Burrow Linings Research Articles

Responses of biomarkers, joint effect and drilosphere bacterial communities to antimony (III and/or V) contamination

Contamination of soils with antimony (Sb) is becoming increasingly severe and widespread, and the associated ecological risks cannot be ignored. To evaluate how different Sb forms affected the earthworm Eisenia fetida in soil, the biomarker response index (BRI), effect addition index (EAI), and microbial diversity were characterized after single and joint application of Sb(III) and Sb(V). The results showed that Sb(III) was better enriched by earthworms than Sb(V). The metallothionein (MT) content in earthworms increased under Sb stress, and the superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) activities also showed an increasing trend, suggesting waken-up antioxidant capacity. Severe alterations for health status were observed under combined treatment. Additionally, the EAI indicated that Sb(III) and Sb(V) had synergistic and antagonistic effects at low and high concentrations, respectively. The bacterial populations in the drilosphere (gut and burrow lining) appeared to be more susceptible to Sb contamination than in the non-drilosphere, their specific microecology may be an important factor in soil Sb migration and transformation. The abundance of Actinobacteria exhibited a significant decrease with increasing concentrations of single Sb(III) and Sb(V), while the abundance of Bacteroidia increased. The correlation heatmap showed that Sphingobacterium faecium was highly tolerant to Sb. These results provide not only an important basis for the ecological risk assessment of Sb in the soil environment but also new insights into the altered drilosphere bacterial communities under Sb stress.

Archaeichnium haughtoni: a robust burrow lining from the Ediacaran–Cambrian transition of Namibia

AbstractFollowing various assignments to Archaeocyatha, worm tubes, and finally incertae sedis, the enigmatic Ediacaran–Cambrian taxon Archaeichnium haughtoni has in recent years come to represent somewhat of a wastebasket taxon to which the indeterminate tapering tubular forms common across this interval are assigned. This ‘catch‐all’ status has been aided in part by both suboptimal specimen photography and the temporary loss of the holotype after its second redescription in 1978. Recent rediscovery of the A. haughtoni holotype in the collections of the Iziko South African Museum in Cape Town has enabled a much‐needed re‐assessment of this critical and cryptic taxon, with results suggesting that this material from the latest Ediacaran or earliest Cambrian of Namibia is among the earliest fossil record examples of marine worm burrow linings, and the oldest examples of linings robust enough to withstand exhumation and current transport. These traces indicate the emergence of this important animalian ecosystem engineering behaviour closer to the Ediacaran–Cambrian boundary than previously thought.

A rock-boring and rock-ingesting freshwater bivalve (shipworm) from the Philippines.

Shipworms are a group of wood-boring and wood-feeding bivalves of extraordinary economic, ecological and historical importance. Known in the literature since the fourth century BC, shipworms are both destructive pests and critical providers of ecosystem services. All previously described shipworms are obligate wood-borers, completing all or part of their life cycle in wood and most are thought to use wood as a primary source of nutrition. Here, we report and describe a new anatomically and morphologically divergent species of shipworm that bores in carbonate limestone rather than in woody substrates and lacks adaptations associated with wood-boring and wood digestion. The species is highly unusual in that it bores by ingesting rock and is among the very few known freshwater rock-boring macrobioeroders. The calcareous burrow linings of this species resemble fossil borings normally associated with bivalve bioerosion of wood substrates (ichnospecies Teredolites longissimus) in marginal and fully marine settings. The occurrence of this newly recognized shipworm in a lithic substrate has implications for teredinid phylogeny and evolution, and interpreting palaeoenvironmental conditions based on fossil bioerosion features.

Diopatra cupreaworm burrow parchment: a cautionary tale of infaunal surface reactivity

