Burrow Networks Research Articles

Cherax latimanus sp. nov., a new burrow-dwelling freshwater crayfish (Decapoda, Parastacidae) from the mid-Murray River catchment, Australia.

A new species of freshwater crayfish in the southern hemisphere family Parastacidae is described from the Murray Darling Basin (MDB), eastern Australia. The Swamp Yabby, Cherax latimanus sp. nov., is found in the mid-Murray River area of the states of New South Wales and Victoria and is only the third species of Cherax found naturally occurring in the MDB. It is morphologically distinguished from all other species of Cherax by the presence of marginal mesial dactylar basal spines and extensive ventral propodal setation. It is found in sympatry with the widespread but morphologically similar Common Yabby, Cherax destructor Clark, 1936, but can be distinguished by a suite of morphometric and meristic characters that include a broad rostrum lacking an apical spine, very broad chelae with deep punctations on the lateral propodal edge and ventral propodal setation, two prominent dactylar teeth, one mesial carpal spine, dorsal meral spines present, no setae on carpal mesial margin, cervical spines absent or tiny, and by genetic data. Cherax latimanus is further diagnosed by its distinctive biology: it is not found in permanent aquatic habitats such as streams or billabongs, spending the majority of its time in extensive, terrestrial, burrow networks containing some water, in ephemerally wet habitats such as drainage lines, roadside drains, depressions, swamps and cleared areas of pasture in lowland to foothill areas. It is occasionally found in stream habitats but only during large flood events when burrow systems are inundated.

Leach’s Storm PetrelsHydrobates leucorhousbreeding on Gloup Holm: the third discovered breeding site in Shetland

In the UK, Leach’s Storm Petrel Hydrobates leucorhous breeding colonies are few and geographically very remote. Single Leach’s Storm Petrels were heard calling from burrows on Gloup Holm, north Shetland, in July 2019, July 2020 and August 2020, in response to call-playback. The occupied burrow network found in August 2020 was examined by endoscope and a Leach’s Storm Petrel eggshell was seen, constituting the first proven breeding record at this site. A sample call was recorded from each bird heard, sonograms produced, and comparison with criteria for determining sex from calls indicated the bird heard in 2019 was female and those in 2020 were one or possibly two males. Currently, Leach’s Storm Petrel breeds in very low numbers in Shetland on just two small islands. Restoration projects to eradicate introduced predators and preserve natural breeding habitat on select other islands could result in increased breeding numbers.

Evidence for the development of a superpermeability flow zone by bioturbation in shallow marine strata, upper Jubaila Formation, central Saudi Arabia

Superpermeability (super-k) flow zones in carbonate reservoirs are thought to be controlled by bioturbation—related burrow networks, e.g., burrow pores of Thalassinoides. To improve the current understanding, this study investigated Thalassinoides and associated passive fill in the Upper Jubaila Member of the Upper Jurassic Jubaila Formation, central Saudi Arabia. Analysis of the elemental and mineralogical compositions of powder samples from the passive fill and burrow matrix, and thin sections of selected burrow matrix samples were conducted to determine the origin of the passive fill. The goal, herein, is to infer the flow properties of the bioturbated strata of the Upper Jubaila Member based on the occurrence of this passive fill in the burrow pores of the Thalassinoides.Compared to the burrow matrix, the analyzed passive fill exhibit marked differences in elemental composition, suggesting a much younger and different origin than that of the marine carbonates of the Upper Jubaila Member. A CaO plus MgO concentration below 28% and an elevated SiO2 plus Al2O3 concentration above 45% suggest a clay-dominated passive fill. The reddish and brownish colorations of the passive fill are attributed to the presence of iron oxyhydroxides, as indicated by the elevated Fe2O3 concentration (a mean of 5.8% ± 1.7%), and a mineralogical composition with elevated percentages of goethite and hematite. The normalized rare earth element (REE) pattern of the passive fill is consistent with that of lithogenous (siliciclastic) sources, which are likely deposited in a well-oxygenated environment, as suggested by the redox-sensitive elements and normalized REEs. These sources probably originate in hot humid environment, as indicated by the chemical index of alteration (CIA) (>80).The above geochemical data suggest that the passive fill was derived from soils similar to Mediterranean Terra Rossa soils and postdate the formation of burrow pores in the Thalassinoides-bearing strata. This could have occurred after exposure of the Upper Jubaila Member. Terra Rossa soil most likely reached the Thalassinoides-bearing strata from the surface through vertical fractures and karst features, filled burrow pores, fractures along bedding plains, and even intercrystalline pores. The occurrence of Terra Rossa soil in the burrows and intercrystalline pores of the Thalassinoides-bearing strata implies that the pore system of the Upper Jubaila Member possessed connected pathways that enabled soil infiltration followed by simultaneous precipitation in the burrows and intercrystalline pores. The presence of these connected burrow pores containing shafts with diameters ranges from 1 to 5 cm suggests a superpermeable storage capacity and presence of a superflow unit in the Upper Jubaila Member. This study provides an excellent example to better understand the controls of super-k zones in carbonate reservoirs.

