Common Periwinkle Littorina Littorea Research Articles

Effects of temperature, salinity and diet on embryonic and early larval development in Littorina littorea (Gastropoda: Littorinimorpha)

IntroductionThe common periwinkle Littorina littorea is a delicacy in southern Europe. Enabling aquaculture production would be measure to avoid future over-harvesting and ensure a constant market supply.MethodsHowever, knowledge gaps in reproductive biology needs to be filled to allow setting up rearing protocols.ResultsWe investigated effects of temperature and salinity on embryonic development by incubating eggs at ten different temperatures in steps every 2°C, form 5 to 23°C) and four salinities (20 – 40). Embryonic development was clearly temperature dependent; eggs hatched after three days at the highest temperature while it took 16 days to hatch at the lowest temperature. Calculating effective day-degrees (DDeff) allowed expressing the thermal history of the embryogenesis and concluding that this species hatches on average at 61 (SD 3.7) DDeff. Larval growth- and developmental rates showed a different response to the temperature extremes as snails with the smallest shell lengths at hatch were found for the highest and lowest temperatures (204.5, SD = 11.6, and 202.9µm, SD = 13.7 respectively). Viable larvae only hatched at temperatures above 9°C. Larvae hatched at lower temperatures did not develop a shell or swimming lobes. Salinity and temperature significantly influenced time-to-hatch and hatching success; the lowest salinity (20PSU) lead to later hatching (80-100DDeff) and lower hatching success compared to higher salinities (25, 30, and 40, hatch around 40-50 DDeff). Neither hatch rate nor time-to-hatch showed differences among the higher salinities, suggesting a salinity threshold below 25. There was no significant interaction between salinity and temperature on time-to-hatch or hatching success. Larval diet had a significant effect on growth rates during the planktonic stage. Veliger larvae fed on two different live microalgae mono-diets (Dunaliella tertiolecta and Rhodomonas baltica) successfully passed their pelagic phase at the same time with no differences in growth rates, while veliger larvae fed on either of two preserved microalgae products (Nannochloropis sp. and Tetrasemis sp. frozen pastes) were not growing.DiscussionWe conclude that embryonal development can be successfully completed at temperatures between 7 and 20°C, while lower or higher temperatures should be avoided. Successfully hatched larvae can be fed on mono-microalgae diets until settlement.

Identification of peptidoglycan recognition proteins in hemocytes and kidney of common periwinkle Littorinalittorea

Peptidoglycan Recognition Proteins (PGRPs) are a diverse group of proteins involved in innate immunity. In particular, PGRPs have been shown to participate in immune pattern recognition in various mollusks. However, they have not been described in Caenogastropoda, a large molluscan group comprising sea, freshwater and land snails. In this study, four short PGRPs with molecular weights ranging from 21 to 34 kDa and their isoforms were identified and structurally characterized in the kidney and hemocytic transcriptomes of a caenogastropod mollusk Littorina littorea. All of them (LlPGRP1-4) are secretory, possess a signal peptide and a characteristic N-terminal N-acetylmuramoyl-l-alanine amidase (Ami) domain with conserved Zn2+ binding- and amidase catalytic sites. The shortest proteins, LlPGRP1 and LlPGRP2, have no additional conserved motifs on the N-terminus. In longer and most abundantly expressed LlPGRP3 and LlPGRP4 the Ami-domain is combined with an N-terminal SH3-domain and a cysteine-rich motif, respectively. Expression analysis showed that LlPGRPs of the common periwinkle were uninvolved in the immune response to infection with trematode Himasthla elongata though they might act in antibacterial defense.

Accidental associates are not symbionts: the absence of a non-parasitic endosymbiotic community inside the common periwinkle Littorina littorea (Mollusca: Gastropoda)

