Burrow Walls Research Articles

Shrimp burrow in tropical seagrass meadows: An important sink for litter

The abundance, burrow characteristics, and in situ behaviour of the burrowing shrimps Neaxius acanthus (Decapoda: Strahlaxiidae) and Alpheus macellarius (Decapoda: Alpheidae) were studied to quantify the collection of seagrass material, to identify the fate of this collected material, and to determine the importance of these burrowing crustaceans in the nutrient (nitrogen and phosphorus) cycling of two tropical seagrass meadows on Bone Batang, South Sulawesi, Indonesia. Alpheus macellarius harvested 0.70 g dry weight (DW) burrow −1 d −1 seagrass material, dominantly by active cutting of fresh seagrass leaves. Neaxius acanthus collected 1.66 g DW burrow −1 d −1, mainly detached leaves which floated past the burrow opening. The A. macellarius and N. acanthus communities together collected in their burrows an amount of seagrass leaf material corresponding to more than 50% of the leaf production in the meadows studied. The crustacean species studied might therefore fulfil an important function in the nutrient cycling of tropical meadows. In the burrow most of the collected material is shredded into pieces. The burrows of both species had special chambers which serve as a storage for seagrass leaf material. Neaxius acanthus incorporated most of the material into the burrow wall lining, which is made of small sediment particles and macerated seagrass leaves. Phosphate concentrations measured in N. acanthus burrows compared with pore-water and water-column concentrations suggests that a substantial amount of the seagrass material undergoes decomposition in the burrows. Oxygen levels measured in these water bodies are indicative for a possible exchange of water between the burrow and its surroundings, most likely supported by the shrimps irrigating their burrows. By collecting leaf material in their burrows, nutrients that are otherwise lost from the seagrass meadow associated with detached leaves and leaf fragments carried away in the water column, are maintained in the meadow and may form an important source of recycled nutrients.

KATBERGIA GEN. NOV., A NEW TRACE FOSSIL FROM UPPER PERMIAN AND LOWER TRIASSIC ROCKS OF THE KAROO BASIN: IMPLICATIONS FOR PALAEOENVIRONMENTAL CONDITIONS AT THE P/TR EXTINCTION EVENT

Abstract: A new ichnogenus and ichnospecies of burrow, Katbergia carltonichnus, are described from Upper Permian and Lower Triassic rocks of the Karoo Basin, South Africa, where they are preserved in pedogenically modified overbank deposits that are interpreted as inceptisols subsequently gleysol overprinted. Sigmoidal burrows consist of a long (≥0.5 m) cylindrical tube, ranging from 1–2 cm in diameter, terminating in a slightly larger living chamber. The burrows are unlined and passively filled, preserving a hierarchy of scratch patterns on the burrow walls. Scratch patterns include longitudinal, transverse, and crescent‐shaped markings found around the circumference of the burrow, but which are less densely concentrated on the burrow floor. Calcareous concretions are associated with burrowed siltstone intervals, generally restricted to the lowermost decimetre, with nodules nucleating around burrows. Stable δ13C and δ18O isotope data on calcite cement in the burrow fill, entombing siltstone, and associated calcareous nodules all cluster together when plotted, indicating that nodule formation occurred following burrow horizon abandonment and a rise in regional water table. Isotopic data reflect calcite precipitation under a semi‐closed system in saturated conditions. A model for burrow emplacement, abandonment and infill, and subsequent cementation by calcite is presented demonstrating that previous interpretations of Late Permian and Early Triassic palaeosol types associated with the P/Tr extinction event must be re‐evaluated.

Accurate quantification of the influence of benthic macro- and meio-fauna on the geometric properties of estuarine muds by micro computer tomography

