Effects of Ilyanassa obsoleta (Say) on the abundance and vertical distribution of Corophium volutator (Pallas) on mudflats of the upper Bay of Fundy

Invertebrates in soft-bottom marine communities exhibit a range of responses to predators and competitors, including both emigration and avoidance. Corophium volutator (Pallas), a burrowing amphipod abundant in the upper Bay of Fundy, Canada, frequently interacts with the eastern mudsnail, Ilyanassa obsoleta (Say), as both species utilize similar habitats and food resources. Typically these interactions result in negative effects on C. volutator. There is evidence that Corophium species exhibit avoidance behaviour when interacting with other species, but whether such a response occurs in the presence of I. obsoleta is unknown. To investigate C. volutator response to I. obsoleta, total C. volutator abundance and vertical distribution within the sediment was examined in a field experiment involving I. obsoleta enclosures and exclosures at two mudflats in the upper Bay of Fundy. I. obsoleta densities were manipulated between June and August 2008 and their effects on C. volutator abundance and vertical distribution observed. Results varied between mudflats and C. volutator size classes. At Peck's Cove, total C. volutator abundance was largely unaffected by I. obsoleta. No size class exhibited a distribution shift in response to I. obsoleta, though both mid-sized individuals and adults occupied deeper layers of sediment late in the summer. Abundance of C. volutator in all size classes at Grande Anse was reduced in July in direct proportion to exposure to I. obsoleta, and adults occupied higher sediment layers in July when I. obsoleta were excluded, suggesting that I. obsoleta curtailed use of these upper layers. Juvenile abundance rebounded in August, possibly due to the mass dispersal of a newly produced juvenile cohort. Adults were reduced in all treatments in August, probably as a result of normal seasonal mortality. Differences in C. volutator responses between mudflats highlight the site-specific nature of such interactions.     

Earthworms, as ecosystem engineers, influence multiple aspects of a salamander��s ecology

Ecosystem engineers create habitat that can be used by other species in multiple ways, such as refuges from predators, places to breed, or areas with increased prey resources. I conducted a series of enclosure experiments to: (1) determine if salamanders use earthworm burrows, and (2) examine the potential influence of earthworm burrow use and indirect effects on salamander intra- and interspecific competition, predator avoidance, and seasonal performance. I found that one species of woodland salamander, Plethodon cinereus, used earthworm burrows 50% of the time when burrows were present. Neither adults nor juveniles of the congeneric P. glutinosus used earthworm burrows. Intraspecific, but not interspecific, competition by P. cinereus affected salamander behavior when earthworms were absent, with P. cinereus found under cover objects >70% of the time when alone or with a P. glutinosus, but only 40% of the time when with another P. cinereus. When earthworms were present, the behavior of P. cinereus was similar across salamander treatments. Earthworms decreased the amount of leaf litter and microinvertebrates, although this did not affect salamander mass. In subsequent experiments using only P. cinereus, the refuge provided by earthworm burrows increased the survival of P. cinereus over the winter and allowed P. cinereus to avoid being consumed by the common garter snake (Thamnophis sirtalis). Because earthworm burrows provide a refuge for P. cinereus during intraspecific encounters, in the presence of a predator and over the winter, they may serve as an important belowground?Caboveground linkage in eastern forests where salamanders are common.     

Intertidal burrows of the air-breathing eel goby, <Emphasis Type="Italic">Odontamblyopus lacepedii</Emphasis> (Gobiidae: Amblyopinae)

Odontamblyopus lacepedii inhabits burrows in mudflats and breathes air at the surface opening. Investigations of the intertidal burrows using resin casting demonstrated a highly branched burrow system. The burrows are composed primarily of branching patterns of interconnected tunnels and shafts that communicate into two to seven surface openings. Bulbous chambers (i.e., dilated portions of the burrow) at branching sections of the tunnels or shafts are common features of the burrow. The presence of these chambers accords the fish adequate space to maneuver inside the burrow, and thus constant access to the surface. The combination of all burrow characteristics and previously reported variability in air breathing patterns are ostensibly of selective value for aerial predator avoidance during air breathing in O. lacepedii.     

