Bioturbation Rates Research Articles

Ray bioturbation rates suggest they shape estuary processes

AbstractBioturbation of sediments is a key ecosystem service in estuarine and marine ecosystems, and rays (superorder Batoidea: skates, stingrays, electric rays and shovelnose rays) are among the largest bioturbators, modifying their habitat through foraging and predation. Ray activities cycle nutrients, increase oxygen penetration and re‐stratify sediments. However, given rays are globally threatened, it is unclear to what extent the loss of rays, and the ecosystem services they provide, would affect ecosystem processes. This study assessed the likely amount of sediment displaced annually by rays during foraging activities at an estuary scale. To achieve this, an aerial drone was used to map daily ray bioturbation activity, as evident from the presence of feeding pits. High‐resolution, 2.6 cm px−1, Digital Elevation Models (DEM) were created and used to measure the volume of sediment displaced by feeding pits. We found rays within the Brisbane Water estuary in NSW, Australia excavated 1.20 (±0.68) tonnes of sediment per day within this 1443 m2 intertidal area, or a rate of 575.2 cm3 m−2 per day. This bioturbation rate is relatively high compared to bioturbation rates documented in other ray species. Spatial autocorrelation analysis indicated that the ray feeding pits were significantly clustered by location as well as size (P < 0.01), suggesting size segregation of ray foraging. When bioturbation rates were conservatively extrapolated across measured feeding area in the estuary, we calculated rays displace 57.6 (±32.4) tonnes of sediment per day, or 21.0 (±11.4) kilotonnes per year. This underlines how ray bioturbation likely shape estuary processes, and how the loss of rays and their ecosystem services would likely have considerable impacts on estuarine sedimentary ecosystems. These findings emphasize the ecological importance of rays in an ecosystem and a need to better understand the consequences of anthropogenic pressures to these services.

Raised water temperature enhances benthopelagic links via intensified bioturbation and benthos-mediated nutrient cycling

Sediment reworking by benthic infauna, namely bioturbation, is of pivotal importance in expansive soft-sediment environments such as the Wadden Sea. Bioturbating fauna facilitate ecosystem functions such as bentho-pelagic coupling and sediment nutrient remineralization capacities. Yet, these benthic fauna are expected to be profoundly affected by current observed rising sea temperatures. In order to predict future changes in ecosystem functioning in soft-sediment environments like the Wadden Sea, knowledge on the underlying processes such as sediment reworking, is crucial. Here, we tested how temperature affects bioturbation and its associated ecosystem processes, such as benthic nutrient fluxes and sediment oxygen consumption, using luminophore tracers and sediment incubation cores. We used a controlled mesocosm experiment set-up with key Wadden Sea benthos species: the burrowing polychaetes Arenicola marina and Hediste diversicolor, the bivalve Cerastoderma edule, and the tube-building polychaete Lanice conchilega. The highest bioturbation rates were observed from A. marina, reaching up to 375 cm2yr−1; followed by H. diversicolor, with 124 cm2yr−1 being the peak bioturbation rate for the ragworm. Additionally, the sediment reworking activity of A. marina facilitated nearly double the amount of silicate efflux compared to any other species. Arenicola marina and H. diversicolor accordingly facilitated stronger nutrient effluxes under a warmer temperature than L. conchilega and C. edule. The oxygen uptake of A. marina and H. diversicolor within the sediment incubation cores was correspondingly enhanced with a higher temperature. Thus, increases in sea temperatures may initially be beneficial to ecosystem functioning in the Wadden Sea as faunal bioturbation is definitely expedited, leading to a tighter coupling between the sediment and overlying water column. The enhanced bioturbation activity, oxygen consumption, and facilitated nutrient effluxes from these invertebrates themselves, will aid in the ongoing high levels of primary productivity and organic matter production.

