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Cowie, GL, Levin LA.  2009.  Benthic biological and biogeochemical patterns and processes across an oxygen minimum zone (Pakistan margin, NE Arabian Sea). Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:261-270.   10.1016/j.dsr2.2008.10.001   AbstractWebsite

Oxygen minimum zones (OMZs) impinging on continental margins present sharp gradients ideal for testing environmental factors thought to influence C cycling and other benthic processes, and for identifying the roles that biota play in these processes. Here we introduce the objectives and initial results of a multinational research program designed to address the influences of water depth, the OMZ (similar to 150-1300 m), and organic matter (OM) availability on benthic communities and processes across the Pakistan Margin of the Arabian Sea. Hydrologic, sediment, and faunal characterizations were combined with in-situ and shipboard experiments to quantify and compare biogeochemical processes and fluxes, OM burial efficiency, and the contributions of benthic communities, across the OMZ. In this introductory paper, we briefly review previous related work in the Arabian Sea, building the rationale for integrative biogeochemical and ecological process studies. This is followed by a summary of individual volume contributions and a brief synthesis of results. Five primary stations were studied, at 140, 300, 940,1200 and 1850 m water depth, with sampling in March-May (intermonsoon) and August-October (late-to-postmonsoon) 2003. Taken together, the contributed papers demonstrate distinct cross-margin gradients, not only in oxygenation and sediment OM content, but in benthic community structure and function, including microbial processes, the extent of bioturbation, and faunal roles in C cycling. Hydrographic studies demonstrated changes in the intensity and extent of the OMZ during the SW monsoon, with a shoaling of the upper OMZ boundary that engulfed the previously oxygenated 140-m site. Oxygen profiling and microbial process rate determinations demonstrated dramatic differences in oxygen penetration and consumption across the margin, and in the relative importance of anaerobic processes, but surprisingly little seasonal change. A broad maximum in sediment OM content occurred on the upper slope, roughly coincident with the OMZ; but the otherwise poor correlation with bottom-water oxygen concentrations indicated that other factors are important in determining sediment OM distributions. Downcore profiles generally showed little clear evidence of in-situ OM alteration, and there was little sign of OM enrichment resulting from the southwest monsoon in sediments collected in the late-to-postmonsoon sampling. This is interpreted to be due to rapid cycling of labile OM. Organic geochemical studies confirmed that sediment OM is overwhelmingly of marine origin across the margin, but also that it is heavily altered, with only small changes in degradation state across the OMZ. More negative stable C isotopic compositions in surficial sediments at hypoxic sites within the OMZ core are attributed to a chemosynthetic bacterial imprint. Dramatic changes in benthic community structure occurred across the lower OMZ transition, apparently related to OM availability and quality as well as to DO concentrations. High-resolution sampling, biomarkers and isotope tracer studies revealed that oxygen availability appears to exert threshold-type controls on benthic community structure and early faunal C processing. Biomarker studies also provided evidence of faunal influence on sediment OM composition. Together, the results offer strong evidence that benthic fauna at sites across the margin play important roles in the early cycling of sediment OM through differential feeding and bioturbation activities. (C) 2008 Published by Elsevier Ltd.

Nordstrom, MC, Currin CA, Talley TS, Whitcraft CR, Levin LA.  2014.  Benthic food-web succession in a developing salt marsh. Marine Ecology Progress Series. 500:43-U69.   10.3354/meps10686   AbstractWebsite

Ecological succession has long been a focal point for research, and knowledge of underlying mechanisms is required if scientists and managers are to successfully promote recovery of ecosystem function following disturbance. We addressed the influence of bottom-up processes on successional assemblage shifts in salt marshes, ecosystems with strong physical gradients, and how these shifts were reflected in the trophic characteristics of benthic fauna. We tracked the temporal development of infaunal community structure and food-web interactions in a young, created salt marsh and an adjacent natural marsh in Mission Bay, California, USA (1996-2003). Macro faunal community succession in created Spartina foliosa habitats occurred rapidly, with infaunal densities reaching 70% of those in the natural marsh after 1 yr. Community composition shifted from initial dominance of insect larvae (surface-feeding microalgivores) to increased dominance of oligo chaetes (subsurface-feeding detritivores) within the first 7 yr. Isotopic labeling of microalgae, N-2-fixing cyanobacteria, S. foliosa and bacteria revealed direct links (or absence thereof) between these basal food sources and specific consumer groups. In combination with the compositional changes in the macroinvertebrate fauna, the trophic patterns indicated an increase in food-web complexity over time, reflecting resource-driven marsh succession. Natural abundance stable isotope ratios of salt marsh consumers (infaunal and epifaunal macroinvertebrates, and fish) initially reflected distinctions in trophic structure between the created and natural marsh, but these diminished during successional development. Our findings suggest that changing resource availability is one of the important drivers of succession in benthic communities of restored wetlands in Southern California.