Functional response of staging semipalmated sandpipers feeding on burrowing amphipods

Despite its fundamental relevance to many ecological processes in predator–prey relationships, the functional response, which relates predator intake rate to prey density, remains difficult to document in the field. Here, I document the functional response of semipalmated sandpipers (Calidris pusilla) foraging on a burrowing amphipod Corophium volutator during three field seasons at the peak of fall migration in the upper Bay of Fundy (New Brunswick, Canada). I gathered data during the ebbing tide when all sandpipers are highly motivated to feed after a lengthy hide-tide fast. As birds follow the receding tideline, foragers encounter prey at different densities and do not aggregate in the richest food patches. Results show that intake rate increased at a decreasing rate with Corophium density, yielding a type II functional response typical of many shorebird species. Intake rate decreased in the later stages of migration stopover at a time where preferred prey items have been shown to occur at lower densities due to prior depletion. At this period of lower prey availability, intake rate also decreased with sandpiper density providing evidence for interference at low prey density. The results illustrate the fact that the functional response may not be unique but instead vary as a function of the type of competitive relationship among foragers.     

Predatory behaviour in the ant-like wasp Methocha stygia (Say) (Hymenoptera: Tiphiidae)

An examination of prey-orienting behaviour of Methocha stygia has demonstrated that adult females regularly transport prey (Cicindela larvae) when they are removed from their burrows. On a single occasion a wasp was also observed to utilize a naturally occurring depression in the soil as a nest site, instead of depending on the prey's own burrow. This flexibility in response might be a carryover of the behaviour that surely existed in the ancestors of the methochine wasps, insects which were close to if not identical with the ancestors of the ants. When Methocha females were crowded together with prey in the laboratory, frequent avoidance and aggressive behaviours were noted, but no sign of any form of co-operation.     

Selection of food patches by sympatric herbivores in response to concealment and distance from a refuge

Small herbivores face risks of predation while foraging and are often forced to trade off food quality for safety. Life history, behaviour, and habitat of predator and prey can influence these trade‐offs. We compared how two sympatric rabbits (pygmy rabbit, Brachylagus idahoensis; mountain cottontail, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush‐steppe of western North America respond to amount and orientation of concealment cover and proximity to burrow refuges when selecting food patches. We predicted that both rabbit species would prefer food patches that offered greater concealment and food patches that were closer to burrow refuges. However, because pygmy rabbits are small, obligate burrowers that are restricted to sagebrush habitats, we predicted that they would show stronger preferences for greater cover, orientation of concealment, and patches closer to burrow refuges. We offered two food patches to individuals of each species during three experiments that either varied in the amount of concealment cover, orientation of concealment cover, or distance from a burrow refuge. Both species preferred food patches that offered greater concealment, but pygmy rabbits generally preferred terrestrial and mountain cottontails preferred aerial concealment. Only pygmy rabbits preferred food patches closer to their burrow refuge. Different responses to concealment and proximity to burrow refuges by the two species likely reflect differences in perceived predation risks. Because terrestrial predators are able to dig for prey in burrows, animals like pygmy rabbits that rely on burrow refuges might select food patches based more on terrestrial concealment. In contrast, larger habitat generalists that do not rely on burrow refuges, like mountain cottontails, might trade off terrestrial concealment for visibility to detect approaching terrestrial predators. This study suggests that body size and evolutionary adaptations for using habitat, even in closely related species, might influence anti‐predator behaviors in prey species.     

