Subtidal Individuals Research Articles

Specific plasticity of the anemone Anthopleura hermaphroditica to intertidal and subtidal environmental conditions of the Quempillén estuary.

The cellular capacity of marine organisms to address rapid fluctuations in environmental conditions is decisive, especially when their bathymetric distribution encompasses intertidal and subtidal zones of estuarine systems. To understand how the bathymetric distribution determines the oxidative damage and antioxidant response of the estuarine anemone Anthopleura hermaphroditica, individuals were collected from upper intertidal and shallow subtidal zones of Quempillén River estuary (Chile), and their response analysed in a fully orthogonal, multifactorial laboratory experiment. The organisms were exposed to the effects of temperature (10°C and 30°C), salinity (10 ppt and 30 ppt) and radiation (PAR, > 400-700 nm; PAR+UV-A, > 320-700 nm; PAR+UV-A+UV-B, > 280-700 nm), and their levels of lipid peroxidation, protein carbonyl and total antioxidant capacity were determined. The results indicated that the intertidal individuals of A. hermaphroditica presented higher levels of tolerance to the stressful ranges of temperature, salinity, and radiation than individuals from the subtidal zone, which was evident from their lower levels of oxidative damage to lipids and proteins. These results were consistent with increased levels of total antioxidant capacity observed in subtidal organisms. Thus intertidal individuals could have greater plasticity to environmental variations than subtidal individuals. Future studies are needed to understand the mechanisms underlying stress adaptation in individuals from this estuarine anemone subjected to different environmental stressors during their life cycles.

Evaluating the effects of ocean warming and freshening on the physiological energetics and transcriptomic response of the Antarctic limpet Nacella concinna

In the Southern Ocean, warming and freshening are expected to be prominent signals of climate change and the reduced ability of Antarctic marine organisms to cope with changing environmental conditions could challenge their future survival. The Antarctic limpet Nacella concinna is a macroinvertebrate of rocky ecosystems, which occurs in high densities in the shallow subtidal zone. Subtidal individuals were exposed to a combination of temperatures (1, 4, 8, 11, 14 °C) and salinities (20 and 30 psu) for a 60-day period. A drastic increment in mortality was observed with seawater warming, showing that N. concinna is highly stenothermal, with limited ability to survive at temperatures warmer than 4 °C, although there was some degree of acclimation at 4 °C and ambient salinity (30 psu). This study confirmed the stenohaline characteristic of this species, with mortality reaching 50% and lower scope for growth at low salinity (20 psu) even at the control temperature (1 °C). At the sub-cellular level, limpets' low tolerance to out-of range salinity is illustrated by the activation of cell remodelling processes whereas the down-regulation of chaperones proteins and plasma membrane ATPase suggest that under the combination of warming and freshening N. concinna experiences a severe level of stress and devote much of its energy to somatic maintenance and survival. The drastic effect observed can be explained by its subtidal origin, an environment with more stable conditions. The surviving individuals at 1 °C and lowered salinity (20 psu) were either more tolerant or showing signs of acclimation after 60 days, but the combination of warming and freshening have a greater combined stress. Projections of climate change for end of the century for this part of the Antarctic can, therefore, result in a significant diminution of the subtidal population of N. concinna, affecting ecological interactions and diversity of the food web.

Small burrowing amphipods cause major damage in a large kelp.

Large herbivores such as sea urchins and fish consume a high proportion of benthic primary production and frequently control the biomass of marine macrophytes. By contrast, small mesograzers, including gastropods and peracarid crustaceans, are abundant on seaweeds but have low per capita feeding rates and their impacts on marine macrophytes are difficult to predict. To quantify how mesograzers can affect macrophytes, we examined feeding damage by the herbivorous amphipods Sunamphitoe lessoniophila and Bircenna sp., which construct burrows in the stipes of subtidal individuals of the kelp Lessonia berteroana in northern-central Chile, southeast Pacific. Infested stipes showed a characteristic sequence of progressive tissue degeneration. The composition of the amphipod assemblages inside the burrows varied between the different stages of infestation of the burrows. Aggregations of grazers within burrows and microhabitat preference of the amphipods result in localized feeding, leading to stipe breakage and loss of substantial algal biomass. The estimated loss of biomass of single stipes varied between 1 and 77%. For the local kelp population, the amphipods caused an estimated loss of biomass of 24–44%. Consequently, small herbivores can cause considerable damage to large kelp species if their feeding activity is concentrated on structurally valuable algal tissue.