Rathburn, AE, Levin LA, Held Z, Lohmann KC.  2000.  Benthic foraminifera associated with cold methane seeps on the northern California margin: Ecology and stable isotopic composition. Marine Micropaleontology. 38:247-266.   10.1016/s0377-8398(00)00005-0   AbstractWebsite

Release of methane from large marine reservoirs has been linked to climate change, as a causal mechanism and a consequence of temperature changes, during the Quaternary and the Paleocene. These inferred linkages are based primarily on variations in benthic foraminiferal stable isotope signatures. Few modem analog data exist, however, to assess the influence of methane flux on the geochemistry or faunal characteristics of benthic foraminiferal assemblages. Here we present analyses of the ecology and stable isotopic compositions of living (Rose Bengal stained) and dead (fossil) foraminifera (>150 mu m) from cold methane seeps on the slope off of the Eel River, northern California (500-525 m), and discuss potential applications for reconstructions of methane release in the past and present. Calcareous foraminiferal assemblages associated with Calyptogena clam bed seeps were comprised of species that are also found in organic-rich environments. Cosmopolitan, paleoceanographically important taxa were abundant; these included Uvigerina, Bolivina, Chilostomella, Globobulimina, and Nonionella. We speculate that seep foraminifera are attracted to the availability of food at cold seeps, and require no adaptations beyond those needed for life in organic-rich, reducing environments. Oxygen isotopic values of the tests of living foraminiferal assemblages from seeps had a high range (up to 0.69 parts per thousand) as did carbon isotopic values (up to 1.02 parts per thousand). Many living foraminiferal isotope values were within the range exhibited by the same or similar species in non-seep environments. Carbon isotopic values of fossil foraminifera found deeper in the sediments (18-20 cm), however, were 4.10 parts per thousand (U. peregrina) and 3.60 parts per thousand (B. subargentea) more negative than living delta(13)C values. These results suggest that delta(13)C values of foraminiferal tests reflect methane seepage and species-specific differences in isotopic composition, and can indicate temporal variations in seep activity. A better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo-seep recognition, and improve interpretations of climatic and paleoceanographic change. (C) 2000 Elsevier Science B.V. All rights reserved.

Neira, C, Levin LA, Grosholz ED.  2005.  Benthic macrofaunal communities of three sites in San Francisco Bay invaded by hybrid Spartina, with comparison to uninvaded habitats. Marine Ecology-Progress Series. 292:111-126.   10.3354/meps292111   AbstractWebsite

A hybrid cordgrass, formed from a cross between Spartina alterniflora (Atlantic cordgrass) and S. foliosa (Pacific cordgrass), has recently spread within the intertidal zone of south San Francisco Bay. Sediment properties and macroinfaunal community structure were compared in patches invaded by Spartina hybrid and adjacent uninvaded patches at 3 sites in San Francisco Bay (2 tidal flats and 1 Salicornia marsh). We hypothesized that (1) sediments vegetated by Spartina hybrid would have reduced sediment grain size, higher organic matter content, lower redox potential, lower salinity and reduced microalgal biomass relative to adjacent unvegetated tidal flat sediments, and (2) that differences in the sediment environment would correspond to changes in the infaunal invertebrate community structure and feeding modes. We observed 75 % lower total macro-faunal density and lower species richness in Spartina-vegetated sediments at Elsie Roemer (30 yr old invasion) than in an adjacent unvegetated tidal flat. This was due to lower densities of surface-feeding amphipods, bivalves, cirratulid and spionid polychaetes. The proportional representation of subsurface-deposit feeders was greater in Spartina patches than in unvegetated sediments. At a more recently invaded site (Roberts Landing; 15 yr invasion), Spartina patches differed from tidal flat sediments in composition, but not in abundance. Native (Salicornia) and Spartina patches exhibited similar sediment properties at San Mateo, where the Spartina hybrid invaded 8 to 10 yr earlier. No differences were detected in densities or proportions of surface- or subsurface-deposit feeders, but the proportion of carnivores/omnivores and grazers increased in the hybrid-invaded patches. These studies suggest that the invasive Spartina hybrid in south San Francisco Bay can have differing effects on sediment ecosystems, possibly depending on the location, age, or type of habitats involved.