Neurokinin-1 receptor activation is sufficient to restore the hypercapnic ventilatory response in the Substance P-deficient naked mole-rat.

Naked mole-rats (NMRs) live in large colonies within densely populated underground burrows. Their collective respiration generates significant metabolic carbon dioxide (CO2) that diffuses slowly out of the burrow network, creating a hypercapnic environment. Currently, the physiological mechanisms that underlie the ability of NMRs to tolerate environmental hypercapnia are largely unknown. To address this, we used whole-body plethysmography and respirometry to elucidate the hypercapnic ventilatory and metabolic responses of awake, freely behaving NMRs to 0%-10% CO2. We found that NMRs have a blunted hypercapnic ventilatory response (HCVR): ventilation increased only in 10% CO2. Conversely, metabolism was unaffected by hypercapnia. NMRs are insensitive to cutaneous acid-based pain caused by modified substance P (SP)-mediated peripheral neurotransmission, and SP is also an important neuromodulator of ventilation. Therefore, we re-evaluated physiological responses to hypercapnia in NMRs after an intraperitoneal injection of exogenous substance P (2 mg/kg) or a long-lived isoform of substance P {[pGlu5-MePhe8-MeGly9]SP(5-11), DiMe-C7; 40-400 μg/kg}. We found that both drugs restored hypercapnia sensitivity and unmasked an HCVR in animals breathing 2%-10% CO2. Taken together, our findings indicate that NMRs are remarkably tolerant of hypercapnic environments and have a blunted HCVR; however, the signaling network architecture required for a "normal" HCVR is retained but endogenously inactive. This muting of chemosensitivity likely suits the ecophysiology of this species, which presumably experiences hypercapnia regularly in their underground niche.

Vertebrate scratch traces from the Middle Triassic Burgersdorp Formation of the main Karoo Basin, South Africa: Sedimentological and ichnological assessment

Containing one of the richest late Early to early Middle Triassic continental biotas globally, the Burgersdorp Formation of the main Karoo Basin in South Africa hosts a diverse vertebrate fossil assemblage. Comparatively, trace fossils in this unit are lesser known, and thus how the Burgersdorp biotas behaved and interacted with their palaeoenvironment remain enigmatic. Here we report on two Middle Triassic continental ichnofossil localities dominated by tetrapod scratch traces from the Anisian part (subzones B and C) of the Burgersdorp Formation in the main Karoo Basin (Eastern Cape, South Africa). Analyses of the trace fossils and associated sedimentary facies aim to identify the possible trace makers, their behaviours and the local depositional conditions in this southern part of Pangea. We establish the palaeoenvironmental context for the ichnofossils combining ichnological data with the sedimentological records of the trace fossil sites and the nearby type area of the Burgersdorp Formation. To facilitate comparisons with similar trace fossils in the future, we quantify the morphometric parameters of these Burgersdorp trace fossils in digital models. Our results show that bilobated, branching and cross-cutting furrow casts with abundant scratch traces: (a) were generated within crevasse splay deposits adjacent to laterally migrating river channels in a semi-arid setting, and (b) can be interpreted as the claw-scratched ventral walls of a therapsid burrow system with a 3D network architecture. This well-developed vertebrate burrow network complex from the Middle Triassic of South Africa is among a handful of similarly complex vertebrate trace fossils in the global pre-Jurassic ichnological record. Collectively, these trace fossils indicate that the Triassic, and in particular the Middle Triassic, was an important period in the evolutionary history of the complex vertebrate burrowing.