Bioturbation by Benthic Stingrays Alters the Biogeomorphology of Tidal Flats

Fishing-down-marine-food-webs has resulted in alarming declines of various species worldwide. Benthic rays are one examples of such overexploited species. On tidal flats, these rays are highly abundant and play an ecologically important role. They use tidal flats as refuge, feeding and resting grounds, during which they bury into the sediment, which results in sediment bioturbation. Changes in bioturbation intensity, following ray removal, may affect the biogeomorphology of tidal flats with possible cascading effects on the macrozoobenthic community. However, it is poorly understood how these indirect effects could influence ecosystem function. We therefore studied the geomorphic impact of benthic rays (specifically the pearl whipray/stingray Fontitrygon margaritella) on the tropical tidal flats of the Bijagós Archipelago, Guinea-Bissau, on a landscape scale. We investigated 1) bioturbation rates by rays using drone and ground surveys, 2) the spatial distribution of ray pits on multiple tidal flats, 3) the impact of rays on sediment properties and macrozoobenthos by experimental exclusion (15 months). Benthic rays bioturbated 3.7 ± 0.35% of the tidal flat’s sediment surface per day over one single 24-h period, which equals a complete top-sediment-surface turnover every 27 days. The spatial distribution of ray pits was affected by tidal flat geomorphology since pits decayed faster at areas exposed to strong hydrodynamic forces. Predator exclusion altered sediment properties, leading to changes in sedimentation (− 17%) and erosion (− 43%) rates. In addition, macrozoobenthic species composition changed, marked by an increase in Capitellidae worms and a greater biomass of Malacostraca over time. These changes indicated substantial effects of ray bioturbation on the biotic and geomorphic landscape of tidal flats. Overall, we conclude that changing abundances of benthic rays can have clear landscape-wide geomorphological effects on intertidal ecosystems. These indirect consequences of fisheries should be incorporated in integrative management plans to preserve tidal flats and connected ecosystems.

Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head

ABSTRACTThe evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides, can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub‐bottom profiles, high‐resolution sediment core analyses (X‐ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine‐grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro‐scale and micro‐scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross‐laminations and fining‐upward successions, which are attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross‐cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re‐establishment of benthos and associated biogenic structures, supporting the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.

Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems.

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Nevertheless, how long-term deoxygenation affects macrobenthic communities, sediment biogeochemistry and their mutual feedback remains poorly understood. Here, we evaluate the response of the benthic assemblages and biogeochemical functioning to decreasing O2 concentrations along the persistent bottom-water dissolved O2 gradient of the Estuary and Gulf of St. Lawrence (QC, Canada). We report several of non-linear biodiversity and functional responses to decreasing O2 concentrations, and identify an O2 threshold that occurs at approximately at 63 μM. Below this threshold, macrobenthic community assemblages change, and bioturbation rates drastically decrease to near zero. Consequently, the sequence of electron acceptors used to metabolize the sedimentary organic matter is squeezed towards the sediment surface while reduced compounds accumulate closer (as much as 0.5-2.5 cm depending on the compound) to the sediment-water interface. Our results illustrate the capacity of bioturbating species to compensate for the biogeochemical consequences of hypoxia and can help to predict future changes in benthic ecosystems.

Intermittent and temporally variable bioturbation by some terrestrial invertebrates: implications for ichnology

Bedding planes and vertical sections of many sedimentary rock formations reveal bioturbation structures, including burrows, produced by diverse animal taxa at different rates and durations. These variables are not directly measurable in the fossil record, but neoichnological observations and experiments provide informative analogues. Comparable to marine invertebrates from many phyla, a captive beetle larva burrowing over 2 weeks showed high rates of sediment disturbance within the first 100 h but slower rates afterwards. Tunnelling by earthworms and adult dung beetles is also inconstant—displacement of lithic material alternates with organic matter displacement, often driven by food availability with more locomotion when hungry. High rates of bioturbation, as with locomotion generally, result from internal and external drives, slowing down or stopping when needs are filled. Like other processes affecting sediment deposition and erosion, rates can drastically differ based on measured timescale, with short bursts of activity followed by hiatuses, concentrated in various seasons and ontogenetic stages for particular species. Assumptions of constant velocities within movement paths, left as traces afterward, may not apply in many cases. Arguments about energetic efficiency or optimal foraging based on ichnofossils have often overlooked these and related issues. Single bioturbation rates from short-term experiments in captivity may not be comparable to rates measured at an ecosystem level over a year or generalized across multiple time scales where conditions differ even for the same species. Neoichnological work, with an understanding of lifetime variabilities in bioturbation and their drivers, helps connect ichnology with behavioural biology and movement ecology.

