TEMPORAL VARIATION IN FORAGING BEHAVIOUR OF PATELLA GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA CONCINNA (BASOMMATOPHORA) ON A SOUTH AFRICAN SHORE

Foraging activity of two mid- to low- shore species of limpet,Patella granulans (Prosobranchia) and Siphonaria concinna (Pulmonata)from an exposed shore on the Eastern Cape coast of South Africawas monitored. In both species, activity was compared duringspring and neap tides and, in P. granularis between summer andwinter. Rhythms of activity of the two species were similar,with foraging excursions being mainly associated with nocturnallow tide times, although some P. granularis foraged during daytimelow tides. It is suggested that foraging excursions in P. granularisare triggered by wave action. Both species foraged further onspring tides than on neap tides and this is suggested to bea result of the limited time limpets have to forage. P. granulariswas also found to forage further during summer when comparedto winter and the possibility that seasonal micro-algal productivityinfluences foraging distances in limpets is discussed. The foraging activity of both species could be divided into3 distinct phases, a relatively rapid outward phase, a muchslower foraging phase and a rapid homeward phase. Whether ornot these limpets graze throughout an excursion is not known.S. concinna was found to home to a fixed scar, although duringthe experiment some scar-swapping occurred. P. granularis didnot home to a fixed scar but possessed a ‘home range’(approx. 5 cm²) to which it returned after each excursion. Patella granularis was found to move randomly during foraging,whilst S. concinna foraged in a non-random direction -whichtook individuals upshore. No tidal-influence is thought to bepresent in this case and the possibility of a learning componentin the foraging behaviour of certain limpet species in relationto the return to optimal feeding patches is discussed. (Received 18 May 1996; accepted 2 September 1996)     

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)     

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.     

Size at sex change and reproductive cycle of the limpets Patella vulgata and Patella ulyssiponensis (Mollusca: Patellogastropoda) from intertidal rocky shores of the Algarve coast (southern Portugal)

ABSTRACT

This study describes the reproductive cycle of the common limpet (Patella vulgata) and rough limpet (Patella ulyssiponensis) from the Algarve coast (southern Portugal). Individuals of both species were sampled monthly during two consecutive years, and subjected to gonad histology and calculation of the mean gonadal index (GI). Both species had balanced sex ratios (P. vulgata = 1M: 0.98F; P. ulyssiponensis = 1M: 1.03F), similar size-frequency distribution between sexes, and equivalent mean shell lengths (SL) and total weights (TW) between males and females. In these protandrous hermaphrodites, the estimated size at sex change was slightly smaller in P. vulgata (SL₅₀ ≈ 29 mm) than in P. ulyssiponensis (SL₅₀ ≈ 36 mm). The reproductive cycles of both species were characterised by a main spawning season in early spring to early summer, sometimes including subsidiary spawning events. A comparison of the main spawning season throughout the species distributional ranges revealed that populations of P. vulgata and P. ulyssiponensis from southern Portugal have later spawning periods than other populations from the northeastern Atlantic Ocean. The present information is relevant for conservation purposes and for the proposal of management measures for the harvesting activity targeting P. vulgata and P. ulyssiponensis in southern Portugal.     

Aerial and underwater metabolism of <Emphasis Type="Italic">Patella vulgata</Emphasis> L.: comparison of three intertidal levels

Intertidal molluscs are known to possess specific respiratory organs that permit aerial breathing during emersion. Patella vulgata is a widely distributed intertidal species found from low-water spring tide to high-water neap tidal level. In order to determine metabolic adaptations to habitat, carbon fluxes associated with respiration and calcification of P. vulgata living at high-shore, middle-shore and low-shore levels were compared. Seasonal aerial respiration was measured using an infrared gas analyser; seasonal underwater respiration and calcification were calculated from dissolved inorganic carbon and total alkalinity. P. vulgata showed net CaCO₃ deposition at all seasons, although the high-shore level limpet annual calcification rate was relatively low due to longer air exposure. Both aerial and underwater respiration rates were highly correlated with seasonal temperature variations and followed the vertical shore gradient, with stronger fluxes for low-shore tidal level limpets and lower fluxes for high-shore level limpets that must limit energy expenditure. P. vulgata appears to be well adapted to aerial exposure, with average hourly respiration fluxes stronger in air than in water. This study demonstrates that P. vulgata calcification and respiration are reduced in upper shore levels and are important factors determining the upper distribution limit of the species.     

