Bioturbation Rates Research Articles

Comparison between infaunal communities of the deep floor and edge of the Tonga Trench: Possible effects of differences in organic matter supply

Hadal trenches are characterised by environmental conditions not found in any other environment, thereby providing new opportunities to understand the processes that shape deep-sea benthic communities. Technological advances have led to an increase in the number of investigations in hadal trenches over the last two decades. However, more quantitative samples including the deepest parts of trenches is needed to better understand trends in benthic diversity, abundance, biomass and community structure in these extreme habitats, and how these may be shaped by environmental and/or evolutionary factors. In this study, we describe and compare the abundance, biomass, vertical distribution in the sediment, diversity, and community structure of nematodes and other infauna in sediments from the Horizon Deep (~10 800m) in the Tonga Trench and a site on the edge of the trench (~6250m). Mean nematode abundance was six times greater at the Horizon Deep site (387 ind. 10cm−2) than at the trench edge site (65 ind. 10cm−2). A similar pattern was observed for biomass (15 vs 2μgDW 10cm−2, respectively), which likely resulted from elevated organic matter supply at the Horizon Deep site. There was no significant difference in nematode species richness between the two sites, but diversity measured using rarefaction was significantly greater at the trench edge site than at the Horizon Deep site [ES(20); 13.8 vs 7.8]. Dominance was much more pronounced in the Horizon Deep, which may be due to competitive exclusion by a small number of opportunistic species. Nematode community structure differed significantly both between sites and among sediment depth layers. The presence of subsurface peaks in pigment concentrations, bacteria abundance, and nematode abundance at the Horizon Deep site is consistent with a recent turbidite event, and may also reflect high rates of bioturbation by larger fauna resulting from high food availability. Determining the relative influences of different environmental factors on hadal trench benthic communities will require further investigation based on quantitative samples encompassing the trench axis as well as the oceanic and continental slopes.

A new Permian bivalve-dominated assemblage in the Rio do Rasto Formation, Paraná Basin, Brazil: Faunal turnover driven by regional-scale environmental changes in a vast epeiric sea

The basal portion of the Permian Rio do Rasto Formation (Serrinha Member), Passa Dois Group, Paraná Basin, Brazil, records an entirely new bivalve fauna intercalated between the underlying Pinzonella neotropica assemblage (uppermost portion of the Teresina Formation) and the overlying Leinzia similis assemblage (Rio do Rasto Formation). Mollusks of these assemblages lived in marginal shallow-water habitats of an immense epeiric sea and were dominated by endemic bivalve species. Taxonomic analysis revealed the presence of Terraia curvata (60.61%), Astartellopsis prosoclina (19.70%), Cowperesia emerita (10.61%), Leinzia curta (4.55%), Terraia bipleura (3.03%) and Beurlenella elongatella (1.52%), which are associated with conchostracans and plant remains. Species composition, abundance, and dominance in this novel assemblage differ notably from the preceding ones, suggesting a substantial evolutionary turnover. Regional-scale environmental changes recognized based on taphonomy, facies analysis, and geochemical data consist of progressive freshening of the marginal habitats of the Paraná Basin and taxic changes that include the following: (a) loss of genera, (b) decrease in bivalve abundance and ecological guilds, (c) disappearance of the dominant bivalve group (Pinzonellinae) and (d) diversification of Terrainae bivalves. The ecological signature also changed notably because only infaunal suspension-feeding bivalves are present, indicating a significant loss of functional diversity at the regional scale. Likely stressor factors (among others) are tied to freshening events, suggesting profound changes in (a) salinity, (b) primary productivity and (c) a lack of coarse, stable substrates coupled with high bioturbation rates. Hence, our regional example could offer valuable clues to benthic (bivalve) community responses in a habitat subjected to (a) rapid climate changes and (b) freshening events in shallow-water settings. Finally, the stratigraphic range of the dominant species (T. curvata) appears to be restricted to the basal portion of the Rio do Rasto Formation. Based on the presence of this species and of C. emerita, the novel assemblage is tentatively correlated with that of the Permian Gai-As Formation in the Huab region of Namibia, thus supporting previous assumptions of a seaway connecting both basins during the Guadalupian Epoch.