This paper describes the novel application of high resolution micro computer tomography (microCT) to the quantification of the properties of marine biogenic structures. CT scanning has been used to examine sediments in the past but the resolution of most previous techniques has been dependent upon commercial medical CT scanners which only have a slice thickness of ≥ 0.625 mm. In addition adequate software has not previously been available to rapidly quantify all the properties of biogenic structures. The microCT technique developed here used a standard core sample of estuarine sediment and new software was developed to calculate the axial variation of the following burrow parameters: number, diameter, volume, surface area and density. The increased resolution has resulted in the first quantification of meiofaunal burrow structures. A test core has shown, as an example, that the total volume of burrows created by macrofaunal organisms decreased from 827 mm 3, within the top 15 mm of the core, to 204.2 mm 3 at a depth 60 –75 mm within the core. Total burrow surface area decreased from 1883 mm 2 to 512 mm 2, for these depth ranges, respectively and burrow diameter ranged from 2.37–2.58 mm, remaining fairly constant between depths. Meiofaunal burrow structures decreased from 1.3–0.1 mm 3 within the top 6 mm of the core with burrow surface area decreasing from 33.52–3.4 mm 2. Again, burrow diameter remained relatively constant, ranging from 0.23–0.25 mm. Quantification to this resolution is required to identify the impact of infaunal organisms on factors such as oxygen penetration, vertical and horizontal (across burrow walls) gradients in redox conditions and chemical/nutrient speciation and flux. The quantification of these burrow properties will improve the ability to examine the interrelationships between chemical, physical and biological processes and their role in ecological functioning. The present study indicates that there is potential for further development of this software to allow more detailed analysis of burrow structures and surface features including parameters such as burrow length, shape and sediment surface roughness.

Seasonal discrepancies in denitrification measured by isotope pairing and N2:Ar techniques

Isotope pairing (IP) and N2:Ar techniques for measuring sediment denitrification were compared in muddy sediments in a shallow sub-tropical embayment. At a concentration of 100 µM 15 NO 3 - (our experimental conditions), IP greatly underestimated denitrification, compared to N 2:Ar, in low-respiration sediments subject to bioturbation, where denitrification produced via coupled nitrifica- tion-denitrification (Dn) dominates overall denitrification. Consistent with this underestimation was the higher N2 flux measured using N2:Ar ratios, accounting for more of the stochimetrically predicted N mineralisation. We suggest that this underestimation is primarily due to non-homogenous mixing of the added 15 NO3 - with the endogenous 14 NO3 - in the sediment, associated with differentials in the rate of diffusion of 15 NO3 - across mucus linings in burrow structures versus rates of 14 NO3 - supply from nitri- fiers in the burrow walls. Strong support for this hypothesis was provided by the relationship between the methods discrepancy and polychaete biomass (r 2 = 0.99; p = 0.001), and the almost complete removal of the methods discrepancy when the upper heterogenous sediment layer that contained the burrow structures was experimentally removed. Due to a significant increase in potential denitrifica- tion sites in association with burrow structures, this effect can potentially cause a large underestima- tion of denitrification (up to 85%) using the IP technique. Our data show no benefit in longer pre- incubation times, suggesting that this effect may represent a fundamental limitation of the IP method in the sediments of oligotrophic (low carbon loading) systems. As such, the N2:Ar flux technique rep- resents a more realistic estimation of net denitrification in sediments with low organic carbon contents and low respiration rates and significant bioturbation. Most importantly, the present study also demon- strated that methodological comparisons need to be made over a range of environmental conditions.

Microbial activity and accumulation of organic matter in the burrow of the mud shrimp, Upogebia major (Crustacea: Thalassinidea)

Microbial activity and accumulation of organic matter in the burrow of the thalassinidean mud shrimp, Upogebia major, were studied on a tidal flat along the northern coast of Tokyo Bay, Japan. The burrow of U. major is Y-shaped with an upper U-shaped part plus a lower I-shaped part. Its lower part can extend to a depth of 2 m. In the present study, we compare electron transport system activity (ETSA), bacterial abundance and organic matter content [total organic carbon (TOC), total nitrogen (TN) and chlorophyll a (chl. a)] of the burrow wall sediment with the tidal flat surface and non-burrow sediments. We also compared the U- and I-shaped part in terms of these parameters. ETSA in the burrow wall was higher than at the tidal flat surface in the warmer season, and was always higher than at surrounding non-burrow sediments. Bacterial abundance in the burrow wall was higher than at the tidal flat surface and surrounding sediment. TOC and TN contents in the burrow wall were two to three times higher than those at the tidal flat surface and non-burrow sediments, regardless of season. However, there was no significant difference in chl. a content between burrow wall and tidal flat surface. These results suggest that organic enrichment of the burrow wall is a result of organic matter particles such as phytodebris accumulation along the burrow wall. For all parameters of the burrow walls, no statistical differences were found between the two parts. Present results indicate that U. major actively transports the water containing suspended organic particles not only through the U-part but also into the deeper I-part. These indicate that burrow of the mud shrimp provides a dynamic environment for microbial community in tidal flat sediment.