Effects of bioturbation by the fiddler crabLeptuca speciosa(Ives, 1891) (Decapoda: Brachyura: Ocypodidae) on mangrove peat in Barnes Sound, Florida, USA

AbstractBioturbation, which includes burrowing and foraging behaviors, is an important component of the functional role of fiddler crabs (Brachyura, Ocypodidae) within mangrove forests because it modifies sediment properties and composition of mangrove substrates. In this study, fiddler-crab population density and burrow architecture were measured to evaluate the influence of bioturbation by the fiddler crab Leptuca speciosa (Ives, 1891) on mangrove peat from Barnes Sound, Florida, USA. Measurements of burrow architecture were used to estimate the contribution of fiddler-crab burrowing to the bioturbation of mangrove peat. Comparisons were made between the total organic matter in bioturbated sediments, including feeding and burrowing pellets. A population density of 12 burrows m–2 was measured with no significant trends in the spatial distribution of fiddler crabs within the site. Although the deepest burrow depth was 18 cm, results show the upper 5 cm of the peat surface was consistently burrowed by crabs. Fiddler crabs were estimated to increase the total below-ground air-peat surface area m–2 by 5% and accounted for 22% of the excavated volume of mangrove peat per year. Fiddler crabs will thus rework the entire peat substrate within five years. Because data on carapace geometric mean size suggested that a juvenile population of L. speciosa was sampled, the bioturbation rate of the peat substrate will accelerate once this population matures. Feeding pellets had significantly lower percentages of total organic matter (P < 0.01) than other bioturbated peat samples, suggesting that fiddler-crab foraging behaviors significantly (P < 0.01) decrease the organic composition of surficial peats. These results imply that fiddler crab burrowing extends the depth of the taphonomically active zone thus enhancing mangrove peat decomposition and changing the bioavailability and distribution of organic matter in mangroves.

A downcore increase in time averaging is the null expectation from the transit of death assemblages through a mixed layer

AbstractUnderstanding how time averaging changes during burial is essential for using Holocene and Anthropocene cores to analyze ecosystem change, given the many ways in which time averaging affects biodiversity measures. Here, we use transition-rate matrices to explore how the extent of time averaging changes downcore as shells transit through a taphonomically complex mixed layer into permanently buried historical layers: this is a null model, without any temporal changes in rates of sedimentation or bioturbation, to contrast with downcore patterns that might be produced by human activity. Assuming stochastic burial and exhumation movements of shells between increments within the mixed layer and stochastic disintegration within increments, we find that almost all combinations of net sedimentation, mixing, and disintegration produce a downcore increase in time averaging (interquartile range [IQR] of shell ages), this trend is typically associated with a decrease in kurtosis and skewness and by a shift from right-skewed to symmetrical age distributions. A downcore increase in time averaging is thus the null expectation wherever bioturbation generates an internally structured mixed layer (i.e., a surface, well-mixed layer is underlain by an incompletely mixed layer): under these conditions, shells are mixed throughout the entire mixed layer at a slower rate than they are buried below it by sedimentation. This downcore trend created by mixing is further amplified by the downcore decline in disintegration rate. We find that transition-rate matrices accurately reproduce the downcore changes in IQR, skewness, and kurtosis observed in bivalve assemblages from the southern California shelf. The right-skewed shell age-frequency distributions typical of surface death assemblages—the focus of most actualistic research—might be fossilized under exceptional conditions of episodic anoxia or sudden burial. However, such right-skewed assemblages will typically not survive transit through the surface mixed layer into subsurface historical layers: they are geologically transient. The deep-time fossil record will be dominated instead by the more time-averaged assemblages with weakly skewed age distributions that form in the lower parts of the mixed layer.

The interplay of temperature and algal enrichment intensifies bioturbation of the intertidal amphipod Corophium volutator