AN ULTRASTRUCTURAL STUDY OF GAMETES AND FERTILIZATION IN PATELLA VULGATA L.

Gametes of Patella vulgata L. have been studied using electronmicroscopy and their ultrastructure described. Changes in ultrastructureoccurring during and after fertilization have been characterized,especially those occurring in the cortical region. These changesinclude appearance of Golgi bodies, mitochondria and agglomerationsof microtubular material. Cortical granules disappear and glycogengranules begin to be degraded. (Received 13 February 1984;     

FACTORS GOVERNING PATTERNS OF FORAGING ACTIVITY IN LITTORAL MARINE HERBIVOROUS MOLLUSCS

Relationships of feeding activity to tidal and day/night cyclesin a variety of littoral herbivorous molluscs are reviewed.Most species are active while submerged by the tide, both byday and night. There are also many that are active only whileemersed, with variation in relation to day/night cycles dependentupon micro-habitat. The third pattern is for activity to occurwhile awash by the tide, often with continued feeding whilethe rocks remain damp. Most species in these three groups haveendogenous rhythms. The fourth type is one with no relationto tidal activity, and is confined to supra-littoral and sub-littoralspecies. Major proposed causes of the evolution of these patterns are:desiccation, together with osmotic and thermal stress whichmay have selected for nocturnal activity; dislodgement by waves;and predation by aquatic carnivores, which is often avoidedby feeding at low tide. Of these desiccation and predation arewidely regarded as most important. A study of Patella vulgata suggests that while predation anddesiccation are major factors controlling activity patterns,they do not fully explain observed activity. A discussion ofthe importance of food supply is given, and it is proposed thatwhere competition for food is low, night-time feeding shouldpredominate; where competition is high, day-time feeding shouldpredominate. This pattern fits observations on limpets at LoughHyne, but needs testing in other field situations.     

Feast or famine for intertidal grazing molluscs: a mis-match between seasonal variations in grazing intensity and the abundance of microbial resources

Distinct seasonal variations in the abundance of photosynthetic microbiota and limpet grazing intensity were recorded at Port St Mary, Isle of Man between January 1994 and June 1996. Microbial abundance was negatively correlated with insolation stress, while grazing intensity was positively correlated with sea and air temperature. These patterns result in a mis-match between the supply of and the demand for microbial resources with maximal grazing intensity during the summer and autumn, but maximal microbial standing stock during the winter and early spring. The importance of top-down control of microbial assemblages by grazing was demonstrated by experimental exclusion of limpets during autumn 1993. This resulted in a four-fold increase in the abundance of cyanobacteria within 6 days, followed by a more gradual proliferation of ephemeral algae during the next 4 weeks. The abundance of diatoms remained relatively constant and was not influenced by the removal of grazers at this time of year. The influence of microbial resource availability on the growth and mortality of limpets was examined using experimental enclosures of differing densities of either Patella vulgata or P. depressa. After 6 months, there were significant relationships between grazer density and both mortality and growth with increased mortality and reduced growth for P. vulgata at increased densities, and reduced growth for P. depressa at increased densities. Hence, the availability of microbial resources may also influence the biomass of grazers on rocky shores from the bottom upwards. A conceptual model is presented which describes seasonal and annual variations in microbial resources and grazing intensity and their potential consequences for other shore dwellers.     