Nutrient dynamics in mangrove crab burrow sediments subjected to anthropogenic input

Bioturbation by burrowing macroinvertebrates has a major impact on sediment properties, pollutant redistribution, and biogeochemical cycling. We assessed the impact of bioturbation on the nutrient dynamics and organic matter of sediments receiving anthropogenic inputs in the Manko wetland, located in southern Okinawa, Japan. We compared sediments that were and were not subjected to the activities of the tidal-flat crab Helice formosensis. The fatty acid composition of sediments indicated that different sources contributed to the organic matter profile. Agricultural and domestic waste discharge seemed to induce a high amount of green macroalgae and bacteria in the tidal flat. Sediments without crabs exhibited 2.1–2.4× more NH 4-N release, which was associated with a low C/N ratio during the summer. In the crab burrow sediments, NO 3-N concentrations were 1.4–1.9× more pronounced during winter. A significant correlation existed between NO 3-N and NO 2-N concentrations in sediments of the burrow chamber (r = 0.837, p < 0.02) and the mixed zone of burrow opening shaft and chamber (r = 0.885, p < 0.01). We suggest that burrow wall sediments provide ideal conditions for nitrate reduction (denitrification). H. formosensis thus contributes to balancing the effects of anthropogenic inputs by removing nitrogen loads in sediments.

Simulated fiddler-crab sediment mixing

Using a lattice-automaton model, we simulate the effects of fiddler crabs on the distribution of excess Pb in marsh sediments. Three previously-identified modes of bioturbation are investigated: (1) removal-and-fill, where material is excavated to the sediment-water interface and burrows, when abandoned, are subsequently filled by surface material, (2) removal-and-collapse, where the infilling occurs by collapse of the burrow walls, and (3) partial-compaction-and-collapse, where part of the excavated sediment is packed into the burrow wall and abandoned burrows subsequently collapse. These various mixing modes lead to somewhat different laterally-integrated Pbex profiles, which are also influenced by burrowing frequency, burrow dimensions, fraction of surface material replaced by new sediment (regeneration), and the fraction of material compacted during burial. Using parameters from a previous study in a South Carolina marsh, we find that data from low-marsh sites are best predicted by the partial-compaction-and-collapse process; this is consistent with the observation that burrow casts indicate far more material is excavated than is deposited as pellets at the sediment-water interface. The profile from the high-marsh site is best simulated by removal-and-fill mixing, with 50% regeneration of material at the sediment-water interface; this is consistent with less frequent flooding at this site. We have also calculated the exchange function for each of these mixing modes and show that they are highly asymmetric, indicating that the mixing is not diffusive. Only in the case of partialcompaction-and-collapse does the exchange function approach a diffusive form when the excavation rate decreases, i.e., the probability of compaction increases.

Occurrence of bioglyphs on Ocypode crab burrows in a modern sandy beach and its palaeoenvironmental implications

The ichnological term “bioglyph” covers biogenic sculpture on burrow walls. Bioglyphs in the burrows of ocypodid crabs were studied in a modern unconsolidated sandy substrate (looseground) on Irino Coast, southwestern Japan. They are seen exclusively on sides and roof of the burrow, and are characteristically seen near the distal end of the burrow. Moist sandy substrate where sand particles are bound together by surface tension of interstitially suspended water might allow the production of such bioglyphs. Although bioglyphs are only partially developed in such burrows, those interpreted to have formed in semi-consolidated substrates (firmground) are known to be sculptured over the entire burrow surface. Such difference in the modes of bioglyph occurrence can be used as a criterion to reconstruct the substrate consistency in the rock record.

