Intertidal Clam Research Articles

Behavioral responses of intertidal clams to compound extreme weather and climate events

Rapidly increasing concentration of carbon dioxide (CO2) in the atmosphere not only results in global warming, but also drives increasing seawater acidification. Infaunal bivalves play critical roles in benthic-pelagic coupling, but little is known about their behavioral responses to compound climate events. Here, we tested how heatwaves and acidification affected the behavior of Manila clams (Ruditapes philippinarum). Under acidified conditions, the clams remained capable of burrowing into sediments. Yet, when heatwaves attacked, significant decreases in burrowing ability occurred. Following two consecutive events of heatwaves, the clams exhibited rapid behavioral acclimation. The present study showed that the behavior of R. philippinarum is more sensitive to heatwaves than acidification. Given that the behavior can act as an early and sensitive indicator of the fitness of intertidal bivalves, whether, and to what extent, behavioral acclimation can persist under scenarios of intensifying heatwaves in the context of ocean acidification deserve further investigations.

Recruitment and Losses through the Life Cycle for Intertidal Clams in Willapa Bay, Washington

Recruitment and Losses through the Life Cycle for Intertidal Clams in Willapa Bay, Washington

Distribution of cadmium and lead levels in the intertidal clam Glauconome virens: A biomonitoring study

The intertidal clam, Glauconome virens, was collected in the northwestern portion of Peninsular Malaysia near Kuala Perlis, Sungai Layar, and Pantai Teluk Air Tawar. This research attempted to determine the cadmium (Cd) and lead (Pb) concentrations in the various G. virens’s organs. The Cd concentrations (mg/kg dry weight) in five distinct soft tissues ranged from 0.90 to 1.89, but the concentrations in shells ranged from 0.95 to 1.25. Pb concentrations (mg/kg dry weight) in the five distinct soft tissues ranged from 27.0 to 44.9, whereas shell concentrations ranged from 74.8 to 75.3. In general, the shell had more Pb than the soft tissue components. Future biomonitoring research on this type of clams should concentrate on certain tissues (such as the remainder, shell, and gill) to identify their potential as biomonitoring organs/materials. This biomonitoring study is of paramount importance to establish the intertidal clams as a good biomonitor under the umbrella of International Mussel Watch. Besides, establishment of such biomonitoring baseline data is important for future references and human health risk assessments.

Brown bear–sea otter interactions along the Katmai coast: terrestrial and nearshore communities linked by predation

AbstractSea otters were extirpated throughout much of their range by the maritime fur trade in the 18th and 19th centuries, including the coast of Katmai National Park and Preserve in southcentral Alaska. Brown bears are an important component of the Katmai ecosystem where they are the focus of a thriving ecotourism bear-viewing industry as they forage in sedge meadows and dig clams in the extensive tidal flats that exist there. Sea otters began reoccupying Katmai in the 1970s where their use of intertidal clam resources overlapped that of brown bears. By 2008, the Katmai sea otter population had grown to an estimated 7,000 animals and was likely near carrying capacity; however, in 2006–2015, the age-at-death distribution (AADD) of sea otter carcasses collected at Katmai included a higher-than-expected proportion of prime-age animals compared to most other sea otter populations in Alaska. The unusual AADD warranted scientific investigation, particularly because the Katmai population is part of the Threatened southwest sea otter stock. Brown bears in Katmai are known to prey on marine mammals and sea otters, but depredation rates are unknown; thus, we investigated carnivore predation, especially by brown bears, as a potential explanation for abnormally high prime-age otter mortality. We installed camera traps at two island-based marine mammal haulout sites within Katmai to gather direct evidence that brown bears prey on seals and sea otters. Over a period of two summers, we gathered photo evidence of brown bears making 22 attempts to prey on sea otters of which nine (41%) were successful and 12 attempts to prey on harbor seals of which one (8%) was successful. We also developed a population model based on the AADD to determine if the living population is declining, as suggested by the high proportion of prime-age animals in the AADD. We found that the population trend predicted by the modeled AADDs was contradictory to aerial population surveys that indicated the population was not in steep decline but was consistent with otter predation. Future work should focus on the direct and indirect effects these top-level predators have on each other and the coastal community that connects them.

