Small-scale spatial and seasonal differences in the distribution of beach arthropods on the northwestern Tunisian coast. Are species evenly distributed along the shore?

Spatial distributions of sand beach arthropods were studied at Zouara (Nefza), a beach dune system along the northwestern coast of Tunisia. Two transects with pitfall traps, perpendicular to the shoreline and placed from sea towards land, captured spontaneously crawling arthropods. The pitfalls were used to obtain data on horizontal zonations for 2 days during different seasons (April, October). In April, in order to assess local, long-shore distributions of surface-active beach invertebrates, ten transects with pitfall traps were placed every 100 m, for 2 days. Core samples were also taken in correspondence with each of the ten transects to obtain the distribution of burrowing individuals. Sand samples were taken for successive laboratory analyses (salinity, grain size and organic contents). Local climatic conditions were also recorded. One isopod (Tylos europaeus, subdivided into three different size classes), two amphipods (Talitrus saltator, Talorchestia brito and indistinguishable juveniles) and four coleopteran species (Eurynebria complanata, Scarites laevigatus, Phytosus nigriventris, Phaleria acuminata) were considered. Mean zonations perpendicular to the shoreline showed that crustaceans were found closer to the sea-line limits than coleopterans and that between seasons some species changed their mean zonation more than others. Local, long-shore distributions of active and burrowing individuals showed that most species were unevenly distributed along the shore. These discontinuous distributions differed according to the species and age class and were mainly related to specific microclimatic conditions and to nutrition.     

Orientation of sandhoppers at different points along a dynamic shoreline in southern Tuscany

Orientation experiments were carried out on Talitrus saltator (Crustacea Amphipoda) at four points along 3 km on a dynamic sandy beach inside the Maremma Regional Park (Grosseto, Italy) to highlight behavioural variation related to distance from a river mouth, to erosion or accretion of shoreline, and to human trampling on the beach. Tests were performed using circular transparent Plexiglas arenas, contemporaneously at the four points. Replicates were made in 2 different months (September 2002 and May 2003), on 2–3 successive days, in the morning and afternoon. The distributions of the angles of orientation were compared for the different points and seasons, and multiple regression analysis was performed to test the effects of environmental and intrinsic variables on orientation. Sandhoppers showed the highest scatter at the eroded shoreline, intermediate scatter at the accreting beach most distant from the river mouth, and consistent orientation seaward at the least disturbed point. Orientation of sandhoppers was significantly affected by season, global radiation, time of day, distance from the river mouth, and human trampling. Sex and air humidity were of minor significance in the multiple regression model. The results, on the one hand, confirm plasticity in orientation of sandhoppers living on a dynamic shoreline, and on the other hand, show that variation in orientation could potentially be used as a bioindicator of shoreline changes.Communicated by R. Cattanevo-Vietti, Genova     

Behavioural adaptations to zonal maintenance of five species of tenebrionids living along a Tyrrhenian sandy shore

The spatial distribution of the following five nocturnal tenebrionid species was studied along a beach dune system: Phaleria provincialis Fauvel, Phaleria bimaculata Linnaeus, Halammobia pellucida Herbst, Xanthomus pallidus Curtis and Xanthomus pellucidus Mulsant. An integrated system of traps was used to sample the beetles during their active and resting phases. Environmental parameters were recorded locally during the experiments. Preference experiments were performed under controlled laboratory conditions. The aim of the study was to understand the environmental constraints influencing the species' spatial distribution and the mechanisms involved in zonal maintenance. The results indicate that beetles exploit chemical and physical gradients of the beach dune system; and the mechanisms used for zonal recovery and/or maintenance are based on behavioural responses to visual and environmental stimuli. Controlled laboratory experiments showed that sand salinity was a limiting factor for all five species. For the two Phaleria species, which had a relatively seaward distribution, sand moistures were also important. In contrast, for the two Xanthomus species, which were distributed more landwards, grain size was a regulating factor. In the present study gradients in beetle responses to different environmental factors were observed. Received: 16 October 1997 / Accepted: 23 November 1998     

Solar and landscape cues as orientation mechanisms in the beach-dwelling beetle Eurynebria complanata (Coleoptera,Carabidae)

