The limpet Patella vulgata L. at night in air: effective feeding on Ascophyllum nodosum monocultures and stranded seaweeds

Opportunistically, the limpet Patella vulgata will switch frommicrophagous grazing to feeding on attached macroalgae or, anovel finding, on accumulations of stranded seaweeds. Macroalgalfood is ingested primarily at night during emersion, when thethalli come to lie on the rock surface and are sufficientlydamp. Monocultures of Ascophyllum nodosum are not immune tothe destructive effects of limpets as previously thought. Patellavulgata can graze them down to complete disappearance, thuspushing Ascophyllum back to refuges where P. vulgata is absentor rare. Such refuges were found along a wide range from verysheltered to strongly wave-exposed rocky shores in Brittany,France. By a combination of its macrophagous and microphagousfeeding habits, P. vulgata can control mid-tidal macroalgalassemblages in a similar fashion to the action of sea urchinsupon kelp communities inhabiting the lower intertidal and shallowsublittoral zones of rocky shores. (Received 30 October 2006; accepted 25 May 2007)     

Purification and partial characterization of a carboxypeptidase from the limpet (Patella vulgata)

A carboxypeptidase A-like enzyme has been purified to apparent homogeneity from commercially available acetone powder from the visceral hump of the limpet, Patella vulgata. A two-step procedure involving affinity chromatography on ?-amino-N-caproyl-d-phenylalanine-Sepharose and gel filtration resulted in a 3000-fold purification with an 80% yield. The enzyme is a single polypeptide chain of M_r = 40,000 and exhibits both peptidase and esterase activities, which are characterized by dramatic excess substrate inhibition. Inhibition studies suggest that a metal ion is required for activity and demonstrate that the affinity label, N-bromoacetyl-N-methyl-l-phenylalanine, and a polypeptide carboxypeptidase inhibitor from potatoes (apparent K_i approx. 2 nm) are effective against the limpet enzyme.     

Changes in membrane properties during in-vitro meiotic maturation of the limpet Patella vulgata

Changes in the membrane properties of the oocyte of the mollusk, Patella vulgata, were analyzed following the induction of meiosis reinitiation by paleopedial ganglia extract or by the weak base ammonia. During maturation it was possible to distinguish between an early phase characterized by an initial hyperpolarization and a late phase consisting of a depolarization which triggers an action potential with a long-term overshoot (20 minutes) of the membrane potential. Major changes in individual ionic permeabilities were studied using both current and voltage clamp conditions. The depolarizing phase appears to depend on decreases in K+ membrane permeability. Finally we observed that the overshoot did not appear to be directly related to germinal vesicle breakdown (GVBD) since it was absent in Na-deprived artificial sea water and could be elicited in the presence of TEA bromide, which did not induce maturation. This last observation suggests that it may result from a change in specific K+ ion permeability due to the possible activation of stretch channels.     

Biomineralization of iron: Isolation of ferritin from the hemolymph of the limpet Patella vulgata

Ferritin has been isolated from the hemolymph of the limpet Patella vulgata. The protein was homogeneous by electrophoretic criteria and appeared under the electron microscope as a central electron dense core surrounded by a polypeptide shell. The iron content of the protein was 22.5%, present in the central core which had a median diameter of 70–75 Å and was poorly crystalline. The polypeptide shell consisted of a single subunit of apparent M_r 25 000.     

Food supply, grazing activity and growth rate in the limpet Patella vulgata L.: a comparison between exposed and sheltered shores

The limpet Patella vulgata L. is an important microphagous grazer on intertidal rocky shores of north-west Europe, occurring across the wave exposure gradient. Groups of P. vulgata were selected at mid-tide level of two exposed shores and two sheltered, fucoid dominated shores on the Isle of Man, British Isles, and manipulated to equivalent densities and population structure. The level of grazing activity and growth rate were determined over a 1-year period. At the same time, the abundance of epilithic microalgae, measured as the concentration of chlorophyll a, was determined as an estimate of food supply. Microagal abundance showed a seasonal pattern in both exposed and sheltered conditions, with higher levels in winter compared to summer. In both seasons, the microalgal resource was more abundant on the sheltered shore studied. The level of grazing activity in P. vulgata showed a seasonal pattern on the exposed but not the sheltered shores. Averaged over the year, grazing activity on the exposed shores was over double that on sheltered shores. Thus, in sheltered conditions, food supply for limpets was high and grazing activity low; in exposed conditions, food supply was low and grazing activity high. The growth rate of P. vulgata, measured as increase in shell length, showed no significant difference between exposed and sheltered shores. Growth rate was also determined in P. vulgata at natural densities. Although the overall density declined with decreasing exposure to wave action, the density per unit area of grazeable substance was higher in shelter. In these populations, the mean growth rate was over twice as high on exposed compared to sheltered shores.     