Influence of hypoxia on biogenic structure in sediments on the Louisiana continental shelf

As part of a study of the effects of seasonal hypoxia on sediment properties, samples were collected during the spring and late summer of 2009 from four sites of similar sediment type and water depth (30–39 m), but different recent history of bottom water oxygen concentration on the continental shelf of Louisiana. Sediment profile imaging (SPI), box coring, X-radiography, and computed tomography (CT) imaging were employed to characterize the biogenic structural differences in surficial sediments among a normoxic control site and three sites subjected to hypoxic events varying in frequency of occurrence. Results of the CT imagery indicated that macrobenthic biogenic structures were the most numerous at the H7 site that had experienced the least hypoxia in the past 23 years. The E4 site that had experienced hypoxia seasonally with a frequency between 50% and 75% of the time had the fewest biogenic structures in spring 2009, but exhibited recovery in terms of their abundance and diameter in summer 2009. E4 also exhibited high rates of bioturbation during the late-summer sampling as determined from excess 234Th. This suggests that the macrobenthos community at this site was in an active phase of recovery from hypoxia. At the A6 site, exposed to hypoxia with an annual frequency ≥75%, biogenic structures were numerous but dimensionally small, correlating with the average individual size of macrobenthos found there. The total volume maxima occupied by biogenic structures in the sediment occurred below the uppermost sediment intervals, with the exception of the spring sample from the D5 site that experienced hypoxia between 25% and 50% of the time. CT-imagery indicating effects of seasonal hypoxia on biogenic structure in the top 10 cm of sediments detected more structures than SPI, X-radiographic imagery, or macrobenthos census data. The presence of relict burrows probably inflated estimates of biogenic structures in the subcores, rendering an integrated result that included creation, destruction, and preservation of burrows and voids over time.

Soil redistribution in abandoned raised fields in French Guiana assessed by radionuclides

AbstractPre‐Columbian agricultural raised fields are widespread in Neotropical wetlands. Many seasonally flooded coastal savannahs of French Guiana are dotted with thousands of small, round mounds, which current research indicates are vestiges of raised fields. It is surprising that these elevated structures persist under the erosive force of heavy tropical rainfall. One hypothesis for this stability is that “engineer” organisms such as plants, earthworms, termites and ants colonize abandoned raised fields and maintain the raised structures against erosion. This “erosion/deposition balance” hypothesis assumes that the landscape is subject to non‐negligible rates of erosion, but that actions of engineer organisms reduce the erodibility of mounds, compensate for erosion by transporting materials to mounds, or both. The hypothesis also predicts greater bioturbation on mounds than in other parts of the landscape. To test these assumptions and predictions, we estimated soil erosion and bioturbation rates in abandoned raised fields in a seasonally flooded savannah in French Guiana by using two radionuclides (137Cs and unsupported 210Pb) as tracers for soil redistribution. Analysis of the vertical and horizontal distribution of radionuclides at the study site showed that soil erosion in the mounds either occurs at a rather low rate or that organisms counteract erosion, or both. We also showed that mounds were heavily influenced by bioturbation. These results validate the fundamental assumptions of the erosion/deposition balance hypothesis.

Geomorphological impacts of a tornado disturbance in a subtropical forest

We studied tree uprooting associated with an EF2 tornado that touched down in portions of the Ouachita Mountains in western Arkansas in 2009. In the severe blowdown areas all trees in the mixed shortleaf pine–hardwood forest were uprooted or broken, with no relationship between tree species or size and whether uprooting or breakage occurred. There was also no significant relationship between tree species and amount of soil displaced, and only a weak relationship between tree size and rootwad size. Uprooting resulted in a mean bioturbation rate of 205m3ha−1 (about 240tha−1). Direct transfer of wind energy via tree uprooting to geomorphic work of soil displacement was about 75 to 190Jm−2. Given the infrequency of tornadoes, this energy subsidy is minor with respect to the long-term energetics of pedogenesis and landscape evolution. However, it does represent a highly significant pulse of geomorphically-significant energy relative to other mechanical processes. Tornadoes such as that of April, 2009—not atypical for the region—are disturbances causing severe, non-selective impacts within the affected area. At a broader, landscape scale, tornadoes are highly localized disturbances, and occur infrequently within any given landform element or forest stand. Only about a third of the uproots revealed root penetration of bedrock, compared to about 90% in other areas of the Ouachita Mountains. This is attributable to the thicker colluvial soils at the study site, and is consistent with the idea that root–bedrock interaction is more likely in thinner regolith covers.