Bioturbation is a central transport process for ecosystem functioning, especially in large soft sediment habitats like the Wadden Sea. The amphipod C. volutator is a dominant bioturbator in the Wadden Sea, due to its great abundance and almost continuous particle movement. Expedition or loss of its bioturbation activity could thus hold ramifications for ecosystem functioning within sediments, like carbon sequestration and nutrient recycling. Here we test the effect that temperature and organic enrichment have on the bioturbation of C. volutator; two prevalent abiotic factors in the Corophiid's habitat that have fluctuated over recent decades, and are expected to change in the future. In-situ experiments were conducted under 8 and 15 °C, with varying levels (0 g, 0.1 g, and 0.2 g) of powdered Ulva compressa enriching cores containing C. volutator. We found a significant interaction effect of temperature and organic enrichment on the bioturbation rate of the amphipod, with bioturbation only increasing with added organic enrichment at 15 °C. Further, a threshold within our experiments was also reached under 15 °C, where the amphipod ceased to expedite bioturbation under higher organic enrichment. This upper limit on this dominant bioturbation imposed with organic enrichment emphasizes the sensitivity of C. volutator. Our findings reveal bioturbation can be limited by temperature in colder months, and opposingly, limited by organic enrichment under warmer conditions. In future Wadden Sea scenarios where temperature is predicted to be warmer and winters milder, enhanced bioturbation activity by C. volutator could prove crucial in continued ecosystem functions.

Long-term quantification of the intensity of clay-sized particles transfers due to earthworm bioturbation and eluviation/illuviation in a cultivated Luvisol

As a result of the limited knowledge on eluviation/illuviation and bioturbation rates, these two processes of soil particles translocation are qualitatively described either as synergic or competing processes. Here we take the opportunity of the recent development of an image analysis procedure to quantify illuvial clay and earthworm’s porosity to quantify the intensity of illuviation and bioturbation cumulated over soil formation in a temperate cultivated Luvisol. The key objectives of the study are i) to quantify the total intensity of illuviation and bioturbation and their depth distributions and ii) to assess the possibility for bioturbation to limit or compensate the depletion of the clay-sized fraction in topsoil horizons due to eluviation. The total quantity of illuvial clay is 1,100 t.ha−1 while the estimated annual amount of clay-sized fraction translocated by eluviation is between 0.08 and 1 t ha−1 yr−1. This is comparable to the annual loss of land by water erosion (between 1 and 5 t ha−1 yr−1) or by arable erosion (3.3 t ha−1 yr−1). Eluviation/illuviation is thus a discrete and active form of soil loss. With approximately 1,900 t.ha−1 of clay-sized fraction, the amount of fine particles displaced at least once by bioturbation is higher than the one related to eluviation/illuviation. At first sight, it therefore seems possible for biological activity to compensate for vertical transfers of the clay-sized fraction by eluviation/illuviation. However, our study shows that a considerable amount of the clay-sized fraction will never be brought up by the bioturbation and will remain definitively lost for the surface horizons as bioturbation decreases non-linearly with depth. Consequently, a preventive management of the depletion of the clay-sized fraction in topsoil horizons by eluviation/illuviation should be preferred to the curative management of its consequences by bioturbation.

High productivity promoted exceptional fossil preservation of the early Middle Triassic Luoping biota of Yunnan Province, China

The early Middle Triassic (Anisian) Luoping biota is representative of marine ecosystems following their full recovery after the Permian-Triassic mass extinction; however, its exceptional preservation remains poorly understood. In this paper, we report multiple geochemical proxies (TOC, TN, P/Al, Cuxs, Nixs, Baxs, δ13Ccarb, and δ13Corg) from Member II of the Middle Triassic Guanling Formation at the Xiangdongpo section in Luoping County, Yunnan Province, China, to assess the relationship between primary productivity and exceptional preservation of the Luoping biota. Variations in TOC, TN, P/Al, Cuxs, and Nixs values show that exceptional preservation coincides with two intervals of high productivity. Relatively low C/N ratios and distributed Δ13Ccarb-org values indicate that primary productivity was dominated by eukaryotic algae and prokaryotic microbes. Based on geochemical analyses and regional correlations, we conclude that, following sea level rise, nutrients were supplied to the Luoping area by upwelling from the open ocean and facilitated the blooming of marine communities in an open platform setting. In the intra-platform depression, increased nutrients supply also fueled high primary productivity in surface waters and oxygen consumption in the water column, causing bottom water anoxia. The lack of oxygen in the bottom water reduced the rate of biomass degradation and bioturbation, promoting growth of microbial mats, leading to the exceptional preservation of macrofauna. This study highlights the important role of elevated primary productivity in exceptional fossil preservation by triggering anoxia of bottom waters. Our findings confirm the widespread development of anoxic conditions during the middle Anisian (Pelsonian), from the eastern Tethys to the Panthalassa, and also reveal the interactions between organisms and the environment after Permian-Triassic mass extinction.