Characterization and identification of bioturbation-associated high permeability zones in carbonate reservoirs of Upper Cretaceous Khasib Formation, AD oilfield, central Mesopotamian Basin, Iraq

Abstract High-permeability zones (HPZ) are common occurrences in carbonate reservoirs of the Middle East and act to improve productivity in primary depletion but lead to water breakthrough in secondary depletion. Bioturbation aggravated the reservoir heterogeneity of the Khasib Formation carbonates in AD oilfield, Iraq, resulting in the development of HPZ. The observations of cores and thin sections, measurements of porosity, permeability, capillary pressure and probe permeability were conducted to investigate the characteristics and genesis of the HPZ. Well log responses of the HPZ in cored wells were analysed to identify the HPZ in uncored wells and predict its distribution. Results demonstrate that the HPZ is demarcated by Glossifungites ichnofacies and Thalassinoides ichnofabric. The burrow systems filled passively with overlying sediments that were apparently different from the unbioturbated matrix, in terms of the lithologic associations, pores types, and pore connectivity. The burrow systems, which contribute to the high permeability of the HPZ, were merely composed of grainstone with well-connected interparticle pores and vugs. The matrix comprises packstone and hardground-associated strongly cemented grainstone, which developed some fractures and exhibited poorly connected pores, including intraparticle, moldic, and residual interparticle pores. The arithmetic mean permeability of the HPZ is 241.0 mD, which is much higher than that of the non-HPZ (17.3 mD). The entry pressure and pore throat radius of the burrows in HPZ is 0.02–0.05 MPa and 5–20 μm, respectively, which reveal the high-quality pore structure of the burrow systems. There is strong heterogeneity within the HPZ. The permeability of burrow systems could reach up to 10133.5 mD with an arithmetic mean permeability of 712.2 mD, while the permeability of the matrix is only 0.05 to 69.29 mD, with an arithmetic mean permeability of 8.7 mD. Interconnected burrow networks in the HPZ were formed by bioturbation. The efficiency of connectivity of the HPZ was further enhanced by the early dissolution occurred within burrow architecture and matrix in the meteoric freshwater environment. These resulted in the formation of the high-permeable network composing of interparticle pores, vugs, and the dissolution-enlarged fractures. The high-permeable burrow systems and low-permeable matrix jointly contributed to the distinct well log responses, which are markedly different from the conventional shoal HPZ. The bioturbated HPZ can be identified by medium natural gamma (GR), high bulk density value (RHOB), low acoustic transit-time value (DT), low compensated neutron (NPHI), high deep induction value (RILD), and high microspherically focused resistivity value (MSFL). A well log-model based three cutoffs, namely RHOBnor/DTnor, RILD*MSFL and GR, was built and shows good prediction of the HPZ.

Rodent burrow network dynamics under human-induced landscape transformation from desert to steppe in Kalmykian rangelands.

Rodents play an important role in rangelands through the engineering of extensive burrow systems, which provides key habitats for many animal and plant species. We have analyzed the long-term variation in the abundance and distribution of rodent burrows in grazing ecosystems of southern Russia (Kalmykia) under the landscape change from desert to steppe caused by the drastic reduction of livestock after the collapse of the USSR in the early 1990s. We conducted burrow surveys in the "desert" (1980) and "steppe" (2017) periods on 19 3-km transects. We found considerable changes in burrow abundance and distribution, as well as evidence of desert habitat fragmentation and isolation caused by the expansion of tall-grass communities. Burrows of the open-dwelling diurnal ground squirrel (Spermophilus pygmaeus), the dominant and the keystone species during the "desert" period, almost completely disappeared from the rodent burrow network by 2017, indicating significant habitat loss. In contrast, the burrows of the folivorous social vole (Microtus socialis) which was rare in the 1980s, became abundant and ubiquitously distributed. The burrow density of the desert-dwelling psammophilous midday gerbil (Meriones meridianus) decreased, while the distances between occupied patches increased, indicating desert habitat fragmentation and loss of population connectivity. Burrows of the folivorous tamarisk gerbils (M. tamariscinus) were recorded only sporadically in both 1980 and 2017. The observed changes in the rodent burrow network, the key component of grazing ecosystems, correlate with rodent species ecology and can have long-term and important consequences for ecosystem functioning.