Biogeomorphically driven salt pan formation in Sarcocornia-dominated salt-marshes

Salt-marshes are under increasing threat, particularly from sea-level rise and increased wave action associated with climate change. The development and stability of these valuable habitats largely depend on complex interactions between biotic and abiotic processes operating at different scales. Also, interactions between biotic and abiotic processes drive internal morphological change in salt-marshes. In this paper we used a biogeomorphological approach to assess the impact of biological activities and interactions on salt pan formation in Sarcocornia-dominated salt marshes. Salt pans represent a key physiographic feature of salt-marshes and recent studies hypothesized that biogeomorphic processes could be related to salt pan formation in SW Atlantic salt-marshes. The glasswort Sarcocornia perennis is one of the dominant plants in the salt-marshes of the Bahía Blanca Estuary (Argentina) where they form patches up to 8m in diameter. These salt-marshes are also inhabited in great densities by the burrowing crab Neohelice (Chasmagnathus) granulata whose bioturbation rates are among the highest reported for salt-marshes worldwide. A set of biological interactions between N. granulata and S. perennis appears to be responsible for salt pan development in these areas which has not been described elsewhere. The main objective of this work was to determine the ecological interactions occurring between plants and crabs that lead to salt pan formation by using field-based sampling and manipulative experiments. Our results showed that S. perennis facilitated crab colonization of the salt-marsh by buffering otherwise stressful physical conditions (e.g., temperature, desiccation). Crabs preferred to construct burrows underneath plants and, once they reach high densities (up to 40 burrowsm−2), the sediment reworking caused plant die-off in the central area of patches. At this state, the patches lose elevation and become depressed due to the continuous bioturbation by crabs. Thus, salt pans are generated in this case by a set of biogeomorphic processes that include pure ecological interactions such as plant facilitation of crab settlement and also indirect negative effects of crabs on plant survival. Furthermore, crab bioturbation affects sediment structure due to concentration of burrowing activity under plant canopies promoting elevation loss and leading, after a few years, to salt pan formation in a previously vegetated substrate.

Assessment of benthic disturbance associated with stingray foraging for ghost shrimp by aerial survey over an intertidal sandflat

One notable type of bioturbation in marine soft sediments involves the excavation of large pits and displacement of sediment associated with predator foraging for infaunal benthos. Batoids are among the most powerful excavators, yet their impact on sediment has been poorly studied. For expansive tidal flats, only relatively small proportions of the habitat can be sampled due to physical and logistical constraints. The knowledge of the dynamics of these habitats, including the spatial and temporal distribution of ray bioturbation, thus remains limited. We combined the use of aerial photogrammetry and in situ benthic sampling to quantify stingray feeding pits in Tomioka Bay, Amakusa, Japan. Specifically, we mapped newly-formed pits over an 11-ha section of an intertidal sandflat over two consecutive daytime low tides. Pit size and distribution patterns were assumed to scale with fish size and reflect size-specific feeding behaviors, respectively. In situ benthic surveys were conducted for sandflat-surface elevation and prey density (callianassid shrimp). The volume versus area relationship was established as a logistic function for pits of varying sizes by photographing and refilling them with sediment. This relationship was applied to the area of every pit detected by air to estimate volume, in which special attention was paid to ray ontogenetic change in space utilization patterns. In total, 18,103 new pits were formed per day, with a mean individual area of 1060cm2. The pits were divided into six groups (G1 to G6 in increasing areas), with abundances of G1, G2+G3, and G4−G6 being medium, high, and low, respectively. Statistical analyses using generalized linear models revealed a marked preference for the higher prey-density areas in G1 and the restriction of feeding grounds of G4−G6 to the lower shore, with G2+G3 being generalists for prey density and sandflat elevation. The lower degrees of overall bioturbation by G1 and G4−G6 were spatially structured for the eight sub-areas demarcated by prey density and sandflat elevation, while G2+G3 homogenized the state over the sandflat. The newly-formed pits׳ sub-areal mean numerical, excavated-areal, and displaced-sediment-volume densities per day were confined to small ranges: 0.14–0.17m−2, 132–223cm2m−2, and 551–879cm3m−2 (latter two including 119 shallow non-pit excavations). These bioturbation rates are positioned at relatively high levels compared with those by rays from other geographic regions. The present procedure is applicable to the assessment of disturbance by any surface-sediment excavators on tidal flats if their pit dimensions are discernible from the air.