Burrow webs: Clawing the surface of interactions with burrows excavated by American badgers

Ecosystem engineers are organisms that influence their environment, which includes alterations leading to habitat provisioning for other species. Perhaps the most well‐examined guild of species provisioning habitat for other species is tree cavity excavators or woodpeckers (Picidae). Many studies have examined the suite of secondary cavity users that rely on woodpeckers, and how the ecological network of secondary users, collectively referred to as the nest web, changes across communities. Despite similar habitat provisioning processes, fewer studies have assessed the suite of species associated with burrowers providing access to subterranean habitat. Here, we begin to characterize the burrow web provisioned by American badgers (Taxidea taxus) and evaluate the diversity and frequency of species interactions we detected at abandoned badger burrows in Wyoming, USA. We deployed camera traps at 23 badger burrows and identified interactions with the burrow by birds, mammals, and reptiles. Overall, we discovered 31 other species utilizing badger burrows, consisting of 12 mammals, 18 birds, and 1 reptile. Mammals, other than American badgers themselves and other fossorial species such as ground squirrels (Urocitellus sp.), frequently using burrows included mice (Peromyscus sp.), long‐tailed weasel (Mustela frenata), pygmy rabbit (Brachylagus idahoensis), and desert cottontail (Sylvilagus audubonii). Of the 18 bird species detected, most accounted for <5% of overall detections, besides chipping sparrows (Spizella passerina) at 7.2%–11.5% of detections. The most common category of detection by bird species was foraging, contrary to mammals, which used the burrow frequently and were commonly observed entering and exiting the burrow. This work provides additional context on the ecological role of American badgers within their environment. More broadly, this work scratches the surface of many remaining questions to explore with the aim of advancing our understandings about burrow webs across the diversity of burrowing species and the communities in which they occur.     

Kangaroo Rats Remodel Burrows in Response to Seasonal Changes in Environmental Conditions

Burrow architecture enhances important animal functions such as food storage, predator avoidance, and thermoregulation. Occupants may be able to maximize fitness by remodeling burrows in response to seasonal changes in climate and predation risk. My objective was to examine how banner‐tailed kangaroo rats (Dipodomys spectabilis) modify the number of burrow entrances in response to seasonal conditions. For 3 yr, I monitored fluctuations in number of burrow entrances in kangaroo rat mounds. Individual kangaroo rats continually remodeled mounds in response to seasonal conditions. Compared to summer, mounds in winter had approximately 50% fewer entrances and plugged entrances were common. Monthly differences in number of entrances were closely linked with seasonal changes in soil temperature and precipitation. Number of entrances decreased as soil temperature and precipitation declined. Changes in burrow entrances likely reflect seasonal differences in the relative importance of burrow functions. Fewer burrow entrances during winter would create a warmer microclimate by reducing convective heat loss in mounds, resulting in thermoregulatory savings for occupants. During the summer, thermoregulatory costs of kangaroo rats are low, but risk of seed cache spoilage and predation from snakes increases. Adding burrow entrances after large summer rainfall events would increase the evaporation rate within mounds, reducing spoilage of seed caches. More burrow entrances would also reduce predation risk in the summer by providing additional escape routes.     

Burrow Architecture of the Ghost Crab Ocypode ceratophthalma on a Sandy Shore in Hong Kong

The ghost crab Ocypode ceratophthalma (Pallas) creates burrows of variety shapes at different ages. Juveniles (mean carapace length 11 mm) produced shallow J-shaped burrows, which incline vertically into the substratum (mean depth 160 mm). Larger crabs (17–25 mm carapace length) have Y-shaped and spiral burrows (mean depth 361 mm). These Y-shaped burrows have a primary arm, which extends to the surface forming the opening, and a secondary arm which terminates in a blind spherical ending. The two arms join in a single shaft and end with a chamber at the base. The secondary arms and chambers are believed to be used for mating or as a refuge from predation. The spiral burrows have spiral single channel ending in a chamber. Older crabs (mean carapace length 32.6 mm) had simple, straight single tube burrows, which inclined into the substratum at mean of 73° and had a mean depth of 320 mm. During summer daytime periods, the burrows shelter the crabs from heat and desiccation stress. The sand surface temperature at the burrow opening was ~48 °C but temperatures inside the burrows can drop to 32 °C at a depth of 250 mm. Variation in the burrow architecture with crab age appears to be related to the crab’s behaviour. Juvenile crabs have smaller gill areas and move out of the burrows regularly to renew their respiratory water and, as a result, they do not need a deep burrow. Larger crabs, in contrast, can tolerate prolonged periods without renewing their respiratory water and therefore create deeper and more complex burrows for mating and refuges.     