Many infaunal marine invertebrates produce mucus excretions that play an important role in metal binding, authigenic mineralization and burrow stabilization. To date, only a handful of studies have characterized the functional groups that control the surface reactivity of burrow linings and backfills. This makes it difficult to place estimates on the overall impact that bioturbation has on metal cycling in tidal flats, the inner shelf, estuaries and other shallow marine environments. Here, we examined the parchment linings of Diopatra cuprea burrows from the Ogeechee River estuary near Savannah, Georgia, USA. Acid–base titrations coupled with Fourier transform infrared spectroscopy demonstrate that the parchment is essentially composed of hydroxyl (R-OH) groups, yielding total ligand densities of only 0.017 mmol/g. To place this value into context, it is orders of magnitude less than previously reported mucopolysaccharides for other marine worms, indicating that D. cuprea is essentially unreactive in the estuarine waters from which it was collected. This was corroborated by minimal Cd2+ adsorption to, and limited silicification of, pre-rinsed parchment. The lack of silica adsorption was surprising given that the parchment was generally coated with an abundance of quartz grains when extracted from the sediment. This suggests that perhaps the physical, rather than chemical, characteristics of the parchment material were responsible for this association. Indeed, scanning electron microscope images show that the parchment is fibrous and envelopes quartz grains, implying that detritus may get trapped by the parchment mesh. It appears that unlike many other infaunal mucopolysaccharide-rich linings that might be produced to provide reactive surfaces to which dissolved metal cations can adsorb for the organism's nutritional benefit, the parchment of D. cuprea may instead function to protect the animal from stresses such as predation or high-energy disturbances.

Feeding strategies in symbiotic and asymbiotic thyasirid bivalves

Many bivalves living in symbiosis with chemoautotrophic bacteria are mixotrophs, deriving nutrients both from their symbionts and from external sources. The bivalve family Thyasiridae contains symbiotic and asymbiotic species that live infaunally and presumably suspension-feed. Symbiotic thyasirids use their foot to construct numerous elongate and ramified burrows, or pedal tracts, in surrounding sediments; pedal tracts were interpreted as conduits for accessing reduced sulfur required by gill-associated symbionts. Recently, some asymbiotic thyasirids were found to form similar burrows, and this behaviour, accompanied by the irrigation of pedal tracts, was thought to be associated with deposit feeding. We used stable isotope analyses to examine the food sources of three taxa of co-occurring symbiotic and asymbiotic thyasirids sampled from a fjord in Newfoundland, Canada at different dates and sampling sites. We considered suspended particulate organic matter, sedimentary organic matter, and sulfur-oxidizing bacteria as potential food sources, and found that sediment organic matter characteristics varied significantly according to site but not sampling date, and that suspended organic matter near the seafloor was of relatively low quality and abundance at all dates and sites. The non-gill tissues of symbiotic and asymbiotic thyasirids had similar carbon isotopic compositions, but nitrogen isotope signatures were heavier and less variable in asymbiotic taxa than in the symbiotic Thyasira cf. gouldi. The two asymbiotic thyasirid species studied herein appeared to vary in their feeding strategies, with Parathyasira appearing to mostly farm sulfur-oxidizing bacteria along burrow linings and then collect them using their foot (a mode of bivalve deposit-feeding known as pedal feeding). This work expands our understanding of the breadth of feeding strategies in the widespread and often abundant thyasirid bivalves, and provides support for microbial farming along burrow linings in some thyasirids.

Bioturbation influence on reservoir rock quality: A case study of Well Bian-5 from the second member Paleocene Funing Formation in the Jinhu sag, Subei basin, China

The bioturbated horizons identified from Member Two of the Paleocene Funing Formation (E1f2) in the Jinhu sag, have not been previously assessed to ascertain their influence on reservoir quality. Owing to that, conventional thin section, pulse decay permeametry, pressure decay porosimetry, Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray Spectroscopy (EDS) methods were used to analyze the significance of bioturbation in controlling porosity and permeability on selected cored intervals from one well. Intensely bioturbated core slab samples A and B selected from Bian-5 Well are dominantly controlled by Ophiomorpha and Macaronichnus, and Macaronichnus, respectively. Results showed that Ophiomorpha and Macaronichnus in sample A exhibited sediment cleaning activity with better sorted grains in burrow fillings. Mud and clay were removed from the burrow filling and directed towards burrow lining and/or host sediment by burrowing organism resulting in well sorted burrow fill matter; the net effect, enhanced isotropy and increased porosity in burrows fills. Macaronichnus ichnofabrics in sample B also exhibited sediment cleaning activity causing reduction of local porosity in host sediment and an outcome of permeability improvement in burrows. Reservoir quality of bioturbated sandstone of Bian-5 well in the Jinhu sag is, therefore, dependent on activity of burrowing organism, burrow structure, bioturbation extent as well as the existence or nonexistence of burrow fill or lining.

