Foraging movements and homing in the limpet Patella vulgata L

In two populations of Patella vulgata in the Isle of Man foraging activity is restricted to daytime high waters, with about 75 per cent of the population foraging on any one day. Movement commences as the tide covers the limpets, and they travel an average of 0·4 m from their home sites to which they return at least an hour before the falling tide exposes them again. The mean speed on the outward and return journey is around 0·60 cm min^?, and during the intervening browsing period about 0·08 cm min^?. This behaviour contrasts with that of the same species in Alderney, where foraging is limited to nocturnal low waters: there is possibly a geographical trend in behaviour. P. vulgata, especially in the Isle of Man, is one of the more mobile limpets.     

The characterization of N-acetylglucosaminidases from the limpet Patella vulgata (L.)

The α- and β-N-acetylglucosaminidase activity of the limpet Patella vulgata (L.) is due to two enzymes. One of these enzymes hydrolyses both α- and β-N-acetylglucosaminidases and is referred to α,β-N-acetylglucosaminidase. The other is a β-N-acetylglucosaminidase (EC 3.2.1.30). Both enzymes have been isolated and characterized as glycoproteins containing 12% hexose, mainly galactose. The amino acid, neutral sugar and amino sugar content of the two enzymes is very similar, and the main difference lies in the presence of 9% sialic acid in β-N-acetylglucosaminidase. The molecular weight of α,β-N-acetylglucosaminidase is 217 000 and that of β-N-acetylglucosaminidase is 136 000. Evidence has been obtained for the presence of an additional sub-unit in the α,β-enzyme.     

Predation by small mobile aquatic predators regulates populations of the intertidal limpet Patella vulgata (L.)

Highly mobile aquatic predators are known to forage in the intertidal during periods of immersion. There is limited quantitative information, however, on the extent to which these predators influence the abundance of grazing molluscs which are known to have a key role in structuring intertidal assemblages. Our preliminary video observations revealed that crabs and small fish were abundant on shores in southwest England during high-tide. We then used manipulative experiments to quantify the effect of small mobile aquatic predators on the abundance of limpets (Patella vulgata L.). On the lower shore at two moderately sheltered rocky shores three treatments were established: complete cage, partial cage (cage control) and uncaged (natural condition). The complete cages excluded all predators. The partial cage treatment allowed full access to small predators and the uncaged treatment allowed access to all predators. After two months, limpet abundance in uncaged and partial cage treatments had declined by around 50% compared to the complete cage treatment. Population structure also changed with survival of larger individuals being greater than smaller individuals in the open and partial cage treatments compared to the complete cage treatment. The effects of excluding predators were consistent at small (meters) and large spatial scales (kilometres) and hence, it would appear that the outcomes of our research are generally applicable to similar shores in the region.To explore the mechanism behind the differential effects of predators according to prey size, we compared the detachment force required to remove limpets of differing sizes from the shore. This was around four times greater for larger individuals than for smaller ones indicating that smaller limpets were more vulnerable to predation. These effects were also consistent between locations. Subsequent laboratory observations showed that the crabs Carcinus maenas (L.), Necora puber (L.) and Cancer pagurus (L.) which are locally abundant predators of limpets, had differing handling behaviour but were all highly efficient at removing limpets from substratum. Hence, shell width and attachment force appeared to be critical factors influencing the vulnerability of limpets to predation by these crabs. Limpets are known to control the abundance of macroalgae on shores in the North-east Atlantic and so our conclusions about the role of mobile predators in regulating the abundance of these grazers are important to our broader understanding of the ecology of these shores.     

Local habitat-induced variations in the population dynamics of Patella vulgata L.

The recruitment, growth and maximum size, life span, standing crop and biomass of Patella vulgata L. reveal considerable local differences in a range of habitats on the same shore. While some differences are related to physical conditions (e.g., standing water, tidal level), others arise from local biological interactions and may reverse expectations based on tidal level alone. Wet and bare surfaces apart, juvenile input is regularly highest among mid- and upper-shore mussels, while growth and maximum size are least among barnacles at any tidal level. The extreme permutations of population characteristics range from high-level, dry barnacle areas where limpet recruitment averages 15 % of standing crop, growth rate and maximum size are low and survival for 15–17 years is possible to low-level, bare rock where input averages 66 %, growth and maximum size are high and life span unlikely to exceed 4–5 years. Population densities vary annually but the relative densities of the different habitats have remained fairly steady as long as the biological conditions have remained similar; the latter largely control the recruitment and survival characteristics upon the balance of which the population density appears to depend. Although liable to distortions due to years of abnormal recruitment, the size-frequency structure of their populations is highly diagnostic of many habitats.     