Competition and habitat suitability: small-scale segregation underpins large-scale coexistence of key species on temperate rocky shores

Identifying the mechanisms that underpin species richness is one of the central issues of community ecology. On rocky shores in north-western Europe, two key limpet species coexist on the mid- and low shore but are segregated at small scales with respect to habitat. Short-term and long-term experiments were done to test whether habitat suitability or habitat-specific competition drives the small-scale segregation of these species and therefore underpins their coexistence at larger spatial scales. In a controlled short-term experiment, Patella vulgata was transplanted onto open rock and into pools that either contained Patella ulyssiponensis and/or their mucus or from which P. ulyssiponensis and/or their mucus had been removed. After 2 days, P. vulgata remained in all experimental plots in similar numbers irrespective of treatment indicating that there was no negative response to P. ulyssiponensis, mucus or the pool habitat. In a long-term experiment, cage enclosures containing both species were set up in pools and on open rock over a 6-month period. P. vulgata grew equally well on both open rock and in pools but suffered higher mortality in pools. P. ulyssiponensis showed lower growth rate and higher mortality on open rock than in pools. P. ulyssiponensis exhibited increased growth in higher intraspecific densities on open rock and reduced growth in higher intraspecific densities in pools, indicating some degree of intraspecific facilitation on open rock and intraspecific competition in pools. There was no evidence of interspecific competition either in the short term or in the long term. Results revealed that habitat suitability was the mechanism causing segregation of these species at smaller spatial scales enabling them to coexist at larger spatial scales. Conflicting results in the short-term and long-term experiments highlight the importance of considering the correct temporal extent for experimental tests of hypotheses.     

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.     

Effects of grazer identity on the probability of escapes by a canopy-forming macroalga

Through their grazing activities limpets have an important role in controlling macroalgal abundance and as a result the structure and dynamics of rocky shore assemblages. Using two congeneric limpet species, with different biogeographic distributions, and whose ranges are expected to alter with climatic warming, we separated the magnitude of their grazing activity over time and the subsequent consequence for macroalgal growth.The northern/boreal limpet, Patella vulgata (L.), consistently grazed more than the southern/lusitanian limpet, P. depressa (Pennant), particularly during spring and summer when P. depressa was reproductively active. Individuals of Fucus vesiculosus (L.) that settled during this time were able to grow to a size where they escaped the grazing activities of P. depressa, resulting in mature F. vesiculosus being present in all P. depressa treatments. In contrast, P. vulgata, which was not reproductively active during this period, exhibited no reduction in its grazing activity and prevented macroalgae from growing in experimental treatments. It therefore appears that P. vulgata has a stronger role, than P. depressa, in controlling macroalgal abundance on shores of southwest Britain.We present a conceptual model highlighting the direct and indirect interactions between these two limpet species and F. vesiculosis. If as predicted, under current warming scenarios, P. depressa becomes the dominant limpet on shores of southwest Britain there will be subsequent changes in rocky shore community structure and ecosystem functioning. Our research emphasises that even closely related species with similar ecological niches can exhibit different behaviours that fundamentally alter their biological interactions with other organisms leading to idiosyncratic responses to predicted changes in climate.     