Assessing the impact of atmospheric heatwaves on intertidal clams

Heatwaves have become more frequent and intense in the last two decades, resulting in detrimental effects on marine bivalves and ecosystems they sustain. Intertidal clams inhabit the most physiologically challenging habitats in coastal areas and live already near their thermal tolerance limits. However, whether and to what extent atmospheric heatwaves affect intertidal bivalves remain poorly understood. Here, we investigated physiological responses of the Manila clam, Ruditapes philippinarum, to heatwaves at air temperature regimes of 40 °C and 50 °C occurring frequently and occasionally at the present day in the Beibu Gulf, South China Sea. With the increasing intensity of heatwaves and following only two days of aerial exposure, Manila clams suffered 100 % mortality at 50 °C, indicating that they succumb to near future heatwaves, although they survived under various scenarios of moderate heatwaves. The latter is couched in energetic terms across levels of biological organization. Specifically, Manila clams acutely exposed to heatwaves enhanced their standard metabolic rate to fuel essential physiological maintenance, such as increasing activities of SOD, CAT, MDA, and AKP, and expression of HSP70. These strategies occur likely at the expense of fitness-related functions, as best exemplified by significant depressions in activities of enzymes (NKA, CMA, and T-ATP) and expression levels of genes (PT, KHK, CA, CAS, TYR, TNF-BP, and OSER). When heatwaves occurred again, Manila clams can respond and acclimate to thermal stress by implementing a suite of more ATP-efficient and less energy-costly compensatory mechanisms at various levels of biological organization. It is consequently becoming imperative to uncover underlying mechanisms responsible for such positive response and rapid acclimation to recurrent heatwaves.

Bioacumulação e depuração de Escherichia coli no molusco de areia Anomalocardia brasiliana em diferentes salinidades

ABSTRACT Anomalocardia brasiliana is an intertidal filter-feeding clam that can accumulate enterobacteria, such as Escherichia coli, and consequently affect human health. Shellfish depuration is a procedure which reduces microbiological contaminants; however, salinity and depuration time can vary across species to adequately reduce bacteria load. To analyze the effect of salinity on the bioaccumulation and depuration of E. coli by A. brasiliana, this study evaluated salinity and depuration time in animals artificially contaminated with E. coli. Each experimental group of clams were acclimated for 6 hours in a recirculating aquaculture system (RAS) and then exposed to E. coli for 18 hours. Following exposure, clams were then held at one of four salinities (35, 30, 25 e 20) for a period of one of four depuration times (0, 12, 24, 36 and 48h). The highest bioaccumulation of E. coli in A. brasiliana was observed in clams held at salinities of 35, 30 and 25. The greatest reduction of E. coli in A. brasiliana was observed in clams held at 25 for 48 hours. A salinity of 20 showed low bioaccumulation and depuration of E. coli. The results of this study will contribute to developing a protocol for depurating A. brasiliana to mitigate human health concerns.

Investigating the influence of temperature and seawater δ18O on Donax obesulus (Reeve, 1854) shell δ18O

The coastline of Peru lacks long-lived marine organisms useful for paleoclimatic reconstructions generating a need for novel archives. Short-lived (<5 years) bivalves are commonly found in geological and archaeological deposits and thus can provide “snapshots” of past climatic variability (i.e., seasonal range), similar to data obtained by individual foraminifera analysis, rather than continuous, cross-dated time series (e.g., trees and corals). Previous studies have found success using the short-lived intertidal clam Mesodesma donacium. However, M. donacium are vulnerable to die-offs from the warmer sea surface temperatures (SST) associated with El Niño events and are functionally extinct in northern Peru thus limiting the possibility of modern analog studies for that region. Here we investigate the short-lived (1–3 years) surf clam, Donax obesulus, commonly found in northern Peru, as a paleoclimate archive. Donax obesulus populations are able to survive the warmer SSTs present during El Niño years although they are vulnerable to colder SSTs associated with La Niñas. We assessed the environmental drivers underlying subannual δ18O variability in D. obesulus from live collected shells from fish markets and coastal beaches near the Nepeña Valley, Peru in 2012 (La Niña), 2014 (ENSO-neutral), and 2016 (El Niño). Forward modeling of pseudo-shell δ18O reveals that SST variations are a dominant driver with secondary contributions from seasonally-varying seawater δ18O (δ18Osw). By accounting for varying δ18Osw, we isolated the temperature dependent variable resulting in a paleotemperature equation for D. obesulus δ18O. We verified our results with the δ18O record of a D. obesulus shell collected in 2006. Our results suggest that the paleotemperature equation we developed is useful for reconstructing El Niño-Southern Oscillation (ENSO)-related climatic variations in this region and the pseudo-shell approach may be useful for understanding shell δ18O in other locations.

