Showing papers on "Shore published in 2002"

Sandy shore ecosystems and the threats facing them: some predictions for the year 2025

Abstract: Pollution, mining, disruption of sand transport and tourism development widely affect sandy shores, and these systems may be subject to increased erosion in future, yet there have been few attempts to review them. The present review focuses largely on ocean sandy beaches, providing an introduction to much of the relevant literature, and predicting possible states of the system by 2025. Sandy shores are dynamic harsh environments, the action of waves and tides largely determining species diversity, biomass and community structure. There is an interchange of sand, biological matter and other materials between dunes, intertidal beaches and surf zones. Storms and associated erosion present the most substantial universal hazard to the fauna. Human-related perturbations vary from beach to beach; however, structures or activities that impede natural sand transport or alter the sand budget commonly lead to severe erosion, often of a permanent nature. Many beaches also suffer intermittent or chronic pollution, and direct human interference includes off-road vehicles, mining, trampling, bait collecting, beach cleaning and ecotourism. These interferences typically have a negative impact on the system. Identified long-term trends include chronic beach erosion, often largely due to natural causes, as well as increased ultraviolet (UV) radiation and changes related to global warming. It is not expected that predicted temperature changes will have dramatic effects on the world's beaches by 2025, but the expected rise in sea level, if coupled with an increase in the frequency and/or intensity of storms, as predicted for some regions, is likely to lead to escalating erosion and consequent loss of habitat. It is suggested that increased UV radiation is unlikely to have significant effects. Increases in coastal human populations and tourism, thus increasing pressure on the shore, while serious, may be largely offset in developed and developing countries by better management resulting from greater understanding of the factors governing sandy-shore systems and better communication with beach managers and developers. Beach nourishment is likely to become more widely practised. However, the continuing hardening of surfaces in and above the dunes is bound to be damaging. Human pressures in many underdeveloped countries show no signs of being mitigated by conservation measures; it is likely that their sandy shores will continue to deteriorate during the first quarter of this century. A long-term trend that cannot be ignored is the excessive amount of nitrogen entering the sea, particularly affecting beaches in estuaries and sheltered lagoons. The data presently available and the uncertainty of a number of predictions do not permit of quantitative assessment or modelling of the state of the world's sandy shores by the year 2025, but some tentative, qualitative predictions are offered.

The High Water Line as Shoreline Indicator

Abstract: Beach erosion rates are often determined by delineating historical shoreline positions from maps and aerial photographs and more recently global positioning systems (GPS). The high water line is usually selected as the shoreline indicator for mapping purposes; it is defined as the wet ted bound and by "markings left on the beach by the last high tide." The high water line that is acquired from field determination or photogrammetric means is assumed to represent the mean shoreline position for that year, but field studies have shown that its position is variable because of changes in water level due to waves, wind, tides, and other factors. This study investigated the short-term variability in the high water line location over tidal cycles, days, and months through field observations and interpretation of videotape data. Studies, undertaken at Assateague Island National Seashore in Maryland and at the Field Research Facility at Duck, North Carolina, indicated that the high water line is a useful shoreline indicator within certain limits. GPS acquired shorelines based on actual identification of the high water line in the field are deemed more accurate than photo-interpreted shorelines for coastal erosion mapping and management.

Factors Controlling Storm Impacts on Coastal Barriers and Beaches-A Preliminary Basis for Near Real-Time Forecasting

Abstract: Analysis of ground conditions and meteorological and oceanographic parameters for some of the most severe Atlantic and Gulf Coast storms in the U.S. reveals the primary factors affecting morphological storm responses of beaches and barrier islands. The principal controlling factors are storm characteristics, geographic position relative to storm path, timing of storm events, duration of wave exposure, wind stress, degree of flow confinement, antecedent topography and geologic framework, sediment textures, vegetative cover, and type and density of coastal development. A classification of commonly observed storm responses demonstrates the sequential interrelations among (1) land elevations, (2) water elevations in the ocean and adjacent lagoon (if present), and (3) stages of rising water during the storm. The predictable coastal responses, in relative order from high frequency beach erosion to low frequency barrier inundation, include: beach erosion, berm migration, dune erosion, washover terrace construction, perched fan deposition, sheetwash, washover channel incision, washout formation, and forced and unforced ebb flow. Near real-time forecasting of expected storm impacts is possible if the following information is available for the coast: a detailed morphological and topographic characterization, accurate storm-surge and wave-runup models, the real-time reporting of storm parameters, accurate forecasts of the storm position relative to a particular coastal segment, and a conceptual model of geological processes that encompasses observed morphological changes caused by extreme storms.