The Seasonal Abundance and Distribution of the Bivalve Lyonsia hyalina (Anomalodesmata: Pandoracea) on a Disturbed New England Mudflat

We investigated a casually recognized pattern of seasonal abundance exhibited by a population of the simultaneously hermaphroditic anomalodesmatid bivalve Lyonsia hyalina (Glassy Lysonia) at Bluff Hill Cove, Galilee, RI, and quantified the distribution of these intertidal to subtidal individuals from June 1993 through April 1994. Density in late spring averaged less than 2 individuals m-2 and was followed by a summer explosion of up to 200 individuals m-2 in localized areas, with an observed patchy distribution. A subsequent massive autumn mortality occurred, when the population returned to the previous low numbers. We propose several factors including predation, reduced temperature, and natural senescence as causes of the autumnal decline.

Flexibility of Physiological Traits Underlying Inter-Individual Growth Differences in Intertidal and Subtidal Mussels Mytilusgalloprovincialis.

Mussel seed (Mytilusgalloprovincialis) gathered from the intertidal and subtidal environments of a Galician embayment (NW, Spain) were maintained in the laboratory during five months to select fast (F) and slow (S) growing mussels. The physiological basis underlying inter-individual growth variations were compared for F and S mussels from both origins. Fast growing seemed to be a consequence of greater energy intake (20% higher clearance and ingestion rate) and higher food absorption rate coupled with low metabolic costs. The enhanced energy absorption (around 65% higher) resulted in 3 times higher Scope for Growth in F mussels (20.5±4.9 J h−1) than S individuals (7.3±1.1 J h−1). The higher clearance rate of F mussels appears to be linked with larger gill filtration surface compared to S mussels. Intertidal mussels showed higher food acquisition and absorption per mg of organic weight (i.e. mass-specific standardization) than subtidal mussels under the optimal feeding conditions of the laboratory. However, the enhanced feeding and digestive rates were not enough to compensate for the initial differences in tissue weight between mussels of similar shell length collected from the intertidal and subtidal environments. At the end of the experiment, subtidal individuals had higher gill efficiency, which probably lead to higher total feeding and absorption rates relative to intertidal individuals.

Differences in feeding adaptations in intertidal and subtidal suspension-feeding gastropods: studies on Crepidula fornicata and Crepipatella peruviana

Suspension-feeding organisms living in the intertidal zone experience reduced feeding times associated with periodic aerial exposure. The potential morphological and physiological adaptations to this reduced feeding time were investigated for two closely related gastropods, Crepidula fornicata and Crepipatella peruviana. Intertidal C. fornicata had heavier gills than subtidal conspecifics, a difference mediated by larger gill surface areas and greater numbers of gill filaments among intertidal individuals of a given size. In contrast, the gills of intertidal and subtidal C. peruviana were morphologically indistinguishable. Despite relatively larger food-collecting organs, individuals of C. fornicata from the intertidal zone had clearance rates (CR) that were not significantly different from those of subtidal conspecifics. In contrast, the CR of intertidal C. peruviana were significantly lower than those of subtidal conspecifics. The low CR of intertidal C. peruviana may be partially explained by significantly lower measured particle transport velocities across their gills. In the context of feeding, intertidal individuals of C. fornicata performed at least as well as subtidal conspecifics, resulting in a population whose adults were as large as those found subtidally. This suggests that C. fornicata has had a long interaction with the environmental heterogeneity associated with intertidal life. In contrast, intertidal individuals of C. peruviana were on average smaller than subtidal individuals and may be stressed in the intertidal.