Comparative Field Trials to Examine the Efficacy of a Traditional Management Tool—Brushing—To Enhance Local Densities of 0-Y Class Recruits in the Soft Shell Clam Mya arenaria L. Fishery in Maine, USA

The intertidal soft-shell clam Mya arenaria fishery in Maine is comanaged under a cooperative agreement, or shellfish ordinance, between coastal communities and the state. The ordinance, among other things, defines conservation tools that encourage communities to engage in activities with a goal to enhance local densities of 0-y class individuals of this infaunal bivalve. One method used by communities for over 75 y is referred to as “brushing,” which involves forcing dozens of the recently cut white spruce Picea glauca boughs (approximately 70 cm in length) vertically into the soft sediments of a mudflat so that 40–45 cm protrudes into the water column. Typically, multiple rows of boughs are deployed on flats in the spring before clam spawning where they remain through the fall after annual settlement and recruitment have ended. Brushing purportedly results in slowing down tidal currents and creating eddies that allow recently settled clams that otherwise are susceptible to bedload transport away from the flat to establish themselves in the vicinity of the boughs. During spring–fall 2019, a comparative field experiment was conducted at three intertidal flats within a 160-km stretch of the Maine Coast to test, for the first time, the efficacy of this traditional management tool versus another approach used to enhance local densities of 0-y class clams—predator-exclusion netting. At each flat, neither treatment enhanced densities when compared with controls of recruits of Mya as well as recruits of another commercially important infaunal bivalve that occurred at a single site, the northern quahog Mercenaria mercenaria. That is, neither bivalve responded positively to experimental additions of spruce boughs to soft sediments at any study site. Passive bivalve collectors demonstrated that both species settled into plots, ruling out recruitment limitation. Comparison of recruit densities between collectors and core samples from both brushed and netted plots demonstrated losses greater than 97% for Mya and greater than 93% for Mercenaria. Collectors also provided data on densities of recruits of the invasive green crab Carcinus maenas, which ranged from 1.2 to 13.9 ind. m–2 across sites, and were 3–6× more abundant in collectors within plots with brush or netting versus adjacent control plots, suggesting that this predator selects heterogeneous versus homogeneous environments during its early life history. As green crab populations in Maine vary directly with seawater temperatures, and the Gulf of Maine is warming relatively rapidly, adding potential habitat for green crabs, such as brush, to intertidal flats should be discontinued in favor of more effective methods to enhance local densities of 0-y class individuals.

Biochemical adaptations of the stout razor clam (Tagelus plebeius) to changes in oxygen availability: resilience in a changing world?

Climate change is producing sea level rise and deoxygenation of the ocean, altering estuaries and coastal areas. Changes in oxygen availability are expected to have consequences on the physiological fitness of intertidal species. In this work we analyze the coping response of the intertidal stout razor clam (Tagelus plebeius (Lightfoot, 1786)) to extreme environmental changes in oxygen concentration. Their biochemical responses to normoxia, hypoxia, and hyperoxia transition at different intertidal level (low–high) were measured through an in situ transplant experiment. The high intertidal level negatively affected the analyzed traits of the T. plebeius populations. The differences in reactive oxygen species production, total oxyradical scavenger capacities, and catalase activity also suggested more stressful conditions at the high level where long-term hypoxia periods occur. Both hypoxia and re-oxygenation provoked re-adjustments in the antioxidant responses and higher lipid oxidative damage (normoxia &lt; hypoxia &lt; re-oxygenation). The observed responses in transplanted clams at the opposite intertidal level suggested the potential acclimation of T. plebeius to cope with new environmental conditions. These findings are discussed within a global changing context where both increasing deoxygenation conditions and sea level rise are predicted to be exacerbated in the area driven by climate change.

Vulnerability of juvenile clams to predation by shore crabs

Predation, especially by crabs, is a common source of mortality for natural and farmed populations of intertidal clams. Consumption of juvenile “seed clams” forces aquaculturists to try to exclude predators and/or raise juveniles in hatcheries until they can reach a size refuge. We ran a variety of lab experiments assessing vulnerabilities of juvenile clams to small, common shore crabs (Hemigrapsus spp.). Crabs <1 cm width can consume hardshell Manila clams larger than those normally used for “seed”, and can readily crush even larger softshell Mya clams. We suggest that using netting to prevent consumption by shore crabs is not practical given that smaller individuals can fit through mesh openings. Raising seed in hatcheries until they are 10–15 mm will provide a size refuge from shore crabs, but not larger cancrid crabs. Farming on beaches with little habitat (e.g., cobbles) for shore crabs can likely reduce juvenile clam mortality. A better understanding of predation threats to commercially important clams is critical, especially as the invasion of the green crab Carcinus to Washington shorelines further threatens survival of juvenile clams.

