Protected Shores Research Articles

Lipophrys pholis is larger, grows faster and is in better condition in protected than in unprotected rocky shores

Abstract Intertidal fish are a key component of littoral food webs, contributing to the diets of birds and commercial fish species. Ascertaining their growth and condition can therefore help understand the health status of local communities. Lipophrys pholis is a fish of the rocky intertidal with a wide distribution throughout the North‐eastern Atlantic (NE Atlantic) that has been recommended for use as an indicator in the environmental biomonitoring of marine ecosystems. However, it is unclear yet if this species is sensitive to the reserve effect. In this study, the size, growth and body condition of specimens caught at protected and unprotected rocky shores of two contrasting marine provinces of the NE Atlantic were analysed to address whether L. pholis is sensitive to the reserve effect. L. pholis were larger, grew faster in weight and were in better condition in the protected shores of both provinces. A faster growth rate was observed in the populations of the warmer province. Inshore waters of unprotected sites in the Northern European Seas sampled in this study have recently been incorporated into a protected area. Thus, these results can help assess the success of the marine conservation programme and the time L. pholis needs to improve its population's health at these shores. Regulating access to shores to avoid trampling and harvesting is a protection measure that can help enhance the health and conservation of L. pholis populations.

Assessing Habitat Suitability for Native and Alien Freshwater Mussels in the River Waal (the Netherlands), Using Hydroacoustics and Species Sensitivity Distributions

Longitudinal training dams (LTDs) in the river Waal are novel river training structures that protect the littoral zone from the adverse effects of navigation providing new habitats for riverine macroinvertebrates. In order to inform river management and to better understand their ecological value for native and alien mussel species, it is important to assess the habitat suitability of the protected LTD shore channels. We applied spatial hydroacoustics surveys consisting of side-scan sonar (SSS) and acoustic Doppler current profiler (ADCP) of the substrate type, water depth and flow velocity in three shore channels in combination with species sensitivity distributions (SSDs) to predict habitat suitability for native and alien mussel species. SSDs allowed for the prediction of habitat suitability as a potentially occurring fraction (POF) of a species pool. High substrate type, water depth, and near-bottom flow velocity POFs were found for ≥ 70%, 100%, and 4–51% of the total shore channel area, respectively, suggesting that shore channels provide suitable habitat for both native and alien mussel species. To enhance the shore channels as habitat for native mussel species, we recommend increasing shallow areas dominated by fine (silt/clay) and sand substrate types with low near-bottom flow velocities (near 0 m/s). In contrast, the total area of hard substrate (e.g., boulders) in the shore channels should be reduced as it strongly favored invasive alien mussel species in our study. Future research should include additional abiotic parameters to enhance the habitat suitability predictions and compare the results for different riverine habitats.

Increased wave action promotes muscle performance but increasing temperatures cause a tenacity-endurance trade-off in intertidal snails (Nerita atramentosa).

Concurrent increases in wave action and sea surface temperatures increase the physical impact on intertidal organisms and affect their physiological capacity to respond to that impact. Our aim was to determine whether wave exposure altered muscle function in intertidal snails (Nerita atramentosa) and whether responses to wave action and temperature are plastic, leading to compensation for altered environmental conditions. We show that field snails from exposed shores had greater endurance and vertical tenacity than snails from matched protected shores (n = 5 pairs of shores). There were no differences in muscle metabolic capacities (strombine/lactate dehydrogenase, citrate synthase and cytochrome c oxidase activities) between shore types. Maximum stress (force/foot area) produced by isolated foot muscle did not differ between shore types, but foot muscle from snails on exposed shores had greater endurance. A laboratory experiment showed that vertical tenacity was greater in animals acclimated for 3 weeks to cool winter temperatures (15C) compared to summer temperatures (25C), but endurance was greater in snails acclimated to 25°C. Acclimation to water flow that mimicked wave action in the field increased vertical tenacity but decreased endurance. Our data show that increased wave action elicits a training effect on muscle, but that increasing sea surface temperature can cause a trade-off between tenacity and endurance. Ocean warming would negate the beneficial increase in tenacity that could render snails more resistant to acute impacts of wave action, while promoting longer term resistance to dislodgment by waves.