Low-frequency noise pollution impairs burrowing activities of marine benthic invertebrates

Sounds from human activities such as shipping and seismic surveys have been progressively invading natural soundscapes and pervading oceanic ambient sounds for decades. Benthic invertebrates are important ecosystem engineers that continually rework the sediment they live in. Here, we tested how low-frequency noise (LFN), a significant component of noise pollution, affects the sediment reworking activities of selected macrobenthic invertebrates. In a controlled laboratory setup, the effects of acute LFN exposure on the behavior of three abundant bioturbators on the North Atlantic coasts were explored for the first time by tracking their sediment reworking and bioirrigation activities in noisy and control environments via luminophore and sodium bromide (NaBr) tracers, respectively. The amphipod crustacean Corophium volutator was negatively affected by LFN, exhibiting lower bioturbation rates and shallower luminophore burial depths compared to controls. The effect of LFN on the polychaete Arenicola marina and the bivalve Limecola balthica remained inconclusive, although A. marina displayed greater variability in bioirrigation rates when exposed to LFN. Furthermore, a potential stress response was observed in L. balthica that could reduce bioturbation potential. Benthic macroinvertebrates may be in jeopardy along with the crucial ecosystem-maintaining services they provide. More research is urgently needed to understand, predict, and manage the impacts of anthropogenic noise pollution on marine fauna and their associated ecosystems.

Quantitative analysis of horizontal bioturbation from Brioverian (Ediacaran - Fortunian) deposits of Brittany (Armorican Massif, NW of France)

Ediacaran-Cambrian bioturbation on bedding planes provides physical and chemical data about the environmental conditions and biological activities of early metazoans. We propose a quantitative method to estimate horizontal disruption of the substrate using bedding-plane trace fossils from Brioverian deposits. This methodology provides the first quantitative analysis of the trace fossil assemblage from the Armorican Massif (Brittany, NW of France). The Ediacaran-Cambrian transition within the Brioverian series is characterized by the abundance of simple and horizontal trace fossils such as Helminthopsis, Helminthoidichnites, and Palaeophycus as well as rare Gordia and Spirodesmos. Recent U-Pb dating has been carried out on detrital zircon grains from the upper Brioverian series suggesting a late Ediacaran to Fortunian age of the fossiliferous deposits (ca. 550 to 530 Ma). With Arc-Gis software, we use a semi-quantitative approach to estimate the relative 2D bioturbation rate recorded on bedding planes. The dataset is used to discuss the feeding strategies and how the seafloor ecospace was colonized by the early bilaterian metazoans. This approach combines new values such as: the length of a trace fossil, the surface of a trace, the cumulative length, and the cumulative surfaces from all of the ichnofossils recorded on the same slate surface, to finally suggest that the bioturbation rate of the microbial grazers impacted the use of the seafloor ecospaces and feeding strategies through the biomats.

The sedimentation, bioturbation and organic matter degradation as revealed by excess 230Th and 210Pb in the Cosmonaut Sea

Sedimentation and bioturbation (the activity of benthic organisms) play an important role in organic matter degradation. The excess 230Th and 210Pb in a sediment core were used to evaluate the sedimentation, bioturbation and organic degradation processes in the Cosmonaut Sea, East Antarctica. Our results show that the sedimentation rate estimated from excess 230Th through the Constant Flux (CF) and Constant Flux and Constant Sedimentation (CFCS) models has changed in the past 200 ka. The mass accumulation and the linear sedimentation rates vary from 0.36 to 0.76 kg m-2 ka-1 and from 0.6 to 1.3 mm ka-1, which are significantly lower than the rates in other Antarctic seas. The stage III (120–202 ka), which corresponds to Marine Isotope Stage (MIS) 6 (glacial period), had the lowest sedimentation rate, indicating less sediment input by sea ice expansion. The bioturbation coefficient estimated by excess 210Pb is as low as 0.023 ± 0.003 cm2 a-1, showing inactive benthic activities. The average C/N ratio of organic matter is 7.2 ± 0.4, which is close to that of fresh organic matter and lower than the typical value of deep-sea sediments, indicating that organic matter is less degraded. The degradation rates of organic carbon and organic nitrogen estimated by the bio-diffusion model are 0.61 ka-1 and 0.29 ka-1, respectively, which are significantly lower than previously reported values for Southern Ocean sites. Despite the low sedimentation rate, low rates of bioturbation and inefficient organic matter degradation are conducive to the preservation of organic matter in sediments of the Cosmonaut Sea.