Effect of bioturbation on petrophysical properties: Insights from geostatistical and flow simulation modeling

As observed in many outcrops and cores, Thalassinoides burrow networks (TBN) within Glossifungites surfaces can be important for permeability enhancement, because the coarse-sediment infill provides permeable pathways in otherwise less permeable media. To explore the effect of bioturbation on reservoir quality, this study uses geostatistical models and fluid-flow-simulation models of TBN and burrow medium (matrix) of hypothetical TBN-bearing strata. Analysis of these models reveals a well-connected burrow network can occur in strata of as little as 12% burrow intensity, and burrow connectivity increases nonlinearly with increases in burrow intensity. Numerical flow simulations of TBN models indicate that gas production cumulative (GPC) is controlled primarily by TBN connectivity and matrix permeability. With an impermeable matrix, production comes through TBN (50 mD average permeability), starts only at burrow intensity of 30%, and GPC increases linearly with burrow intensity. With a permeable matrix (5 mD average permeability), and low permeability contrast between matrix and TBN (one order of magnitude) production starts at relatively low TBN intensity (4%), and GPC increases nonlinearly with burrow intensity. The interaction between matrix and TBN seems to connect more isolated TBN bodies, and increase GPC, and likely help the gas diffusion from matrix through TBN. The fluid flow simulation also illustrates the likelihood of the presence of permeability that drives early water breakthrough (super k) at burrow intensity > 50%. The results advance quantitative understanding of the impact of burrow connectivity on fluid flow properties of TBN-bearing strata and provide a workflow that can be used to model other burrow morphologies to understand their impact on flow properties of bioturbated reservoirs.

Fossil burrow assemblage, not mangrove roots: reinterpretation of the main whale-bearing layer in the late Eocene of Wadi Al-Hitan, Egypt

The UNESCO World Heritage Site of Wadi Al-Hitan near Fayum in the Western Desert of Egypt is well-known for its remarkable abundance and diversity of late Eocene marine fossils, especially well-preserved cetaceans and sirenians. However, the taphonomy of the early Priabonian whales and sea cows is still not fully understood. These marine mammals often occur on specific horizons in the Birket Qarun Formation, for example, on a distinctive firmground called the Camp White Layer (CWL). Vertical, rod-like structures in the CWL were previously interpreted as “mangrove pneumatophores,” which have influenced hypotheses about the habitat of early whales. Here, we reexamine the rod-like structures of the CWL and show that they do not represent mangrove rooting structures based on an analysis of their morphology and an extensive comparison with rooting structures of living mangroves. Instead, the morphology of the rod-like structures indicates that they are trace fossils representing five size classes of marine invertebrate burrows, including burrows of weakly umbonate clams and Ophiomorphidae. The complex overprinting of all burrows toward the top of the CWL indicates stratigraphic condensation caused by low overall rates of sedimentation on a marine flooding surface in the transgressive systems tract. The large number of whale carcasses, abundant invertebrate skeletal remains, logs, marine invertebrate-encrusted celestine crystals, and an extensive, diverse burrow network reflect a combination of environmental and temporal condensation. A peculiar feature of the CWL, celestine crystal aggregates and gastropod celestine pseudomorphs, indicate an evaporative phase that is difficult to reconcile with the current sequence stratigraphic framework.

Biogeomorphic impact of oligochaetes (Annelida) on sediment properties and Salicornia spp. seedling establishment

AbstractOligochaetes (Annelida) are active bioturbators that can be present in high densities in the transition zone between intertidal flats and salt marshes, though their occurrence and functional role remain understudied. This study aimed to clarify the biogeomorphic role of oligochaete bioturbation in facilitating or hindering vegetation establishment. Two microcosm experiments were performed to assess the effect of oligochaete bioturbation on sediment properties, oxidation depth, algal biomass, seed distribution, and germination success of pioneer species Salicornia spp. Oligochaetes created burrow networks in the sediment matrix, which, together with upward conveyor belt feeding, lead to substrate mixing. Sediment reworking rates of oligochaetes were compared with those of polychaete macrofauna. Bioturbation and bio‐irrigation of burrows can stimulate resource flows into the sediment. Oxidation depth increased almost tenfold in the presence of oligochaetes. Their bioturbation did not seem to affect sediment properties such as dry bulk density, porosity, and organic matter content. Sediment reworking, however, significantly reduced algal biomass at the surface with possible cascading effects on sediment stability and erodibility. Oligochaete conveyor belt feeding buried Salicornia spp. seeds until below the critical germination depth, thus negatively affecting Salicornia spp. germination and seedling establishment. Our study indicates that small, though numerous, oligochaete bioturbators may reduce lateral expansion potential of salt marshes by hindering the establishment of pioneer vegetation in the transition zone. Additionally, in dynamic fine‐grained habitats, these oligochaetes have the feature to quickly oxygenate the sediment top layer.