Reniformichnus katikatii (New Ichnogenus and Ichnospecies): Continental Vertebrate Burrows from the Lower Triassic, Main Karoo Basin, South Africa

ABSTRACTThe formal ichnotaxonomic assignment of a new ichnogenus and ichnospecies, Reniformichnus katikatii, is presented based on the holotype and several field specimens from the Lower Triassic Katberg Formation in the main Karoo Basin of South Africa. The holotype is an inclined, burrow cast with bilobate base and reniform cross-section. Its width ranges from 12.6 to 14.7 cm, and its height is 5 to 7.4 cm resulting in an aspect ratio of 1.89 to 2.74. The surface preserves 70–180 mm long ridges running parallel to the long axis of the burrow on the upper parts of the walls and lower parts of the dorsum and shorter ridges (average length ∼27 mm) are preserved on the more ventral areas in two opposite orientations, cross-cutting each other in a rhomboid pattern. Burrow fills are passive and consist of slightly bedded, laminated, or massive clastic rocks that are coarser than the host mudstones. The burrow casts are isolated, never occurring in clusters. This simple burrow shows no evidence for branching, spiralling, interconnected tunnels, burrow linings, terminal chambers, or entrances. Preserved in fluvial floodplain mudstone units, the burrows were passively filled by layered, laminated, or massive sand and other coarser clastic sediments. The burrow casts are morphologically similar to unnamed Antarctic ichnotaxa that have been attributed to tetrapods (e.g., therapsids, procolophonids), extending the geographic range of the potential producers of Reniformichnus isp. to continental settings in southern Gondwana. Biostratigraphic evidence on the temporal distribution of Reniformichnus isp. suggests that the trace maker emerged in the aftermath of the Permo-Triassic mass extinction event to successfully burrow throughout the Early Triassic.

Echinoderm ichnology: bioturbation, bioerosion and related processes

AbstractAmong invertebrates and both in modern and ancient marine environments, certain echinoderms have been and are some of the most active and widespread bioturbators and bioeroders. Bioturbation and/or bioerosion of regular and irregular echinoids, starfish, brittle stars, sea cucumbers and crinoids are known from modern settings, and some of the resulting traces have their counterparts in the fossil record. By contrast, surficial trails or trackways produced by other modern echinoderms, e.g., sand dollars, exhibit a lower preservation rate and have not yet been identified in the fossil record. In addition, the unique features of the echinoderm skeleton (e.g., composition, rapid growth, multi-element architecture, etc.) may promote the production of related traces produced by the reutilization of echinoderm ossicles (e.g., burrow lining), predation (e.g., borings), or parasitism (e.g., swellings or cysts). Finally, the skeletal robustness of some echinoids may promote their post mortum use as benthic islands for the settlement of hard-substrate dwellers.

Three-Dimensional Morphology of Beaconites capronus from Northeast England

ABSTRACTBeaconites capronus is a winding meniscate backfilled trace fossil differentiated from comparable ichnotaxa Taenidium and Ancorichnus on the basis of its distinct and unornamented burrow lining. Typically, horizontal to subhorizontal B. capronus also includes vertical pipes, which serve as a point of entry for endobenthic deposit feeding activity. The burrows do not self-cross but often display secondary successive branching potentially indicating coprophagous feeding strategies in lower nutrient sediment. Beaconites capronus material is examined and discussed from the Carboniferous offshore transition zone deposits near Howick, United Kingdom. Samples were collected and analyzed using high-resolution serial grinding and modeling techniques documenting fine detail in three dimensions. As the burrows are actively backfilled and do not maintain a connection to the sediment water interface the trace making organism must have a method of coping with the low oxygen porewater conditions. Four methods are considered herein, as follows: 1) revisiting the sediment-water interface; 2) creating periodic shafts; or 3) employing the use of obligate anaerobic metabolism. Based on the material presented herein, an emended ichnospecific diagnosis is provided.