Preying at the edge of the sea: the nemertine Tetrastemma melanocephalum and its amphipod prey on high intertidal sandflats

In the European Wadden Sea, the nemertine Tetrastemma melanocephalumoccurs together with its prey, the amphipod Corophium arenarium, in the upper intertidal zone. T. melanocephalumleaves the sediment when the tide has receded and captures C. arenarium in its U-shaped burrow. Highest abundances of T. melanocephalumon the sediment surface were found on summer evenings, 2–4 h after high tide, when just a thin film of water was left on the flats. Laboratory Y-maze experiments indicated that gradients of substances produced by C. arenarium in this film of water play a role in tracking the prey. In the field, T. melanocephalum appeared in significantly higher numbers on experimental high density patches of C. arenarium. The amphipod in turn is able to recognize the nemertine. In aquarium experiments, significantly more amphipods escaped from the sediment into the water column when the predator was present. In the field, both predator and prey showed a high mobility by drifting in tidal waters. Benthic abundance maxima of T. melanocephalum and C. arenariumusually did not coincide spatially. It is assumed that the nemertines avoid tidal flats that dry out quickly leaving too little time for prey capture. T. melanocephalum is not able to dig into the sediment, but lives in burrows of Nereis diversicolor. The abundance of this polychaete was inversely related to C. arenarium, presenting a dilemma for T. melanocephalum: the spatial overlap of food and accommodation was rather small.     

Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow

Fossorialism is a beneficial adaptation for brooding, predator avoidance and protection from extreme climate. The abundance of fossilised burrow casts from the Early Triassic of southern Africa is viewed as a behavioural response by many tetrapods to the harsh conditions following the Permo-Triassic mass-extinction event. However, scarcity of vertebrate remains associated with these burrows leaves many ecological questions unanswered. Synchrotron scanning of a lithified burrow cast from the Early Triassic of the Karoo unveiled a unique mixed-species association: an injured temnospondyl amphibian (Broomistega) that sheltered in a burrow occupied by an aestivating therapsid (Thrinaxodon). The discovery of this rare rhinesuchid represents the first occurrence in the fossil record of a temnospondyl in a burrow. The amphibian skeleton shows signs of a crushing trauma with partially healed fractures on several consecutive ribs. The presence of a relatively large intruder in what is interpreted to be a Thrinaxodon burrow implies that the therapsid tolerated the amphibian’s presence. Among possible explanations for such unlikely cohabitation, Thrinaxodon aestivation is most plausible, an interpretation supported by the numerous Thrinaxodon specimens fossilised in curled-up postures. Recent advances in synchrotron imaging have enabled visualization of the contents of burrow casts, thus providing a novel tool to elucidate not only anatomy but also ecology and biology of ancient tetrapods.     

Hidden burrow plugs and their function in the tiger beetle, Cosmodela batesi (Coleoptera, Cicindelidae)

Tiger beetle larvae excavate and live in underground burrows, whose openings they sometimes plug with soil. This study documents the burrow plugging behavior of the tiger beetle, Cosmodela batesi (Fleutiaux), in the field. We also tested the function of burrow plugs in the laboratory. In the field, C. batesi more frequently made a plug when it rained. Most larvae made plugs inside their burrows (rather than at the soil surface), and the use of an endoscope was necessary to detect these sub-surface plugs. In the laboratory, flooding was simulated by artificially introducing water into specially-made arenas. Water filled the entire burrow when there was no plug, whereas plugged burrows maintained air chambers inside. When a plug was broken with a wire, burrows filled up with water. The burrowing and plugging behavior described in this study is likely an important adaptation of C. batesi to its habitat.     