Grazing dynamics in intertidal rockpools: Connectivity of microhabitats

Differences between rockpool and emergent rock communities are often attributed to their contrasting physical conditions. However, differences in grazing pressure between rockpools and open rock could also exert an important structuring role. Greater densities and/or the lack of tidal constraints on foraging may allow grazing intensity to be greater in rockpools. Here, wax discs were deployed to compare grazing intensity between rockpool and emergent rock habitats at each of three tidal heights on a moderately exposed shore in SW England. Grazing intensity was then examined in relation to herbivore density. Grazing intensity in pools was twice that on emergent rock, despite a lower density of herbivores in the rockpools. Of these herbivores, patellid limpets are the dominant grazers on rocky shores throughout the NE Atlantic and are recognised to have a major role in structuring intertidal communities. Thus, subsequent experiments focussed on the influence of limpets in determining the differences in consumer pressure between rockpools and emergent rock. Three alternative explanations were considered: (1) the effect of continuous immersion on grazing intensity in rockpools; (2) differences in limpet species abundance between the two habitats; (3) movement of limpets from emergent rock into pools to feed. The level of grazing pressure exerted by Patella ulyssiponensis (Gmelin), the predominant species living constantly immersed in rockpools, was similar to that of P. vulgata (Linnaeus) which is predominantly found on emergent rock. P. vulgata were observed moving from emergent rock into rockpools during high tide. Manipulative experiments confirmed that these foraging excursions resulted in a 2-fold increase in grazing intensity in the pools. Grazing activity of P. vulgata in rockpools was not consistent between sites and may be influenced by differences in wave exposure and/or the abundance of microbial resources. Elevated consumer pressure in rockpools may be an important factor influencing algal assemblages and probably explains the predominance of grazer resistant-species in these pools.     

COMPARISON OF THE STRUCTURE OF THE PALLIAL TENTACLES OF SEVEN SPECIES OF SOUTH AFRICAN PATELLID LIMPET

The ultrastructure of the pallial tentacles of seven speciesof patellid limpet is described. The tip of most of the tentaclesexamined bears a crown of long cilia, whereas the shaft of thetentacles has small tufts (5–10 µm diameter) ofshorter cilia. Sections through the ciliated tufts show themto be composed of several cells, each bearing cilia. The ciliacontain 5–7 central microtubules and therefore do nothave the conventional 9 + 2 arrangement of microtubules. Nerveprocesses run from the base of each ciliated cell to a nervebundle in the centre of the tentacle, suggesting a sensory function.Estimates of densities of ciliated tufts suggest that the territoriallimpets (Patella cochlear and P. longicosta) have the greaternumber of tufts. Electron dense plate-like structures are foundin the centre of the pallial tentacles of Patella cochlear,P. longicosta, P. granularis, P. barbara and Helcion pruinosus.Each plate is about 0.2 µm wide and is surrounded by adouble membrane. It is suggested that these may play a rolein scattering or reflecting light and thus form part of thedermal light sensing ability of these animals. (Received 26 January 1987;     

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.     

Heimfindevermögen und Ortstreue bei Patella L. (Gastropoda,Prosobranchia)