Contemporary Dynamics of the Sea Shore of Kaliningrad Oblast

Abstract The article presents estimations of coastline retreat and advance in Kaliningrad Oblast at 85 monitoring points for a ten-year period of 2007–2017, based on monitoring data supplemented with satellite image analysis. The mean annual rate of coastline retreat and advance was estimated in general for each of the four major morpholithodynamic segments of the coastline: the Vistula (−0.2 m/year) and Curonian (−0.4 m/year) spits, as well as the western (−0.5 m/year) and northern (−0.2 m/year) shores of the Sambia Peninsula. The analysis of the shore protection measures implemented in Kaliningrad Oblast from 2007 to 2017 showed that the length of protected shore segments increased by 30% to 14.5 km, which is 10% of the total coastline. The obtained scheme of long-term mean annual rates of coastline retreat and advance clearly demonstrates an uneven distribution of eroded segments along the shores of Kaliningrad Oblast, however the sea shore of Kaliningrad Oblast is mainly susceptible to erosion (44%). Accumulative segments of the shore make up only 17% of the total coastline, and the remaining 39% of the shore is relatively stable. The results obtained demonstrate that the long-term mean annual rate of coastline retreat has decreased to −0.3 m/year from −1 m/year in the earlier period of 2000–2010. The general condition of the entire coastline of Kaliningrad Oblast can therefore be described as relatively sustainable]. The changes are related to several factors, such as an increase in the length of protected shore segments, the resumption of sand pulp dumping in the beach area by the Amber Mining Plant, and an increase in the amount of analytical data from an expanded local monitoring network.

Habitat structure and zonation patterns of northwestern Mediterranean shoreline strands

We studied the habitat structure (macrofaunal assemblages and bottom types) and zonation patterns of 29 unvegetated shoreline strands along the 900-km coast of Catalonia (NW Mediterranean Sea). Organisms were sampled with grabs, pitfall traps, sticky traps, clam nets and spades to ensure capture of the different proportions of macrofaunal assemblages from the supra-, medio- and infralittoral levels. We collected 211 taxa: 194 animals and 17 algae. The most abundant and dominant organisms collected with van Veen grabs were Nematoda, Oligochaeta and Collembola at the supralittoral level; the polychaetes Saccocirrus spp. and Pisione remota, the amphipod Corophium orientale, Nematoda, and Turbellaria at the mediolittoral level; and Nematoda at the upper infralittoral level. SIMPER analysis revealed great dissimilarity between the organisms inhabiting the supralittoral and the other littoral levels. Regarding the epifauna, the sticky traps used at the supralittoral level mainly collected Collembola, which were nearly absent in pitfall traps. The qualitative study performed with a clam net and a small spade revealed that Nematoda, Saccocirrus spp., Turbellaria, Nemertea and the polychaete P. remota were the most abundant animals at both the medio- and the infralittoral levels and no differences were found between these levels. Different qualitative sampling methodologies showed that in fine sediments the bivalves Donax trunculus and D. semistriatus determined more than 97% of dissimilarity from coarse-sand sites. Richness increased in protected sandy and cobble shores. Littoral level and bottom-type features were only to a certain extent valid indicators of specific biotic components for a specific habitat.

Seaweed traits linked to wave exposure determine predator avoidance

Greater attention to habitat-specific species interactions should improve our ability to predict the context-dependency of species interactions. Predator avoidance depends upon resource traits that can vary predictably between habitats, but few studies have linked predator avoidance to habitat-specific resource traits. For example, predator avoidance in herbivores may depend upon wave exposure, because wave-exposed and wave-protected seaweeds display strong intraspecific differences in morphology and physiology that likely influence their value to herbivores. In 2 sets of laboratory mesocosm experiments we compared predator avoidance in the herbivorous snail Littorina obtusata offered the bladder wrack Fucus vesiculosus from either wave-exposed or protected shores. The effect of predation risk by the green crab Carcinus mae- nas on avoidance by L. obtusata depended on wave exposure, with a stronger effect of predation risk for snails on wave-exposed F. vesiculosus. To explore the traits responsible for this pattern, we conducted multi-choice feeding experiments with F. vesiculosus from 3 wave-exposed and 3 pro- tected sites. F. vesiculosus from protected sites (where avoidance behaviors were weak) was more palatable than F. vesiculosus from wave-exposed sites. Although several morphological (e.g. blade width and vesicle number) and physiological traits (e.g. C:N ratio) of F. vesiculosus depended upon wave exposure, these were unrelated to snail feeding and predator avoidance. Therefore, L. obtusata displayed stronger predator avoidance on less palatable, wave-exposed seaweed. We suggest that the different effects of predators on rocky shores may partly reflect the influence of exposure-specific seaweed traits that determine predator avoidance.