Antipredator behaviour and predator recognition in Belding's ground squirrels

This study evaluates whether Belding's ground squirrels (Spermophilus beldingi) recognize predators under natural conditions. I observed these squirrels for 300 h during two consecutive summers, during which I described 1029 aerial and terrestrial interactions, including 299 interactions with animals known to prey on squirrels. Squirrels responded differentially to predators and non-predators, to predators that hunt differently, and to contextually different interactions with the same predator. Responses shown in encounters with predators included Trill and Chirp vocalizing, upright Posting, crouching, running to burrow entrances, entering burrows, Approaching or chasing predators, and doubling-back on pursuing predators. Ground squirrels appear to adjust their antipredator behaviour depending on the amount and kind of danger they face during an encounter.     

Foraging at the thermal limit: burrowing spiders (Seothyra,Eresidae) in the Namib desert dunes

Summary In the Namib Desert dunes, the web of Seothyra sp. (Eresidae) comprises sticky silk lining the edges of a horizontal mat on the sand surface. The spider sits in a silk-lined burrow attached to the mat. Arthropods become entangled in the sticky silk of the mat and are attacked and pulled into the burrow by the spider. We investigated the influence of sand surface temperature on the activity of spiders during the summer. We determined the range of thermal conditions encountered by spiders, their temperature tolerance and the influence of temperature on foraging activity and prey handling behavior. The environmental temperatures available to Seothyra vary from 17–33° C at the coolest time of day to 33–73° C at the hottest. When prevented from retreating into burrows, spiders showed signs of thermal stress at about 49° C, whereas unrestrained spiders continued to forage at web temperatures above 65° C by moving between the hot surface mat and the cooler burrow. Spiders responded quicker to prey stimuli during the hot hours of the day and completed prey capture sequences in significantly less time at surface temperatures above 49° C than below. Furthermore, captured arthropods succumbed more quickly at high surface temperatures. Our study supports the hypothesis that web design and thermoregulatory behaviors enable Seothyra to hunt under extreme thermal conditions.     

Zur Nahrungsaufnahme vonTetrastemma melanocephalum (Nemertini)

The proboscis of hoplonemerteans is armed with a stylet apparatus, which is used for capturing prey.Tetrastemma melanocephalum (Johnston) is a common hoplonemertean in the littoral of the Baltic Sea and the North Sea. It lives in the phytal and on sand- and mudflats and occurs in large numbers in theCorophium belts in the waddenseas.T. melanocephalum feeds on arthropods, mainly on copepods and amphipods. The prey is caught with the proboscis, penetrated by the stylet and grows weak (reduction of movements) within a few seconds; it is then sucked out. During the summer, a 15–35 mm long nemertean captures about 3 specimens ofCorophium volutator of 3.5–6 mm length per day. In theCorophium belt at Sahlenburg, German Bight, North Sea, 29 nemerteans/0.25m² were found; they feed mainly onC. volutator, so that on average more than 10 000 specimens ofC. volutator/m²/month are sucked out by these nemerteans. Hence,T. melanocephalum is an important consumer ofCorophium.     

Predation by early Cambrian trilobites on infaunal worms - evidence from the Swedish Mickwitzia Sandstone

Evidence of early Cambrian predation is found in trace fossils from the Mickwitzia Sandstone of VastergÖtland, Sweden. The arthropod burrow Rusophycw dispar was dug down to spreite burrows in such a manner that mere coincidence of place is unlikely. The predator is identified as an olenellacean trilobite, mainly through the presence of a cephalic impression. The prey, a worm that may have been a priapulid, was localized visually or chemically at the spreite-burrows apertures. The predator lacked legs specialized for seizing prey, as indicated by the parallel, but laterally displaced position of the Rusophycus above the spreite burrow. In this stance prey could be gripped by flexing the supposedly spinose legs of one side around it. When a spreite burrow of limited horizontal extension was encountered, parallel orientation was obtained prior to digging, probably through chemical sensing, whereas parallel orientation to an extended burrow required a number of diggings. These traces are important evidence of early Cambrian predation and of the predatorial capability of trilobites. □ Lower Cambrian, Sweden predation, trilobites, priapulids , Rusophycus.     