Modeling the migration of fallout radionuclides to quantify the contemporary transfer of fine particles in Luvisol profiles under different land uses and farming practices

Soil mixing and the downward movement of solid matter in soils are dynamic pedological processes that strongly affect the vertical distribution of all soil properties across the soil profile. These processes are affected by land use and the implementation of various farming practices, but their kinetics have rarely been quantified. Our objective was to investigate the vertical transfer of matter in Luvisols at long-term experimental sites under different land uses (cropland, grassland and forest) and different farming practices (conventional tillage, reduced tillage and no tillage). To investigate these processes, the vertical radionuclide distributions of 137Cs and 210Pb (xs) were analyzed in 9 soil profiles. The mass balance calculations showed that as much as 91±9% of the 137Cs was linked to the fine particles (≤2μm). To assess the kinetics of radionuclide redistribution in soil, we modeled their depth profiles using a convection–diffusion equation. The diffusion coefficient represented the rate of bioturbation, and the convection velocity provided a proxy for fine particle leaching. Both parameters were modeled as either constant or variable with depth. The tillage was simulated using an empirical formula that considered the tillage depth and a variable mixing ratio depending on the type of tillage used. A loss of isotopes due to soil erosion was introduced into the model to account for the total radionuclide inventory. All of these parameters were optimized based on the 137Cs data and were then subsequently applied to the 210Pb (xs) data. Our results show that the 137Cs isotopes migrate deeper under grasslands than under forests or croplands. Additionally, our results suggest that the diffusion coefficient decreased with depth and that it remained negligible below the tillage depth at the cropland sites, below 20cm in the forest sites, and below 80cm in the grassland sites.

Sedimentation, bioturbation, and sedimentary fabric evolution on a modern mesotidal mudflat: A multi-tracer study of processes, rates, and scales

A study of muddy tidal-flat sedimentation and bioturbation was undertaken in the Waitetuna Arm of Raglan Harbor, New Zealand, to evaluate the physical and biological processes that control cycling of sediment between the intertidal seabed and sediment–water interface, and also the formation of tidal flat sedimentary fabric and fine-scale stratigraphy. Cores were collected along an intertidal transect, and analyzed for sedimentary fabric, 210Pb and 7Be radiochemical distributions, and grain size. At the same locations, a new approach for time-series core-X-radiography study was undertaken (spanning 191 days), using magnetite-rich sand as a tracer for sedimentation and bioturbation processes in shallow tidal flat sediments. Sedimentary fabric consists of a shallow stratified layer overlying a deeper zone of intensely bioturbated shelly mud. Bioadvection mixes the deeper zone and contributes fine sediment to the surface stratified layer, via biodeposition. Physical resuspension and deposition of surface muds by wave and tidal flow are also likely contributors to formation of the surficial stratified layer, but physical stratification is not observed below this depth. The deliberate tracer study allowed calculation of bioadvection rates that control strata formation, and can be used to model diagenetic processes. Results suggest that the upper ∼15 cm of seabed can be fully mixed over timescales <1.75 y. Such mixing will erase pre-existing sedimentary fabric and transport buried sediment and chemical compounds back to the tidal-flat surface. Shallow biodiffusion also exists, but produces much slower and shallower mass transport. Best fits for 210Pb profiles using a diagenetic bioadvection/sedimentation model and independently measured tiered bioadvection rates suggest that sediment accumulation rates (SARs) on the tidal flat are ∼0.25 cm/y, near the low end of contemporary New Zealand muddy intertidal SARs. Frequent deposition and erosion of the surface layer demonstrates that long-term sediment accumulation captures only a small fraction of sediment deposited at any one time. Model results also suggest that our magnetite tracer method may slightly underestimate short-term shallow mixing rates (demonstrated by 7Be profiles), and slightly overestimate longer-term, deeper bioturbation rates (demonstrated by 210Pb profiles).

Quantifying the rate and depth dependence of bioturbation based on optically‐stimulated luminescence (OSL) dates and meteoric 10Be

ABSTRACTBoth the rate and the vertical distribution of soil disturbance modify soil properties such as porosity, particle size, chemical composition and age structure; all of which play an important role in a soil's biogeochemical functioning. Whereas rates of mixing have been previously quantified, the nature of bioturbation's depth dependence remains poorly constrained. Here we constrain, for the first time, the relationship between mixing rate and depth in a bioturbated soil in northeast Queensland, Australia using a novel method combining OSL (optically‐stimulated luminescence) ages and meteoric beryllium‐10 (10Be) inventories. We find that the best fit mixing rate decreases non‐linearly with increasing soil depth in this soil and the characteristic length scale of 0.28 m over which the mixing coefficient decays is comparable to reported rooting depth coefficients. In addition we show that estimates of surface mixing rates from OSL data are highly dependent on erosion rate and that erosion rate must be constrained if accurate mixing rates are to be quantified. We calculate surface diffusion‐like mixing coefficients of 1.8 × 10−4 and 2.1 × 10−4 m2 yr−1 for the studied soil for two different estimates of soil erosion. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley &amp; Sons Ltd.