Intertidal sea stars (Pisaster ochraceus) alter body shape in response to wave action

Sea stars are some of the largest mobile animals able to live in the harsh flow environment of wave-exposed, rocky intertidal shores. In addition, some species, such as the northeastern Pacific Pisaster ochraceus, are ecologically significant predators in a broad range of environments, from sheltered lagoons to the most wave-exposed shorelines. How they function and survive under such an extreme range of wave exposures remains a puzzle. Here we examine the ability of P. ochraceus to alter body form in response to variation in flow conditions. We found that sea stars in wave-exposed sites had narrower arms and were lighter per unit arm length than those from sheltered sites. Body form was tightly correlated with maximum velocity of breaking waves across four sites and also varied over time. In addition, field transplant experiments showed that these differences in shape were due primarily to phenotypic plasticity. Sea stars transplanted from a sheltered site to a more wave-exposed site became lighter per unit arm length, and developed narrower arms, after 3 months. The tight correlation between water flow and morphology suggests that wave force must be a significant selective factor acting on body shape. On exposed shores, narrower arms probably reduce both lift and drag in breaking waves. On protected shores, fatter arms may provide more thermal inertia to resist overheating, or more body volume for gametes. Such plastic changes in body shape represent a unique method by which sea stars adapt to spatial, seasonal and possibly short-term variation in flow conditions.

Microhabitat segregation of the amphipod genus Gammarus (Crustacea: Amphipoda) in the Northern Baltic Sea

Closely related species may occupy very similar niches but are often found to diverge by one or more traits when they share the same habitat. Five indigenous and sympatric Gammarus species are characteristic for the Baltic rocky littoral ecosystem. Yet, the species-specific distribution of these sympatric gammarids has not been well studied in the northern Baltic Sea. This study was undertaken to assess the spatial distribution of gammarid amphipods along wave exposure and depth gradients to study whether they show segregation in their microhabitat use. We sampled 12 rocky sublittoral shores along a wave exposure gradient over a period of 5 years. Samples differed with respect to depth and macroalgal type. Three of the five gammarid species occurred mainly in different depth zones and among different macroalgae at the exposed shores. In contrast, on protected shores, where algal zonation is weaker, a link to zonation and macroalgal type was almost absent. Moreover, the microhabitat use was strongest during the reproductive seasons of the species. The observed microhabitats of the three gammarid species fit well to their species-specific mean body sizes.

DENSITIES AND COVER DATA FOR INTERTIDAL ORGANISMS IN THE GULF OF MAINE, USA, FROM 2003 TO 2007

Experimental clearings in macroalgal (Ascophyllum nodosum) stands were made in 1996 to determine if mussel beds and macroalgal stands on protected intertidal shores in New England represent alternative community states. Uncleared control plots and four sizes of circular clearings, which mimicked ice scour events, were established in A. nodosum stands at 12 sites on Swan's Island, Maine, USA. The purpose of this data set is to provide access to data on densities and percent cover in the 60 experimental plots from 2003 to 2007 and to update data from 1996 to 2002 that are already published in Ecological Archives. Data include densities of mussels (Mytilus edulis and Modiolus modiolus), an herbivorous limpet (Tectura testudinalis), herbivorous snails (Littorina littorea, Littorina obtusata), a predatory snail (Nucella lapillus), a barnacle (Semibalanus balanoides), and fucoid algae (Ascophyllum nodosum and Fucus vesiculosus), and percent cover by mussels, barnacles, fucoids, and other sessile organisms.

Feeding Behavior Reveals the Adaptive Nature of Plasticity in Barnacle Feeding Limbs