One of the most thoroughly studied marine snails in the world is the North Atlantic periwinkle Littorina littorea. In 2013, Buckland-Nicks et al. reported upon an “extensive community of organisms” living “inside” L. littorea in Nova Scotia, Canada. Conflicting with this report is a vast body of research on this snail since the mid-nineteenth century that has never identified the presence of such a taxonomically diverse endosymbiotic community, with the exception of a well-known assemblage of parasitic digenean trematodes that utilize the snail as a first-intermediate host. The absence of prior reports of a non-parasitic endosymbiotic community, and our own long-term observations, inspired us to study the biological community associated with L. littorea in two locations (Nova Scotia and Connecticut). We were unable to verify the endosymbiotic nature of any of the species (other than trematodes) noted by Buckland-Nicks et al. (Can J Zool 91:293–301, 2013) associated with L. littorea. Instead, we identified three likely sources of associated taxa reported by Buckland-Nicks et al. (Can J Zool 91:293–301, 2013) and by us: species were (1) ingested and defecated alive; (2) attached to the mucous-covered foot and drawn into the mantle cavity when the snail closed its operculum; and/or (3) associated with shell surface cracks and crevices, including within encrusting algae. We could not find any evidence that L. littorea hosts a diverse community of endosymbionts. Instead, we argue that the organisms interpreted as members of an endosymbiotic community by Buckland-Nicks et al. are instead free-living taxa that are transiently associated with the snails.

Not simply accept relationships: editorial comment on the article “Accidental associates are not symbionts: the absence of a non-parasitic endosymbiotic community inside the common periwinkle Littorina littorea (Mollusca: Gastropoda)” by J. T. Carlton et al. (2020)

Not simply accept relationships: editorial comment on the article “Accidental associates are not symbionts: the absence of a non-parasitic endosymbiotic community inside the common periwinkle Littorina littorea (Mollusca: Gastropoda)” by J. T. Carlton et al. (2020)

δ18O-inferred salinity fromLittorina littorea(L.) gastropods in a Danish shell midden at the Mesolithic–Neolithic transition

Norsminde Fjord has received extensive geoarchaeological investigation, hosting one of the classic Stone Age shell midden sites in Denmark, and one of the best examples of the widespread oyster decline at the Mesolithic–Neolithic transition. Here, intra-shell δ18O (and δ13C) analyses from the common periwinkle Littorina littorea (L.) are used to infer inter-annual environmental changes at the Mesolithic–Neolithic transition (four from each period). This study utilises a modern δ18O L. littorea-salinity training set previously developed for the Limfjord, Denmark to quantify winter salinity. δ18O values range between +1.6% and +4.0% in the late Mesolithic and ‒6.3% to +2.0% in the early Neolithic. Using maximum δ18O values, winter salinity at the known temperature of growth cessation in L. littorea (i.e. +3.7 ± 1°C) for the first annual cycle of each shell ranges between 25.5 and 26.8 psu (standard deviation (SD): 0.56) for the late Mesolithic, with an average salinity of 26.1 psu. Early-Neolithic shells range between 19.4 and 28.2 psu (SD: 4.59) with an average salinity of 23.7 psu. No statistically significant change in salinity occurs between the late Mesolithic and early Neolithic. This result supports recent diatom/mollusc-based inferences that salinity was not the sole cause of the oyster decline, although some evidence is presented here for more variable seasonal salinity conditions in the early Neolithic, which (along sedimentary change and temperature deterioration) might have increased stress on oyster populations in some years. It is recommended here that for robust palaeoenvironmental inferences, where possible, multiple specimens should be used from the same time period in conjunction with multiproxy data.

Experimental Evaluation of Seaweeds as a Vector for Microplastics into Marine Food Webs.

The ingestion of microplastics has been shown for a great variety of marine organisms. However, benthic marine mesoherbivores such as the common periwinkle Littorina littorea have been largely disregarded in studies about the effects of microplastics on the marine biota, probably because the pathway for microplastics to this functional group of organisms was not obvious. In laboratory experiments we showed that the seaweed Fucus vesiculosus retains suspended microplastics on its surface. The numbers of microplastics that adhered to the algae correlated with the concentrations of suspended particles in the water. In choice feeding assays L. littorea did not distinguish between algae with adherent microplastics and clean algae without microplastics, indicating that the snails do not recognize solid nonfood particles in the submillimeter size range as deleterious. In periwinkles that were feeding on contaminated algae, microplastics were found in the stomach and in the gut. However, no microplastics were found in the midgut gland, which is the principle digestive organ of gastropods. Microplastics in the fecal pellets of the periwinkles indicate that the particles do not accumulate rapidly inside the animals but are mostly released with the feces. Our results provide the first evidence that seaweeds may represent an efficient pathway for microplastics from the water to marine benthic herbivores.