The release and persistence of radioactive anthropogenic nuclides

Abstract Atmospheric testing of nuclear weapons during the period 1945–1980 ushered in the ‘atomic age’ and released large quantities of anthropogenic radiogenic nuclides into the atmosphere. These radionuclides were subsequently deposited as fallout to the entire surface of the planet. While many have decayed to negligible levels, long-lived radionuclides persist and will do so for thousands of years. Isotopes of plutonium, 239 Pu (half-life 24 100 years) and 240 Pu (half-life 6563 years), provide the best chronological markers for the onset of this anthropogenic event both now and into the future due to their long half-lives, particle-reactivity, and the fact that they were present in negligible quantities prior to anthropogenic production and release. Chronostratigraphic markers established by distinct Pu concentration profiles and Pu isotope changes in sediment sequences and ice and coral cores can provide high-resolution dating over the last 60 years. However, even though fallout has ceased, it is found that the Pu inventory currently held in surface soil layers and the oceans will continue to supply Pu to sediment deposition zones for millennia and centuries, respectively. The delivery of this Pu will depend on soil erosion and bioturbation rates, and the rate of removal of dissolved Pu from the ocean.

Bioturbation, germination and deposition of Alexandrium fundyense cysts in the Gulf of Maine

Like many other dinoflagellate species, Alexandrium fundyense possesses a benthic resting cyst which enables long-term persistence and annual blooms of this species in the Gulf of Maine. The size and extent of these harmful algal blooms are associated with high cyst concentrations in the top 1cm of sediment. Despite the importance of this resting stage in the life history of A. fundyense, little work has been done on bioturbation of cysts in the deep-water cyst beds of the western Gulf of Maine. Our work intensively examined one site within a major regional “seedbed” from February 2003 until August 2005, a time span that included an extraordinarily large bloom of A. fundyense in 2005.Over the course of 2 years we collected samples for benthic infauna and cyst profiles down to a depth of 30cm. We also measured sediment porosity, organic carbon, 210Pb, and porewater dissolved oxygen. On several dates we measured depth profiles of cyst autofluorescence. Profiles of cysts revealed large subsurface maxima peaking between 10 and 15cm depth with cyst concentrations declining strongly toward the sediment surface. On one sampling date (August 2004) we observed a cyst concentration peak at the sediment surface. Using these data we constructed a mechanistic model of cyst bioturbation, mortality, germination, and deposition. Modeled bioturbation was calibrated using 210Pb and modeled cyst profiles were compared to measured profiles. Model runs with constant and interannually-varying rates of cyst deposition produced similar time-averaged cyst profiles. Results indicate that the deeper portions of cyst profiles are determined primarily by bioturbation, germination and cyst mortality and less so by interannual variation in cyst depositional history. This is due to the relatively low sedimentation rate at the study site compared to the rate of bioturbation, and the fact that the number of cysts deposited each year tends to be a small fraction of the total inventory. Seasonal and interannual variation in cyst deposition strongly influenced concentrations of cysts in the top few millimeters of the sediment, however. When cyst deposition rates are low, bioturbation and germination are sufficient to rapidly deplete cysts in this surface layer, leaving relatively few cysts within the sediment depth range that allows germination. But, bioturbation is not rapid enough to homogenize surface sediments within one year. As a result, cyst deposition results in a concentration peak at the sediment surface that persists to fuel germination the following year. Because of this phenomenon, the model predicted that years with high rates of germination follow years with large levels of cyst deposition. Over longer time scales, bioturbation transports cysts from the sediment surface to depth, which, along with germination, creates a persistent subsurface maximum in cyst concentration. Bioturbation also serves to maintain persistence of A. fundyense by transporting older cysts from these deeper layers to the sediment surface where they can germinate. Since high concentrations of cysts near the sediment surface indicate large numbers of cysts deposited during the previous year, if enhanced germination leads to large blooms of A. fundyense, these blooms are predicted to occur in years following large cyst deposition events.