Gage, JD, Levin LA, Wolff GA.  2000.  Benthic processes in the deep Arabian Sea: introduction and overview. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:1-7.   10.1016/S0967-0645(99)00095-8   AbstractWebsite
Levin, L, Gutierrez D, Rathburn A, Neira C, Sellanes J, Munoz P, Gallardo V, Salamanca M.  2002.  Benthic processes on the Peru margin: a transect across the oxygen minimum zone during the 1997-98 El Nino. Progress in Oceanography. 53:1-27.   10.1016/s0079-6611(02)00022-8   AbstractWebsite

Oxygen minimum zones (OMZs) are widespread features in the most productive regions of the world ocean. A holistic view of benthic responses to OMZ conditions will improve our ability to predict ecosystem-level consequences of climatic trends that influence oxygen availability, such as global warming or ENSO-related events. Four stations off Callao, Peru (-12'S, Station A, 305 m; Station B, 562 m; Station C, 830 nu and Station D, 1210 m) were sampled to examine the influence of the low bottom-water oxygen concentration and high organic-matter availability within the OMZ (O(2) < 0.5 ml L(-1)) on sediments, benthic communities, and bioturbation. Sampling took place during early January 1998, an intense El Ni (n) over tildeo period associated with higher-than-normal levels of O(2) on the shelf and upper slope. Peru slope sediments were highly heterogeneous. Sediment total organic carbon content exceeded 16%, lamination was present below 6 cm depth, and filamentous sulfur bacteria (Thioploca spp.) were present at Station A, (305 m, 0, < 0.02 ml L(-1)). Deeper sites contained phosphorite crusts or pellets and exhibited greater bottom-water oxygenation and lower content and quality of organic matter. X-radiographs and (210)Pb and (234)Th profiles suggested the dominance of lateral transport and bioturbation over pelagic sedimentation at the mid- and lower slope sites. Macrofauna, metazoan meiofauna and foraminifera exhibited coherence of density patterns across stations, with maximal densities (and for macrofauna, reduced diversity) at Station A, where bottom-water oxygen concentration was lowest and sediment labile organic matter content (LOC: sum of protein, carbohydrate and lipid carbon) was greatest. Metazoan and protozoan meiofaunal densities were positively correlated with sediment LOC. The taxa most tolerant of nearly anoxic, organic-rich conditions within the Peru OMZ were calcareous foraminifera, nematodes and gutless phallodrilinid (symbiont-bearing) oligochaetes. Agglutinated foraminifera, harpacticoid copepods, polychaetes and many other macrofaunal taxa increased in relative abundance below the OMZ. During the study (midpoint of the 1997-98 El Ni (n) over tildeo), the upper OMZ boundary exhibited a significant deepening (to 190 m) relative to 'normal', non-El Ni (n) over tildeo conditions (< 100 m), possibly causing a mild, transient oxygenation over the upper slope (200-300 m) and reduction of the organic particle flux to the seabed. Future sampling may determine whether the Peru margin system exhibits dynamic responses to changing ENSO-related conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.

Levin, LA, Mendoza GF, Grupe BM, Gonzalez JP, Jellison B, Rouse G, Thurber AR, Waren A.  2015.  Biodiversity on the rocks: Macrofauna inhabiting authigenic carbonate at Costa Rica methane seeps. PLoS ONE. 10:e0131080.: Public Library of Science   10.1371/journal.pone.0131080   Abstract

The activity of anaerobic methane oxidizing microbes facilitates precipitation of vast quantities of authigenic carbonate at methane seeps. Here we demonstrate the significant role of carbonate rocks in promoting diversity by providing unique habitat and food resources for macrofaunal assemblages at seeps on the Costa Rica margin (400–1850 m). The attendant fauna is surprisingly similar to that in rocky intertidal shores, with numerous grazing gastropods (limpets and snails) as dominant taxa. However, the community feeds upon seep-associated microbes. Macrofaunal density, composition, and diversity on carbonates vary as a function of seepage activity, biogenic habitat and location.