Lectin-like molecules in transcriptome of Littorina littorea hemocytes

The common periwinkle Littorina littorea was introduced in the list of models for comparative immunobiology as a representative of phylogenetically important taxon Caenogastropoda. Using Illumina sequencing technology, we de novo assembled the transcriptome of Littorina littorea hemocytes from 182 million mRNA-Seq pair-end 100 bp reads into a total of 15,526 contigs clustered in 4472 unigenes. The transcriptome profile was analyzed for presence of carbohydrate-binding molecules in a variety of architectural contexts. Hemocytes' repertoire of lectin-like proteins bearing conserved carbohydrate-recognition domains (CRDs) is highly diversified, including 11 of 15 lectin families earlier described in animals, as well as the novel members of lectin family found for the first time in mollusc species. The new molluscan lineage-specific domain combinations were confirmed by cloning and sequencing, including the fuco-lectin related molecules (FLReMs) composed of N-terminal region with no sequence homology to any known protein, a middle Fucolectin Tachylectin-4 Pentaxrin (FTP) domain, and a C-terminal epidermal growth factor (EGF) repeat region. The repertoire of lectin-like molecules is discussed in terms of their potential participation in the receptor phase of immune response. In total, immune-associated functions may be attributed to 70 transcripts belonging to 6 lectin families. These lectin-like genes show low overlap between species of invertebrates, suggesting relatively rapid evolution of immune-associated genes in the group. The repertoire provides valuable candidates for further characterization of the gene functions in mollusc immunity.

Molecular cloning of α-2-macroglobulin from hemocytes of common periwinkle Littorina littorea

We report the sequence of the proteinase inhibitor with a wide inhibition spectrum, α-2-macroglobulin (α2M), belonging to the thioester superfamily of proteins. This is the first α2M sequence from coenogastropod prosobranch snails. The full-length cDNA was cloned by RACE method, spans 7897 bp and contains an open reading frame of 5460 bp. The ORF encodes a protein of 1819 amino acids. The deduced mature protein contains 1795 amino acids with a molecular weight of 200 kDa and isoelectric point of 5.00. Littorina littorea α2M bears 4 conserved α2M domains and one internal thioester. Phylogenetic analysis showed that the sequence forms well supported cluster with Mollusca species and other representatives of Lophotrochozoa.

Caste formation in larval Himasthla elongata (Trematoda) infecting common periwinkles Littorina littorea

Reproductive division of labour is well-known in several animal groups but the ecological factors driving the evolution of such social organization are still being discussed. Recent studies have discovered social organization in four marine species of trematode parasites having two distinct castes specialized for reproduction and defence of the clonal intra-molluscan larval colony, respectively. Here, we provide novel evidence for social structure also in colonies of the trematode Himasthla elongata infecting the common periwinkle Littorina littorea. We found two types of rediae, the parthenogenetic larval offspring of the parasite: small non-reproductive rediae and considerably larger reproductive rediae. Both redial types possessed a digestive system, collar and posterior appendages and, hence, aside from dimensions, were morphologically similar. However, in vitro experiments showed that non-reproductive morphs attacked heterospecific competing parasites at a higher rate (2–3 fold) than reproductive morphs did. No within-colony antagonism was observed. In contrast to a previous study on a congeneric trematode species, our findings suggest a relatively weak caste formation in H. elongata, possibly resulting from a corresponding weaker level of interspecific competition.

Alien epibiont (Crassostrea gigas) impacts on native periwinkles (Littorina littorea)

In marine sedimentary coastal environments such as the Wadden Sea (coastal south-eastern North Sea) shells of epibenthic molluscs are the only major available settlement substrate for an increasing number of alien sessile organisms. We investigated the effects of Pacific oyster Crassostrea gigas epibionts on body weight, mobility and fecundity of the native common periwinkle Littorina littorea. Body dry weight of snails without oyster overgrowth was twice as high compared to periwinkles covered with oysters. Also crawling speed of snails with oyster epigrowth was significantly slowed down and about ten times lower than in unfouled periwinkles. Additionally, oyster epibionts caused a strong decrease in reproductive output. In laboratory experiments, egg production of fouled L. littorea was about 100-fold lower than in periwinkles free of oysters. Field surveys in different years and habitats demonstrated that up to 10% of periwinkles occurring on epibenthic bivalve beds and up to 25% of snails living on sand flats may be fouled by C. gigas. However, oysters are not the only epibionts on L. littorea in the area. In previous studies it was shown that periwinkles can also be strongly overgrown by other alien epibionts such as Australian barnacles Austrominius modestus and American slipper limpets Crepidula fornicata. These epibiotic structures may cause similar effects as revealed for C. gigas. Thus, we conclude that an alien epibiont accumulation on L. littorea may have a significant impact on periwinkle population dynamics and its ecological functions in the Wadden Sea.