The present paper reports on the first orientation experiments conducted on the strand-living beetle Eurynebria complanata (Linnaeus, 1767) (Coleoptera, Carabidae). The experiments were carried out from June to October 1988. Two different populations were used: one inhabiting a Tyrrhenian beach in Italy and the other a beach on the Atlantic coast of France. Response to sun compass cues was demonstrated in each population at the collection site and for the French population after transportation to Italy, where experiments were carried out on a differently oriented beach. Landscape cues were shown to improve the beetle's orientation capacity when these were tested together with a visible sun. Artificial landscapes were also tested under laboratory conditions. Different-sized silhouettes were placed in the four cardinal directions, and these envoked different responses depending on their height. The beetles oriented towards a black silhouette when this subtended an angle of 25°. The results obtained for the two populations are compared and discussed from an eco-ethological point of view.     

Temporal and spatial use of stranded wrack by the macrofauna of a tropical sandy beach

During two field studies the macrofauna associated with wrack stranded on a tropical sandy shore was analysed. During the first period all animals present in small wrack deposits were randomly collected with cores. During the second field study active animals were sampled in larger wrack deposits for an entire lunar period, and tube traps were used. After a comparison between the two studies, only the data from the tube traps were examined from a temporal and spatial point of view. The aim of the present work was to gain information on how, when and where wrack was colonised by invertebrates, keeping in mind cyclical aspects such as lunar, diel and tidal phases. Predatory taxa, such as Staphylinoidea and the amphipods Talorchestia martensii, were most abundant, whereas Diptera larvae and Tenebrionidae were scarce. Successional changes of beach wrack colonisation were evident throughout a semi-lunar period, with molluscs invading wrack during the first days of deposition and histerids during the last ones. Strictly nocturnal or diurnal surface-active species were found to be active in the wrack during both the day and the night. The analysis of the tidal component of species activity in the wrack showed that some species moved at ebbing tide, and others moved at rising tide. Differences were found also in the mean hours of tidal activity, calculated separately during day and night periods. The study of the zonation of each species showed that in some cases wrack deposits were closely followed by the fauna as their position changed during the semi-lunar phase. In other cases differences occurred between species zonation during day and night periods and tidal phases. Cluster analysis indicates that most species exploit the wrack in different ways (as refuges and/or feeding site), both in space and in time. Received: 11 July 1999 / Accepted: 20 January 2000     

Environmental factors influencing the surface activity and zonation of Tylos europaeus (Crustacea: Oniscidea) on a Tyrrhenian sandy beach

The present study considers a population of Tylos europaeus Arcangeli, 1938 living on a Tyrrhenian sandy beach (Burano, GR, Italy). Monthly surveys were carried out between April 1986 and March 1987 with directional pitfall traps so as to intercept the isopods moving in four directions on the beach surface. In addition a bimonthly study was performed from March 1991 to January 1992 using two methods of capture: pitfall traps joined by 10-cm high strips of fibreglas for surface-active individuals and sieving for those burrowed in the sand. Capture frequencies allowed analysis of annual abundance, daily activity and zonation of juveniles and male and female adults. Variations of these spatio-temporal data were correlated by means of multiple regression with many environmental parameters: temperature and relative humidity of the air and sand, evaporation, wind direction and speed, global radiation, atmospheric pressure, rainfall, the sand salinity and granulometric parameters. T. europaeus was found to be mainly active in summer and autumn and during the night, and was zoned along the eulittoral. The surface activity was influenced by almost all the environmental factors when they were limiting but especially by the relative humidity of the air. The mean zonation of active specimens, however, varied hourly according to the sand temperature. On the other hand, the zonation of the buried individuals depended on the mean grain size, which involves many other parameters, such as moisture and oxygen contents.     

Distribution patterns of different age classes and sexes in a Tyrrhenian population of <Emphasis Type="Italic">Talitrus saltator</Emphasis> (Montagu)