Sperling, EA, Frieder CA, Levin LA.  2016.  Biodiversity response to natural gradients of multiple stressors on continental margins. Proceedings of the Royal Society of London B: Biological Sciences. 283   10.1098/rspb.2016.0637   Abstract

Sharp increases in atmospheric CO2 are resulting in ocean warming, acidification and deoxygenation that threaten marine organisms on continental margins and their ecological functions and resulting ecosystem services. The relative influence of these stressors on biodiversity remains unclear, as well as the threshold levels for change and when secondary stressors become important. One strategy to interpret adaptation potential and predict future faunal change is to examine ecological shifts along natural gradients in the modern ocean. Here, we assess the explanatory power of temperature, oxygen and the carbonate system for macrofaunal diversity and evenness along continental upwelling margins using variance partitioning techniques. Oxygen levels have the strongest explanatory capacity for variation in species diversity. Sharp drops in diversity are seen as O2 levels decline through the 0.5–0.15 ml l−1 (approx. 22–6 µM; approx. 21–5 matm) range, and as temperature increases through the 7–10°C range. pCO2 is the best explanatory variable in the Arabian Sea, but explains little of the variance in diversity in the eastern Pacific Ocean. By contrast, very little variation in evenness is explained by these three global change variables. The identification of sharp thresholds in ecological response are used here to predict areas of the seafloor where diversity is most at risk to future marine global change, noting that the existence of clear regional differences cautions against applying global thresholds.

Blair, NE, Levin LA, Demaster DJ, Plaia G, Martin C, Fornes W, Thomas C, Pope R.  2001.  The biogeochemistry of carbon in continental slope sediments. Organism-sediment Interactions. ( Aller JY, Woodin S, Aller RC, Belle W. Baruch Institute for Marine Biology and Coastal Research. , Eds.).:243-262., Columbia: Published for the Belle W. Baruch Insitute for Marine Biology and Coastal Research by the University of South Carolina Press Abstract
Demaster, DJ, Pope RH, Levin LA, Blair NE.  1994.  Biological mixing intensity and rates of organic carbon accumulation in North Carolina slope sediments. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 41:735-753.   10.1016/0967-0645(94)90045-0   AbstractWebsite

Sediment accumulation rates and biological mixing intensities were determined at three sites on the North Carolina slope based on profiles of naturally occurring C-14, Pb-210 and(234) Th. The three sites all were at a water depth of 850 m with a spacing of 150-180 km between sites. Sediment accumulation rates increase from south to north from values of 7 cm ky(-1) at Site I, to 160 cm ky(-1) at Site II, to 1100 cm ky(-1) at Site III. The organic carbon burial rate at these sites also increases in the northward direction from 0.65 (Site I) to 20 (Site II) to less than or equal to 150 g C-org m(-2) year(-1) (Site III). These data indicate that continental margin environments can exhibit highly variable carbon fluxes over relatively small distances on the seafloor. The rate of organic carbon accumulation at Site III is one of the highest values reported for the marine environment. Based on these accumulation rates and dissolved inorganic carbon flux estimates from each site, the seabed organic carbon preservation efficiency (i.e. the ratio of C-org accumulation rate to C-org deposition rate times 100) was estimated to vary from 6.0% to 54% to 88% at Sites I, II and III, respectively. The C-14 age of organic matter in surface sediments was older at Site III (1800 years BP) than at Sites I and II (800 years BP), indicating that Site III receives a greater proportion of old sediment from either up-slope areas or from terrigenous sources. Inventories of excess Th-234 (half-life of 24 days) were used as a tracer for particle flux covering the 100 days prior to the October 1989, July-August 1990 and August 1991 cruises. The mean Th-234 inventories al the three sites were 4.7 +/- 1.9, 8.4 +/- 6.3 and 23.1 +/- 7.3 dpm cm(-2) for Sites I, II and III, respectively. Profiles of excess Th-234 activity reveal that the biological mixing intensity is greater at Site III (mean D-b = 19 +/- 11 cm(2) year(-1), n = 5) than at either Site I (mean D-b = 6.0 +/- 6.2 cm(2) year(-1) n = 6) or Site II (mean D-b = 4.6 +/- 5.2 cm(2) year(-1), n = 9). In addition to the trend in mixing coefficients, the depth of particle mixing on a 100-day time scale generally is greater at Site III than at the other two sites. These observations of particle mixing intensity are consistent with the northward increase in the mean abundance of macrofauna (>300 microns) from mean values of 9400 m(-2) at Site I, to 21,400 m(-2) at Site II, to 55,500 m(-2) at Site III. For the three study sites off North Carolina, a strong correlation (R(2) = 0.99,p = 0.06) exists between macrofaunal abundance and the organic carbon deposition rate. An equally strong correlation (R(2) = 0.99, P = 0.04) occurs between macrofaunal abundance and the Th-234 inventories (index of 100-day particle flux). Fine-sand size glass tracer beads were dispersed at these three sites by submersible and then the field plots were sampled similar to 1 year later. The vertical distributions of beads at the three sites are consistent with a higher mixing intensity at Site III than at the other two sites, but the estimated mixing coefficients generally are lower than those determined from the profiles of Th-234. The slower mixing of the glass beads may be the result of their low food value and/or their relatively large size (compared to the surrounding fine-grained sediments).