The role of cyclins in the maturation of Patella vulgata oocytes.

We have cloned and sequenced the cDNAs encoding Patella vulgata cyclins A and B. The cDNA clones contain an open reading frame of 426 and 408 amino acids respectively, which present similarity with cyclins from other species. Cyclin A and B RNAs are present as polyadenylated and non-polyadenylated RNA in prophase oocytes and are completely polyadenylated in metaphase I. During the first cleavages after fertilization the level of cyclin A and B mRNAs is high and drops when the free swimming stage is reached. Using p13suc1-Sepharose bead precipitation we demonstrate that cyclin synthesis is triggered during maturation and that inhibition of protein synthesis makes the cyclins disappear rapidly from the metaphase I oocytes, which shift to interphase condition. By microinjecting antisense oligonucleotides into metaphase I oocytes, we demonstrate that in vivo ablation of cyclin A and B messengers together gives the same result, whereas microinjection of only one oligonucleotide does not show any effect.     

Structural and material design of mature mineralized radula teeth of Patella vulgata (gastropoda)

The molluscan radula is a cutting apparatus employed in feeding. It is a toothed ribbon located in the mouth cavity. This study focuses on the characterization, organization, and hardness of the various components in full grown, mineralized, radula teeth of the common limpet Patella vulgata. Three major components are identified: Fibrous organic material, acicular crystals of goethite (α-FeOOH), and silica (SiO₂). Each forms a coherent network intertwined with the other two. The goethite crystals lie parallel to the fibers in the organic framework. The orientations of fibers and crystals are described in detail. The hardness of the leading part, i.e., the part that leads in the cutting direction, is about twice the hardness in the trailing part. It is argued that this difference results from the greater compactness of the mineral matter in the leading part. The function of the tooth as a cutting device is discussed on the basis of the data presented in this study.     

Metabolic responses of the limpet Patella caerulea (L.) to anoxia and dehydration.

This study examined the metabolic responses of the limpet Patella caerulea (L.) to anoxia and dehydration, attempting to tease apart the effect of these two stressful conditions, which are often not clearly distinguished in experiments. Specimens were exposed to: (a) oxygen-free sea water; (b) oxygen-saturated water (controls); (c) low-humidity air (55% RH); and (d) high-humidity air (100% RH). For each of the treatments, we took samples of five specimens after 6 and 18 h of exposure to the experimental conditions and determined the concentrations in the foot muscle of succinate, acetate, propionate, aspartate and alanine. Exposure to anoxia caused an increase in the levels of succinate (6 and 18 h) and acetate and propionate (18 h) with respect to control specimens. Anoxia also induced a decrease of aspartate and an increase of alanine after both 6 and 18 h. Exposure to both moist and dry air generally had negligible effects on the organic acid levels. Aspartate content increased after 18 h of exposure to moist air. Alanine levels also increased with respect to control values after exposure to air, with dry air having the more pronounced effect. In conclusion, the results of this study suggest that one should be cautious when inferring anaerobic conditions from the simple exposure of intertidal species to air, without strict control of the experimental conditions and actual respiration rates.     

Basal bodies in the odontoblasts of the limpet,Patella coerulea L. (Gastropoda)

Summary The odontoblasts in the long radular gland of Patella coerulea L. are arranged in a terminal position; therefore newly formed teeth already have an upright position. The long and slender odontoblasts have only one to three lengthy and ramifying apical microvilli. Between these pinnate microvilli a fine filamentous material appears which probably corresponds to chitin microfibrils. Therefore, the pattern of chitin microfibrils seems to depend on the arrangement of odontoblasts' microvilli. For the first time, basal bodies were found in the apical part of odontoblasts which led to the assumption that the radular gland originally might have been a mucous gland, the secretion of which was transported by cilia.