A Smithian (Early Triassic) ichnoassemblage from Lichuan, Hubei Province, South China: Implications for biotic recovery after the latest Permian mass extinction

A late Smithian ichnoassemblage is reported from the Lower Triassic succession from the Lichuan section, western Hubei Province, South China. This ichnoassemblage comprises 13 ichnogenera, which include simple, horizontal traces (Cochlichnus, Cosmorhaphe, Didymaulichnus, Gordia, Circulichnis, and Planolites), vertical traces (Arenicolites, Laevicyclus), oblique- or horizontal branching traces (Palaeophycus), slightly complex burrow networks (Thalassinoides, and Treptichnus), and grazing traces (Cosmorhaphe and Gyrochorte). These traces are also categorized into fodinichnia, domichnia, pascichnia, and repichnia ethologic types, suggesting a fairly high degree of behavioral complexity. Of these, the fodinichnia traces are most abundant. The ichnoassemblage horizons usually have rather high ichnofabric indices (ii), reaching ii 4–5. Bedding plane coverage is up to 70–90%, resulting in high bedding plane bioturbation index as well (BPBI 4–5). The Lichuan ichnoassemblage traces have mean and maximum diameters of 4.8mm and 9mm, respectively (n=342). The traces penetrate to a depth of up to 30mm into the sediment, with an average depth of penetration of 15mm, indicating third to fourth tiering levels (3–4). Overall, the Lichuan ichnofauna shows an abrupt increase in ichnodiversity, burrow width, behavioral complexity, and ecologic tiering level, which are indicative of recovery stages of 2–3 in the late Smithian. When compared to five coeval ichnoassemblages from other sections in South China (Yashan, Susong, Daxiakou, Gaimao, and Tianshengqiao) and coeval ichnoassemblages from elsewhere (northern Italy, Western Australia, western US), the Lichuan trace-fossil assemblage reaches similar level of diversity during this time interval. Paleoenvironmental analysis indicates that the late Smithian recovery pulse is typically confined to the offshore transition setting, whereas more distal zones record much lower levels of recovery. Therefore, time and environmental conditions were the two crucial factors controlling the rate and degree of recovery of trace-making organisms in the aftermath of the latest Permian mass extinction.

Chemical Composition of Thalassinoides Boxwork Across the Marine K–PG Boundary of Central New Jersey, U.S.A.

Thalassinoides isp. burrow networks filled with green to dark bluish-gray glauconite pellets occur in the Cretaceous to Paleogene Hornerstown Formation and in the uppermost 1–2 m of the underlying Upper Cretaceous Navesink and New Egypt Formations at many central New Jersey Cretaceous–Paleogene (K/Pg) boundary sections. Near the base of the Hornerstown Formation is a renowned bonebed, the Main Fossiliferous Layer (MFL), which contains isolated to articulated Cretaceous marine reptiles, turtles, birds, and crocodiles interpreted as a thanatocoenosis. We investigated the bulk chemical composition of the burrow fill and surrounding matrix in the largely unconsolidated sections of the K–Pg interval at two sites, Inversand and Walnridge (Meirs) Farm, New Jersey, using a Niton XL3t XRF analyzer to place them in proper stratigraphic context. Bulk matrix Zr and Ti concentrations decrease up section as a result of transgression, deepening, and increased distance from source areas. In contrast, an increase in K is attributed to greater amounts and maturity of the glauconite, due to decreasing sedimentation rates. Zr and Ti concentrations in burrow fills below the MFL are virtually the same as in overlying sediments above the MFL and much less than in the surrounding matrix. This suggests that burrows in the Cretaceous strata were passively filled with Paleogene sediments. K concentrations of burrow fills are generally intermediate between the high values encountered in the Paleogene matrix and the lower values of the Cretaceous matrix. Although this may have resulted from removal of glauconite during bioturbation and burrow filling, it is more likely that immature glauconite was sequestered in the burrow fills below the depth of glauconitization before it could attain full maturity. Therefore, burrows originating above the formational contact at or above the MFL penetrate as much as two meters into underlying Cretaceous sediments, and are passively filled with Paleogene sediment. Burrows originating above the MFL may translocate diagnostic Danian microfossils, shocked quartz, and Ir, effectively diffusing the K–Pg boundary. This research demonstrates that care must be taken in sampling pervasively bioturbated strata to avoid incorporating stratigraphically younger burrow-fill sediments.