Morphological and behavioral differences in the gastropod Trophon geversianus associated to distinct environmental conditions, as revealed by a multidisciplinary approach

The gastropod Trophon geversianus exhibits shell polymorphisms along its distribution in subtidal and intertidal habitats. Our hypothesis is that morphological and behavioral patterns of T. geversianus represent habitat-specific constrains; subsequently we expect an association between shell morphology, attachment behavior, and habitat. In order to test this hypothesis we compared individuals from intertidal and subtidal habitats, at three sites in Golfo Nuevo (Argentina). We analyzed shell morphology using classic morphometric variables, 3D geometric morphometrics and computing tomography scan. The results were complemented with field observations of attachment to substrate and turning time behavior, as well as of the number of shell scars produced by crab predation. Our results showed differences in shell size and shape between intertidal and subtidal-collected individuals. Centroid size, total weight and shell weight, as well as shell density and thickness were significantly lower in intertidal individuals than in subtidal ones. Gastropods from intertidal habitats presented a low-spired shell and an expanded aperture which might allow better attachment to the bottom substrate, while subtidal individuals presented a slender and narrower shell shape. The number of crab scars was significantly higher in shells from subtidal individuals. Observations of the behavior of gastropods placed at the intertidal splash zone showed 100% of attachment to the bottom in the intertidal individuals, while subtidal specimens only attached in average in 32% of the cases. These latter took 12 times longer to re-attach to the bottom when faced up. Phylogenetic analysis of COI gene fragments showed no consistent differences among individuals sampled in both habitats. All these results suggest that T. geversianus has developed two ecomorphs with distinct morphological and behavioral responses to physically stressful conditions registered in north Patagonian intertidals, as opposed to lower physical stress but higher predation pressure in the subtidal habitats. The findings of this work constitute a starting point in the study of ecological adaptation processes in gastropods from Patagonian coastal environments.

Thermal tolerance of Crepidula fornicata (Gastropoda) life history stages from intertidal and subtidal subpopulations

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 486:173-187 (2013) - DOI: https://doi.org/10.3354/meps10355 Thermal tolerance of Crepidula fornicata (Gastropoda) life history stages from intertidal and subtidal subpopulations Casey M. Diederich*, Jan A. Pechenik Biology Department, Tufts University, Medford, Massachusetts 02155, USA *Email: casey.diederich@tufts.edu ABSTRACT: The ability to withstand high summer temperatures is an extremely important determinant of species distributions in the intertidal zone; most marine organisms cannot live intertidally because of the harsh conditions experienced during aerial emersion. The members of some species, though, live both intertidally and subtidally, and their physiological tolerance to stressors may differ depending on their genetic connectivity, acclimatization, and differential postsettlement mortality. Furthermore, tolerances of organisms at different life-history stages within both habitats may differ and will play an important role in determining adult distributions. To determine the effect of habitat and life-history stage on physiological tolerance and the likely contribution of upper thermal tolerance limits to the native distribution of an important invasive species, the slippershell snail Crepidula fornicata, we compared the thermal tolerance of intertidal and subtidal embryos and adults in relation to conditions that they experience in the field. We found C. fornicata living both intertidally and subtidally in Bissel Cove, Rhode Island, where they experienced drastically different thermal conditions. Intertidal individuals achieved body temperatures as high as 42°C, more than 15°C higher than those recorded in subtidal conspecifics. However, subtidal individuals had remarkably high thermal tolerances that were nearly identical to those of intertidal conspecifics (lethal range = 33-37°C following a 3 h exposure). Furthermore, embryos were even more tolerant to high thermal stress than adults. These results are surprising: the few previous studies that have compared thermal tolerances among individuals at different life-history stages have found differences among them, and early stages are generally more sensitive than adults. Interestingly, the markedly higher temperatures that intertidal animals experienced in this study had little effect on their thermal tolerance. Intertidal (but not subtidal) slippershell snails are now living dangerously close to their upper thermal limits and will almost certainly be relegated to the subtidal as global temperatures rise. KEY WORDS: Intertidal · Subtidal · Crepidula · Thermal stress · Physiological tolerance Full text in pdf format PreviousNextCite this article as: Diederich CM, Pechenik JA (2013) Thermal tolerance of Crepidula fornicata (Gastropoda) life history stages from intertidal and subtidal subpopulations. Mar Ecol Prog Ser 486:173-187. https://doi.org/10.3354/meps10355 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 486. Online publication date: July 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Metabolism in blue mussel: intertidal and subtidal beds compared