Barnacle feeding limbs are extremely plastic in response to spatial and temporal differences in wave exposure: individuals have long, thin feeding limbs in habitats with little wave action, and short, thick feeding limbs in wave-exposed habitats. This difference in feeding limb morphology is assumed to be adaptive. Individuals with shorter limbs may have the ability to feed in breaking waves because their limbs are better suited to withstanding drag forces than are those of individuals with longer feeding limbs. I tested this hypothesis by observing the feeding behavior of two populations of Balanus glandula (one from a protected shore and one from a wave-exposed shore) subjected to five different water velocities. Differences between populations in the ability to feed with the cirral net fully extended were highly significant. The wave-exposed population fed with the cirral net fully extended at all velocities tested (up to 49 cm/s), whereas full cirral extension ceased between 7.25 and 21.4 cm/s in all individuals from the protected-shore population. Clearly, barnacles possessing long, thin feeding limbs experience a strong disadvantage when feeding in faster flowing water, confirming earlier hypotheses that differences in feeding limb length between protected and wave-exposed shores are adaptive. Acorn barnacles are suspension feeders that extend three pairs of modified thoracic limbs (cirri) into ambient flow to capture plankton and smaller food particles (1). The feeding apparatus of many barnacle species is remarkably plastic with respect to wave exposure (2‐4). In the northeastern Pacific, the common intertidal barnacle Balanus glandula Darwin, 1854, shows the greatest degree of plasticity in feeding leg form. Individuals from wave-protected shores possess feeding limbs nearly twice as long and 25% thinner at the base than conspecifics living on wave-exposed shores (3), and experiments show that this species can alter the length and width of its feeding limbs to suit local flow conditions in one or two molts (2). Because of the functional importance of barnacle feeding limbs, their phenotypic plasticity is assumed to be adaptive—shorter, stouter legs may allow barnacles to feed in high-velocity flow under breaking waves. However, the consequences of possessing differently shaped feeding limbs have not been investigated, and thus the adaptive nature (5) of differences in feeding limb length remains speculative.

Reconstructing past biological invasions: niche shifts in response to invasive predators and competitors

Studying historic invasions can provide insight into the ongoing invasions that threaten global biodiversity. In this study, we reconsider the impacts of Littorina littorea and Carcinus maenas on the rocky intertidal community of the Gulf of Maine. Past research using invader-removal experiments demonstrated strong top-down effects of L. littorea on algal community structure; however, such removal experiments may overlook the long-term effects of niche shifts and local extinctions caused by invasive species. We considered how a niche-shift in the native littorine, Littorina saxatilis, may change the interpretation of L. littorea impacts. Using a factorial experiment crossing predator presence/absence with L. littorea presence/absence, we found that L. saxatilis is able to exert top-down control on ephemeral algae similar to that exerted by L.␣littorea and that both competition by L. littorea and predation by C. maenas have strong, negative impacts on L. saxatilis. We also found higher predation rates on protected shores and at lower tidal heights and preferential predation on L.␣saxatilis compared to L. littorea. While movement experiments demonstrate that behavioral response to tidal height is the proximate cause of L. saxatilis exclusion from the lower intertidal, our study suggests that the ultimate causes are the additive effects of competition from and predation by invasive species.

Spatial patterns and response to wave exposure of shallow water algal assemblages across the Canarian Archipelago: a multi-scaled approach

We conducted a mensurative survey to investigate spatial variability and the effect of wave exposure at a range of spatial scales including islands (100s of km apart), locations within islands (10s of km apart), and sites within locations (100s of m apart), on the composition, abundance and distribution of shallow water algal assemblages across subtidal hard bottoms of the Canarian Archipelago (eastern Atlantic). A multi-scaled hierarchical sampling design provided the framework for quantifying the variation among samples due to spatial scale and level of wave exposure. Ran- domly placed 50 × 50 cm squares were deployed in shallow rocky-reefs to assess community struc- ture and dominance. Non-parametric multivariate techniques, as well as univariate tests, provided evidence to collectively suggest that shallow water algal assemblages differed between protected (leeward) and exposed (windward) shores, with a consistency of effects across islands, while differ- ent spatial scales were also involved in the variability and patchiness of these assemblages. In this sense, differences were clearly taxon and/or group-specific. In general, the presence and abundance of frondose fucoid species was greater on exposed shores than on protected shores, whereas turf- algae dominated along the protected shores of each island. Dissimilarities between islands with regard to the overall algal assemblage generally increased with the distance between islands. In par- ticular, the presence and abundance of fucoid species was greater in the eastern islands, while turf and bush-like algae increased in the western islands. The large-scale gradient of the oceanographic conditions in an east-to-west direction across the Canarian Archipelago provided a partial explana- tion for this observation although some inconsistencies were observed in the overall regional pattern.