Heavy metal complexation in polluted molluscs I. Limpets (Patella vulgata and Patella intermedia)

The accumulation of cadmium, zinc and copper by the marine gastropod molluscs Patella vulgata and Patella intermedia has been studied by gel permeation chromatography of water-soluble extracts of environmentally contaminated shellfish.A major proportion of the water-soluble cadmium and copper in these molluscs is associated with a protein of molecular weight 10 800 daltons. Evidence is presented supporting the similarity of this protein with mammalian metallothionein. This protein contained only a small proportion of the zinc found in the samples.     

Morphological and molecular tools in identifying the Mediterranean limpets Patella caerulea, Patella aspera and Patella rustica

Allozyme electrophoresis, a partial nucleotide sequence of a mitochondrial gene for cytochrome oxidase I (COI) and discriminant analysis of shell morphometric characters were used to study the relationships among the Sicilian marine gastropods of the Patella genus. Allozyme and mtDNA markers unequivocally distinguished the species and were very useful markers in correctly classifying the different species when morphological characters overlapped each other. Several allozyme loci and many nucleotide positions were diagnostic of species. In contrast, the discriminant analysis of simple morphometric shell characters failed to adequately discriminate the species, suggesting that environmental factors influence colouration and morphological patterns in the Patella species. Our results underline the importance of a genetic approach, as compared to a morphological approach, in discriminating the Mediterranean Patella species.     

Duration tenacity: A method for assessing acclimatory capacity of the Antarctic limpet, Nacella concinna

The limpet, Nacella concinna, collected from the Antarctic Peninsula (67°S), was incubated at − 0.3 °C and 2.9 °C for 9 months to test if the previously reported absence of acclimation capacity in Antarctic marine ectotherms could be due to the extended time it takes for them to adjust their physiology to a new stable state. Acclimation was tested through acute measurements of upper lethal limit and a modified measure of tenacity, that tested muscle capacity by measuring the length of time that N. concinna were able to remain attached to the substratum at different temperatures. Both measures acclimated in response to incubation to the higher temperature. Lethal limits were elevated in N. concinna incubated at 2.9 °C (8.1 ± 0.3 °C) compared to those incubated at − 0.3 °C (6.9 ± 0.4 °C). 2.9 °C incubated N. concinna also had a maximum tenacity at 2.1 °C, a higher temperature than the maximum tenacity of those incubated at − 0.3 °C, which occurred at − 1.0 °C. This study is the first to show that the Antarctic limpet can acclimate its physiology, but that it requires a greater period of time for acclimation to occur than previous studies have allowed for.     

A case of germinoma in a limpet (Patella coerulea) (Patellogastropoda)

Germinoma is a gonadal neoplasm originating from progenitor cells in germinal epithelium. Frequently described in some populations of bivalve molluscs, to our knowledge, germinoma has never been reported in gastropods so far. In this paper we describe the histopathological findings of some atypical cellular masses, originating in the undifferentiated germ cell layer in the male gonads of a limpet (Patella coerulea), whose morphological appearance resembled that of a germ cell tumor. The abnormal, and independent growth with no evidence of maturation of the undifferentiated and atypical germ cells, the limited number of follicles involved (n < 10%) and the absence of tissue invasion, supported a diagnosis of Stage 1 germinoma.     

Distribution and population dynamics of the limpet Patella aspera (Lamarck) in Bantry Bay

The population ecology of Patella aspera (Lamarck) was studied as part of an oil pollution baseline study. Contrary to earlier reports, P. aspera appears to be a protandrous hermaphrodite. Maturation of the gonads began in May-June and spawning took place in October. Variations in density, standing crop, and mean size were related to exposure to wave action and tidal level. The low shore in extreme exposure may be designated as the centre of P. aspera's range; abundance is high but biomass and mean size are reduced. Higher on the shore, and in reduced exposure to wave action, P. aspera attains a greater mean size and biomass, but is eventually replaced by P. vulgata L. Two main factors are adduced as being critical to competition between the two species. In terms of tidal level, P. aspera is less tolerant of desiccation than P. vulgata, while in terms of the exposure-shelter gradient, P. aspera appears to have a much less variable growth rate. P. aspera may be defined, therefore, as a non-migratory, low shore, specialist species, highly adapted to a specific set of environmental conditions, but lacking the ability to adapt to others.     