Mesoscale patterns in the Cape São Vicente (Iberian Peninsula) upwelling region

Abstract: [1] The coastal upwelling region near Cape Sao Vicente, the southwestern tip of the Iberian Peninsula where the southern zonal coast meets the meridional western coast, was studied using over 1200 advanced very high resolution radiometer (AVHRR) satellite images of sea surface temperature and time series of sea level height, wind velocities, and nearshore sea surface temperature recorded at coastal sites within 200 km of the cape. Summer upwelling is more intense and persistent off the western coast than off the southern coast, where a recurrent warm coastal countercurrent flows westward, and at times turns northward along the western coast after reaching the cape. In this region the equatorward current jet of cold water upwelled off the western coast is no longer bounded by a coast. Three preferred directions for the spreading of this water are identified. The most persistent is eastward along the southern shelf break and slope, possibly merging with waters previously upwelled locally, which becomes separated from shore by the coastal progression of the warmer counterflow. The second preferred direction results in the southward development of a cold filament feature fed by cold waters upwelled farther north and represents the southernmost extent of the intense coastal upwelling jet, which overshoots the cape. The least frequent feature to develop is a cold filament that grows westward at the latitude of the cape, appearing to result from the meandering of the equatorward jet. The coastal countercurrent is seen to interact with the equatorward jet at times of relaxation, not only by separating the cold upwelled water from the coast but, when it is energetic enough, breaking westward offshore through the equatorward cold flow and separating the eastward and southward cold features from the upcoast cold waters. Empirical evidence shows the presence of an alongshore pressure gradient, stronger in summer, driving the coastal progression of the warm counterflow. Wind forcing plays an important role in the circulation by augmenting or diminishing the effect of the preexisting alongshore pressure gradients. The extent of the progression of the warm coastal countercurrent along the southern and western coast is dictated by the the strength of the upwelling favorable wind stress, which is able to balance and reverse the alongshore flow, at least in the upper layers.

The near‐coastal microseism spectrum: Spatial and temporal wave climate relationships

Abstract: [1] Comparison of the ambient noise data recorded at near-coastal ocean bottom and inland seismic stations at the Oregon coast with both offshore and nearshore buoy data shows that the near-coastal microseism spectrum results primarily from nearshore gravity wave activity. Low double-frequency (DF), microseism energy is observed at near-coastal locations when seas nearby are calm, even when very energetic seas are present at buoys 500 km offshore. At wave periods >8 s, shore reflection is the dominant source of opposing wave components for near-coastal DF microseism generation, with the variation of DF microseism levels poorly correlated with local wind speed. Near-coastal ocean bottom DF levels are consistently ∼20 dB higher than nearby DF levels on land, suggesting that Rayleigh/Stoneley waves with much of the mode energy propagating in the water column dominate the near-coastal ocean bottom microseism spectrum. Monitoring the southward propagation of swell from an extreme storm concentrated at the Oregon coast shows that near-coastal DF microseism levels are dominated by wave activity at the shoreline closest to the seismic station. Microseism attenuation estimates between on-land near-coastal stations and seismic stations ∼150 km inland indicate a zone of higher attenuation along the California coast between San Francisco and the Oregon border.

Intertidal Rocky Shore Communities of the Continental Portuguese Coast: Analysis of Distribution Patterns

Abstract: A general description of rocky shore distribution patterns (“zonation”) along the whole Portuguese coast is given to provide the context for comparisons of distribution patterns of mid-shore organisms. In order to test if there was any variation in species distribution and abundance in the upper and lower mid-shore zone (eulittoral) along the entire intertidal Portuguese coast, three main regions were studied (north, centre and south) and nine shores were visited in each region. At each one of the 27 locations, the shore was levelled and a general qualitative description was made, which also aided stratification of subsequent quantitative sampling. An upper zone (littoral fringe) characterised by the presence of encrusting lichens, small littorinid gastropods and cyanobacteria was found on most of the shores along the Portuguese coast. The mid-shore zone (eulittoral) is essentially dominated by barnacles and sometimes mussels. The distribution patterns observed on the lower shore (sub-littoral fringe) showed a distinction between northern shores, where large brown algae are present, and shores located in the central and southern regions, essentially dominated by red algal turf species. Multidimensional analysis and the ANOSIM test have revealed clear differences in the structure of the upper and lower mid-shore zone. Within each level, the northern region was considerably different from the south and central regions. SIMPER analysis revealed the species which contributed to the separation between shore levels and regions. It has also given important information on the geographical decline in abundance of species.