224Ra:228Th disequilibrium in coastal sediments: Implications for solute transfer across the sediment–water interface

We utilized 224Ra/228Th disequilibrium in the sediment to investigate processes that regulate solute transfer across the sediment–water interface. Depth profiles of dissolved and surface-bound 224Ra and 228Th in the upper 0–20cm sediment column were measured using a delayed coincidence counter during a cruise to the Yangtze estuary from 15 to 24 August 2011. Along with 224Ra and 228Th, depth profiles of 234Th were collected to determine the bioturbation rate in the sediment. At most study sites, a significant deficit of 224Ra relative to 228Th was observed in the upper 0–10cm. In contrast, 224Ra was in excess with respect to 228Th in the upper 0–5cm at the river mouth, possibly due to redistribution of 224Ra from the mid-salinity region. By modeling the 224Ra depth profiles in the sediment using the general diagenetic equation, we demonstrated that in most cases molecular diffusion and bioturbation together can account for only ∼20–30% of the measured flux of 224Ra. We concluded that other mechanisms, especially irrigation, must be invoked to explain the remnant 70% of the observed deviation of 224Ra relative to 228Th. On the basis of the 224Ra/228Th disequilibrium in the sediment and a concept of increased surface area for exchange by irrigation as developed by early investigators, we proposed a new approach – the 224Ra/228Th disequilibrium approach to quantify the transfer rate of other dissolved species across the sediment–water interface. We have utilized this new approach to determine the benthic consumption rate of dissolved O2. The result reveals that benthic consumption is an important loss term of dissolved O2 in the Yangtze estuary and must be considered as one of the mechanisms that lead to hypoxia in this area.

Conditional Responses of Benthic Communities to Interference from an Intertidal Bivalve

Habitat-modifying organisms that impact other organisms and local functioning are important in determining ecosystem resilience. However, it is often unclear how the outcome of interactions performed by key species varies depending on the spatial and temporal disturbance context which makes the prediction of disturbance-driven regime shifts difficult. We investigated the strength and generality of effects of the filter feeding cockle Cerastoderma edule on its ambient intertidal benthic physical and biological environment. By comparing the magnitude of the effect of experimental cockle removal between a non-cohesive and a sheltered cohesive sediment in two different periods of the year, we show that the outcome of cockle interference effects relates to differences in physical disturbance, and to temporal changes in suspended sediment load and ontogenetic changes in organism traits. Interference effects were only present in the cohesive sediments, though the effects varied seasonally. Cockle presence decreased only the density of surface-dwelling species suggesting that interference effects were particularly mediated by bioturbation of the surface sediments. Furthermore, density reductions in the presence of cockles were most pronounced during the season when larvae and juveniles were present, suggesting that these life history stages are most vulnerable to interference competition. We further illustrate that cockles may enhance benthic microalgal biomass, most likely through the reduction of surface-dwelling grazing species, especially in periods with high sediment load and supposedly also high bioturbation rates. Our results emphasize that the physical disturbance of the sediment may obliterate biotic interactions, and that temporal changes in environmental stressors, such as suspended sediments, may affect the outcome of key species interference effects at the local scale. Consequently, natural processes and anthropogenic activities that change bed shear stress and sediment dynamics in coastal soft-sediment systems will affect cockle-mediated influences on ecosystem properties and therefore the resilience of these systems to environmental change.

Enhancement of the benthic communities around an isolated island in the Antarctic Ocean

Insular marine biotas are often richer in faunal diversity than those from the open sea in the same geographical region. The existence of particular island effects were tested under polar conditions by comparing infaunal benthic assemblages on Peter I Island with those of similar latitudes in the open ocean at the Bellingshausen Sea and also from the coast of the Antarctic Peninsula. Sampling was carried out aboard the R/V Hesperides during the expedition named BENTART-2003 from 24 January to 3 March 2003. Benthic samples were collected at 18 stations ranging from 90 to 2 044 m depth, using an USNEL-type box corer (BC) dredge. Representatives of 32 higher taxa of invertebrates were found. Univariate and multivariate analyses revealed various patterns in the data. First, significant differences in polychaete abundance were detected between the stations located in the open sea and the remaining sites (island plus mainland sites). Bivalve abundances were also distinct between island and mainland sampling sites. Sediment columns taken from the island seafloor exhibited the highest rate of bioturbation by the infauna. These findings confirm the model that islands develop distinct assemblages characterized by the enhancement of the benthic communities even in cold waters. Several abiotic factors were measured simultaneously at the seafloor and along the water column to investigate faunal distribution patterns. Significant correlations were found between the benthic assemblages and a combination of two environmental variables: “island effect” (measured as a categorical variable) and the redox state of sediments. Richer andmore complex benthic assemblages were found in Peter I Island’s sea bottom, whereas the more depauperate bottoms remained in the open sea.