Establishment of the invasive perennial herb Bunias orientalis L.: An experimental approach

A 2-year field experiment was performed to assess regeneration, establishment and growth of the invasive polycarpic perennial Brassicaceae Bunias orientalis L. from transplanted juveniles and propagules (seeds, fruits and root fragments). Further treatments were: different planting depths of the propagules, different root fragment sizes and a varied competition intensity by the matrix vegetation. In contrast to a high number of individuals established from planted juveniles (ca. 90 %), only relatively few propagules gave rise to seedlings or regenerating plants (0–16 %). However, upon emergence, all plants showed low mortality. Although the number of regenerated or recruited plants was affected by all treatments, only one treatment level (the use of very small root fragments of 1 cm length) completely failed in establishing plants. Plants experiencing low competition intensity attained high aboveground performance and reproductive output as well as reproductive success within two growth periods. Under high competition intensity recruitment, regeneration and growth were strongly negatively affected. The high morphological plasticity of rosette growth of B. orientalis seems to be advantageous for persistence in such situations. The results show that young B. orientalis plants are robust and can efficiently sequester and translate elevated resources into rapid growth and early reproductive output although the species is a rather long-lived iteroparous perennial. In addition, population foundation or regeneration can be based on both seeds and root fragments, even when buried under a thick soil layer. This seems to be a very efficient adaption to habitats which are subject to anthropogenic soil perturbations.     

Recognizing biotic breakage of the hard clam, Mercenaria mercenaria caused by the stone crab, Menippe mercenaria: An experimental taphonomic approach

The ability to assign lethal traces left on prey to particular durophagous predators enhances our understanding of predation pressure in the fossil record. To determine whether stone crabs (Menippe mercenaria Say 1818) leave diagnostic traces in the act of feeding on hard clams (Mercenaria mercenaria Linnaeus 1758), live clams were offered to crabs in laboratory aquaria over several months and the fragments produced during predation were examined for diagnostic breakage patterns. These fragments were then compared both macroscopically and using scanning electron microscopy to the fracture patterns produced by tumbling clams in a rock tumbler which simulated breakage during transport in the surf zone, and crushing clams using an Instron which simulated breakage resulting from sediment compaction. Fossil specimens of Mercenaria mercenaria were also examined to determine whether the criteria for recognizing predation traces generated experimentally could be recognized. While not all acts of predation produce diagnostic traces, when larger fragments (greater than 50% shell remaining) are produced during feeding, predatory-diagnostic breakage ranges from 70 to 80%. Macroscopic breakage patterns generated during the predation experiments were also present in fossil specimens. Damage caused by abiotic mechanisms (tumbling and crushing) is highly unlikely to be confused with damage produced by this predator.     

Field reproductive dynamics of the invasive slipper limpet, Crepidula fornicata

At least part of the invasive success of the slipper limpet, Crepidula fornicata, in European waters must be due to reproductive characteristics, yet the events underlying the easily-observed brooding and non-brooding periods have not yet been studied in this species. The reproductive system dynamics were therefore investigated using topological histology and quantitative histological techniques. Specimens were sampled twice monthly for 18 months from Bourgneuf Bay, France, a mid-latitudinal point in the European distribution of C. fornicata. Both the testicles and ovaries showed active and resting phases, corresponding to the brooding and non-brooding periods, respectively. Maximum spermatozoan production corresponds to the female brooding period (female incubation of oviposited eggs, mid-March to late August), and allows males to possess full spermatozoan stocks at the height of fresh mature oocyte availability. The year-round presence of mature oocytes in the female gonad is misleading, since the histological aspect reveals that they are vestigial oocytes which slowly degenerate during the brooding period, possibly providing metabolites for the developing oocytes that become increasingly abundant during this period. A complete scheme of the C. fornicata reproductive cycle is presented, showing the events in the major reproductive organs.The seminal vesicle shows high inter-month variability in sperm presence, suggesting year-round copulation and sperm storage in the seminal receptacle. The seminal receptacle shows a uniform covering of spermatozoa throughout the year, suggesting rapid renewal after fertilization, again in line with multiple copulation throughout the year. Given the limited available space on the seminal epithelium, against which all spermatozoa abut, as well as polyandrous copulation, it is postulated that sperm competition may take place.     