Do Storms Cause Long‐Term Beach Erosion along the U.S. East Barrier Coast?

Abstract: In a few hours or days, scores of meters of beach width can be lost due to a severe storm. However, newly available shoreline data from the U.S. East Coast show that beaches recover after storms to positions consistent with their long‐term (100+ yr) trend. Even the largest storms, such as the Ash Wednesday Storm of 1962, considered to be the most damaging in the twentieth century, appear to have had little effect on the long‐term trend. The gradual recession of beaches along the U.S. East Coast is mainly controlled by other factors such as sea‐level rise and variations of sediment supply. Therefore, it follows that barrier beaches in a coastal plain setting would not experience long‐term erosion in response to storm impact if the sea were to stop rising and sediment supply did not change.

A freshwater jet on the east Greenland shelf

Abstract: In August 1997, RRS Discovery cruise 230 (World Ocean Circulation Experiment (WOCE) section A25) ran a hydrographic section into Cape Farewell on the southern tip of Greenland. The closest approach to the shore was 2 nm in a water depth of 160 m over the east Greenland shelf. Analysis of the hydrographic data (conductivity-temperature-depth (CTD), vessel-mounted acoustic Doppler current profiler, and thermosalinograph) has revealed a current flowing southwestward, ~15 km wide, 100 m deep, and centered ~10 km offshore. We believe it to be driven by meltwater runoff from Greenland. This feature, which we call the East Greenland Coastal Current (EGCC), carries a little less than 1 Sv (106 m3 s-1) with peak current speeds of ~1 m s-1 at the surface. The center of the EGCC lies on a salinity front with maximum salinity contrast ~4 practical salinity units (psu) between coast and shelf break and between surface and bottom. A spot value of freshwater transport is 0.06 Sv (1800 km3 yr-1), which is equivalent to ~30% of the Arctic freshwater gain. The presence of the EGCC and its continuity up the east Greenland coast as far as Denmark Strait is confirmed in satellite sea surface temperature images and surface drifter tracks. We estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be >25% per 1°C.

Evaluation of nutritive condition and reproductive status of migrating gray whales (Eschrichtius robustus) based on analysis of photogrammetric data

Abstract: Vertical aerial photographs were collected of gray whales migrating along the California Coast between 1994 and 1998 to readdre ss some published findings on the biology and life history of this population based on examination of specimens. For each whale, an att empt was made to measure standard total length, the width of the whale at its widest point, the distance from the tip of the rostrum to the widest point, and the width of the flukes. For southbound gray whales, early migrants were longer on average and more likely to be parturient than those migrating later. Near-term pregnant females were wider relative to their length than other southbound gray whales. This differe nce was easily detected by visual inspection of the images and through statistical evaluation of length and width data. There was 100% agreement between identification of parturient females based on linear regression analysis of length and width and discriminate analysis of all measurements. Based on the proportion of parturient females to those with calves during sampling of southbound whales, the medi an calving date was estimated to be 13 January. Southbound calves averaged 4.6m in length; those photographed northbound in late A pril, at an age of about three months, averaged 7.1m. Average length for yearlings, based on combined southbound and northbound data, wa s 8.5m. Residuals from a regression of width on length were compared, and significant changes in the relationship were detected which w ere consistent with changes in nutritive condition or fatness described from examination of whales taken along the California Coast between 1959 and 1969 (Rice and Wolman, 1971). Parturient females were the widest relative to their length and northbound cows with cal ves were the narrowest in the sample. The relationship between length and width for migrating gray whales that were not parturient or as sociated with a calf, showed that southbound gray whales were significantly wider than northbound whales photographed approximately 60 d ays later. These results indicate that the predictable but relatively small changes in condition or fatness of gray whales associat ed with fasting during their winter migration can be reliably detected in measurements from vertical aerial photographs.