Mytilids occur worldwide, and mussel beds are a prominent intertidal and subtidal system feature. Brittany (France) has a complex population structure in which pure genotypes alternate with hybrids of Mytilus edulis and M. galloprovincialis, referred to here as 'mussels'. Mussels live attached to the substrate in subtidal and intertidal areas and are regularly exposed to strong environmental variations (e. g. desiccation, light, and temperature). The resistance of mussels to emersion is based on a combination of different strategies, such as metabolic rate depression, anaerobic metabolism and air breathing. In the present study, we have evaluated the differences in aerial and underwater mussel metabolism between an intertidal mussel bed and a subtidal one. Metabolism was measured seasonally for small (shell length 24 to 26 mm) and large (43 to 66 mm) individuals. Mussel aerial respiration fluxes were directly correlated with air temperature. In contrast, underwater carbon (DIC) fluxes seemed to be influenced by additional factors such as food availability and/or reproduction period. Underwater metabolism was higher in small mussels (intertidal: 35.9 mu mol DIC g AFDW(-1) h(-1); subtidal: 51.4 mu mol DIC g AFDW(-1) h(-1)) than in large mussels (intertidal: 26.4 mu mol DIC g AFDW(-1) h(-1); subtidal: 21.3 mu mol DIC g AFDW(-1) h(-1)). In contrast, aerial respiration showed different adaptations: small intertidal and subtidal mussels had similar respiration under emerged conditions, while large intertidal individuals showed higher carbon fluxes during emersion compared to subtidal individuals. These data suggest that while underwater fluxes were similar for the 2 mussel beds, all small and large intertidal mussels are far better able to tolerate emersion than large subtidal animals. Subtidal mussels seem thus to lose their ability to respire in air after becoming adult.

Heat-shock response and antioxidant defense during air exposure in Patagonian shallow-water limpets from different climatic habitats

Climate warming involves not only a rise of air temperature means, but also more frequent heat waves in many regions on earth, and is predicted to intensify physiological stress especially in extremely changeable habitats like the intertidal. We investigated the heat-shock response (HSR) and enzymatic antioxidant defense levels of Patagonian shallow-water limpets, adapted to distinct tidal exposure conditions in the sub- and intertidal. Limpets were sampled in the temperate Northern Patagonia and the subpolar Magellan region. Expression levels of two Hsp70 genes and activities of the antioxidants superoxide dismutase (SOD) and catalase (CAT) were measured in submerged and 2- and 12-h air-exposed specimens. Air-exposed Patagonian limpets showed a tiered HSR increasing from South to North on the latitudinal gradient and from high to low shore levels on a tidal gradient. SOD activities in the Magellan region correlated with the tidal rhythm and were higher after 2 and 12h when the tide was low at the experimental site compared to the 6h value taken at high tide. This pattern was observed in intertidal and subtidal specimens, although subtidal individuals are little affected by tides. Our study shows that long-term thermal adaptation shapes the HSR in limpets, while the oxidative stress response is linked to the tidal rhythm. Close to the warm border of their distribution range, energy expenses to cope with stress might become overwhelming and represent one cause why the limpets are unable to colonize the shallow intertidal zone.

Why are intertidal snails rare in the subtidal? Predation, growth and the vertical distribution of Littorina littorea (L.) in the Gulf of Maine