The reproductive response of the protobranch bivalve Yoldia hyperborea to an intermittent influx of phytodetritus. An experimental approach

Yoldia hyperborea (Loven) is a deposit feeder species living in muddy sediments of Conception Bay (Newfoundland, Canada) where it is exposed to a seasonal input of sinking phytoplankton during spring. Data field indicates that this species exhibits an increasing gonad development shortly after the sinking of phytodetritus event, suggesting a close relationship between this food pulse and reproduction. Laboratory experiments carried out with a mixture of laboratory-grown senescent algae Isochrysis galbana, Tetraselmis suecica and Chaetoceros affinis were able to mimic the reproductive response described for Yoldia individuals inhabiting Conception Bay.A dual marker experiment using ¹⁴C and ⁶⁸Ge radiolabelled Thalassiosira nordenskioldii demonstrated that Y. hyperborea fed on T. nordenskioldii and 14C was incorporated into the gonad tissue. Consequently experimental individuals periodically supplied with senescent algae concentrate produced more and larger oocytes than control individuals. These results would help to understand the influence of the sinking phytodetritus in the reproductive activity of Y. hyperborea at Conception Bay.     

Embryogenesis in Najas marina L.: Structural and histochemical approach

In Najas marina L. few polysaccharide grains are observed in zygote, basal cell and embryonal cells until the initiation of embryonic shoot-apex. With the formation of the shoot-apex, numerous polysaccharide grains engorge in the embryonal cells. The basal cell wall, subjacent to the nucellus, stains intensely with PAS (Peiodic Schiff's)-reaction. The concentration of proteins and RNA increases in the basal cell.Interestingly, the embryo shows intraseminal germination. The cells of embryonic shoot-apex, embryonic leaves, root primordium and procambial cells show a few polysaccharide grains while the cells of hypocotyledonary and cotyledonary regions are engorged with polysaccharide (starch) grains. Uniform distribution of proteins and RNA is observed in the embryonic shoot-apex, embryonic-leaves, root primordium and procambium, but the cells of hypocotyledonary and cotyledonary zones exhibit a low profile for these metabolites. The initial root-primordium remains quiescent. Three or 4 epidermal cells, subjacent to this quiescent primordium, differentiate; show densely stained, polarised, protein bands; and act as the future root primordium.The nucleus of the basal cell becomes polyploid and densely stains for proteins, RNA and DNA. At the globular proembryo stage, numerous nucleolar bodies migrate towards the periphery of the nucleus and at the 3-leaf embryo stage, these nucleolar bodies, rich in proteins and RNA, are located in the cytoplasm revealing nucleo-cytoplasmic interaction. The basal cell that never divides, but only enlarges, is persistent in the mature seed.     

Shell form,behaviour, and tolerance to water movement in the limpet Patina pellucida (L.) (Gastropoda: Prosobranchia)

The diotocardian gastropod Patina pellucida (L.) is a macro-herbivore common upon the fronds of laminarian algae. Considerations of shell shape, adhesive tenacity, and current tolerance, together with calculations of expected hydrodynamic drag, indicate that this limpet is effectively streamlined. Smaller individuals are relatively more resistant to dislodgement than are larger ones. Experimental animals of 6.0–13.5 mm shell length resisted constant flows of up to 0.9-1.3 m s^?1. An orientation, in which the longitudinal axis of a limpet is aligned parallel to the direction of the prevailing flow, is induced by currents faster than ≈ 0.5 m s^?1, and is an adaptation to conditions of directional water streaming. P. pellucida appears to show a seasonal change in orientatory preference, individuals tending to point distally with respect to the algal lamina in spring and proximally in autumn: this change may be associated with the annual growth cycle of the host plant.     

An experimental study of the oxygen consumption,growth, and metabolism of the COD (Gadus Morhua L.)

The rate of oxygen consumption of cod in sea water at 12 °C containing MS222 (25 mg/l) can be expressed as: Q_o2 = 0.245 W^0,82(mg/h), where W is the lived weight of the fish (g). The maximum efficiency of conversion of assimilated food into growth was 24% during the feeding experiment. Digestion efficiencies were estimated at over 98% using fillets of plaice as food. The effect of increasing the rate of food intake was to increase liver weight and condition factor. The relative proportions of protein and lipid in the body did not change over the range of feeding levels used. The conversion efficiency had a maximum value at an intermediate feeding rate.     