Buhl-Mortensen, L, Vanreusel A, Gooday AJ, Levin LA, Priede IG, Buhl-Mortensen P, Gheerardyn H, King NJ, Raes M.  2010.  Biological structures as a source of habitat heterogeneity and biodiversity on the deep ocean margins. Marine Ecology-an Evolutionary Perspective. 31:21-50.   10.1111/j.1439-0485.2010.00359.x   AbstractWebsite

Biological structures exert a major influence on species diversity at both local and regional scales on deep continental margins. Some organisms use other species as substrates for attachment, shelter, feeding or parasitism, but there may also be Mutual benefits from the association. Here, we highlight the structural attributes and biotic effects of the habitats that corals, sea pens, sponges and xenophyophores offer other organisms. The environmental setting of the biological structures influences their species composition. The importance of benthic species as substrates seems to increase with depth as the complexity of the surrounding geological substrate and food supply decline. There are marked differences in the degree of mutualistic relationships between habitat-forming taxa. This is especially evident for scleractinian corals, which have high numbers of facultative associates (commensals) and few obligate associates (mutualists), and gorgonians, with their few commensals and many obligate associates. Size, flexibility and architectural complexity of the habitat-forming organism are positively related to species diversity for both sessile and mobile species. This is mainly evident for commensal species sharing a facultative relationship with their host. Habitat complexity is enhanced by the architecture of biological structures, as well as by biological interactions. Colony morphology has a great influence on feeding efficiency for suspension feeders. Suspension feeding, habitat-forming organisms modify the environment to optimize their food uptake. This environmental advantage is also passed on to associated filter-feeding species. These effects are poorly understood but represent key points for understanding ecosystems and biodiversity on continental margins. In this paper we explore the contributions of organisms and the biotic structures they create (rather than physical modifications) to habitat heterogeneity and diversity on the deep continental margins.

Mora, C, Wei CL, Rollo A, Amaro T, Baco AR, Billett D, Bopp L, Chen Q, Collier M, Danovaro R, Gooday AJ, Grupe BM, Halloran PR, Ingels J, Jones DOB, Levin LA, Nakano H, Norling K, Ramirez-Llodra E, Rex M, Ruhl HA, Smith CR, Sweetman AK, Thurber AR, Tjiputra JF, Usseglio P, Watling L, Wu TW, Yasuhara M.  2013.  Biotic and human vulnerability to projected changes in ocean biogeochemistry over the 21st century. Plos Biology. 11   10.1371/journal.pbio.1001682   AbstractWebsite

Ongoing greenhouse gas emissions can modify climate processes and induce shifts in ocean temperature, pH, oxygen concentration, and productivity, which in turn could alter biological and social systems. Here, we provide a synoptic global assessment of the simultaneous changes in future ocean biogeochemical variables over marine biota and their broader implications for people. We analyzed modern Earth System Models forced by greenhouse gas concentration pathways until 2100 and showed that the entire world's ocean surface will be simultaneously impacted by varying intensities of ocean warming, acidification, oxygen depletion, or shortfalls in productivity. In contrast, only a small fraction of the world's ocean surface, mostly in polar regions, will experience increased oxygenation and productivity, while almost nowhere will there be ocean cooling or pH elevation. We compiled the global distribution of 32 marine habitats and biodiversity hotspots and found that they would all experience simultaneous exposure to changes in multiple biogeochemical variables. This superposition highlights the high risk for synergistic ecosystem responses, the suite of physiological adaptations needed to cope with future climate change, and the potential for reorganization of global biodiversity patterns. If co-occurring biogeochemical changes influence the delivery of ocean goods and services, then they could also have a considerable effect on human welfare. Approximately 470 to 870 million of the poorest people in the world rely heavily on the ocean for food, jobs, and revenues and live in countries that will be most affected by simultaneous changes in ocean biogeochemistry. These results highlight the high risk of degradation of marine ecosystems and associated human hardship expected in a future following current trends in anthropogenic greenhouse gas emissions.