Coexisting living stromatolites and infaunal metazoans.

Microbialites, bioaccretionary structures formed during the growth and metabolism of microorganisms (principally cyanobacteria) were the dominant lifeform in shallow late-Archean and Proterozoic oceans. During the Cambrian radiation of metazoan life, which began ~540 Mya, microbialite abundance and diversity further declined following a peak in the Mesoproterozoic. Notwithstanding contention, grazing and bioturbation effects of metazoans have been hypothesized as the dominant driver of modern microbialite scarcity. However, this metazoan-microbialite exclusion has not been fully explored in the few extant microbialites. Here we provide further evidence showing that living marine layered microbialites (stromatolites) coexist with a persistent assemblage of benthic macro-invertebrates, as has previously been demonstrated in some thrombolitic (clotted) microbialites. Surprisingly, these metazoans have active habits, such as burrowing, which should be expected to disrupt the layered matrix. As other studies have shown, through a network of burrows, metazoans can exploit local diurnal oxygen refugia within microbialites as well as escape predation. Our results, therefore, add novel evidence in support of the hypotheses that geologically, metazoans are not always incompatible with stromatolites, while ecologically, microbialites may act as micro-refugia for modern metazoans and historically have performed a similar inferred role in past ecosystems.

The Role of Ocean Tides on Groundwater-Surface Water Exchange in a Mangrove-Dominated Estuary: Shark River Slough, Florida Coastal Everglades, USA

Low-relief environments like the Florida Coastal Everglades (FCE) have complicated hydrologic systems where surface water and groundwater processes are intimately linked yet hard to separate. Fluid exchange within these low-hydraulic-gradient systems can occur across broad spatial and temporal scales, with variable contributions to material transport and transformation. Identifying and assessing the scales at which these processes operate is essential for accurate evaluations of how these systems contribute to global biogeochemical cycles. The distribution of 222Rn and 223,224,226Ra have complex spatial patterns along the Shark River Slough estuary (SRSE), Everglades, FL. High-resolution time-series measurements of 222Rn activity, salinity, and water level were used to quantify processes affecting radon fluxes out of the mangrove forest over a tidal cycle. Based on field data, tidal pumping through an extensive network of crab burrows in the lower FCE provides the best explanation for the high radon and fluid fluxes. Burrows are irrigated during rising tides when radon and other dissolved constituents are released from the mangrove soil. Flushing efficiency of the burrows—defined as the tidal volume divided by the volume of burrows—estimated for the creek drainage area vary seasonally from 25 (wet season) to 100 % (dry season) in this study. The tidal pumping of the mangrove forest soil acts as a significant vector for exchange between the forest and the estuary. Processes that enhance exchange of O2 and other materials across the sediment-water interface could have a profound impact on the environmental response to larger scale processes such as sea level rise and climate change. Compounding the material budgets of the SRSE are additional inputs from groundwater from the Biscayne Aquifer, which were identified using radium isotopes. Quantification of the deep groundwater component is not obtainable, but isotopic data suggest a more prevalent signal in the dry season. These findings highlight the important role that both tidal- and seasonal-scale forcings play on groundwater movement in low-gradient hydrologic systems.