Temporal and spatial distribution patterns of a population of Talitrus saltator living on the Tyrrhenian coast of Tuscany (Italy) were studied. Bimonthly surveys were performed from March 1991 to January 1992 along transects using a standard system of pitfall traps and sieves for surface-active and burrowed individuals, respectively. Captured individuals were subdivided into sex and age classes (on the basis of the number of articles of the flagellum of the second antenna). Abundances were calculated for each sampling period and sex ratios were determined. For each sampling period the mean hour of surface activity was calculated together with the mean zonation of both surface-active and burrowing sandhoppers belonging to the different sex and age classes. Shifts in mean zonation between the resting and active phase were also determined. For each category of sex, age, and reproductive phase, simple and multiple regression analyses were used to find relationships of the mean zonation of surface-active animals with climatic data, and of the number of burrowed individuals with surface sand parameters recorded in correspondence to the sieves. On the whole, the results show that this Tyrrhenian population of T. saltator exhibited a bivoltine reproductive cycle and that the sex ratios of active sandhoppers were male or female biased according to the season. The variations in the mean hour of surface activity and in the zonation patterns of sandhoppers depended more on the age than on the sex. Furthermore distribution patterns were generally related to seasonal changes in the local climatic and substrate parameters. The observed differences between burrowing and activity zonations were interpreted on the basis of the nocturnal migrations of the different categories.     

Multiple regression analysis of the sources of variation in orientation of two sympatric sandhoppers, <Emphasis Type="Italic">Talitrus saltator</Emphasis> and <Emphasis Type="Italic">Talorchestia brito</Emphasis>, from an exposed Mediterranean beach

Two sympatric species from an exposed sandy beach in north-western Tunisia, the sandhoppers Talitrus saltator (Montagu) and Talorchestia brito Stebbing, were compared as regards orientation under natural conditions. Sets of experiments were carried out on the beach using two experimental arenas, one permitting the view of both the sky and landscape and the other of the sky only. Replicates were made at different hours of the day, in different days and period of the year and with various climatic conditions. Multiple regression models were fitted to the angular data obtained. These models allow an estimate of the trends of variation depending on a combination of factors. The simultaneous effects of environmental factors influencing orientation were quantified for each species. The sun was confirmed as the major orientation cue in these populations, but the concentration of directional choices was enhanced by the landscape vision. The climatic factors affected orientation in different ways depending on the time of day and year. When the two species were compared, Talitrus saltator showed a higher flexibility of response than Talorchestia brito under the same environmental conditions, supporting the hypothesis of a higher level of terrestrialization of the former species.     

Spatial and temporal strategies in the surface activity of some sandy beach arthropods living along the French Atlantic Coast

During a field study on the eco-ethology of sandy beach arthropods conducted along the French Atlantic Coast it emerged thatTylos europaeus, Phaleria cadaverina andLabidura riparia were among the most abundant species that lived in the eulittoral. Tetradirectional pitfall traps, placed from the base of the dune to the tidal limits, were used. The traps intercepted surface-active arthropods, and the number of traps varied according to the levels of the tides. Data were recorded hourly during two periods corresponding to a spring tide and the following neap tide. At the saine time the most important environmental parameters were registered each hour. The results indicate that all three species show prevalently nocturnal surface activities. ForT. europaeus andPh. cadaverina an influence of the synodic and tidal phases was found on the zonation of the surface activity and on the extent of movement. The latter was due to the greater or smaller distances that the isopods and tenebrionids had to move from the diurnal burrowing sites to the foraging zones. ForL. riparia no variations in the total mean zonations were found between the two synodic phases, and only at neap tide were seaward, followed by landward movements found. Multiple regression analysis showed that the environmental parameters registered in this period were never limiting, as threshold values in this case probably were not reached.     

Surface activity,zonation and migrations of Talitrus saltator on a Mediterranean beach

The present study considers a population of Talitrus saltator (Montagu, 1808) living along a Mediterranean beach (Burano, Grosseto, Italy). From April 1986 to March 1987 the annual and daily patterns of amphipod activity were analysed together with zonation and the direction and extent of movements. An annual bimodal activity pattern was established with a first peak of activity in late spring and another one in autumn. Daily activity was predominantly nocturanl with two peaks, one of which could be suppressed or depressed in accordance with particular climatic conditions. The species studied was generally limited to the eu- and supralittoral part of the beach, but the extent of zonation could vary according to climate. Differences between juveniles and adults appeared both for activity patterns and for zonation. Movements were predominantly (ca. 85%) along the sea/land axis with a landward migration always followed by seaward one. Under conditions of high relative humidity and rain, the migrations towards land could extend to the dune. Movements parallel to the shoreline were demonstrated in a separate experiment (in June and October 1987 and June 1988) using the capture-mark-recapture method. The maximum distance covered registered in one night was 200 m.