Short-Term Beach Rotation Processes in Distinct Headland Bay Beach Systems

Abstract: This paper investigates morphological changes in headland bay beaches with emphasis on short-term beach rotation processes, elucidating how it is affected by the planform/degree of curvature of the beach, and by the different morphodynamic characteristics of the beach systems monitored. The beaches monitored in the present study were Balneario Camboriu, Brava and Taquaras/Taquarinhas beaches. They have different lengths, degrees of curvature, and levels of exposure to the incident waves, and represent different beach types. Indentation ratio and the SL/CL ratio were measured, and beach profile surveys every 15 days were made in order to measure variations of beach volume and width for each beach. Visual wave and beach observations were recorded daily. Results indicate that morphological changes in headland bay beaches are influenced mainly by beach planform and indentation ratios, presence of rip currents and submerged bars, shoreline length, and beach type. The beach volume and with variations demonstrated that headland bay beaches have defined sectors with different behaviour, as influenced by headland impact on incident waves and longshore currents. Short-term beach rotation is manifested as out of phase variation of beach volume and width between opposite ends of a headland bay beach. Rotation amplitude of about 20 meters was observed at a dissipative beach (Balneario Carnboriu), and on the reflective beach of Taquaras/Taquarinhas. Brava beach did not show clear patterns of short-term beach rotation, but there was a subdivision of the beach into two sectors with different magnitudes of sediment removal and behaviour. The occurrence of short-term beach rotation processes in some of the beaches indicates that, erosive events are often caused by a realignment of the beach shoreline in response to a shift in incident wave direction. In these cases the sediment eroded is not lost from the beach system but deposited elsewhere along the beach, and often returning to the initial location in response to a new shift in wave direction.

Artificial armored shorelines: sites for open-coast species in a southern California bay

Abstract: Artificial hard substrates have been used to stabilize naturally soft bay shorelines for centuries. Despite the loss of over half of the natural shoreline in many bays, little attention has been paid to the communities inhabiting armored shorelines and to the ecological implications of armoring. The goal of the present study was to examine factors affecting spatial and temporal variation of intertidal, hard-substrate biota (emergent species and fishes), with emphases on the influence of exposure, distance from the open ocean, and similarity to open-coast, hard-substrate communities. We examined community composition at eight San Diego Bay (California, USA) sites (an exposed and a protected site at four bay locations) in June and November 2000 and two open-coast sites in August 2000. At all bay sites, the shore was armored with granite boulders, a form of shoreline stabilization referred to as "riprap." Community structure was more variable spatially than temporally on the scales we studied, affected more by distance from the bay mouth and exposure to wave energy than by differences between June and November. Exposed sites near the bay mouth were more similar to natural open-coast sites, sharing about 45% of their species, than protected sites and sites farther from the mouth, which shared as few as 8%. Species richness was generally higher in exposed than protected bay sites. Species tended to occur higher in the intertidal zone at exposed than protected sites, and higher in November, when sea level was higher, than in June. Such results will be useful to shoreline managers who examine the ecological implications of hardening long stretches of coastline and may suggest ways to incorporate artificial structures into ecosystems in a more meaningful way.

Sewage and environmental impacts on rocky shores: necessity of identifying relevant spatial scales

Abstract: The concentration of contaminants usually decreases with increasing distance from a point-source disturbance, so sampling to detect ecological impacts is usually done at 1 spatial scale, often at regular intervals from the point of discharge. There is, however, concern that the choice of an inappropriate scale will cause failure to detect impacts or failure to identify and estimate the size of impacts. In this study, the putative impact of a shoreline sewage outfall on the abundance of green ephemeral algae and gastropods was sampled at 2 spatial scales (tens of metres and several kilo- metres from the point of discharge) in order to determine whether the ecological impact of effluent was comparable across these, as would be expected if the abundance of species follows the gradient of contaminants. Such sampling also enabled the putative impact of this outfall on the spatial vari- ability of taxa to be examined at 3 spatial scales: (1) among quadrats in the site with the outfall com- pared to variance among quadrats in other sites on the shore with the outfall; (2) among quadrats in non-outfall sites on the shore with the outfall compared with variance among quadrats in sites on con- trol shores; (3) between non-outfall sites on the shore with the outfall in comparison to among sites on the control shores. A greater abundance of Enteromorpha spp. was found close to the outfall than fur- ther away at both spatial scales. Patterns in the abundance of many other taxa differed between the 2 spatial scales of sampling. The density of the limpet Patelloida latistrigata was much greater close to than far from the outfall, when considered on a large spatial scale. At the smaller scale among sites on a single shore, the impact was completely reversed—densities were much smaller close to than away from the outfall. Variances, like abundances, did not always follow the gradient of contami- nants and different patterns were often seen at different spatial scales. Thus, putative impacts should be sampled on multiple spatial scales using nested sampling designs. Where this is not possible, the spatial scale at which an impact might be detected or interpreted needs to be clearly stated because the generalisation that a disturbance has a similar impact at all spatial scales relevant to the popula- tion being studied cannot be made without explicit tests.