More than a trace of oxygen: Ichnological constraints on the formation of the giant Zn-Pb-Ag ± Ba deposits, Red Dog district, Alaska

Sediment-hosted massive sulfide (SHMS) deposits are an important source of global zinc resources, and the Red Dog Pb-Zn-Ag ± Ba district in Alaska (USA) contains giant deposits of this type. The existing model for ore formation at Red Dog involves early diagenetic replacement of sediment deposited in a restricted basin with stratified suboxic bottom waters. We present new observations of trace fossils Schaubcylindrichnus ichnospecies (isp.) and Chondrites isp. in several Red Dog deposits. The presence of the trace fossils, the size of the largest burrows, and the pervasiveness of the ichnofabric indicate that at least some intervals of the host sediment were deposited in an oxygenated middle to outer shelf environment. The burrow linings and infill are replaced by barite, hydrothermal quartz, and sulfide minerals, and the lack of compaction suggests that mineralization was diagenetically early. To reconcile these data with those from previous regional sedimentological and lithogeochemical studies, we propose a new model whereby the ore-hosting sediment was deposited in a shelfal setting in which redox conditions were affected by a fluctuating oxygen minimum zone. The strong spatial correlation between bioturbation and Red Dog SHMS deposits suggests that the presence of trace fossils may have played an important role in controlling the flow of ore-forming fluids by increasing host sediment permeability.

Statistical modeling of biogenically enhanced permeability in tight reservoir rock

Bioturbation is generally perceived to be detrimental to bulk permeability by reducing primary grain sorting, homogenizing sediment, and introducing mud as burrow linings and feces. Recent studies show, however, that some ichnogenera and biogenic fabrics serves to increase porosity and permeability. In tight hydrocarbon reservoirs, subtle changes in sand and silt distributions, such as may be generated by bioturbation, can greatly affect the resulting porosity and permeability distribution. Despite this, permeability across unfractured sedimentary reservoirs is commonly assessed solely on the basis of average grain size. This study of the Lower Cretaceous Viking Fm integrates sedimentary and ichnologic features to define recurring “hydrofacies” that possess distinct permeability grades. Grain size, lithology, bioturbation index, and trace fossil suites were described from a cored section of well 14-30-22-16W4. The kmax values from small plugs and full-diameter core samples were used to represent each hydrofacies. Hydrofacies were qualitatively defined at the bed/bedset scale, based on sedimentary, ichnological and permeability attributes, all of which affect flow pathways in heterolithic facies. The Markov chain method was employed to compare the vertical transitions of permeability (kmax) within a borehole against grain size and hydrofacies at the bed to bedset scale. This provided an intuitive framework for interpreting facies relationships such as coarsening-upwards successions. The results show that in the studied core, grain size only correlates to permeability in homogeneous rock units. The transiograms show that the volumetric proportions of different kmax classes show a 15% correlation with grain size, compared to a 97% correlation with the hydrofacies, indicating that variations in permeability down the well are strongly related to variations in the hydrofacies. The hydrofacies approach potentially can be used as a conceptual framework for the spatial modeling of permeability in tight hydrocarbon reservoirs, where grain size may not be the primary factor on permeability distributions.

Effect of bioturbation on reservoir rock quality of sandstones: A case from the Baram Delta, offshore Sarawak, Malaysia

Abstract With the Baram Delta in Malaysia as research subject, the effect of bioturbation on porosity and permeability of reservoir sandstones is evaluated and analyzed based on core and thin section analysis, EDX (energy-dispersive X-ray), FESEM (Field Emission Scanning Electron Microscope), mercury porosimetry and spot permeametry measurement. Samples are from cored intervals of two wells in the Baram Delta, W-1 and W-6. Analysis results indicate that the cored intervals in well W-1 are dominated by Diplocraterion ichnofabrics, intensely bioturbated, sediment packing activity is observed, and fine grade materials (clays and organic matter) from the host sediment are incorporated into burrow fills and linings, thereby decreasing isotropy and sorting of the sediments and reducing the local porosity and permeability in the burrows. The cored intervals in well W-6 are dominated by Ophiomorpha ichnofabrics, highly to intensely bioturbated, sediment cleaning activity by burrowing organisms results in cleaner and well sorted burrow fill materials, and clays and mud are cleaned from the burrow fill and host sediment and concentrated in the burrow linings. Porosity and permeability of reservoir rocks in the Baram Delta have therefore either been enhanced or reduced by bioturbation depending on the type of burrow, fill material and burrowing activity.