The North Atlantic gastropod Littorina littorea exhibits a characteristic “intertidal” distribution: the snail is abundant in the littoral zone but scarce in the shallow subtidal and the relatively few subtidal individuals are larger (in shell size) on average than those in the intertidal zone. For highly mobile species like L. littorea, this vertical distribution is primarily determined by directional movement. Biotic and abiotic factors vary across tidal heights, and natural selection for movement to shore levels where fitness is maximized provides the ultimate (evolutionary) explanation for vertical distribution patterns. In this study, we asked whether variation in growth rate and/or predation pressure among tidal heights provide an ultimate explanation for vertical gradients in L. littorea size and abundance. We used a cage experiment to compare juvenile growth rate among tidal heights and a series of field and laboratory experiments to examine variation in predation pressure among tidal heights and snail size classes. Juvenile growth rates were highest in the low intertidal zone, declining at both higher and lower levels. Predation risk for tethered L. littorea increased with both decreasing tidal height and decreasing body size (shell height). Almost all tethered prey were consumed by shell- breaking predators and a census revealed that the two most abundant such predators were the crabs Carcinus maenas and Cancer borealis. Laboratory feeding experiments were used to compare size-dependent prey vulnerability and prey-size preferences for these two key predators. We found that L. littorea vulnerability decreased with increasing snail size and increased with increasing size of both predator species. However, whereas C. borealis were capable of consuming even the largest L. littorea, most Carcinus were unable to feed on individuals larger than 10 mm in shell height. Additionally, C. borealis preferred larger sizes of L. littorea than did Carcinus. Thus, Carcinus, which co-occurs with L. littorea in the intertidal, is a much less effective predator than C. borealis, which is found primarily in the subtidal. We conclude that predation on L. littorea by C. borealis and other subtidal consumers has resulted in the scarcity of this ecologically important grazer in the subtidal. This effect has been produced both through direct predation and by imposing strong selection for movement of L. littorea to higher tidal zones.

Hermit crabs

Hermit crabs

INTRASPECIFIC VARIATION IN STRESS‐INDUCED HYDROGEN PEROXIDE SCAVENGING BY THE ULVOID MACROALGA ULVA LACTUCA1

We investigated the presence and kinetics of the oxidative stress response in intertidal and subtidal individuals of the ulvoid macroalga Ulva lactuca L. Stress responses, as measured with both enzymatic and fluorescent‐based antioxidant assays, differed between individuals collected from a subtidal and an intertidal habitat. Subtidal individuals secreted significantly more hydrogen peroxide (H2O2) than intertidal individuals when subjected to osmotic stress or desiccation. The activity of reactive‐oxygen‐scavenging enzymes and the ability to scavenge exogenous H2O2 were lower in subtidal than in intertidal individuals, suggesting that subtidal individuals are less stress tolerant. In vitro experimentation demonstrated that millimolar concentrations of dimethylsulfoniopropionate (DMSP) and its breakdown products could efficiently scavenge H2O2, with DMSP being a less‐effective scavenger than dimethyl sulfide (DMS), acrylic acid, and acrylate. The addition of H2O2 at concentrations of 2.5 mM or greater induced the cleavage of DMSP into DMS and acrylic acid in subtidal individuals. Intertidal individuals were affected in the same manner with the addition of 5 mM H2O2. There were no differences in the amounts of DMSP cleavage in subtidal and intertidal algae when the algae were subjected to hyposaline conditions. Our data suggest that the oxidative‐stress‐induced cleavage of DMSP affords products with efficient H2O2‐scavenging abilities. In addition, U. lactuca individuals growing in intertidal habitats are better acclimatized to changing environments and thus have a higher threshold for oxidative stress than conspecifics in subtidal habitats.

Inducible variation in hypoxia tolerance across the intertidal–subtidal distribution of the blue mussel Mytilus edulis

The distribution of the blue mussel Mytilus edulis spans a steep gradient of environmen- tal stress between intertidal and subtidal habitats, and can provide insight into population-scale pat- terns and underlying processes of variation in physiological tolerances. I conducted a 7 wk reciprocal transplant of mussels between the upper intertidal and subtidal portion of their natural depth distri- bution, and then assayed their tolerance to either aerial exposure or submerged hypoxia in the labo- ratory. Intertidal mussels transplanted back to the intertidal had a tolerance to aerial exposure 50% higher than subtidal mussels that remained in the subtidal. That difference can be explained by changes in mussel physiology induced by ambient conditions, since the tolerance of mussels trans- planted between the intertidal and subtidal became similar to mussels occurring naturally in each habitat. The tolerance of mussels to submergence in hypoxic water —an environmental stress exacerbated by anthropogenic factors that experimental mussels had not encountered in the field — followed a pattern qualitatively similar to the aerial exposure assay: intertidal mussels had higher survivorship in hypoxic water than those from the subtidal, and an elevated tolerance was induced by transplanting subtidal individuals to the intertidal. These results suggest that the response of mussels to a change in environmental conditions could vary between the center and edge of their depth distribution as a function of stress previously encountered.