Evolving Phytoplankton Stoichiometry Fueled Diversification of the Marine Biosphere

The availability of nutrients and the quantity and quality of food at the base of food webs have largely been ignored in discussions of the Phanerozoic record of biodiversity. We examine the role of nutrient availability and phytoplankton stoichiometry (the relative proportions of inorganic nutrients to carbon) in the diversification of the marine biosphere. Nutrient availability and phytoplankton stoichiometry played a critical role in the initial diversification of the marine biosphere during the Neoproterozoic. Initial biosphere expansion during this time resulted in the massive sequestration of nutrients into biomass which, along with the geologically slow input of nutrients from land, set the stage for severe nutrient limitation and relatively constant marine biodiversity during the rest of the Paleozoic. Given the slow nutrient inputs from land and low recycling rates, the growth of early-to-middle Paleozoic metazoans remained limited by their having to expend energy to first “burn off” (respire) excess carbon in food before the associated nutrients could be utilized for growth and reproduction; the relative equilibrium in marine biodiversity during the Paleozoic therefore appears to be real. Limited nutrient availability and the consequent nutrient imbalance may have delayed the appearance of more advanced carnivores until the Permo-Carboniferous, when widespread orogeny, falling sea level, the spread of forests, greater weathering rates, enhanced ocean circulation, oxygenation, and upwelling all combined to increase nutrient availability. During the Meso-Cenozoic, rising oxygen levels, the continued nutrient input from land, and, especially, increasing rates of bioturbation, enhanced nutrient availability, increasing the nutrient content of phytoplankton that fueled the diversification of the Modern Fauna.

Chlorophyll, lipid profiles and bioturbation in sediments around a fish cage farm in the Gulf of Eilat, Israel

Sediment biogeochemical processes were measured on a transect of 4 stations FF 20W, 40W and 80W (number is metres from the fish farm, FF, to the west) at the Ardag gilthead seabream Sparus aurata farm in the Gulf of Aqaba, a highly oligotrophic system renowned for its clear water and diverse corals. At each station samples were taken for analysis of macrofaunal community and benthic oxygen demand, together with depth profiles of CHN, porosity, chlorophyll a and fatty acids. The macrobenthos was dominated by the small marine snail Nassarius sinusigerus. In contrast to many fish farms in temperate waters, a large abundance of small, opportunist worms was not observed near the fish farm although sulphide oxidising bacteria Beggiatoa spp. were observed. Oxygen demands (108–154mmolm−2d−1) near the farm were lower than those observed elsewhere despite the high water temperature (~26°C). Bioturbation rates derived from chlorophyll profiles were low (0.013–0.069cm2d−1) compared to results from a farm in Scotland as a consequence of the much lower infaunal abundance. Porosity, organic carbon and carbon/nitrogen ratio profiles showed clear discrimination between the stations near the cages (FF and 20W) and those more distant. A Multi-Dimensional Scaling plot of 31 sediment fatty acid concentrations from each of the 4 stations (averaged to 4cm sediment depth) shows a trend in fatty acid composition that allows good discrimination between 80W, 40W and the two stations near the farm, which overlap. An increase in the proportion of bacterial fatty acids with distance from the farm indicates a change from profiles dominated by farm wastes (with a high proportion of fish feed derived mono-unsaturated fatty acids) near the farm to background conditions where the profiles are dominated by benthic biomass. The data presented are discussed by contrasting these with earlier studies in mesotrophic systems. The results indicate that the Pearson–Rosenberg paradigm of benthic succession may be altered owing to the dominance of the benthos by N. sinusigerus and low animal abundance and so benthic indicators of impact would have to be tailored for the characteristics of this environment. Sediment water content, organic carbon content, C/N ratios and fatty acids all showed trends with distance from the farm and could be considered as indicators, as could the density of N. sinusigerus and the presence of Beggiatoa sp. mats.