Shoreline change mapping and management along the U.S. east coast

Abstract: There have been remarkable advancements in the science and technology of shoreline change mapping; the earlier problems of obtaining accurate erosion rates have been overcome in recent decades. Historical shoreline mapping and trend analysis can provide the requisite data for projection of future shoreline positions for implementation of FEMA's coastal erosion management program, Identification of erosion hazard zones (E-zones) will represent a significant advancement toward fulfilling the intent of the National Flood Insurance Program (NFIP).

Uranium, thorium, and potassium in soils along the shore of Lake Issyk-Kyol in the Kyrghyz Republic.

Abstract: The Kyrghyz Republic, located in the southeastern region ofthe former Soviet Union, maintains a population of more thanone-half-million persons and is heavily dependent on LakeIssyk-Kyol, both to draw tourists to the area and for itsutilization by some as a food and recreation source. Historical surveys, conducted primarily for geologicalexploration, have indicated that localized areas ofshoreline on Lake Issyk-Kyol have relative radiation levelsin excess of ambient background by as much as a factor often. Uranium mining operations in the mountains borderingthe lake to the south may have resulted in the contaminationof a number of areas on the lake's southern shore. Concentrations of naturally occurring uranium, thorium, andpotassium are present in these soils in elevated quantities. This paper presents the results of an investigation of soilconcentrations along the shoreline of Lake Issyk-Kyolrelative to previously discovered areas of high exposurerate.

A model of sediment transport over an intertidal transect, comparing the influences of biological and physical factors

Abstract: This paper compares modeled biotic and physical effects on intertidal sediment transport, using parameterizations that are based on laboratory and field experiments. A one-dimensional model of an intertidal transect is constructed. The model is aligned cross shore and includes movement of water and suspended sediment. Within the model, tidal currents cause erosion, and bioturbation by the clam, Macoma balthica, alters the erodability of the bed sediment. The concentration of chlorophyll a in the surface sediment (which is an indicator of microphytobenthos density) alters the critical erosion velocity. External sediment supply is specified as an offshore suspended matter concentration. The model is applied within Spurn Bight (Humber Estuary, UK). The effects of various tide heights, biota densities, and external suspended sediment concentrations are investigated. Offshore sediment supply dominates the net deposition below midtide level, but factors affecting intertidal sediment erosion and deposition become important at higher shore levels. Changes in erosion or deposition caused by natural variation in biota densities are as large as those caused by changes in tidal range and currents over a spring-neap cycle, or by doubling external supply. Seasonal variations in densities of stabilizing microphytobenthos can alter the magnitude of net deposition on the upper shore by a factor of two. Interannual variation in numbers of bioturbating clams can change net deposition by a factor of five. These results show that biotic influences on transport of sediment within the intertidal zone are significant and will play a role in determining sediment budgets over tidal to monthly timescales.