210Pb-Derived Bioturbation Rates in Sediments Around Seamounts in the Tropical Northwest Pacific

To evaluate bioturbation coefficients (DB) and mixing depths (L), 210Pb and 226Ra activity was measured in two sediments cores (from water depths of 5,398 m and 4,428 m), which were collected from seamount areas in the Northwest Pacific. Using a steady-state diffusion mode, we estimated DB values of 16.8 and 24.1 cm2/a, higher than those in abyssal sediments and those predicted by traditional empirical equations. Corresponding L values varied between 19.3 and 23.1 cm. These high values indicate that seamounts are the area of active bioturbation. A one-dimensional model for the transport of total organic carbon (TOC) from the surface layer of sediments to the deep layer was developed using the distribution pattern of the specific activity of excess 210Pb (210Pbex) and its relationship with TOC. The model showed that the TOC flux transmitted downward by bioturbation was 0.09 mmol/(cm2⋅a) and 0.12 mmol/(cm2⋅a).

Species‐specific foraging behaviors define the functional roles of sympatric stingrays

AbstractAnimals that disrupt sediments through burrowing or foraging contribute to ecosystem function through bioturbation and ecosystem engineering processes linked to their excavation behavior. Empirical evidence linking behavior with function is rare; yet this information is critical for assessing species‐specific functional roles. Using two stingray species, Himantura australis and Pastinachus ater, as model ecosystem engineers, we empirically investigated how foraging behavior influenced the functional roles of sympatric species. Drone observations of stingray foraging revealed a strong link between behavior and function. Excavation feeding created the largest feeding pits and accounted for 58–67% of sediment turnover despite occurring in only 22–31% of feeding events. Although both H. australis and P. ater were capable of excavation feeding, less disruptive foraging behaviors were often favored over excavation. Differences in space use and behavior revealed that functional roles of sympatric stingrays are different yet complementary, which may enhance ecosystem productivity. High feeding rates combined with frequent use of disruptive feeding behaviors resulted in higher bioturbation rates for H. australis than for P. ater. On the other hand, P. ater made fewer feeding pits but foraged over a broader sandflat area than H. australis. Consequently, H. australis have intense, localized bioturbation and ecosystem engineering impacts, while P. ater is likely to promote nutrient dispersal over a larger area. Overall, results suggest that functional roles are dependent on complex interactions between feeding behavior and space use, meaning an extensive understanding of engineering activities is required before similar functional roles can be assumed for even morphologically similar species.

Bioturbation by black soldier fly larvae-Rapid soil formation with burial of ceramic artifacts.

Bioturbation involves the incorporation of residues from the surface soil into the subsoil; however, common small soil ‘bioengineers’, such as earthworms or termites, are unlikely to transport human artifacts to deeper soil horizons. However, such artifacts occur in the deeper soil horizons within Amazonian Anthrosols (Terra Preta). Here we test the assumption that such tasks could be carried out by fly larvae, which could thus play a crucial role in waste decomposition and associated soil mixing under tropical conditions. We performed two greenhouse experiments with sandy substrate covered with layers of organic waste, ceramic fragments, and black soldier fly larvae (BSFL) (Hermetia illucens (L.) (Dipt.: Stratiomyidae)). We used in-situ images to assess the rate of bioturbation by BSFL, and then designed our main study to observe waste dissipation (reduction of organic carbon and phosphorus contents from waste model trials with and without charcoal) as related to larval-induced changes in soil properties. We found that the bioturbation of macroinvertebrates like BSFL was able to bury even large (> 5 cm) ceramic fragments within hours, which coincided with high soil growth rates (0.5 cm h-1). The sandy soil was subsequently heavily enriched with organic matter and phosphorus originating from organic waste. We conclude that BSFL, and possibly other fly species, are important, previously overlooked soil ‘bioengineers’, which may even contribute to the burial of artifacts in Anthrosols and other terrestrial waste dumps.