The relationship between Chironomus plumosus burrows and the spatial distribution of pore‐water phosphate, iron and ammonium in lake sediments

Summary1. To study the influence of chironomids on the distribution of pore‐water concentrations of phosphate, iron and ammonium, we conducted a laboratory experiment using mesocosms equipped with two‐dimensional pore‐water samplers, filled with lake sediment and populated with different densities of Chironomus plumosus.2. Specially designed mesocosms were used in the study. A 6‐mm deep space between the front plate and the pore‐water sampler at the back plate was just thick enough to allow the chironomids to live undisturbed, yet thin enough to force all the burrows into a two‐dimensional plane.3. The courses of the burrows were observed during the experiment as oxidised zones surrounding them, as well as being identified with an X‐ray image taken at the end of the experiment.4. We investigated the relationship between C. plumosus burrows and spatial patterns of pore‐water composition. Concentrations of the three ions were significantly less around ventilated burrows (54% to 24%), as bioirrigation caused a convective exchange of pore‐water enriched with dissolved species compared with the overlying water, and also because oxygen imported into the sediment resulting in nitrification of ammonium, oxidation of iron(II) and a co‐precipitation of phosphate with Fe(III) oxyhydroxides.5. In mesocosms with chironomids, new (redox) interfaces occurred with diffusive pore‐water gradients perpendicular to the course of burrows and the site of major phosphate, ammonium and iron(II) release shifted from the sediment surface to the burrow walls.

Influences of Infaunal Burrows on the Community Structure and Activity of Ammonia-Oxidizing Bacteria in Intertidal Sediments

Influences of infaunal burrows constructed by the polychaete (Tylorrhynchus heterochaetus) on O(2) concentrations and community structures and abundances of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in intertidal sediments were analyzed by the combined use of a 16S rRNA gene-based molecular approach and microelectrodes. The microelectrode measurements performed in an experimental system developed in an aquarium showed direct evidence of O(2) transport down to a depth of 350 mm of the sediment through a burrow. The 16S rRNA gene-cloning analysis revealed that the betaproteobacterial AOB communities in the sediment surface and the burrow walls were dominated by Nitrosomonas sp. strain Nm143-like sequences, and most of the clones in Nitrospira-like NOB clone libraries of the sediment surface and the burrow walls were related to the Nitrospira marina lineage. Furthermore, we investigated vertical distributions of AOB and NOB in the infaunal burrow walls and the bulk sediments by real-time quantitative PCR (Q-PCR) assay. The AOB and Nitrospira-like NOB-specific 16S rRNA gene copy numbers in the burrow walls were comparable with those in the sediment surfaces. These numbers in the burrow wall at a depth of 50 to 55 mm from the surface were, however, higher than those in the bulk sediment at the same depth. The microelectrode measurements showed higher NH(4)(+) consumption activity at the burrow wall than those at the surrounding sediment. This result was consistent with the results of microcosm experiments showing that the consumption rates of NH(4)(+) and total inorganic nitrogen increased with increasing infaunal density in the sediment. These results clearly demonstrated that the infaunal burrows stimulated O(2) transport into the sediment in which otherwise reducing conditions prevailed, resulting in development of high NH(4)(+) consumption capacity. Consequently, the infaunal burrow became an important site for NH(4)(+) consumption in the intertidal sediment.

Effects of ghost shrimp on zinc and cadmium in sediments from Tampa Bay, FL

This study investigated the effects that ghost shrimp have on the distribution of metals in sediment. We measured levels of HNO 3-extractable zinc and cadmium in surface sediment, in ghost shrimp burrow walls and in sediment ejected by the ghost shrimp from their burrows, at five sandy intertidal sites in Tampa Bay. Ghost shrimp densities and their rate of sediment ejection were also quantified, as were sediment organic content and silt + clay content. Densities of ghost shrimp ( Sergio trilobata and Lepidophthalmus louisianensis) averaged 33/m 2 at our sites, and they ejected sediment at an average rate of 28 g/burrow/day. Levels of both Zn and Cd were significantly higher in burrow walls than in surface sediments. Sediment ejected by the shrimp from their burrows had elevated levels of Zn (relative to surface sediments) at one of the sites. Sediment organic content and silt + clay content were higher in burrow-wall sediments than in ejected sediment, which in turn tended to have values above those of surface sediments. Differences in levels of HNO 3-extractable Zn and Cd among sediment types may be a consequence of these sediments differing in other physiochemical characteristics, though the differences in metal levels remained statistically significant for some sites after correcting for differences in organic content and silt + clay content. We conclude that the presence of ghost shrimp burrows contributes to spatial heterogeneity of sedimentary metal levels, while the ghost shrimp bioturbation results in a significant flux of metals to the sediment surface and is expected to decrease heterogeneity of metal levels in sedimentary depth profiles.