Feeding in flow extremes: dependence of cirrus form on wave-exposure in four barnacle species

Wave-exposure influences the form of many organisms. Curiously, the impact of flow extremes on feeding structures has received little attention. Barnacles extend feather-like legs to feed, and prior work revealed a highly precise association between leg length and water velocity in one species. To assess the generality of this flow-dependence, we quantified variation in four leg traits (ramus length, ramus diameter, seta length, and intersetal spacing) in four intertidal barnacles (Balanus glandula, Chthamalus dalli, Semibalanus cariosus, Pollicipes polymerus) over a wave-exposure gradient in the North-Eastern Pacific. All species exhibited a negative allometric relation between leg length and body mass. Proportionally longer feeding legs may permit smaller barnacles to avoid lower flow and particle flux associated with boundary layers. Although coefficients of allometry did not vary with wave-exposure, form differences among wave-exposures were substantial. Depending on the species, acorn barnacles of the same size from protected shores had feeding legs that were 37-80% longer and 18-25% thinner, and setae that were 36-50% longer and up to 25% more closely spaced, than those from exposed shores. Differences were less pronounced for the gooseneck barnacle, P. polymerus. Moreover, in situ water velocity explained an impressive percentage of overall leg-length variation: 92% in B. glandula, 67% in C. dalli, 91% in S. cariosus, and 92% in P. polymerus. Clearly, both size and shape of barnacle feeding legs respond to local flow conditions. This response appears widespread--across two orders of thoracican barnacles, Pedunculata and Sessilia, and two superfamilies of acorn barnacles (Balanoidea and Chthamaloidea)--and likely adaptive. Longer rami and setae would yield a larger feeding area in low flow, whereas shorter, stouter rami with shorter setae would be less vulnerable to damage in high flow. Finally, the proportionally most variable species was abundant in the widest range of habitats, suggesting that increased plasticity may permit a wider niche breadth.

LEGISLATIVE VS. PRACTICAL PROTECTION OF AN INTERTIDAL SHORELINE IN SOUTHEASTERN AUSTRALIA

Harvesting of intertidal biota is a concern in many areas of the world. While the published literature is focused on reports of strong impacts of subsistence harvesting, recreational collection of biota can also have a strong effect. In either case, the management of these impacts is a major concern and is most often done by complete or partial closures of sections of coastline. This management method may require ongoing intervention, in the form of policing, education, or construction of barriers, and it is important to identify the effectiveness of these actions. We have previously shown that physical closure of a section of rocky coastline in southeastern Australia resulted in increased mean sizes of a range of intertidal molluscs collected for food and bait. The shoreline in question had legislative protection and mechanical barriers, and we present data that demonstrate that the mechanical barrier was a critical component. Removal of barriers resulted in changes in mean sizes and abundance of some gastropods over a period of 5 yr. The two most heavily harvested species, Turbo undulatus and Cellana tramoserica, showed reductions in mean size of ∼15%, relative to nearby areas that had been exploited for many years, while two less harvested species, Austrocochlea constricta and Nerita atramentosa, showed no changes following opening of the former protected areas. Three control (i.e., nonharvested) species, Bembicium nanum, Lepsiella vinosa, and Cominella eburnea, continued to show no differences between harvesting categories. Abundance of these gastropods, measured by catch per unit effort (CPUE), declined for the two harvested species over the 5 yr following opening of the protected shores. For Cellana, CPUE fell at sites in the reserve from 36% above exploited areas to similar values; for Turbo, CPUE values at the time of opening were 200–300% higher in the protected areas, but then fell to match values for exploited shores. These results show that legislative protection, which applied to the entire coastline, is ineffective in this section of the Australian coast, and effective protection requires physical barriers to exclude humans, or greatly increased enforcement.

Legislative vs. Practical Protection of an Intertidal Shoreline in Southeastern Australia

Harvesting of intertidal biota is a concern in many areas of the world. While the published literature is focused on reports of strong impacts of subsistence harvesting, recreational collection of biota can also have a strong effect. In either case, the management of these impacts is a major concern and is most often done by complete or partial closures of sections of coastline. This management method may require ongoing intervention, in the form of policing, education, or construction of barriers, and it is important to identify the effectiveness of these actions. We have previously shown that physical closure of a section of rocky coastline in southeastern Australia resulted in increased mean sizes of a range of intertidal molluscs collected for food and bait. The shoreline in question had legislative protection and mechanical barriers, and we present data that demonstrate that the mechanical barrier was a critical component. Removal of barriers resulted in changes in mean sizes and abundance of some gastropods over a period of 5 yr. The two most heavily harvested species, Turbo undulatus and Cellana tramoserica, showed reductions in mean size of ∼15%, relative to nearby areas that had been exploited for many years, while two less harvested species, Austrocochlea constricta and Nerita atramentosa, showed no changes following opening of the former protected areas. Three control (i.e., nonharvested) species, Bembicium nanum, Lepsiella vinosa, and Cominella eburnea, continued to show no differences between harvesting categories. Abundance of these gastropods, measured by catch per unit effort (CPUE), declined for the two harvested species over the 5 yr following opening of the protected shores. For Cellana, CPUE fell at sites in the reserve from 36% above exploited areas to similar values; for Turbo, CPUE values at the time of opening were 200–300% higher in the protected areas, but then fell to match values for exploited shores. These results show that legislative protection, which applied to the entire coastline, is ineffective in this section of the Australian coast, and effective protection requires physical barriers to exclude humans, or greatly increased enforcement.