The polychaete worm Nereis diversicolor increases mercury lability and methylation in intertidal mudflats

The polychaete worm Nereis diversicolor engineers its environment by creating oxygenated burrows in anoxic intertidal sediments. The authors carried out a laboratory microcosm experiment to test the impact of polychaete burrowing and feeding activity on the lability and methylation of mercury in sediments from the Bay of Fundy, Canada. The concentration of labile inorganic mercury and methylmercury in burrow walls was elevated compared to worm-free sediments. Mucus secretions and organic detritus in worm burrows increased labile mercury concentrations. Worms decreased sulfide concentrations, which increased Hg bioavailability to sulfate-reducing bacteria and increased methylmercury concentrations in burrow linings. Because the walls of polychaete burrows have a greater interaction with organisms, and the overlying water, the concentrations of mercury and methylmercury they contain is more toxicologically relevant to the base of a coastal food web than bulk samples. The authors recommend that researchers examining Hg in marine environments account for sediment dwelling invertebrate activity to more fully assess mercury bioavailability.

MID-PALEOZOIC TRILOBITE LAGERSTATTEN: MODELS OF DIAGENETICALLY ENHANCED OBRUTION DEPOSITS

Spectacular trilobite Lagerstatten occur in distinctive offshore calcareous mudstone facies through the Late Ordovician to Devonian, and reflect a combination of mass mortality or molting and burial, coupled with early diagenetic enhancement. Evidence indicates two distinct modes of burial, Type I and II assemblages, which show evidence for burial without or with seafloor disturbance, respectively. Type I assemblages suggest rapid (hours to days), but not instantaneous burial, without bottom disruption, enabling preservation of in situ behavior, including mass aggregations and molt ensembles. Most occurrences contain bedding planes in which trilobites exhibit incipient disarticulation. These assemblages were buried by cascades of flocculated sediment from hypopycnal, detached flows. Type II assemblages show well-articulated, enrolled, semi-enrolled, and outstretched trilobites in varied orientations relative to bedding. In such cases, bottom flows and seafloor disruption by storm or seismic disturbances in shallow waters suspended large amounts of flocculated muds as viscous slurries, which developed into hyperpycnal flows that entrained carcasses of trilobites and other organisms. In many cases, both Type I and II obrution was followed by additional sedimentation, geochemical zones moved upward through the sediment column, and there was little tendency to form diagenetic overprints. Alternatively, if burial was followed by an interval of sediment starvation, the sediments were bioturbated and very early diagenetic mineralization was superimposed, first, in rare cases, as mineralized soft parts in entombed carcasses, and later as pyritization of burrow linings. Development of the concretionary layers required more prolonged periods of stability of the sulfate reduction zone. Cementation of sediment shielded organism bodies from most or all effects of compaction. Thus, ironically, the best preservation of delicate remains required rapid burial, associated with mass mortality, and very low rates of background sedimentation following the event.

Distinct microbial and faunal communities and translocated carbon in Lumbricus terrestris drilospheres

Lumbricus terrestris is a deep-burrowing anecic earthworm that builds permanent, vertical burrows with linings (e.g., drilosphere) that are stable and long-lived microhabitats for bacteria, fungi, micro- and mesofauna. We conducted the first non-culture based field study to assess simultaneously the drilosphere (here sampled as 0–2 mm burrow lining) composition of microbial and micro/mesofaunal communities relative to bulk soil. Our study also included a treatment of surface-applied 13C- and 15N-labeled plant residue to trace the short-term (40 d) translocation of residue C and N into the drilosphere, and potentially the assimilation of residue C into drilosphere microbial phospholipid fatty acids (PLFAs). Total C concentration was 23%, microbial PLFA biomass was 58%, and PLFAs associated with protozoa, nematodes, Collembola and other fauna were 200-to-300% greater in the drilosphere than in nearby bulk soil. Principal components analysis of community PLFAs revealed that distributions of Gram-negative bacteria and actinomycetes and other Gram-positive bacteria were highly variable among drilosphere samples, and that drilosphere communities were distinct from bulk soil communities due to the atypical distribution of PLFA biomarkers for micro- and mesofauna. The degree of microbial PLFA 13C enrichment in drilosphere soils receiving 13C-labeled residue was highly variable, and only one PLFA, 18:1ω9c, was significantly enriched. In contrast, 11 PLFAs from diverse microbial groups where enriched in response to residue amendment in bulk soil 0–5 cm deep. Among control soils, however, a significant δ 13C shift between drilosphere and bulk soil at the same depth (5–15 cm) revealed the importance of L. terrestris for translocating perennial ryegrass-derived C into the soil at depth, where we estimated the contribution of the recent grass C (8 years) to be at least 26% of the drilosphere soil C. We conclude that L. terrestris facilitates the translocation of plant C into soil at depth and promotes the maintenance of distinct soil microbial and faunal communities that are unlike those found in the bulk soil.