Himasthla elongata: Effect of infection on expression of the LUSTR-like receptor mRNA in common periwinkle haemocytes

The first mollusc mRNA coding G-protein-coupled transmembrane receptor (GPСR), homologous to human receptors LUSTR 1 (GPR107) and LUSTR 2 (GPR108), was isolated from haemocytes of common periwinkle Littorina littorea. The analyses showed that the full-length cDNA is 1935 bp long and is predicted to encode a 614 amino acid protein (named Lit-LUSTR) with a calculated molecular mass of 69.6 kDa and theoretical isoelectric point 7.59. Pair-wise comparisons between Lit-LUSTR and LUSTR proteins from human or mouse have approximately 38% identity and 56% similarity. Lit-LUSTR clusters with LUSTR-A sub-family proteins and is a first characterization of proteins containing Lung7TM-R domain in Mollusca. Significant differences were found between the Lit-LUSTR mRNA levels in haemocytes of healthy periwinkles and those naturally infected with the echinostome trematode Himasthla elongata. Down regulated expression of the LUSTR-like receptor caused by infection illustrates modification of the haemocyte receptor system and may be attributed to the previously demonstrated greater numbers of “immature” haemocytes in the circulation of infected snails.

Limited value of the common periwinkle snail Littorina littorea as a biological control for the invasive tunicate Didemnum vexillum

Didemnum vexillum is an invasive tunicate that aggressively grows on and fouls all manner of substrates in coastal New England habitats. Most alarmingly, D. vexillum acts as a shellfish pest and is capable of completely encapsulating and smothering bivalves, causing them to have reduced growth or be killed. Fouling by D. vexillum on aquaculture gear and product requires remediation. While there are numerous manual eradication methods, they are labor intensive and expensive. We investigated whether the common periwinkle snail Littorina littorea can be utilized as a biological control for D. vexillum. The only known predator of senescing D. vexillum is the snail L. littorea and there are no known predators of healthy D. vexillum. Field observations indicated that L. littorea may be consuming, scouring, or otherwise removing stressed D. vexillum from rocks in intertidal pools at Sandwich, Massachusetts, during all seasons. We used two methods to investigate whether L. littorea could be used as a biological control by either consuming or scouring D. vexillum off shellfish. We examined L. littorea’s fecal pellets and conducted a laboratory experiment to determine if the snails would “clean” unhealthy D. vexillum from aquaculture product. Fecal pellets from L. littorea collected on unhealthy D. vexillum contained the characteristic spicules of this tunicate, thus confirming that L. littorea consumes D. vexillum under field conditions. The laboratory experiment indicated that L. littorea did not notably consume or scour D. vexillum from shellfish under the conditions we provided. At this time, we recommend that manual eradication methods be considered the primary defense for shellfish aquaculturists and others interested in controlling D. vexillum and that L. littorea should merely be considered as a supplement to these more reliable control methods.

Grazing of the invasive alga Codium fragile ssp. tomentosoides by the common periwinkle Littorina littorea: Effects of thallus size, age and condition

We examined the potential of herbivory by the common periwinkle Littorina littorea to limit recruitment and vegetative re-growth of the invasive green alga Codium fragile ssp. tomentosoides in a series of manipulative field experiments in tidepools on a wave-exposed rocky shore in Nova Scotia, Canada. Snails were excluded or included from circular plots (14 to 20 cm diameter) with cages to compare growth and survival of C. fragile against procedural (partial cages) or natural (uncaged) control plots. Our results show that L. littorea may restrict growth and survival of C. fragile by grazing new recruits (< 2 cm thallus length), fronds of adult thalli that are bleached and necrotic, and residual holdfasts (< 2 mm thickness) of detached thalli (artificially severed to mimic wave dislodgement). Once recruits grow beyond a critical size (~ 3 cm), or damaged tissues or holdfasts regenerate, grazing of C. fragile by L. littorea appears to be limited and ineffectual. Our experimental results corroborate correlative evidence from previous studies that herbivory by L. littorea limits the abundance of C. fragile in tidepools on the Atlantic coast of Nova Scotia, particularly pools in the high intertidal zone where these snails are abundant. Lower on the shore, littorinid grazing and physical stressors that render algae more vulnerable to grazers (e.g. UV radiation and freezing) are less intensive, and probably have less of a regulatory effect on populations of C. fragile.