Submergence and Herbivory as Divergent Causes of Marsh Loss in Long Island Sound

Tidal marsh degradation has been attributed to a number of different causes, but few studies have examined multiple potential factors at the same sites. Differentiating the diverse drivers of marsh loss is critical to prescribing successful interventions for conservation and restoration of this important habitat. We evaluated two hypotheses for vegetation loss at two marshes in Long Island Sound (LIS): (1) marsh submergence, caused by an imbalance between sea-level rise and marsh accretion, and (2) defoliation associated with herbivory by the purple marsh crab, Sesarma reticulatum. At our western LIS site, we found no evidence of herbivory: crabs were scarce, and crab-exclusion cages provided no benefit. We attribute degradation at that site to submergence, a conclusion supported by topographic and hydrologic data showing that loss of vegetation occurred only in wetter parts of the marsh. In contrast, at our central LIS site, our observations were consistent with herbivory as a driving force: There were substantial populations of Sesarma, crab-exclusion cages allowed plants to thrive, and vegetation loss took place across a variety of elevations. We also analyzed soil conditions at both sites, in order to determine the signatures of different degradation processes and assess the potential for restoration. At the submergence site, unvegetated soils exhibited high bulk density, low organic content, and low soil strength, posing significant biogeochemical challenges to re-colonization by vegetation. At the herbivory site, unvegetated soils had a characteristic “riddled-peat” appearance, resulting from expansion and erosion of Sesarma burrow networks. The high redox potential and organic content of those soils suggested that revegetation at the herbivory site would be likely if Sesarma populations could be controlled before erosion leads to elevation loss.

Identification of earthworm burrow origins by near infrared spectroscopy: Combining results from field sites and laboratory microcosms

A major obstacle to understanding feeding and burrowing behaviour of earthworms and their impact on soil structure in natural field conditions is that it remains impossible to identify the origins of burrows in the soil matrix. This gap in our knowledge makes it difficult to understand the roles of different earthworm species in creating the burrow network in soils. We tested the utility of near infrared spectroscopy (NIRS) as a new tool to overcome this obstacle. For the first time, we studied the ability of NIRS to detect specific chemical footprints left by different earthworms during the production of burrows, and thereby to identify the origins of burrows produced in the same soil matrix in the field, in terms of the earthworm species that produced them. The method was tested in three study sites (in sandstone, schist and marl geologies), differing in soil mineralogical composition and texture, with well-characterized and partially overlapping earthworm faunas. Burrows collected in the field were identified by comparing their NIR spectral signatures to the signatures of macroaggregates produced by the same earthworm species living in the same soil in laboratory conditions. We showed clearly that burrows of anecic and epi-endogeic earthworm species were characterized by specific NIR spectral signatures, resulting from quantitative and qualitative differences of OM in burrows among species. PLS-DA models conducted on NIR spectral data showed that NIRS technique allowed identification of a mean of 57.1% (±7.4) of burrows in soil monoliths at the sandstone site, 51.6% (±10.2) at the schist site and 46.5% (±8.1) at the marl site. Our study reveals some clear limitations in this method: low predictive abilities in surface soils, inability to discriminate among endogeic species and the requirement for a calibration procedure through the establishment of a site-dependent reference database.

Early Triassic trace fossils from the Three Gorges area of South China: Implications for the recovery of benthic ecosystems following the Permian–Triassic extinction

The Lower Triassic Daye and Jialingjiang formations of the Three Gorges area (South China) record the recovery interval of benthic tracemaking invertebrates following the P–Tr mass extinction. A total of 17 ichnospecies in 14 ichnogenera are documented from Smithian and Spathian strata. Our trace fossil data, in combination with previously published studies, show that ichnodiversity in the Middle Yangtze region increased markedly in the early Spathian. Trace fossils in the Smithian are dominated by simple, small, horizontal burrows, including Didymaulichnus and Planolites, whereas Spathian trace fossils are diverse and abundant with moderate–high bioturbation levels and complex burrow networks, such as Thalassinoides. Both burrow sizes and penetration depths increased gradually from the early Spathian to the middle–late Spathian, implying a gradual recovery pattern for benthic ecosystems. Early Triassic ichnofossils are characterised by aspects of opportunistic behaviour (e.g., low-to-moderate ichnodiversity, low-to-moderate bioturbation, small burrow widths, and shallow tiering), suggesting stressed environmental conditions. The recovery tempo and pattern of ichnocoenoses in South China is likely structured by temporal and spatial changes of the refuge zone in the Early Triassic.

How will the greening of the Arctic affect an important prey species and disturbance agent? Vegetation effects on arctic ground squirrels.