Time-resolved pH imaging in marine sediments with a luminescent planar optode

A laboratory-based optical pH sensor for 2-dimensional pH imaging at benthic interfaces is presented. The sensor consists of a single-layer hydrogel matrix embedding the fluorescent pH indicator 2′, 7′-dihexyl-5(6)-Noctadecyl-carboxamidofluorescein ethyl ester (DHFAE) and the phosphorescent ruthenium(II)-Tris-4,7-diphenyl1,10-phenanthroline incorporated in nanoparticles, serving as an inert reference standard. The measuring principle is based on time domain dual-lifetime referencing (t-DLR). The fluorophore/phosphor couple is simultaneously excited by a green LED (λ max 530 nm) pulsed in the microsecond range, and the sensor emission is recorded by a fast-gateable CCD camera. For each pH image, intensity images in 2 time windows (1 during and 1 after the excitation phase) are taken. The ratio of these 2 images is proportional to the pH of the sample and not affected by the overall signal intensity. The sensor has a dynamic range suitable for marine conditions (pH 7.3 to 9.3) with an apparent pK a of 8.3. The sensor was long-term stable (months) when kept in darkness and had a response time of < 200 s when going from pH 8.3 to 7.6. Light proved to have a negative effect on the sensor performance due to photobleaching of the pH indicator, resulting in a negative drift in the signal ratio at higher pH after prolonged light exposure. The spatial resolution (83 by 83 μm/pixel) of the sensor was capable of resolving smallscale spatial variability in the pH at a heterogeneous sediment-water interface, and time series of calibrated pH images also expressed a marked temporal variability in the pH distribution across this interface. Hotspots with intensified microbial activity were observed, and pH minima along burrow walls of polychaetes indicated elevated diagenetic activity in these zones. Individually extracted profiles from the pH images agreed well with independently measured pH microelectrode profiles, confirming the robustness of the approach.

Two-dimensional pH distributions and dynamics in bioturbated marine sediments

The seafloor is the site of intense biogeochemical and mineral dissolution–precipitation reactions which generate strong gradients in pH near the sediment-overlying water interface. These gradients are usually measured in one-dimension vertically with depth. Two-dimensional pH distributions in marine sediments were examined at high resolution (65 × 65 μm pixel) and analytical precision over areas of ∼150 to 225 cm 2 using a newly developed pH planar fluorosensor. Dramatic three-dimensional gradients, complex heterogeneity, and dynamic changes of pH occur in the surficial zone of deposits inhabited by macrofauna. pH can vary by ±2 units horizontally as well as vertically over millimeter scales. pH minima zones often form in association with redoxclines within a few millimeters of inner burrow walls, and become more pronounced with time if burrows remain stable and irrigated for extended periods. Microenvironmental pH minima also form locally around decaying biomass and relict burrow tracks, and dissipate with time (∼5 d). H + concentrations and fluxes in sandy mud show complex acid–base reaction distributions with net H + fluxes around burrows up to ∼12 nmol cm −2 d −1 and maximum net reaction rates varying between −90 (consumption) to 120 (production) μM d −1 (∼90 nmol cm −1 d −1 burrow length). Acid producing zones that surround irrigated burrows are largely balanced by acid titration zones along inner burrow walls and outer radial boundaries. The geometry and scaling of pH microenvironments are functions of diagenetic reaction rates and three-dimensional transport patterns determined by sediment properties, such as diffusive tortuosity, and by benthic community characteristics such as the abundance, mobility, and size of infauna. Previously, undocumented biogeochemical phenomena such as low pH regions associated with in-filled relict biogenic structures and burrowing tracks are readily demonstrated by two-dimensional and time-dependent images of pH and sedimentary structure.