Late Weichselian and Holocene shore displacement history of the Baltic Sea in Finland

Abstract: About 62 percent of Finland’s current surface area has been covered by the waters of the Baltic basin at some stage. The highest shorelines are located at a present altitude of about 220 metres above sea level in the north and 100 metres above sea level in the south-east. The nature of the Baltic Sea has alternated in the course of its four main postglacial stages between a freshwater lake and a brackish water basin connected to the outside ocean by narrow straits. This article provides a general overview of the principal stages in the history of the Baltic Sea and examines the regional influence of the associated shore displacement phenomena within Finland. The maps depicting the various stages have been generated digitally by GIS techniques. Following deglaciation, the freshwater Baltic Ice Lake (12,600–10,300 BP) built up against the ice margin to reach a level 25 metres above that of the ocean, with an outflow through the straits of Oresund. At this stage the only substantial land areas in Finland were in the east and south-east. Around 10,300 BP this ice lake discharged through a number of channels that opened up in central Sweden until it reached the ocean level, marking the beginning of the mildly saline Yoldia Sea stage (10,300–9500 BP). As the connecting channels rose above sea level, however, the Baltic Sea became confined once more, to form the Ancylus Lake (9500–8000 BP). During its existence the outflow channel to the ocean shifted to the Straits of Denmark and the major lake systems of central Finland became isolated from the Baltic basin. After the brief Mastogloia transition phase, a greater influx of saline water began to take place through the Straits of Denmark, marking the Litorina Sea stage (7500– 4000 BP), to be followed by a somewhat less saline stage known as the Limnea Sea. After a transgressive period early in the Litorina Sea stage, shoreline displacement in Finland has proceeded at a steadily declining rate.

Middle Holocene Sea-Level and Evolution of The Gulf of Mexico Coast (USA)

Abstract: Recently published data suggest middle Holocene sea level along the Texas Gulf Coast was at -9 m at ca. 7800-7700 yrs BP, then rose rapidly to +2 m or more during the middle Holocene. This view contrasts with the traditional, widely accepted interpretations of continual submergence. Recently recognized Holocene beach-ridge plains on the mainland central Texas coast, landward of Holocene barriers, may represent the geomorphic manifestation of this highstand. Long considered to be part of the last interglacial period shoreline, these Holocene beach-ridge plains attain elevations of 2.5-3 m, extend for 10s of kms along the mainland shore, and can be 1-3 kms in width, roughly the same scale as the Holocene barriers. We have also investigated previously mapped Holocene shorelines along the Alabama coast. A series of optical luminescence ages suggest that some of the shorelines are middle Holocene in age, ca. 6700-4000 yrs BP, whereas others are late Holocene in age, ca. 3500-2500 yrs BP. In aggregate, these data suggest that relative sea level was at, or very close to, present elevations throughout the middle to late Holocene along the Gulf of Mexico shoreline, both to the west and east of the subsiding Mississippi depocenter, and the model of continual submergence needs reevaluation.

Installation for harvesting ocean currents (IHOC)

Abstract: Installation for harvesting kinetic energy of ocean currents in deepwaters is based on utilization of a semisubmersible platform and the multiple of vertically oriented Darrieus type hydraulic turbines with funnels. The turbines are located bellow sea level on distance sufficient to exclude them from being affected by wave actions. The electric power generators are located on a structure above water and transmit electric power to the shore utilizing flexible cable from semisubmersible to the sea bottom and underwater cable going to the shore, where it connected to the power distributing network. One of the Embodiments of this invention is designed to harvest energy of tides in deepwaters.

An Application of LIDAR to Analyses of EI Nino Erosion in the Netarts Littoral Cell, Oregon

Abstract: El Nino produces coastal and beach erosion along the West Coast of the USA by elevating mean water levels so that tides are significantly higher than predicted, and by altering the paths of storms that generate large waves. In the past it has been difficult to adequately document the erosion impacts since they are so widespread. This difficulty has been solved through the application of LIDAR, which uses a scanning laser mounted in a small aircraft to rapidly and accurately survey beach elevations. This study uses LIDAR to document the beach changes and shoreline erosion that occurred during the 1997-98 El Nino within the Netarts Littoral Cell on the Oregon coast, a 14-km long "pocket beach" between large rocky headlands. The LIDAR surveys demonstrate that sand generally migrated northward within the cell due to the southwest approach of the El Nino storm waves, but there was a complex pattern of beach-elevation change due to the superposition of eroded rip-current embayments. The greatest beach erosion occurred near the south end of the cell, where it impacted Cape Lookout State Park, and to the north of the inlet to Netarts Bay where it threatened The Capes, a development of condominiums located on a high bluff. In both cases the LIDAR data proved to be extremely useful in quantifying the erosion, and in providing a better understanding of the erosion processes that occur during an El Nino.

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

Abstract: 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.