Functional characterization of Littorina littorea (Gastropoda: Prosobranchia) blood cells

The main functional characteristics of haemocytes from the common periwinkle Littorina littorea (phagocytic ability, acid phosphatase activity, cytotoxic properties and generation of reactive oxygen intermediates) were investigated. The blood cells of L. littorea demonstrated phagocytic activity for zymozan particles in both plasma and seawater. However, the level of phagocytosis in plasma was higher than in seawater, suggesting the presence of some soluble factors with opsonizing activity for yeast cell walls in the snail haemolymph. Acid phosphatase was detected in haemocytes following phagocytosis of zymosan. Zymosan particles as well as soluble inducers of respiratory burst (mannan, phorbol-myristate acetate, lipopolysaccharide from Escherichia coli) were shown to trigger superoxide anion production in L. littorea blood cells as evidenced by nitroblue tetrazolium (NBT) reduction. Haemocytes exposed simultaneously to both inducer and the superoxide scavenger enzyme—superoxide dismutase demonstrated a lower ability to reduce nitrobluetetrazolium. Periwinkle blood cells showed plasma-independent cytotoxic activity for human erythrocytes which may be due to the release of superoxide intermediates into the extracellular environment. These results, together with previously obtained data, suggest that haemocytes are the main effectors in the internal defence system of L. littorea, with humoral factors playing an accessory role in recognition and elimination of pathogens.

Modulation of mitogen-activated protein kinases (MAPK) activity in response to different immune stimuli in haemocytes of the common periwinkle Littorina littorea

The modulation of mitogen-activated protein kinase (MAPK) activity in haemocytes of the common periwinkle ( Littorina littorea) in response to immune challenges by lipopolysaccharide from Echerichia coli (LPS), mannan from baker's yeast Saccharomyces cerevisiae and secretory-excretory products (SEP) of trematodes Himasthla elongata (Echinostomatidae) or after the treatment with phorbol ester (PMA) has been studied by Western blotting using affinity purified rabbit polyclonal antibodies. Exposure of the cells in suspension to PMA, LPS and mannan triggered an activation of p38 and ERK2. The JNK-mediated cascade was modulated differently by the elicitors examined. PMA treatment caused a transient activation of the JNK54 isoform, LPS exposure resulted in a decrease in activity of JNK46, and mannan had no effect on JNK phosphorylation status. Incubation of periwinkle haemocytes in culture medium containing trematode SEP did not affect the activity of any MAPK.

Rediae of echinostomatid and heterophyid trematodes suppress phagocytosis of haemocytes in Littorina littorea (Gastropoda: Prosobranchia)

A modulation of the phagocytic activity of hemocytes from the common periwinkle Littorina littorea by secretory–excretory products (SEP) released by trematode rediae during axenic in vitro cultivation was studied. The SEP released by the parasites Himasthla elongata (Echinostomatidae) and Cryptocotyle lingua (Heterophyidae) were found to inhibit the phagocytosis of zymozan particles by periwinkle hemocytes. The specificity of SEP effects was assessed: SEP of Himasthla militaris and Cryptocotyle concavum, two trematodes belonging to the same genera but infecting another closely related prosobranch snail Hydrobia ulvae, were also shown to be able to suppress L. littorea hemocytes phagocytic activity. However, no decrease in phagocytosis rate was observed when SEP of H. elongata and C. lingua were applied to monolayers of hemocytes from the bivalve mollusc Mytilus edulis. SEP from H. elongata was fractionated; only those fractions containing proteins of molecular weight more than 50 kDa were shown to possess inhibitory activity. Different H. elongata SEP concentrations were tested in for their ability to suppress phagocytosis by L. littorea hemocytes. Even very low SEP concentrations were shown to retain their ability to decrease phagocytosis rate, the inhibitory effect being dose-dependent. Hemocytes derived from snails naturally infected with H. elongata were also found to have lower phagocytic ability as compared to healthy individuals.