Relationship between bacterial diversity and function under biotic control: the soil pesticide degraders as a case study

In soil, the way biotic parameters impact the relationship between bacterial diversity and function is still unknown. To understand these interactions better, we used RNA-based stable-isotope probing to study the diversity of active atrazine-degrading bacteria in relation to atrazine degradation and to explore the impact of earthworm-soil engineering with respect to this relationship. Bulk soil, burrow linings and earthworm casts were incubated with (13)C-atrazine. The pollutant degradation was quantified by liquid chromatography-mass spectrometry for 8 days, whereas active atrazine degraders were identified at 2 and 8 days by sequencing the 16S ribosomal RNA in the (13)C-RNA fractions from the three soil microsites. An original diversity of atrazine degraders was found. Earthworm soil engineering greatly modified the taxonomic composition of atrazine degraders with dominance of α-, β- and γ-proteobacteria in burrow linings and of Actinobacteria in casts. Earthworm soil bioturbation increased the γ-diversity of atrazine degraders over the soil microsites generated. Atrazine degradation was enhanced in burrow linings in which primary atrazine degraders, closely related to Pelomonas aquatica, were detected only 2 days after atrazine addition. Atrazine degradation efficiency was not linearly related to the species richness of degraders but likely relied on keystone species. By enhancing soil heterogeneity, earthworms sustained high phylogenetic bacterial diversity and exerted a biotic control on the bacterial diversity-function relationships. Our findings call for future investigations to assess the ecological significance of biotic controls on the relationships between diversity and function on ecosystem properties and services (for example, soil detoxification) at larger scales.

Bioturbation influence on reservoir quality: A case study from the Cretaceous Ben Nevis Formation, Jeanne d'Arc Basin, offshore Newfoundland, Canada

The delineation Ben Nevis L-55 well, located in the Hebron-Ben Nevis field, offshore Newfoundland, targeted the Cretaceous Ben Nevis Formation in the petroleum-rich Jeanne d'Arc Basin. This case study focuses on the bioturbated net-pay horizons and assesses the importance of animal-sediment interactions in controlling the porosity and permeability of sandstone reservoir intervals. Our data reveal that bioturbation can either reduce permeability and porosity by as much as approximately 33% or enhance it by up to 600%, dependent on burrow type and behavior of the trace-making organism. The net-pay interval in the cored interval of Ben Nevis L-55 is characterized by Ophiomorpha-dominated ichnofabrics. The action of bioturbators can be classified in terms of sediment mixing, sediment cleaning, sediment packing, and pipe-work-building strategies. Bioturbation has the potential to (1) increase isotropy or uniformity of grain size by destroying sedimentary laminae through burrow homogenization, or (2) decrease isotropy by selectively sorting grains into burrow lining and fill by grain size, and through creation of open-burrow systems filled with later sediments of differing character to the host sediment. The petrophysical characteristics of the reservoir facies are highly dependent on trace fossil morphology, presence or absence of burrow linings, nature of burrow fills, burrow size, and bioturbation intensity. Mudstone-rich facies and ichnofabrics containing mudstone-filled and/or lined burrows (e.g., Ophiomorpha and clusters of Chondrites) have the net effect of permeability reduction. In contrast, permeability enhancement is documented from muddy sandstone facies with clean sand-filled burrows (e.g., Thalassinoides) and clean sandstones with burrow-mottled or diffuse to massive textures.