PHENOTYPIC PLASTICITY IN THE FOOT SIZE OF AN INTERTIDAL SNAIL

The risk of dislodgment due to hydrodynamic forces on rocky intertidal shores is greater on wave-exposed than on protected shores, and this is believed to represent an important selective force in intertidal communities. For intertidal snails, the probability of dislodgment by a given flow is determined, in part, by shell size and shape, and by the attachment strength of the foot. This study addressed two questions. First, do habitat-specific differences in traits that reduce the risk of dislodgment of an intertidal snail (Littorina obtusata) parallel differences in wave energies? To address this question, I measured variation in (1) shell size (defined as the maximum projected surface area, MPSA); (2) foot size; (3) maximum shear dislodgment force; and (4) tenacity (dislodgment force per unit foot size) of two wave-exposed and three protected snail populations. Second, are habitat-specific differences in foot size, and hence attachment strength, the product of selection or of phenotypic plasticity in response to increased hydrodynamic stress? I conducted field transplant experiments and a laboratory flume experiment that manipulated water velocity to test for plasticity in foot size. Wave-exposed snails exhibited traits that reduce the risk of dislodgment. Their shells were smaller (MPSA) and more squat (shell height relative to MPSA and shell length) than were shells of protected conspecifics. Wave-exposed snails also had larger foot sizes and were thus able to resist greater shear dislodgment forces than protected conspecifics of similar MPSA. Neither wave exposure nor collection site influenced tenacity, indicating that the greater dislodgment forces of wave-exposed snails were due to their larger foot sizes. Assuming that MPSA is proportional to speed-specific drag, which is reasonable for bluff bodies, I found that dislodgment force was proportional to drag. Foot size scaled isometrically with MPSA, and dislodgment force scaled isometrically with foot size, indicating that the risk of dislodgment does not change as snails grow. The field and laboratory flume experiments provide the first clear demonstration that increased hydrodynamic stress induces plastic increases in foot size. Protected snails raised on a wave-exposed shore produced a larger foot than controls raised on their native shore. Selection on the foot size of protected snails raised on both shores was not detected in either habitat. Protected snails also produced larger foot sizes when raised in high-velocity flumes relative to snails raised under low-velocity flow. In contrast, wave-exposed snails exhibited no change in foot size when raised under both high- and low-velocity flow. Hence, variation in the foot size of wave-exposed snails is less flexible than that of protected conspecifics. If natural selection favors plasticity in heterogeneous environments, an asymmetry may be favored as well, especially if there are risks associated with improper adjustments to unpredictable environmental cues.

The effect of wave action, prey type, and foraging time on growth of the predatory snail Nucella lapillus (L.)

Growth rates of intertidal snails vary among populations differentially exposed to wave action; individuals from sheltered habitats typically grow more quickly than do those from more exposed coasts. A series of field and laboratory experiments were conducted to separate the genetic and phenotypic components of this variation in Nucella lapillus (L.) and to investigate the extent to which prey type and foraging time, which also vary across the wave-exposure gradient, affect growth. Juvenile and adult whelks were reciprocally transplanted between an exposed and a protected shore and subsequent growth followed. Independent of origin, whelks grew more on the sheltered shore. By contrast, growth rates for snails from exposed and protected shores were similar when reared under uniform conditions in the laboratory. Together these findings suggest that the variation observed in nature does not represent genetic differentiation, but reflects the influence of proximal factors that depress growth on wave-swept shores. Growth rates of juveniles from exposed and protected shores maintained in the laboratory on a diet of an overabundance of (1) barnacles, (2) mussels, (3) both, and (4) both, but only 67% of the time, indicated that prey type and foraging time affect growth. Whelks grew best on a diet of mussels, either singly or in combination with barnacles, grew less on barnacles alone, and least when foraging time was restricted. Because growth rates on specific prey in the laboratory were opposite the observed trend in nature, variation in prey across the exposure gradient cannot be invoked to account for the difference in growth between N. lapillus from exposed and protected shores. The slower growth rates when foraging time was restricted are consistent with the notion that wave energies on exposed coasts depress growth by limiting foraging time or by reducing foraging efficiency.