Increases in terrestrial primary productivity across the Arctic and northern alpine ecosystems are leading to altered vegetation composition and stature. Changes in vegetation stature may affect predator-prey interactions via changes in the prey's ability to detect predators, changes in predation pressure, predator identity and predator foraging strategy. Changes in productivity and vegetation composition may also affect herbivores via effects on forage availability and quality. We investigated if height-dependent effects of forage and non-forage vegetation determine burrowing extent and activity of arctic ground squirrels (Urocitellus parryii). We collected data on burrow networks and activity of arctic ground squirrels across long-term vegetation monitoring sites in Denali National Park and Preserve, Alaska. The implications of height-specific cover of potential forage and non-forage vegetation on burrowing behaviour and habitat suitability for arctic ground squirrels were investigated using hierarchical Bayesian modelling. Increased cover of forbs was associated with more burrows and burrow systems, and higher activity of systems, for all forb heights. No other potential forage functional group was related to burrow distribution and activity. In contrast, height-dependent negative effects of non-forage vegetation were observed, with cover over 50-cm height negatively affecting the number of burrows, systems and system activity. Our results demonstrate that increases in vegetation productivity have dual, potentially counteracting effects on arctic ground squirrels via changes in forage and vegetation stature. Importantly, increases in tall-growing woody vegetation (shrubs and trees) have clear negative effects, whereas increases in forb should benefit arctic ground squirrels.

Effects of endogeic earthworms on the soil organic matter dynamics and the soil structure in urban and alluvial soil materials

Earthworms are considered as key actors of soil processes at different spatial and temporal scales and provide essential ecosystem services linked to climate regulation or primary production. However, little is known about their basic functional roles (e.g. organic matter decomposition, soil structuring processes) in perturbed systems such as urban or alluvial soils. Alluvial soils are characterized by regular physical perturbation through flooding and associated erosion/sedimentation processes which are rather similar to perturbations (e.g. temporal instability, spatial heterogeneity) affecting urban soils. Due to their close soil characteristics, we hypothesized that in both cases, soil functioning is similar with respect to soil fauna activity. Under controlled conditions, our objective was to investigate the effects of two endogeic earthworm species, Allolobophora chlorotica (pink morph) and Aporrectodea rosea (the two most abundant species found in the studied urban site), on soil organic matter (SOM) dynamics and soil structure (network of earthworm burrows) comparing an urban and an alluvial soil. We investigated the growth of individuals (weight gain and reproduction success) and assessed their effects on SOM decomposition (cumulative C–CO2 emission, nitrogen and phosphorus mineralization) and soil structure (macroporosity, total length and connectivity of segments) after one and three months of incubation. Our results showed higher growth of A. rosea in the alluvial soil compared to the urban soil. However, the total length of burrows, carbon and nitrogen mineralization were often higher in the urban soil especially when the two species were combined. This trend can be mainly explained by lower organic matter content found in the urban soil which may influence positively the burrowing activity and negatively the growth of earthworms. Endogeic earthworms appear a key feature of the soil functioning in the urban context through their roles on organic matter transformation, the formation and maintenance of the soil structure.

Sedimentological evidence for the Late Holocene sea level change at the Enjefa Beach exposures of Kuwait, NW Arabian Gulf

The mid-late Holocene drop in relative sea level has resulted in the deposition and progradation of coastal facies along the Enjefa Beach in Kuwait, NW Arabian Gulf. These coastal facies display various depositional subenvironments, including landward foreshore beach, tidal channel, shallow tidal channel, and coastal sand flat. The foreshore beach facies consist of dominantly planar laminated beds. Main tidal channel subenvironments are interpreted for the trough cross-bedded facies. The shallow tidal channel deposits are composed of variable oriented planar wedge-shaped and ripple cross-bedded facies. The coastal sand flat deposits consist of extensively burrowed beds with a large network of Ophiomorpha burrows. These exposures are overlain by the recent continental deposits of rubbles and artificial infill. The mere exposed occurrence of these rocks as well as the above facies stacking pattern reflects progradation as a result of relative drop in sea level. Based on the carbon dating of these sediments, the last phase of the relative sea level drop likely occurred around 1,800 years ago. Neotectonics of local structuring, due to the regional northeastward movement of the Arabian Plate under the Zagros Fold Belt, might have a role in this sea receding