Ventilatory responses of the burrowing Owl and Bobwhite to hypercarbia and hypoxia

Summary The fractional concentration of CO₂ within the occupied burrows of burrow-dwelling birds has been measured at 0.065 or higher while the fractional concentration of O₂ can be 0.14 or lower. The ventilatory responses of the Burrowing Owl (Athene cunicularia) and a non-burrowing bird, the Bobwhite (Colinus virginianus), to the levels of hypercarbia, hypoxia and hypoxic hypercarbia likely encountered by this owl within its burrow were assessed. Ventilatory responses toFi _{CO 2} of 0.01, 0.03, 0.05 and 0.07 at normoxia; toFi _{CO 2} of 0.19, 0.17, 0.15 and 0.13 at normocarbia; and to combinedFi _{CO 2} andFi _{O 2} of 0.01:0.19, 0.03:0.17, 0.05:0.15 and 0.07:0.13 were measured by volumetric plethysmography. The Burrowing Owl exhibited a significantly attenuated ventilatory response to these levels of hypercarbia, hypoxia and hypoxic hypercarbia compared to the non-burrow-dwelling Bobwhite. A reduced ventilatory response to the hypoxic and hypercarbic stimuli has been previously observed in fossorial mammals, and is reported here for the first time in a burrow-dwelling bird. This reduced response is believed to represent an adaptation to burrow atmospheric conditions.Abbreviations F fractional concentration (of O₂ and CO₂) - f respiratory frequency - V _T tidal volume - V _D dead space (tracheal volume)     

Microscale oxygen distribution in various invertebrate burrow walls

Profiles of dissolved oxygen were measured in pore waters of unburrowed sediment and the burrow walls of seven invertebrate dwellings. Burrows studied include those of Corophium volutator, Heteromastus filiformis, Arenicola marina, Saccoglossus bromophenolosus, Clymenella sp., Hemigrapsus oregonensis and Cirriformia luxuriosa all from mudflats in Willapa Bay, Washington. These animals comprise a range of burrow architectures ranging from simple, unlined burrows to more complex, mucous lined burrows. Oxygen penetrated unburrowed sediment between depths of 0.4–2.6 mm, whereas oxygen penetrated the burrow walls from 0.3 mm to 2.3 mm. Three groups of burrows are recognized based on the oxygen diffusive properties relative to the unburrowed sediment including those that: (1) slightly impeded oxygen penetration, (2) clearly inhibited oxygen penetration, and (3) enhanced oxygen penetration. Differences in the diffusive properties of the burrow wall are related to the burrow microstructure and presumably the microbial communities living within the burrow microenvironment. The results of this study suggest that burrow shape and burrow‐wall architecture may play an important role in controlling the diffusion of oxygen, and possibly of other dissolved gases (i.e. CO₂, H₂S). The results further demonstrate that simplified assumptions (i.e. that bioturbation uniformly enhances oxygen diffusion into suboxic and anoxic sediments), while requisite for numerical modelling, are not necessarily representative of field data.     

