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Baco, AR, Rowden AA, Levin LA, Smith CR, Bowden DA.  2010.  Initial characterization of cold seep faunal communities on the New Zealand Hikurangi margin. Marine Geology. 272:251-259.   10.1016/j.margeo.2009.06.015   AbstractWebsite

Cold-seep communities have been known from the North Atlantic and North Pacific for more than 20 years, but are only now being explored in the Southern Hemisphere While fisheries bycatch had suggested the presence of cold seeps on the New Zealand margin, the biodiversity and distribution of these communities remained unknown. Explorations using towed cameras and direct sampling gear revealed that cold seep sites are abundant along the New Zealand Hikurangi margin Initial characterization of the faunal communities at 8 of these sites indicates a fauna that is associated with particular sub-habitats but which varies in abundance between sites Community composition is typical, at higher taxonomic levels, of cold seep communities in other regions The dominant. symbiont-bearing taxa include siboglinid (tube) worms, vesicomyid clams and bathymodiolin mussels At the species level, much of the seep-associated fauna identified so far appears either to be new to science, or endemic to New Zealand seeps, suggesting the region may represent a new biogeographic province for cold-seep fauna Some overlap at the species and genus level is also indicated between the sampled seep communities and the fauna of hydrothermal vents on the Kermadec Arc in the region. Further taxonomic and genetic identifications of fauna from this study will allow us to fully test the levels of species overlap with other New Zealand chemosynthetic ecosystems as well as with other cold seep sites worldwide These apparently novel communities exhibit evidence of disturbance from a deep bottom-trawl fishery and appear to be threatened along the entire New Zealand margin. As bottom fisheries, mining, and fossil-fuel exploitation move into deeper waters, seep communities may be endangered worldwide, necessitating the initiation of conservation efforts even as new seep ecosystems are discovered and explored. Our findings highlight the unique nature of anthropogenic impacts in the deep-sea. in which reservoirs of biodiversity can be impacted long before they are even known. (C) 2009 Elsevier B V All rights reserved

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Cordes, EE, Cunha MR, Galeron J, Mora C, Olu-Le Roy K, Sibuet M, Van Gaever S, Vanreusel A, Levin LA.  2010.  The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity. Marine Ecology-an Evolutionary Perspective. 31:51-65.   10.1111/j.1439-0485.2009.00334.x   AbstractWebsite

Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic Sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the 'species sorting' concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.

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Davis, JLD, Levin LA.  2002.  Importance of pre-recruitment life-history stages to population dynamics of the woolly sculpin Clinocottus analis. Marine Ecology-Progress Series. 234:229-246.   10.3354/meps234229   AbstractWebsite

The relative influence of pre- versus post-recruitment life-history events on population size has been the subject of much recent debate. In the marine realm, much work has focused on intertidal invertebrates and on tropical reef fishes, with mixed results. We addressed this problem for a temperate intertidal fish, Clinocottus analis. Our main goal was to determine which life-history stage was most responsible for temporal changes in population size from 1996 to 2000 at 2 sites in San Diego, California, both seasonally and during the 1997 to 1998 El Nino Southern Oscillation (ENSO) event. We approached the problem using cohort analysis and matrix population modeling. Recruitment pulses were evident in population size structure for up to a year, unobscured by post-recruitment mortality, which was not density-dependent, Recruitment was not correlated to spawning adult biomass of 3 mo earlier, suggesting that egg, larval, or early post-settlement processes during those 3 mo determined the magnitude of recruitment, and ultimately, population size. Stage-structured population projection matrices were constructed to compare population growth rates and sensitivities among seasons and between climate periods (El Nino and non-El Nino), Elasticity (prospective) and decomposition (retrospective) analyses of these matrices indicated that the vital rates to which population growth rate (lambda) was theoretically most sensitive were not necessarily those responsible for observed temporal differences in lambda. Although, was most sensitive to juvenile growth and adult survivorship, fertility (which in this model included fecundity and egg, larval, and early post-settlement survivorship), in addition to juvenile growth, drove observed seasonal differences in lambda C. andlis population size decreased during the 1997 to 1998 El Nino event due to a decrease in recruitment, a decrease in batch fecundity (hydrated eggs per female) and, at 1 site, changes in juvenile survivorship, Results of the study emphasize the power of early life-history events to structure C. analis populations on both seasonal and longer timescales.