Burrows of Pestarella tyrrhena (Decapoda: Thalassinidea): hot spots for Nematoda, Foraminifera and bacterial densities

Burrow wall sediment (BWS) and chamber debris (CD) of Pestarella tyrrhena burrows were isolated and compared to surrounding sediments differentiated into surface sediment (SS), deep ambient sediment (DAS) and embedded ambient organic debris (EAD). The focus was on the meiofauna community along with granulometric characteristics including organic content (OC) and bacterial abundances.Clear trends were found for all parameters: the shrimp significantly increased OC within its burrow and affected grain size distributions. The oxidized burrow walls were highly consolidated, consisted of poorly sorted sediment enriched with silt and clay, and contained small particles of macrophyte debris, while coarse inorganic and organic particles &gt;500 μm were concentrated in the CD. Bacterial abundances (epifluorescence microscopy direct counts, SYBR Gold staining) were positively correlated with OC and were significantly higher in BWS than in SS or DAS. Nematode numbers were elevated three-fold and foraminiferal densities by two orders of magnitude in BWS versus non-burrow sediments. Among the anoxic sediments (DAS, EAD, CD) meiofauna densities in CD were highest. Nematode community analysis (PCA, CANOCO) revealed considerable differences between BWS and SS. The BWS harboured more taxa and was dominated by deposit feeders, while in SS epistrate feeders prevailed.These effects on different levels demonstrate the ability of P. tyrrhena to create a specific microenvironment within the burrow. The burrow walls were most influenced by the shrimp's activity, which corresponds to their nutritional role.

High Temporal Resolution Oxygen Imaging in Bioirrigated Sediments

A technique is presented for temporal characterization of the bioirrigation activity of benthic macrofauna and for quantitative estimation of its effects on the oxygen exchange between the sediment and the overlying water. The technique is based on high temporal resolution (15-30 s) oxygen imaging aided by a planar oxygen optode and can be applied under laboratory and field conditions, both freshwater and marine. It allows direct observation of the complex 2D oxygen dynamics in the sediment around the burrow while the animal dwells undisturbed in its natural environment. The conditions to which the animal is exposed can easily be controlled or manipulated. Chironomus plumosus, widely distributed freshwater insect larvae, were used in a case study. Their bioirrigation activity was divided into a random succession of pumping intervals (duration 5.4 +/- 1.7 min) and rest periods (duration 9.2 +/- 5.8 min). The burrow ventilation resulted in a highly variable volume of the oxygenated sediment surrounding the burrow and the associated sedimentary oxygen uptake rate through the burrow wall (OUB), both changing dramatically within minutes. Their variability was higher in a burrow under construction than around a stationary burrow. The average OUB rate (approximately 0.15 micromol O2 h(-1)), when translated into a time-averaged 02 flux across the burrow wall, constituted approximately 64% of the stationary diffusive oxygen flux measured at the sediment-water interface (approximately0.9 mmol O2 m(-2) h(-1)).

Possible burrows of mylagaulids (Rodentia: Aplodontoidea: Mylagaulidae) from the late Miocene (Barstovian) Pawnee Creek Formation of northeastern Colorado

The massive siltstone beds of the late Miocene (Barstovian) Pawnee Creek Formation in Logan County, northeastern Colorado, contain abundant terrestrial vertebrate burrows. Among these are distinctive claw-marked burrows attributable to the extinct mylagaulid rodent Pterogaulus [= Mylagaulus] laevis Korth, 2000. These burrows differ in several respects from the spiraling Daemonelix burrows of fossorial beavers. The Pawnee Creek burrows are slightly ovate in cross-section, tubular, and sinuous rather than helical. They consist of primary tunnels of up to at least 7 m long and range from 11 to 18 cm in diameter. They occasionally branch into secondary tunnels. Burrow walls and terminations show prominent, parallel ridges in sets of two to three, up to 9.3 mm deep and 3.7 mm wide. The burrows are too large to have been made by anything but a vertebrate, and their considerable length and complexity implies a mammalian excavator. The meandering, branching morphology resembles the burrow systems of extant fossorial rodents, such as pocket gophers ( Geomys) and mole rats ( Spalax, Myospalax). Skeletal remains of P. laevis are abundant at sites where the burrows occur, with at least eight individuals represented by humeri in a collected sample. Although mylagaulid remains are not unequivocally associated with fossil burrows, the curved, laterally compressed claws and phalangeal arrangement of mylagaulids produce marks very similar in size and morphology to the ridges on the burrows. Position and pattern of the ridges indicate downward-and-backward motions of the mani, possibly supplemented by motions of the pedes to kick loosened soil backward. A new ichnogenus, Alezichnos, and new ichnospecies, chelecharatos, are erected to describe these burrows.