The effects of temperature and salinity on ventilation behavior of two species of ghost shrimp (Thalassinidea) from the northern Gulf of Mexico: a laboratory study

Thalassinidean shrimp are among the most important bioturbators in coastal ecosystems. The species Lepidophthalmus louisianensis and Callichirus islagrande are found in dense aggregations (up to 400 burrows m⁻²) along sandy and muddy shores of the northern Gulf of Mexico. These shrimp actively ventilate their burrows to provide oxygen and eliminate wastes. In doing so, they expel nutrient-rich burrow water to the overlying water column, potentially altering nutrient cycling and benthic primary productivity. To develop a mechanistic understanding of the role of burrowing shrimp in nutrient processes, we must first examine how changes in environmental conditions alter the frequency, strength, and duration of ventilation. Field measurements of burrow temperature and salinity suggest that the burrow serves as a buffer from the highly variable conditions found in these estuarine, intertidal habitats. Temperatures at sediment depths >30 cm were generally warmer in winter and cooler in summer than at the sediment surface. Burrow salinities, measured at low tide, were consistently higher than adjacent open water. We used these measurements to parameterize laboratory studies of burrow ventilation in artificial burrows made of plastic tubing and in more natural sediment mesocosms, and studies of oxygen consumption in small glass containers. Rates of oxygen consumption and burrow ventilation by L. louisianensis were lower than those of C. islagrande, perhaps reflecting a lower overall activity rate in the former species which resides in less permeable sediments. Generally, increased temperature had a significant positive effect on oxygen consumption for both species. Salinity had no effect on oxygen consumption by L. louisianensis, reflecting the ability of this species to exist in a wide range of salinities. In contrast, oxygen consumption rates of C. islagrande, which is less tolerant of low salinity, were significantly higher at 35‰ than at 20‰. Ventilation rates were highly variable, and shrimp in artificial burrows tended to have consistently higher ventilation rates than those in sediment mesocosms. There is a trend toward more frequent ventilation at 30 °C for both species. Salinity had no effect on ventilation for either species. Our results suggest that thalassinideans exhibit highly variable and species-specific ventilation patterns that are more likely to be affected by temperature than salinity. Increased ventilation at higher temperatures seems to coincide with increased oxygen consumption at these temperatures, although a similar finding was not made for salinity treatments.     

Biodiversity of benthic invertebrates and organic matter processing in shallow marine sediments: an experimental study

The main objective of this study was to measure the impact of benthic invertebrate diversity on processes occurring at the water-sediment interface. We analyzed the effects of interactions between three shallow water species (Cerastoderma edule, Corophium volutator, and Nereis diversicolor). The impacts of different species richness treatments were measured on sediment reworking, bacterial characteristics, and biogeochemical processes (bromide fluxes, O₂ uptake, nutrient fluxes, and porewater chemistry) in sediment cores. The results showed that the three species exhibited different bioturbation activities in the experimental system: C. edule acted as a biodiffusor, mixing particles in the top 2 cm of the sediments; C. volutator produced and irrigated U-shaped tubes in the top 2 cm of the sediments; and N. diversicolor produced and irrigated burrow galleries in the whole sediment cores. C. edule had minor effects on biogeochemical processes, whereas the other species, through their irrigation of the burrows, increased the solute exchange between the water column and the sediment two-fold. These impacts on sediment structure and solute transport increased the O₂ consumption and the release of nutrients from sediments. As N. diversicolor burrowed deeper in the sediment than C. volutator, it irrigated a greater volume of sediments, with great impact on the sediment cores.Most treatments with a mixture of species indicated that observed values were often lower than predicted values from the addition of the individual effects of each species, demonstrating a negative interaction among species. This type of negative interaction measured between species on ecosystem processes certainly resulted from an overlap of bioturbation activities among the three species which lived and foraged in the same habitat (water-sediment interface). All treatments with N. diversicolor (in isolation and in mixture) produced similar effect on sediment reworking, water fluxes, nutrient releases, porewater chemistry, and bacterial characteristics. Whichever species associated with N. diversicolor, the bioturbation activities of the worm hid the effect of the other species. The results suggest that, in the presence of several species that use and modify the same sediment space, impact of invertebrates on ecosystem processes was essentially due to the most efficient bioturbator of the community (N. diversicolor). In consequence, the functional traits (mode of bioturbation, depth of burrowing, feeding behaviour) of an individual species in a community could be more important than species richness for some ecosystem processes.