Are rocky shore ecosystems affected by nutrient-enriched seawater? Some preliminary results from a mesocosm experiment

The response of rocky shore ecosystems to increased nutrient availability was examined in eight land-based mesocosms designed for hard-bottom littoral communities built at Marine Research Station Solbergstrand (Norway). The average seawater volume in each basin was 9 m3 with an average water residence time of about 2 h. A tidal regime resembling that in the fjord was maintained in the basins, and waves were generated regularly. NH4NO3 and H3PO4, at a constant molar NP ratio of 16:1, was added into 6 basins at concentrations 1, 2, 4, 8, 16, 32 μM DIN above the background DIN concentration during 1 1/2 years. Two mesocosms were kept as control treatment. Marine communities were introduced into the basins two years prior to the start of nutrient dosage. The effects of nutrient enrichment were few and only marginal during the first year of nutrient addition, while some effects became more obvious during the second year. The growth rate of the periphyton and fast-growing macroalgae communities was stimulated by nutrient enrichment, while the response was less evident among the perennial fucoids. The structure of the macroalgal communities, however, did not change during 16 months' measurements. In contrast, growth on artificial rock substrates during the same period of time revealed intensive growth of the fast-growing Ulva lactuca in high-dosed basins compared with low-dosed and control basins, which were dominated by the fucoid Fucus serratus. The fauna communities exhibited only a minor response to nutrient treatment. The common periwinkle Littorina littorea, however, appeared with increased abundance in the high-dosed basins. The total system metabolism tended to increase slightly, but not significantly, with increased nutrient loading.

Digestion of algal pigments by the common periwinkle Littorina littorea L. (Gastropoda)

Digestion of the phaeophyte carotenoids fucoxanthin, violaxanthin and neoxanthin and the chlorophylls a and c by the phytophagous snail Littorina littorea was studied in feeding experiments. Gut-passage results in alterations of pigment composition: (i) Chlorophylls are rapidly turned into pheophytin and, to a lesser extent, into pheophorbide in the snails' foregut and digestive gland. (ii) The mono-epoxide pigments fucoxanthin and neoxanthin were not (or only negligibly) reduced in the digestive system. (iii) The di-epoxide violaxanthin was completely de-epoxidized and converted into zeaxanthin. This means that the cyanophyte marker zeaxanthin (3,3′-dihydroxy-β-β-carotene), analysed in sediment samples with possible phaephyte input, may derive from this source material as a r eduction product of violaxanthin. (iv) Absorption of algal pigments in the digestive system seems to be a function of the nutritional state of the animals. Prolonged periods of starvation result in a more efficient digestion of later ingested food material and a practically complete destruction of the algal pigments.

Short-term toxic effects of 1-naphthol on the digestive gland-gonad complex of the marine prosobranchLittorina littorea (L): A light microscopic study

The short-term toxic effects of both sublethal and lethal concentrations of 1-naphthol were studied by light microscopy examination of the digestive gland-gonad complex of the common periwinkle Littorina littorea. Exposure to naphthol produced severe tissue alterations characterized by disruption of digestive cells and presence of a high number of basophilic cells in the digestive tubules and infiltration of digestive, connective and gonadal tissues by hemocytes. Morphologically, the infiltrating hemocytes comprised of hemocytes with a small nucleus and eosinophilic cytoplasm, and hemocytes with a large nucleus and scarce cytoplasm. In addition, breakdown of ripe ova and resorption of gametes occurred, even at the sublethal concentration of 2.075 mg/L of naphthol, apparently related to phagocytosis by hemocytes. Differences in the hemocytic infiltration incidence were observed between male and female individuals, suggesting a different sensitivity to the experimentally induced stress condition between the two sexes.

Effects of the periwinkle Littorina littorea (L.) and of intraspecific competition on growth and survivorship of the limpet Notoacmea testudinalis (Müller)

The common periwinkle Littorina littorea (L.) and the limpet Notoacmea testudinalis (Müller) commonly co-occur on rocky shores in the Gulf of Maine, U.S.A. Periwinkles are found throughout the intertidal zone while N. testudinalis is confined to moist areas at lower intertidal levels but is common throughout the subtidal zone. Short-term experiments over a 4-yr period showed that exclusion of L. Littorea enhanced the growth, gain of weight, and survival of N. testudinalis. A second experiment, in which the densities of both periwinkles and limpets were manipulated, confirmed interspecific effects on growth but did not detect interspecific effects on gain of weight nor mortality or any intraspecific effect among N. testudinalis. Although N. testudinalis were caged at greater than normal densities, growth rates were greater than rates reported by other researchers.