Putting sea cucumbers on the map: projected holothurian bioturbation rates on a coral reef scale

Bioturbation of reef sediments aerates the upper sediment layers and releases organic material to benthic communities. Despite being the larger and more conspicuous bioturbators on coral reefs, the value of holothurians (sea cucumbers) to reef ecosystems is less often attributed to their ecosystem services than their value for fisheries. This may be because they are considered to have an insignificant effect on reef health relative to other animals. Here, we ground-truthed remote sensing data obtained from drone and satellite imagery to estimate the bioturbation rates of holothurians across the 19 km2 Heron Island Reef in Queensland, Australia. Ex situ bioturbation rates of the most abundant holothurian, Holothuria atra, were assessed during 24-h feeding experiments. Using density measurements of holothurians across reef flat zones in a 27,000 m2 map produced from drone imagery, we extrapolated bioturbation across the reef using satellite remote sensing data. Individual H. atra were estimated to produce approximately 14 kg of bioturbated sediment per year. On a reef scale (excluding the reef lagoon) and accounting for varying densities of holothurians across different reef zones, total bioturbation from holothurians at Heron Reef was estimated at over 64,000 metric tonnes per year, slightly more than the mass of five Eiffel Towers. These results highlight the scale of structural and biochemical impacts that holothurians have on reef flats and their importance to ecosystem functioning and services. Management of these animals on reefs is imperative as overharvesting would likely cause substantial negative effects on sedimentary ecosystems and their biogeochemistry in corals reefs.

Rapid organic matter cycling in North Sea sediments

Coastal shelf seas are zones of intense nutrient cycling, where a strong coupling between the sediment and the water column enhances primary productivity. To identify factors that control the strength of this benthic-pelagic coupling we measured sediment characteristics, solute fluxes, and porewater nutrient profiles in spring along a south - north transect in the North Sea crossing distinct regions: the shallow Oyster Grounds closest to the Dutch shore, the shallow Dogger Bank, the 80-m deep central North Sea, and the 150-m deep Fladen Grounds between the north of Scotland and Norway. The data were used to constrain rates of different mineralization processes with the 1-D diagenetic model (OMEXDIA). Surprisingly, we found no major differences in the biogeochemical signature along the 670 km long North Sea transect, despite sediments ranging in median grainsize from 25 to 217 μm, and a permeability range >3 orders of magnitude. Total carbon mineralization ranged between 4 and 13.5 mmol C m−2 d−1, and decreased significantly northward. Oxic mineralization was the dominant mineralization process in all studied sites. Finest, least permeable sediments were found in the Fladen Grounds where highest denitrification rates were recorded, linked to high nitrate concentrations in the overlying water. The coarsest, most permeable sediments of the shallow Dogger Bank represented a transition area between the Oyster Grounds, where oxic mineralization was highest (75–90%), and the central North Sea samples, where anoxic mineralization increased relative to oxic mineralization due to higher bioturbation rates (oxic: 59–72%, anoxic: 27–39%). Overall, denitrification rates increased, while phosphorus removal tended to decrease northward. This contrasting behaviour in nitrogen and phosphorus removal was identified as a possible cause for decreasing DIN:DIP ratios in the water column towards the north.

An Invasive Mussel (Arcuatula senhousia, Benson 1842) Interacts with Resident Biota in Controlling Benthic Ecosystem Functioning

The invasive mussel Arcuatula senhousia has successfully colonized shallow soft sediments worldwide. This filter feeding mussel modifies sedimentary habitats while forming dense populations and efficiently contributes to nutrient cycling. In the present study, the density of A. senhousia was manipulated in intact sediment cores taken within an intertidal Zostera noltei seagrass meadow in Arcachon Bay (French Atlantic coast), where the species currently occurs at levels corresponding to an early invasion stage. It aimed at testing the effects of a future invasion on (1) bioturbation (bioirrigation and sediment mixing) as well as on (2) total benthic solute fluxes across the sediment–water interface. Results showed that increasing densities of A. senhousia clearly enhanced phosphate and ammonium effluxes, but conversely did not significantly affect community bioturbation rates, highlighting the ability of A. senhousia to control nutrient cycling through strong excretion rates with potential important consequences for nutrient cycling and benthic–pelagic coupling at a broader scale. However, it appears that the variability in the different measured solute fluxes were underpinned by different interactions between the manipulated density of A. senhousia and several faunal and/or environmental drivers, therefore underlining the complexity of anticipating the effects of an invasion process on ecosystem functioning within a realistic context.