Summary It is known that numerous gastropods show homing ability. Many limpets return to well defined sites. Patella L. acquires a home spot also on the smooth glass surfaces of aquarium. Before leaving, the limpet scrapes its home, particularly the anterior part of the footprint. After each return it makes characteristic movements with its shell.When homing Patella nearly always retraces its outward track, at least in part; sometimes it reaches its home over the shortest route possible.Site and tracks are marked by chemical substances. The animal orientates itself by contact chemoreception on the track and by distance chemoreception when near its home. Apparently there also exists a kinesthetic mechanism of orientation based on a measurement of distance on the outward journey.At the home spot Patella always manoeuveres exactly into the same position. Often it has to turn or to glide around slightly. It finally settles down with small movements of its shell.The footprint shows chemical differences in a wide marginal zone. Probably, different chemoreceptors on the sole of the foot are associated to the various regions of the footprint.The chemical differentiation of the footprint has the same orientation-value for all individuals of the same size group. In addition there exists an individual marking, shown e.g. by avoidance reactions of alien animals.The individual specificity of the foot's secretum is particularly marked on the tracks, for each Patella follows its own trail only and thus normally reaches its own home. On an uneven substratum this is the only place where the margin of its shell fits the ground exactly.For establishing a home site and keeping to it, several environmental conditions have to be met. Patella settles only on surfaces overgrown with small algae. In an aquarium it favours the sides most exposed to light. On vertical walls the animal is gravity-oriented. Most limpets are attached head-end down. Patella is able to perceive the distance from the water-line, and may orient itself with respect to fixed objects in the aquarium by means of a Ferntastsinn. When first choosing a home spot on an uneven substratum, the limpet often adjusts its position by turning movements, so that the contacts between shell and ground are as close as possible. Selective growth at the shell's margin then results in a perfect fit to the irregularities of the ground.All prerequisites for the establishment of a home site are also determining the animal's keeping to its home. If changes are introduced with respect to the fitting of the shell to the ground, to the position of neighbouring objects, to water-level, light, or direction of gravity, the animal may leave its home site and reorient itself in an equivalent new one. The attractiveness of the chemical markings of the old site nevertheless compete with all these conditions for some time.Rest and activity are controlled by light-dark and tidal cycles. — Inter-and intraspecific differences were obtained under experimental conditions. Almost all individuals were preferentially active in darkness. P. caerulea moved at high tide; P. vulgata was active either at low tide only, or both at high and low tide, or — rarely—at high tide only. All animals reacting to tidal rhythms were synchronized even by unnaturally frequent changes in the water-level. The tidal dependence of the activity of individual P. vulgata may perhaps be interpreted as the persistence of an adaptation to drought and submergence acquired at the original habitat. The reactive ability towards high and low tide can be modified. The activity-phase may be stopped prematurely by changing light or tidal conditions. Animals keeping constantly to their homes returned to them at once, whereas others — having no defined home —generally prolonged their excursions. When light and water-level are kept constant the locomotory activity of P. vulgata and P. caerulea has the characteristics of an endogenous tidal rhythm. Changes in water-level soon approximately catch the freerunning periodicity, alteration of light and darkness synchronize it less readily but more precisely.     

RELATIONSHIPS BETWEEN PATELLA FERRUGINEA GMELIN, 1791 AND THE OTHER TYRRHENIAN SPECIES OF PATELLA (GASTROPODA: PATELLIDAE)

The external morphology of soft parts of the rare Patella ferrugineaGmelin, 1791 is described, and its relationships with P. caerulea,P. rustica and P. ulys-siponensis are investigated on both morphologicaland electrophoretic grounds. Soft part morphology is a gooddiscriminative tool, but of little help in detecting affinities.Electrophoretic data on 19 presumptive loci suggest that P.rustica is the closest species to P. ferruginea, whereas P.caerulea and P. ulyssiponensis are clustered separately. Meanobserved heterozyg-osities arc higher in P. ferruginea and P.rustica. It is concluded that in case of subdivision of thegenus Patella L., 1758, P. ferruginea and P. rustica shouldbe placed together in the subgenus Patellastra Mon-terosato,1884. (Received 6 January 1993; accepted 23 February 1993)     

Phenological changes in intertidal con‐specific gastropods in response to climate warming

There is substantial evidence from terrestrial and freshwater systems of species responding to climate change through changes in their phenology. In the marine environment, however, there is less evidence. Using historic (1946–1949) and contemporary (2003–2007) data, collected from rocky shores of south‐west Britain, we investigated the affect of recent climate warming on the reproductive phenology of two con‐specific intertidal limpet grazers, with cool/boreal and warm/lusitanian centres of distribution. Reproductive development in the southern limpet, Patella depressa, has advanced, on average, 10.2 days per decade since the 1940s, with a longer reproductive season and more of the population reproductively active. The peak in the proportion of the population in advanced stages of gonad development was positively correlated with sea surface temperature (SST) in late spring/early summer, which has increased between the 1940s and 2000s. The advance in peak reproductive development of this species is double the average observed for terrestrial and freshwater systems and indicates, along with other studies, that marine species may be responding faster to climate warming. In contrast, the northern limpet, Patella vulgata, has experienced a delay in the timing of its reproductive development (on average 3.3 days per decade), as well as an increase in reproductive failure years and a reduction in the proportion of the population reaching advanced gonad stages. These results are the first to demonstrate a delay in the reproductive development of a cool‐temperate, winter spawner, towards cooler more favourable environmental conditions in response to climate warming. Such a delay in spawning will potentially lead to trophic miss‐matches, resulting in a rapid nonlinear decline of this species.     