Paleoenvironmental and taphonomic implications of trace fossils in Ordovician kukersites

Abstract In an examination of the trace fossils of the Upper Ordovician Yeoman Formation of southeastern Saskatchewan, close relationships were observed between dispersed organic matter (DOM) or macerals (kerogen) and biogenic sedimentary structures. Macerals in these sediments are dominantly composed of the microfossil, Gloeocapsomorpha prisca alginite. To date, no agreement has been reached concerning the life habit of this organism, or the mechanism for accumulation of beds rich in G. prisca. The more popular view is that G. prisca was a non-photosynthetic, prokaryotic, benthic algal mat; others believe it was a photosynthetic, eukaryotic or prokaryotic, planktonic organism, which bloomed episodically throughout the Ordovician. Differing evidence and conclusions may be explained by the fact that the alga was preserved at various stages in its life cycle; i.e. it could be either planktonic or benthic. Depending on the nature of G. prisca, these algal microfossils were consumed and processed differently by burrowing infauna. Fluctuations in abundance of G. prisca are represented by fluctuations in feeding habits represented by the trace fossils and by fluctuating abundance of G. prisca preserved in the sediment. Periods of lowered G. prisca availability are represented by early life cycle, small disseminated type A G. prisca thinly lining the burrows of suspension-feeders. When conditions shifted and G. prisca was more abundant, larger, vegetative, disseminated type B G. prisca are also found in the burrow linings and fills. At maximum blooms, kukersites (beds rich in disseminated type B G. prisca) were preserved. In all phases of the bloom, G. prisca is absent from the fill of deposit-feeding Planolites, but occurs in the linings of suspension-feeding Palaeophycus. Based on the distribution of G. prisca within trace fossils in the Yeoman Formation, a planktonic nature for this microfossil better explains the accumulation of kukersite beds rich in G. prisca that occur in southeastern Saskatchewan. Although conditions causing these blooms and the scale of cyclicity need to be further examined, a restriction of the sea-floor is suggested by the limited trace fossil suite as well as dominance of a single species of phytoplankton, G. prisca.

Soldier crab ( Dotilla myctiroides) distribution, food resources and subsequent role in organic matter fate in Ao Tang Khen, Phuket, Thailand

This study aimed to elucidate Dotilla myctiroides (H. Milne-Edwards) food resources and how the soldier crab influences the organic matter composition on the intertidal flat. A preliminary assessment of D. myctiroides size, sex, and population distribution was conducted to clarify the characteristics of the inhabiting population. Overall, D. myctiroides size and abundance was normal across the tidal flat area. Comparison of different sediment types from the soldier crab habitat (surface sediments, igloos, burrow lining, burrow pellets, feeding pellets, and feces) using the fatty acid (FA) analysis technique revealed D. myctiroides removes organic matter via the significantly lower contributions of polyunsaturated FAs, essential FAs, and dinoflagellates in the feeding pellets. Dotilla myctiroides tissue analysis of the hepatopancreas and hindgut in individuals that had been starved for 24 h confirmed not only the consumption of dinoflagellates, but diatoms and macroalgae as well. In addition, the FA metabolism within the digestive system implied the ability of the soldier crab to synthesize highly unsaturated FAs (HUFAs) such as 20:4 n–6, 20:5 n–3 and 22:6 n–3.

VARIATION IN BURROW-WALL MICROMORPHOLOGIES OF SELECT INTERTIDAL INVERTEBRATES ALONG THE PACIFIC NORTHWEST COAST, USA: BEHAVIORAL AND DIAGENETIC IMPLICATIONS

Abstract Burrow-wall micromorphologies produced by nine different intertidal invertebrates were characterized by scanning electron microscopy. Minimally disturbed burrows and host sediment associated with Heteromastus filiformis, Saccoglossus bromophenolosus, Corophium volutator, Clymenella sp., Phoronopsis viridis, Cirriformia luxuriosa, Arenicola marina, Nereis virens, and Upogebia pugettensis were collected from various locales along the western coast of Washington and California. Scanning electron micrographs show several unique sedimentary characteristics present in the burrow lining of each invertebrate. Three traits—grain orientation and grain-size distribution, the nature of the mucus lining, and the presence of wall sculpture—appear significant in describing the microscale burrow lining. In several burrow types, the burrow structure was distinguishable from the matrix by changes in the modal grain size and sorting of the burrow-wall sediment. Variations in the type of packing—cubic versus rhomboh...