Microscale oxygen distribution in various invertebrate burrow walls

ABSTRACTProfiles 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.

Bioirrigation in permeable sediments: Advective pore-water transport induced by burrow ventilation

The physical mechanism that drives bioirrigation is strongly dependent on the permeability of the sediment. We advance two mechanisms, each described by a corresponding microenvironment model. In muds, burrow water cannot penetrate the sediment, so bioirrigation is intrinsically driven by diffusional transfer across the burrow wall. This “diffusive” mode of bioirrigation is accurately described by the classical tube irrigation model. In sands, ventilation flows can penetrate the surrounding sediment via dead end burrows. To quantify this “advective” mode of bioirrigation, we propose a novel two-dimensional pocket injection model. This model’ principal features are that (1) organisms indent the sediment-water interface with burrow structures, (2) the specific structure of the burrow can be neglected except for the location of a feeding pocket, and (3) burrow water is injected from this feeding pocket into the surrounding sediment. We tested the adequacy of the pocket injection model in a detailed case study of the lugworm Arenicola marina, comparing model simulations and experimental data from core incubations. Simulation of two different sets of inert tracer experiments shows good agreement between model and data, indicating that our model captures the relevant aspects of lugworm bioirrigation in permeable sediments.

The sediment-water interface increment due to the complex burrows of macrofauna in a tidal flat

The architecture of macrofaunal burrows and the total area of the sediment-water interface created by biogenic structure were investigated in the Donggeomdo tidal flat on the west coast of Korea. Resin casting methods were applied to recover burrows of four dominant species, Macrophthalmus japonicus, Cleistostoma dilatatum, Perinereis aibuhitensis, and Periserrula leucophryna, and whole burrows within the casting area at three sites in different tidal levels.P. leucophryna excavated the largest burrow in terms of a surface area among them. In the case of whole burrow casting, the space occupied by the biogenic structure was extended into deeper and expanded more greatly at the higher tidal level. In the uppermost flat, the burrow wall surface area within sediment was more extensive than the sediment surface area. Increased oxygen supply through the extended interface could enhance the degradation rates of organic carbon and also change the pathways of degradation. Quantifying the relationship between the extended interface and mineralization rate and pathway requires more extensive study.

Irrigation patterns in permeable sediments induced by burrow ventilation: a case study of Arenicola marina

In sandy sediments, a strong connection exists between the physics of flow and the ecol- ogy of burrow-ventilating macrofauna. We developed a general modelling procedure that quantifies this link involving 3 steps. (1) Burrow-ventilating organisms can be described as mechanical pumps. (2) The pumping of burrow water into blind-ending tubes induces advective flow in the sediment. (3) The resistance to pore water flow is governed by the friction between solid and fluid, i.e. Darcy's law. This analysis allows the determination of the operation point of an 'organism pump' under in situ conditions, and we applied it in a detailed modelling study of the lugworm Arenicola marina. A 3-dimensional finite element model encompasses the lugworm's J-shaped burrow and represents a typical lugworm territory at in situ density. We simulated the associated flow patterns in the sediment and analysed the factors that influence the lugworm's ventilation rate. Since the lugworm's oxygen supply critically depends on the burrow ventilation rate, we advance the following 2 ecological hypotheses: (1) decreasing the permeability of the burrow lining greatly increases the efficiency of oxygen supply, as it prevents the re-entry of anoxic pore water; and (2) the permeability of the bulk sediment constrains the lugworm's habitat. When permeability falls below a critical threshold, the sediment's resistance becomes too high, thus resulting in an insufficient oxygen supply. Overall, we show that permeability exerts an important control on ventilation activity, and hence resource avail- ability, in sandy sediment ecosystems. From an evolutionary point of view, we anticipate biological feedbacks on this physical control — in particular, behavioural adaptations that increase the perme- ability in the bulk sediment but decrease the permeability near the burrow wall.