Shellfish, Geophytes, and Sedentism on Early Holocene Santa Rosa Island, Alta California, USA

Archaeobotanical remains recovered from a large ∼8000-year-old-shell midden (CA-SRI-666) on Santa Rosa Island provide the first ancient plant data from this large island, shedding light on ancient patterns of plant use, subsistence, and sedentism. Faunal data from shell midden samples retrieved from three site loci contain evidence for harvesting of rocky intertidal shellfish and estuarine clams and oysters from a paleo-estuary in the vicinity. CA-SRI-666 appears to have been an Early Holocene village site occupied year round. A key to the development of early sedentary societies on the island may have been geophytes, especially Brodiaea-type corms, which provided an abundant source of carbohydrates and calories that complemented marine resources rich in fat and whole animal proteins. Our data demonstrate the value of integrating paleobotanical and zooarchaeological data from island and coastal archaeological sites to help elucidate human social, cultural, and environmental dynamics, including sedentism.

Intertidal clams exhibit population synchrony across spatial and temporal scales.

Long‐term datasets can be particularly useful for parsing out factors influencing populations, yet few studies have utilized continuous datasets to quantify population dynamics in bivalve molluscs. We used dynamic factor analysis on a clam biomass dataset spanning 28 yr and five distinct regions in the southern Salish Sea to determine (1) if native intertidal clam populations exhibit synchrony and (2) what environmental covariates may be correlated with these population trends. Once covariates were accounted for, the model with the most data support included three predominant trends to describe multidecadal change in clam biomass. Intraspecific synchrony was highest among Saxidomus gigantea and Leukoma staminea populations, with no clear evidence of covariance in Clinocardium nuttallii. Specifically, we quantified a pronounced decadal decline in L. staminea and an increase in S. gigantea biomass on most beaches. No beaches showed synchrony in trends across all three species, indicating that species‐specific trends (regardless of location) were more common than beach‐specific trends (regardless of species). Seven environmental covariates were evaluated in their capacity to explain variability in annual mean biomass. Of these, the North Pacific Gyre Oscillation lagged 4 yr prior to the observation year was most supported by the data in the best fitting model, implying that 4 yr old clam biomass is partially determined by oceanographic processes affecting larval clams. Although results suggest large‐scale density‐independent factors play a role in venerid clam population dynamics, it is also likely local factors account for variability not explained by our model.

Reproduction, growth and size of a burrowing intertidal clam exposed to varying environmental conditions in estuaries

Bivalves in estuaries are exposed to many environmental variables but little is known about how such variables, including reduced salinity, affect reproduction and growth in burrowing clams. These were measured in the New Zealand little-neck clams, Austrovenus stutchburyi, from one urban and three rural estuaries with different contaminant inputs. Two shellfish sites were selected within each estuary reflecting high- and low-salinity exposure. Reproductive activity was seasonal and similar amongst the estuarine systems. The gravimetric condition index (CI) of the clams decreased significantly on exposure to low-salinity regimes. The gonad index increased significantly with CI and per cent glycogen in the foot tissue. At most sites, shell length increased significantly with the age of the clam, and maximum shell length and growth was reduced in clams exposed to the low-salinity regime. Reproductive indices of the clams did not correlate with sediment characteristics or sediment trace metal pollution index. It was concluded that salinity was the main factor affecting shellfish condition and that seasonal CI measurements could be a good indicator of growth and reproductive success. This knowledge is useful for the future management of this and other similar shellfish species.

Intermittent hypoxia leads to functional reorganization of mitochondria and affects cellular bioenergetics in marine molluscs.