Fornes, WL, Demaster DJ, Levin LA, Blair NE.  1999.  Bioturbation and particle transport in Carolina slope sediments: A radiochemical approach. Journal of Marine Research. 57:335-355.   10.1357/002224099321618245   AbstractWebsite

In situ tracer experiments investigated short-term sediment mixing processes at two Carolina continental margin sites (water depth = 850 m) characterized by different organic C fluxes, (234)Th mixing coefficients (D(b)) and benthic assemblages. Phytoplankton, slope sediment, and sand-sized glass beads tagged with (210)Pb, (113)Sn, and (228)Th, respectively, were placed via submersible at the sediment-water interface at both field sites (Site I off Cape Fear, and Site m off Cape Hatteras). Experimental plots were sampled at 0, 1.5 days, and 90 days after tracer emplacement to examine short-term, vertical transport. Both sites are initially dominated by nonlocal mixing. Transport to the bottom of the surface mixed layer at both sites occurs more rapidly than (234)Th-based D(b) values predict; after 1.5 days, tagged particles were observed 5 cm below the sediment-water interface at Site I and 12 cm below at Site III. Impulse tracer profiles after 90 days at Site m exhibit primarily diffusive distributions, most likely due to a large number of random, nonlocal mixing events. The D(b) values determined from 90-day particle tagging experiments are comparable to those obtained from naturally occurring (234)Th profiles (similar to 100-day time scales) from nearby locations. The agreement between impulse tracer mixing coefficients and steady-state natural tracer mixing coefficients suggests that the diffusive analogue for bioturbation on monthly time scales is a realistic and useful approach. Tracer profiles from both sites exhibit some degree of particle selective mixing, but the preferential transport of the more labile carbon containing particles only occurred 30% of the time. Consequently, variations in the extent to which age-dependent mixing occurs in marine sediments may depend on factors such as faunal assemblage and organic carbon flux.

Levin, LA, Rathburn AE, Gutierrez D, Munoz P, Shankle A.  2003.  Bioturbation by symbiont-bearing annelids in near-anoxic sediments: Implications for biofacies models and paleo-oxygen assessments. Palaeogeography Palaeoclimatology Palaeoecology. 199:129-140.   10.1016/s0031-0182(03)00500-5   AbstractWebsite

Anoxic or nearly anoxic conditions ( < 4 muM O(2)) have long been associated with the absence of bioturbation and animal traces. This premise has guided interpretation of paleoceanographic conditions from rocks and sediments. We recently observed a high-density, living assemblage of highly mobile, symbiont-bearing, burrowing, phallodrilinid oligochaetes within a nearly anoxic basin ( <1 muM O(2) [0.02-0.03 ml l(-1)]) on the Peru margin (305 m). These observations were made during the most intense part of the 1997-98 El Ni (n) over tildeo when there may have been slight oxygenation of an otherwise anoxic basin, but oligochaete presence prior to this event is likely. The occurrence of symbiont-bearing gutless oligochaetes mainly within the upper 5 cm of the sediment column coincided with a bioturbated zone overlying distinctly laminated sediments. Our observations redefine the lower oxygen limit of macrofaunal bioturbation to much less than2 muM, and indicate a need to modify currently accepted ideas about the relationship between bioturbation and paleo-oxygen concentration. These results also address an ongoing debate about the lifestyles of bioturbating organisms in oxygen-poor settings. (C) 2003 Elsevier B.V. All rights reserved.

Levin, LA, Greenblatt PR.  1981.  Bottoms up: Juvenile terebellid polychaetes feeding in the water column. Bulletin - Southern California Academy of Sciences. 80:131-133. AbstractWebsite