PHENOTYPIC PLASTICITY IN AN INTERTIDAL SNAIL: THE ROLE OF A COMMON CRAB PREDATOR.

Prey species may reduce their risk of predation in many ways (for reviews, see Edmunds 1974; Vermeij 1978, 1987). Although avoidance behaviors and chemical defenses can act as deterrents to predation in marine environments, morphological changes have received the greatest emphasis. For example, spines in a marine bryozoan (Harvell 1984), barnacle shape (Lively 1986a), and numerous gastropod shell traits (Vermeij 1978) are known to deter predation. In intertidal environments, predation by invertebrate predators often parallels gradients in wave exposure and is often most important on shores protected from direct wave energy (Menge 1978). Likewise, variation in the shell thickness of intertidal gastropods also tends to parallel gradients in wave exposure and predation intensity. Thick-shelled morphs are typically found on protected shores where crab predators are more abundant, whereas thin-shelled morphs are found on wave-exposed shores (Kitching et al. 1966; Kitching and Lockwood 1974; Reimchen 1982; Palmer 1985a, 1990). Extreme turbulence probably inhibits crab foraging on waveexposed shores (Kitching et al. 1966; Crothers 1968; Menge 1978). Shell thickness of intertidal gastropods varies among intertidal shores, in part because of differential predation by crabs (Kitching et al. 1966; Kitching and Lockwood 1974; Vermeij 1978, 1987; Seeley 1986). Although natural selection by crabs has been suggested to promote the evolution of thicker-shelled snails (Seeley 1986), predator-induced phenotypic plasticity may also influence shell thickness (Appleton and Palmer 1988; Palmer 1990). Predator-induced morphological defenses are a unique example of phenotypic plasticity in which the predator or a cue associated with the predator (often chemical in nature) induces the formation of structures in the prey that deter predation. This phenomenon is common in aquatic rotifer and zooplankton assemblages (for a review, see Dodson 1989). Most examples of predator-induced defenses involve plants (Baldwin and Schultz 1983; Haukioja and Neuvonen 1985; Rhoades 1985) or clonal (e.g., the cladoceran zooplankton examples cited in Dodson 1989) and colonial organisms (Harvell 1984, 1986). Cases of predator-induced defenses in solitary organisms appear to be rare. Curiously, cases involving solitary organisms, with the exception of Bronmark and Miner (1992), have been found in intertidal environments (Lively

Physiological variation in the dog-whelk Nucella lapillus, L. either side of a cline in allozyme and karyotype frequencies

Genetic constitution in the intertidal gastropod Nucella lapillus influences variation in shell shape and growth rate which in turn are correlated with such habitat variables as wave action and temperature. We have investigated the response to hyperosmotic stress of samples from a cline in karyotype and allozyme frequencies and shell shape. Animals with a shell shape associated with environments where temperature and desiccation stress are important respond less to hyperosmotic stress than animals living in a high wave energy environment. With regard to the interaction between shell shape, physiology and habitat, animals with elongate shells associated with protected shores are shown to exhibit a reduced response to hyperosmotic stress compared to animals with a more spherical shell shape; this is discussed in relation to the production of an adaptive phenotype.

Physiological variation in the dog-whelk Nucella lapillus, L. either side of a cline in allozyme and karyotype frequencies

Genetic constitution in the intertidal gastropod Nucella lapillus influences variation in shell shape and growth rate which in turn are correlated with such habitat variables as wave action and temperature. We have investigated the response to hyperosmotic stress of samples from a cline in karyotype and allozyme frequencies and shell shape. Animals with a shell shape associated with environments where temperature and desiccation stress are important respond less to hyperosmotic stress than animals living in a high wave energy environment. With regard to the interaction between shell shape, physiology and habitat, animals with elongate shells associated with protected shores are shown to exhibit a reduced response to hyperosmotic stress compared to animals with a more spherical shell shape; this is discussed in relation to the production of an adaptive phenotype.