pathways has evolved to the extent that is adaptively relevant. There is a distinct asymmetry of the lability of development, whereby nodulose snails are much more likely to switch to development of striate shell than the reverse; this directionality occurs naturally as well as in transplant experiments. Rather than representing an underlying constraint, the asymmetry probably reflects a greater advantage of nodules in smaller snails. The only clear developmental constraint affecting this dimorphism is the association of the production of nodules with slower growth, an expected consequence of the rate-limiting process of shell deposition.

Associations with habitat versus geographic cohesiveness: size and shape of Bembicium vittatum Philippi (Gastropoda: Littorinidae) in the Houtman Abrolhos Islands

In the Houtman Abrolhos Islands, Western Australia, the direct-developing littorine snail Bembicium vittatum occupies a wide range of habitats, which are replicated across the three major groups of islands. Earlier studies showed that allozyme similarities followed patterns related to gene flow, independent of habitat, providing an excellent opportunity to test for associations with habitat for traits more likely to be adaptively important. As the first test for adaptive divergence, we examined variation in size and shape of shells among 131 populations in the Abrolhos Islands. Two-fold variations were found in width of adults, the allometric coefficient of height with width, and shell height scaled to a standard width. Quantification of habitat characteristics was summarized by principal components analysis. In contrast with the patterns of divergence for allozymes, shell height, adjusted for width, was strongly associated with habitat: flatter shells are found on exposed, vertical shores, while domed, more globose shells predominate in sheltered sites. This association was stronger for shape of adult-sized snails than for height scaled to an arbitrary size, highlighting the importance of using biologically relevant measures. Even highly isolated and allozymically less variable populations in tidal ponds conformed to this association. Because differences in shape are highly heritable in B. vittatum, this association of shape with habitat, independent of patterns of gene flow, indicates local adaptation. Shell size also varied with habitat, but because growth rate is highly plastic, variation in size cannot be interpreted simply in terms of adaptation. Nevertheless, the pattern of variation indicates that, within realized limits, larger size is generally favourable, but may be constrained by local conditions. Thus, variation in size signals the potential for adaptive divergence of life histories among the many, isolated populations of this species.