Relationships between Nutrient Enrichment and Benthic Function: Local Effects and Spatial Patterns

Eutrophication-induced changes to benthic faunal activities are problems of significant ecological impact, affecting global nutrient budgets as well as local trophic connections. We address the question of how nitrogen loads to estuarine embayments alter the bioturbation activities of benthic fauna. Specifically, we related local benthic activities to calculated local nitrogen concentrations for 22 northeastern US estuaries. These local nitrogen concentrations were derived from the calculated nitrogen loading for the embayment together with the spatial distribution of the local flushing time. Our results showed a maximum bioturbation rate at intermediate nitrogen concentrations or a “hump-shaped” pattern of response. This behavior was evident in all embayments that had a range of concentrations including low, intermediate, and high values. Embayments where sampling did not include this full range did not show this behavior. This work provides methods and guidance to help managers make decisions concerning the effects of nitrogen loading on the activities and well-being of benthic fauna in coastal embayments. The novelty of this approach lies in identifying the response of bioturbation to nitrogen loading in many systems, without costly and time-consuming speciation of benthic fauna, and also in rapidly identifying embayments and aquatic areas with vulnerable fauna. These results are ecologically significant in supporting the hypothesis that benthic organism abundance and activity will peak at mid-levels of nitrogen due to the interplay of food availability and oxygen levels, noting that the critical levels of these factors differ among water bodies.

Bioturbation on wildfire-affected southeast Australian hillslopes: Spatial and temporal variation

Abstract The importance of bioturbation as an agent of soil and geomorphological change is well known but few observations have been made of spatial and temporal variations in bioturbation rates. We quantified variations in surface bioturbation by ants (particularly Aphaenogaster longiceps) and vertebrates in the sandstone terrain of the Blue Mountains, southeast Australia. Following wildfire during the period late 2001–early 2002, we monitored thirty-three 5 m2 plots positioned in six different slope units and in two catchments affected by different wildfire severities. Measurements were made seasonally for six years. Overall, mean rates of ant mounding and surface scraping by vertebrates were similar (246 ± 339 g m− 2 yr− 1 and 274 ± 179 g m− 2 yr− 1, respectively). However, rates varied substantially according to slope unit, showing a marked maximum for both ant mounding and total bioturbation on footslopes. Possible reasons for this spatial variation are discussed. A complex response to various soil and ecological factors such as soil texture, soil moisture and vegetation patterns is the most likely explanation. Associated estimates of topsoil (0–30 cm depth) turnover times, based on ant mounding rates alone, ranged from 300 to 100,000 years for different slope units. In contrast to previous findings, wildfire severity did not seem to affect bioturbation, possibly because of ant survival in deep nests and spatial patchiness of fire severity. There was likewise no clear link between temporal changes in bioturbation and fire severity; high rates in the first two years after wildfire were followed by lower rates for all burn severity types. There was also seasonal variability that was not directly related to rainfall. The results substantiate the importance of bioturbation in modifying soil characteristics and influencing soil erosion, especially following a major disturbance event like wildfire.

Sediment accumulation and bioturbation rates in the deep Northeast Atlantic determined by radiometric techniques

Abstract Carvalho, F. P., Oliveira, J. M., and Soares, A. M. M. 2011. Sediment accumulation and bioturbation rates in the deep Northeast Atlantic determined by radiometric techniques. – ICES Journal of Marine Science, 68: . The upper layers of boxcore bottom-sediment samples from the Porcupine Abyssal Plain (five cores) and from the Iberian Abyssal Plain (eight cores) in the Northeast Atlantic were analysed for porosity, grain size, organic carbon, calcium carbonate, and radionuclides. Radiometric ages of sediment layers were determined using 230Th excess (the 230Thexc/232Th ratio method) and 14C radionuclides. Sediment accumulation rates were 0.14 and 3.2 cm kyear−1 at the Porcupine and Iberian Abyssal Plains, respectively. Sediment mixing, determined through 210Pb excess, was in the upper 5–11 cm sediment layer, likely as a result of infauna activity. Biodiffusion coefficients averaged 0.40 ± 0.37 and 1.05 ± 1.02 cm2 year–1 and were not significantly different in the sediments of either abyssal plain. The low rates of sediment accumulation and bioturbation in the abyssal depths of the Northeast Atlantic suggested that immobilization of sediment-reactive man-made radionuclides released near the seafloor will take place very slowly and with limited sediment burial.