Ecological contrasts across an Antarctic land–sea interface

Abstract We report the composition of terrestrial, intertidal and shallow sublittoral faunal communities at sites around Rothera Research Station, Adelaide Island, Antarctic Peninsula. We examined primary hypotheses that the marine environment will have considerably higher species richness, biomass and abundance than the terrestrial, and that both will be greater than that found in the intertidal. We also compared ages and sizes of individuals of selected marine taxa between intertidal and subtidal zones to test the hypothesis that animals in a more stressed environment (intertidal) would be smaller and shorter lived. Species richness of intertidal and subtidal communities was found to be similar, with considerable overlap in composition. However, terrestrial communities showed no overlap with the intertidal, differing from previous reports, particularly from further north on the Antarctic Peninsula and Scotia Arc. Faunal biomass was variable but highest in the sublittoral. While terrestrial communities were depauperate with low biomass they displayed the highest overall abundance, with a mean of over 3 × 105 individuals per square metre. No significant differences in ages of intertidal and subtidal individuals of the same species were found, with bryozoan colonies of up to 4 years of age being present in the intertidal. In contrast with expectation and the limited existing literature we conclude that, while the Antarctic intertidal zone is clearly a suboptimal and highly stressful habitat, its faunal community can be well established and relatively diverse, and is not limited to short‐term opportunists or waifs and strays.

Oxygen and carbon isotope composition, magnesium and strontium contents of calcite from a subtidal Patella coerulea shell

A Patella coerulea shell from a subtidal environment has been divided into 31 samples (concentric rings) which have been examined for δ 13C, δ 18O, and Mg, Ca and Sr contents. δ 18O-values are well correlated with δ 13C and show a range of calcification temperatures in the lower part of the ambient annual cycle, in good agreement with the mineralogical composition of the shell. Isotopic temperatures also indicate a more continuous and higher rate of calcification for subtidal individuals compared with intertidal ones. Mg and Sr are correlated with the temperature of calcification on a whole-year basis. Both correlations, if calculated for limited time intervals, show different gradients between cold and warm seasons. In the winter the Mg values are not correlated with temperatures at all.

Physiological responses of Mytilus edulis and Cardium edule to aerial exposure

Physiological responses of two bivalves (Mytilus edulis L. and Cardium edule L.) to intertidal conditions were studied. Specimens were collected from S. W. England in autumn/winter, 1980, and acclimatized to either intertidal or subtidal regimes before measurement of rates of heat dissipation \(\left( {{}_t\dot q} \right)\) and oxygen uptake \(\left( {\dot \upsilon _{{\rm O}_2 } } \right)\) during 5 h of air exposure, and rates of \(\dot \upsilon _{{\rm O}_2 }\), particle clearance, ammonia excretion, and food-absorption efficiency during 7 h of reimmersion. Subtidal individuals were either intermittently or continuously fed in order to distinguish the effects of periodic food supply from the effects of air exposure. Specimens of M. edulis had low aerial rates of \({}_t\dot q\) (14 to 20% of aquatic rate), and \({}_t\dot q\) was greater than the energy equivalent of \(\dot \upsilon _{{\rm O}_2 }\), indicating that they were largely anaerobic. In contrast, C. edule “air-gaped” and had higher aerial rates of \({}_t\dot q\) and \(\dot \upsilon _{{\rm O}_2 }\) (50 to 75% of aquatic rate). There were behavioural and metabolic differences in the responses of intertidally and subtidally acclimatized mussels and cockles to air exposure. Intertidal individuals of both species were more quiescent, had lower aerial rates of \({}_t\dot q\) and \(\dot \upsilon _{{\rm O}_2 }\), and showed a conditioned response at the “expected” time of reimmersion. The reduction in aerial rate of \({}_t\dot q\) was an energy-saving mechanism and the payment of the “oxygen-debt” within 2 h of reimmersion represented a significant “cost”. The “heat increment” associated with feeding and digestion was estimated as 15 to 17% of the oxygen uptake by M. edulis during all stages of recovery. M. edulis adapted to the intertidal regime by reducing its time-averaged aerial and aquatic rates of ammonia excretion. In contrast, C. edule maintained a high aerial and aquatic rate of ammonia excretion. The clearance rates of M. edulis recovered rapidly (0.5 to 1.5 h) following reimmersion, whereas those of C. edule recovered more slowly, particularly for the subtidal individuals following acute exposure (>4 h). There was no evidence of increased clearance rate or absorption efficiency by intertidal individuals to compensate for the loss of feeding time. Intertidally acclimatized individuals of M. edulis and C. edule had more energy available for growth (scope for growth) integrated over a 12 h period and higher growth efficiencies than subtidal individuals subjected to acute air exposure and intermittent feeding regimes. This was the result of reduced aerial and aquatic rates of energy expenditure, a relatively small “cost” in terms of the payment of “oxygen-debt” and a rapid recovery of clearance rate following reimmersion.