Fluctuations in oxygen (O2) concentrations represent a major challenge to aerobic organisms and can be extremely damaging to their mitochondria. Marine intertidal molluscs are well-adapted to frequent O2 fluctuations, yet it remains unknown how their mitochondrial functions are regulated to sustain energy metabolism and prevent cellular damage during hypoxia and reoxygenation (H/R). We used metabolic control analysis to investigate the mechanisms of mitochondrial responses to H/R stress (18 h at <0.1% O2 followed by 1 h of reoxygenation) using hypoxia-tolerant intertidal clams Mercenaria mercenaria and hypoxia-sensitive subtidal scallops Argopecten irradians as models. We also assessed H/R-induced changes in cellular energy balance, oxidative damage and unfolded protein response to determine the potential links between mitochondrial dysfunction and cellular injury. Mitochondrial responses to H/R in scallops strongly resembled those in other hypoxia-sensitive organisms. Exposure to hypoxia followed by reoxygenation led to a strong decrease in the substrate oxidation (SOX) and phosphorylation (PHOS) capacities as well as partial depolarization of mitochondria of scallops. Elevated mRNA expression of a reactive oxygen species-sensitive enzyme aconitase and Lon protease (responsible for degradation of oxidized mitochondrial proteins) during H/R stress was consistent with elevated levels of oxidative stress in mitochondria of scallops. In hypoxia-tolerant clams, mitochondrial SOX capacity was enhanced during hypoxia and continued rising during the first hour of reoxygenation. In both species, the mitochondrial PHOS capacity was suppressed during hypoxia, likely to prevent ATP wastage by the reverse action of FO,F1-ATPase. The PHOS capacity recovered after 1 h of reoxygenation in clams but not in scallops. Compared with scallops, clams showed a greater suppression of energy-consuming processes (such as protein turnover and ion transport) during hypoxia, indicated by inactivation of the translation initiation factor EIF-2α, suppression of 26S proteasome activity and a dramatic decrease in the activity of Na(+)/K(+)-ATPase. The steady-state levels of adenylates were preserved during H/R exposure and AMP-dependent protein kinase was not activated in either species, indicating that the H/R exposure did not lead to severe energy deficiency. Taken together, our findings suggest that mitochondrial reorganizations sustaining high oxidative phosphorylation flux during recovery, combined with the ability to suppress ATP-demanding cellular functions during hypoxia, may contribute to high resilience of clams to H/R stress and help maintain energy homeostasis during frequent H/R cycles in the intertidal zone.

Frequency, Magnitude, and Possible Causes of Stranding and Mass-Mortality Events of the Beach Clam Tivela mactroides (Bivalvia: Veneridae).

Stranding combined with mass-mortality events of sandy-beach organisms is a frequent but little-understood phenomenon, which is generally studied based on discrete episodes. The frequency, magnitude, and possible causes of stranding and mass-mortality events of the trigonal clam Tivela mactroides were assessed based on censuses of stranded individuals, every four days from September 2007 through December 2008, in Caraguatatuba Bay, southeastern Brazil. Stranded clams were classified as dying (closed valves did not open when forced) or dead (closed valves were easily opened). Information on wave parameters and the living intertidal clam population was used to assess possible causes of stranding. This fine-scale monitoring showed that stranding occurred widely along the shore and year-round, with peaks interspersed with periods of low or no mortality. Dead clams showed higher mean density than dying individuals, but a lower mean shell length, attributed to a higher tolerance to desiccation of larger individuals. Wave height had a significant negative relationship to the density of dying individuals, presumed to be due to the accretive nature of low-energy waves: when digging out, clams would be more prone to be carried upward and unable to return; while larger waves, breaking farther from the beach and with a stronger backwash, would prevent stranding in the uppermost areas. This ecological finding highlights the need for refined temporal studies on mortality events, in order to understand them more clearly. Last, the similar size structure of stranded clams and the living population indicated that the stranded individuals are from the intertidal or shallow subtidal zone, and reinforces the ecological and behavioral components of this process, which have important ecological and socioeconomic implications for the management of this population.

Clam predator protection is effective and necessary for food production

Shellfish aquaculture is a widely practiced way of producing food for human consumption in coastal areas. When farming intertidal clams, farmers commonly protect young seedling clams from predatory losses by covering farmed plots with netting or screening. Recent discussion of the effectiveness of protective nets or screens and their environmental effects has raised questions concerning the utility of the practice. We provide data based on a review of more than 35 peer-reviewed articles, as well as our own research that demonstrates the efficacy of predator protection for clam farms in various habitats around the world. In addition, we evaluate the effects of screening on temperature, and comment on ancient practices of clam gardening as conducted in the Pacific Northwest.

Location is everything: evaluating the effects of terrestrial and marine resource subsidies on an estuarine bivalve.