Phylogeny and phylogeography of the genus Patella based on mitochondrial DNA sequence data

Although some molecular phylogenies of Patella species have been published in recent years, unresolved questions concerning the phylogeny and taxonomy of this genus still remain. We sequenced the mitochondrial genes cytochrome c oxidase subunit I, 12S rRNA and 16S rRNA for all Patella species (Patella vulgata, Patella depressa, Patella candei, Patella caerulea, Patella lugubris, Patella ferruginea, Patella pellucida and the continental and Macaronesian forms of Patella ulyssiponensis and Patella rustica) and Cymbula safiana. Our results revealed the occurrence of five strongly supported clades, although relationships between these are not well supported. According to our data P. vulgata is a genetically distinct lineage and the close phylogenetic relationship between this species and P. depressa, found in previous mitochondrial DNA studies, is not supported. The Mediterranean Sea and the Macaronesian Islands seem to have played an important role in the speciation and diversification of this genus, although different clades show different phylogeographic patterns. Our dataset point to the necessity of a taxonomic revision, as P. candei is paraphyletic relative to P. lugubris.     

SPATIAL VARIATION IN THE FAUNA ASSOCIATED WITH MYTILUS EDULIS ON A WAVE-EXPOSED ROCKY SHORE

The fauna associated with Mytilus edulis at a rocky wave-exposedlocality in North Wales is reported. A total of fifty-nine taxawith representatives from most of the main invertebrate phylawas recorded. In terms of species richness the community wasdominated by crustaceans (25 taxa), molluscs (10 taxa) and cheliceratearthropods (9 taxa), mainly mites. Fora-miniferans and crustaceanswere the most abundant taxa, representing 25% and 23% of thetotal associated fauna respectively. Nemerteans and nema-todeswere also well represented. The mussel bed was broadly stratifiedinto three distinct layers each dominated by a single species.Thus, the foramini-feran Ammonia batavus was restricted to thesediment in the bottom layer, the barnacle Semibalanus balanoidesoccurred only on the outer exposed surfaces of the mussel shells,whilst the tiny brooding bivalve, Lasaea rubra, nestled mainlyamongst the complex matrix of byssal threads and shell fragmentsin the middle layer of the bed. Species richness and diversitydecreased systematically with tidal elevation and both theseindices were also signifocantly depressed amongst mussel communitiesfrom high-shore tide pools. Inclination of the rock surfacehad little or no effect on the mussel populations or their associatedfauna. Small mussel patches generally supported fewer taxa perunit area and had a lower diversity than larger, more extensivepatches. These marked, small-scale spatial variations exhibitedby the fauna associated with M. edulis appear to be relatedlargely to the degree of aerial and tidal exposure, mussel density,the amount of accumulated sediment and mussel patch size. (Received 2 August 1993; accepted 8 November 1993)     

A FIELD TECHNIQUE FOR RECORDING THE ACTIVITY OF LIMPETS

A field technique for recording both temporal and spatial parametersof activity in limpets was tested on a Tyrrhenian populationof Patella rustica Linnaeus which shows definite homing behaviour.Timing of foraging excursions was recorded using reed switchesactivated by a magnet glued to the shell apex. The ‘lsquo;athome-away’ status of each animal was continuously screenedthroughout one month by interfacing the sensors with a computer.Moreover, individual excursions were minutely reconstructedby using a moto-graphic technique which combined LED-tracking(nocturnal activity) and instantaneous photography (daytimemovements). An original wave-meter was designed to monitor thesea-status during the study period. The quality of the temporaland spatial data obtained with this technique is evaluated,and further improvements of the technique are discussed. (Received 24 October 1989; accepted 25 January 1990)