The effect of Stratiotes aloides L. and nutrients on the growth rate of Lemna minor L.

We tried to find the reasons for frequently observed low biomass of Lemna minor among floating rosettes of Stratiotes aloides as opposed to the abundance of Spirodela polyrhiza in these stands. The effect of S. aloides on L. minor was analysed in outdoor culture experiments. The duckweed collected from among dense stands of the floating form of S. aloides (test sites) showed a significantly lower growth rate than that from stands free of the water soldier (control sites). Water from the latter stands was significantly richer in nitrate-nitrogen and ammonium-nitrogen, but not in soluble reactive phosphorus suggesting possible nutrient depletion as a reason for observed differences. Growth rates of L. minor were indeed significantly correlated with in situ concentrations of all dissolved nutrients and showed saturation at around 0.18 mg N-NH₄ dm⁻³ and 0.05 mg SRP dm⁻³ above which the growth rates did not increase significantly. We used stepwise regression to test the combined effect of nutrients and the presence/absence of S. aloides on the growth rate of L. minor. The regression showed a negligible effect of ammonium ions and nitrates on the growth rate of the duckweed. At low concentrations of soluble reactive phosphorus the presence of both the S. aloides and SRP concentrations significantly affected the growth of L. minor. Above saturating SRP concentrations none of the two effects was significant. Results of our experiments seem to suggest that the presence of S. aloides exerts a negative effect on the growth of L. minor only at low concentrations of soluble phosphorus. Since the depletion of nutrients in water by the floating form of S. aloides is unlikely, we point to S. polyrhiza as a superior competitor for nutrients and suggest a possible allelopathic effect of the water soldier on L. minor.     

Cold,freezing, and desiccation tolerance of the limpet Acmaea digitalis (Eschscholtz)

Cold, freezing, and desiccation tolerance were examined in the limpet, Acmaea digitalis (Eschscholtz). Fifty percent of the experimental population survived freezing at temperatures between ?10 ° and ?12 °C for at least 24 hr. In this temperature range, 60–80 % of the body water was frozen. The LD₅₀ for water loss by desiccation was 76.5% ± 1.3_δ. At 70–80% body water loss, solutes were concentrated between 350 and 500%. Some limpets failed to survive immersion in 450% seawater for 6 hr (100% scawater = salinity of 31‰), suggesting that much of the damage from freezing and desiccation was from an increased solute concentration. No glycerol could be detected in extracts of the foot and the visceral mass of A. digitalis during winter, confirming similar results in studies carried out on other intertidal molluscs.     

Mechanisms and consequences of competition between an alien mussel, Mytilus galloprovincialis, and an indigenous limpet, Scutellastra argenvillei

The influence of an alien mussel Mytilus galloprovincialis (Lamarck) on an indigenous limpet Scutellastra argenvillei (Krauss) was investigated on the west coast of South Africa by comparing four situations in which limpets occupied rock patches surrounded by mussels: (1) ‘established patches’ of high-density adult limpets; (2) ‘experimentally cleared patches’ from which mussels were manually removed; (3) ‘naturally disturbed patches’ where mussels had been eliminated by wave action; and (4) ‘half-density’ patches formed by thinning established patches. Limpets in established patches were most effective in retarding settlement and lateral invasion by mussels, but all patches shrank due to mussel encroachment. As patches shrank, limpet density fell in established and naturally disturbed patches due to emigration. Limpets living on mussel beds were small, sparse and never achieved sexual maturity; 60% shifted to rock, whereas only 7% moved from rock to mussels. The limpets showed highest fidelity to established patches (79% after 12 months) and lowest fidelity in naturally disturbed patches (20%). Thinning of established patches reduced fidelity to 26%. Mussel beds did not provide a suitable alternative substratum for S. argenvillei after they displaced the limpets from rocks. Moreover, elimination of mussels by waves failed to allow S. argenvillei to re-establish dense, adult populations resembling those prior to arrival of the mussel. Adults of S. argenvillei feed collectively by trapping kelp blades. On the topographically complex mussel beds limpets cannot feed this way. In sum, on exposed shores where M. galloprovincialis achieves maximal recruitment and growth, S. argenvillei is incapable of preventing mussel encroachment and is likely to become completely displaced. Semi-exposed shores do, however, offer a refuge preventing global extinction of the limpet.