Estuaries are amongst the world’s most productive ecosystems, lying at the intersection between terrestrial and marine environments. They receive substantial inputs from adjacent landscapes but the importance of resource subsidies is not well understood. Here, we test hypotheses for the effects of both terrestrial- and salmon-derived resource subsidies on the diet (inferred from stable isotopes of muscle tissue), size and percent nitrogen of the soft-shell clam (Mya arenaria), a sedentary estuarine consumer. We examine how these relationships shift across natural gradients among 14 estuaries that vary in upstream watershed size and salmon density on the central coast of British Columbia, Canada. We also test how assimilation and response to subsidies vary at smaller spatial scales within estuaries. The depletion and enrichment of stable isotope ratios in soft-shell clam muscle tissue correlated with increasing upstream watershed size and salmon density, respectively. The effects of terrestrial- and salmon-derived subsidies were also strongest at locations near stream outlets. When we controlled for age of individual clams, there were larger individuals with higher percent nitrogen content in estuaries below larger watersheds, though this effect was limited to the depositional zones below river mouths. Pink salmon exhibited a stronger effect on isotope ratios of clams than chum salmon, which could reflect increased habitat overlap as spawning pink salmon concentrate in lower stream reaches, closer to intertidal clam beds. However, there were smaller clams in estuaries that had higher upstream pink salmon densities, possibly due to differences in habitat requirements. Our study highlights the importance of upstream resource subsidies to this bivalve species, but that individual responses to subsidies can vary at smaller scales within estuaries.

Kwakwaka’wakw “Clam Gardens”

Abstract The indigenous peoples of the Northwest Coast of North America actively managed natural resources in diverse ways to enhance their productivity and proximity. Among those practices that have escaped the attention of anthropologists until recently is the traditional management of intertidal clam beds, which Northwest Coast peoples have enhanced through techniques such as selective harvests, the removal of shells and other debris, and the mechanical aeration of the soil matrix. In some cases, harvesters also removed stones or even created stone revetments that served to laterally expand sediments suitable for clam production into previously unusable portions of the tidal zone. This article presents the only account of these activities, their motivations, and their outcomes, based on the first-hand knowledge of a traditional practitioner, Kwakwaka’wakw Clan Chief Kwaxistalla Adam Dick, trained in these techniques by elders raised in the nineteenth century when clam “gardening” was still widely practiced.

Species and size-selective predation by raccoons (Procyon lotor) preying on introduced intertidal clams

Raccoons (Procyon lotor (L., 1758)) are known for their dietary plasticity and ability to exploit new resources. We studied raccoons preying on introduced intertidal clams and hypothesized that raccoons maximized energetic profit by foraging selectively. Raccoons discarded Manila clams (Venerupis philippinarum (A. Adams and Reeve, 1850)) but selected large varnish clams (Nuttallia obscurata (Reeve, 1857)), although varnish and Manila clam densities did not differ significantly and small varnish clams were more abundant than large ones. We determined the energy content of different-sized varnish and Manila clams by subtracting the cost of cracking a clam from its soft-tissue energy. Varnish clams with less shell mass than Manila clams required less energy to open, but for their size Manila clams were more profitable. We suggest that raccoons, limited to preying on clams when the tide is low and at risk feeding on an open beach, select varnish clams because they need less handling, but maximize profit by selecting large clams. Our calculations indicate that a raccoon eating large varnish clams could obtain up to 8.4% of its daily basal metabolic needs in 10 min, making varnish clams a potentially valuable new prey resource.

Fine-scale spatial distribution of the common lugworm Arenicola marina, and effects of intertidal clam fishing

Despite its ubiquity and its role as an ecosystem engineer on temperate intertidal mudflats, little is known of the spatial ecology of the lugworm Arenicola marina. We estimated lugworm densities and analyzed the spatial distribution of A. marina on a French Atlantic mudflat subjected to long-term clam digging activities, and compared these to a nearby pristine reference mudflat, using a combination of geostatistical techniques: point-pattern analysis, autocorrelation, and wavelet analysis. Lugworm densities were an order of magnitude greater at the reference site. Although A. marina showed an aggregative spatial distribution at both sites, the characteristics and intensity of aggregation differed markedly between sites. The reference site showed an inhibition process (regular distribution) at distances <7.5 cm, whereas the impacted site showed a random distribution at this scale. At distances from 15 cm to several tens of meters, the spatial distribution of A. marina was clearly aggregated at both sites; however, the autocorrelation strength was much weaker at the impacted site. In addition, the non-impacted site presented multi-scale spatial distribution, which was not evident at the impacted site. The differences observed between the spatial distributions of the fishing-impacted vs. the non-impacted site reflect similar findings for other components of these two mudflat ecosystems, suggesting common community-level responses to prolonged mechanical perturbation: a decrease in naturally-occurring aggregation. This change may have consequences for basic biological characteristics such as reproduction, recruitment, growth, and feeding.