Intraspecific variation in the population dynamics and growth of the limpet, Cellana tramoserica.

Populations of the limpet Cellana tramoserica (Sowerby) from high, mid, and low intertidal regions, and from a subtidal zone, were studied at Cape Banks (N.S.W.), Australia. Individuals from the subtidal population had the largest mean and maximum shell size, the low and high shore populations were intermediate, while the midshore population had both the smallest mean and maximum size. The density of adults showed the reverse trend: the midshore region had the greatest adult population density while the subtidal population had the smallest density. The density of juveniles and recruits was negatively correlated with tidal height in the intertidal areas, but the density of both age-classes was smallest in the subtidal region. The rate of growth of individuals was negatively correlated to the adult density of a site; individuals from the subtidal population grew the fastest, while those from the midshore region grew the slowest. The level of adult mortality of the four populations was similar, with an annual rate of between 50-60%. Juvenile mortality did, however, differ among populations; reduced percentages of juveniles reached adult size in the mid and low shore populations than in the highshore and subtidal populations.The expected lifetime fecundity of individual females differed among the four populations. Subtidal individuals were expected to spawn 40 times the amount of gonad material during their life than were individuals from the midshore population. Individuals from the high and low populations probably spawn 10 times more than those from the midshore region. Differences in the fecundities of individuals were not likely to be the result of genetic differences because experimental transplants and manipulations of density showed that individuals from all the intertidal populations could increase their growth rate to match that of subtidal individuals. The implications of the difference in lifetime fecundity among populations are discussed.

Variability in the reproductive effort of the limpet, Cellana tramoserica.

The reproductive effort of the limpet, Cellana tramoserica was investigated in high, mid, and low intertidal areas of the rocky shore as well as in a subtidal population. The reproductive effort of individuals within a population was independent of age. There was, however, a noticeable difference among populations with respect to the relative amount of gonad material spawned per year. The individuals from the subtidal population had the greatest reproductive effort, spawning the equivalent of 101% of their somatic weight per year, while the low, mid and high intertidal populations spawned the equivalent of 66%, 20%, 51%, respectively.Experimental transplants showed that individuals from all three intertidal populations increased their reproductive effort to match that of subtidal individuals. It was unlikely, therefore, that the observed patterns were the result of genetic differences among the populations. The reproductive effort of the populations was also not correlated with the rate of mortality of the adults in the four populations. The observed differences could be explained by a combination of the availability of food and intraspecific competition. The flexibility in the reproductive pattern of Cellana is hypothesised to be a result of this species having a dispersive larval stage, which may result in selection for plasticity of reproductive allocation, depending upon the environmental conditions at the site of settlement and growth to adult size.

TEMPERATURE VARIATION IN THE INFAUNAL ENVIRONMENT OF A SAND FLAT

Temperature variation within intertidal sands was observed at two stations in Tomales Bay, California. The annual range and seasonal trend temperature at 10 cm beneath the sand surface are similar to those in the open water of the bay. The daily variation resembles that observed in terrestrial soils. Animals living in the upper 1 cm are exposed to a daily temperature range as great as three times that experienced by subtidal individuals of the same species. The animals living at 10 cm or deeper are subject to a temperature regime similar to that of the subtidal environment.