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Levin, LA, Talley T.  2000.  Influences of vegetation and abiotic environmental factors on salt marsh benthos. Concepts and controversies in tidal marsh ecology. ( Weinstein M, Kreeger D, Eds.).:661-708., Dordrecht ; Boston: Kluwer Academic Abstract
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Levin, LA, Plaia G, Huggett CL.  1994.  The influence of natural organic enhancement on life histories and community structure of bathyal polychaetes. Reproduction, larval biology, and recruitment of the deep-sea benthos. ( Young CM, Eckelbarger KJ, Eds.).:261-283., New York: Columbia University Press Abstract
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Levin, LA, Huggett DV.  1990.  Implications of alternative reproductive modes for seasonality and demography in an estuarine polychaete. Ecology. 71:2191-2208.   10.2307/1938632   AbstractWebsite

The consequences of alternative developmental patterns for the seasonal dynamics and demography of benthic marine invertebrates were examined by comparing two local demes (1.5 km apart) of the polychaete Streblospio benedicti Webster (Spionidae). One was dominated by individuals exhibiting planktotrophy, where large numbers of offspring develop from small eggs as feeding larvae, and the other was dominated by individuals exhibiting lecithotrophy, in which fewer numbers of larvae develop from large eggs without feeding. Over a 2.5-yr period we studied development mode, benthic abundances, recruitment, recolonization of disturbed areas, size structure, and reproductive output at the two sites, to evaluate possible effects of larval development mode on: (a) level of population fluctuation, (b) colonization ability, (c) secondary production, and (d) demographic properties. Size-structured population models were used to evaluate seasonal and annual population growth rates (@l). Sensitivity and life-table response analyses were carried out to examine the relative contribution of fecundity and survivorship to differences in @l between demes and among seasons. Strong similarity was observed between planktotroph- and lecithotroph-dominated demes in magnitude and timing of fluctuations in recruitment and total abundance, in benthic population size structure, and in secondary production, average production: biomass ratio, and annual population growth rates. S. benedicti data and a review of the literature provide no support for Thorson's (1950) hypothesis that species with planktotrophic development experience much greater levels of population fluctuation than those with lecithotropic development. However, in this study the planktotrophs exhibited superior colonization ability. They also exhibited stronger seasonality and more variability in production and some demographic properties. These factors combined suggest that populations with planktotrophic development should exhibit different patch dynamics than those with lecithotrophic development. The lecithotroph-dominated deme exhibited a consistent survivorship advantage in larval and juvenile stages that was balanced almost precisely in the planktotroph-dominated deme by a fecundity advantage in early adult stages. This led to similar population growth rates (@l wk^-^1), calculated from annual projection matrices, at both sites in both years (range: 1.004 to 1.078 wk^-^1). At both sites seasonal (cohort) population growth rates were lowest in spring (0.46-0.76) and highest in early summer and fall (usually @>1.10). Population growth potential for the plankotroph-dominated deme was always greater than for the lecithotroph-dominated deme in early summer; the reverse was true for the fall, overwintering cohort. Comparison of this study with an age-structured analysis of laboratory-reared S. benedicti populations from the same location, but subject to excess food and no predation or seasonality (Levin et al. 1987), revealed greatest demographic similarity between the lab populations and the fall, overwintering cohort from the field. The similar demographic consequences of planktotrophy and lecithotrophy have significance for efforts to model the evolution of life-history patterns, and for understanding the intraspecific and interspecific occurrence of contrasting developmental modes.

Levin, LA.  1982.  Interference interactions among tube-dwelling polychaetes in a dense infaunal assemblage. Journal of Experimental Marine Biology and Ecology. 65:107-119.   10.1016/0022-0981(82)90039-9   AbstractWebsite

Interactions involving contact between the feeding organs of the tube building polychaetes Pseudopolydora paucibranchiata Okuda, Streblospio benedicti Webster, and Fabricia limnicola Hartman were observed through a dissecting microscope and quantified for frequency of occurrence and effects on foraging time and withdrawal. These surface feeding species form a dense intertidal assemblage ( > 100000 individuals · m−2) and can be readily transferred to the laboratory and observed in undisturbed sediment cores. Interspecific contact with Pseudopolydora often resulted in withdrawal and consequently a 4 to 7% loss of foraging time for individuals of other species, while intraspecific interactions among Pseudopolydora did so rarely. Larger individuals of all three species experience more interaction. The probability and duration of withdrawal due to contact with Pseudopolydora is size dependent in Fabricia and Streblospio: juvenile Fabricia and adult Streblospio show the greatest interference. The observation that Pseudopolydora interferes with individuals of other species more than with conspecifics contradicts the small-scale dispersion of these species as well as previous reports of interference behavior. A possible explanation is the relatively recent coexistence of these three species, two of which were introduced to the eastern Pacific since 1900.

Levin, LA, Dibacco C.  1995.  Influence of sediment transport on short-term recolonization by seamount infauna. Marine Ecology-Progress Series. 123:163-175.   10.3354/meps123163   AbstractWebsite

Rates and mechanisms of infaunal recolonization in contrasting sediment transport regimes were examined by deploying hydrodynamically unbiased colonization trays at 2 sites similar to 2 km apart on the flat summit plain of Fieberling Guyot in the eastern Pacific Ocean. Both study sites experienced strong bottom currents and high shear velocity (u* exceeding 1.0 cm s(-1) daily). Macrofaunal recolonization of defaunated sediments on Fieberling Guyot was slow relative to observations in shallow-water sediments, but rapid compared to other unenriched deep-sea treatments. Microbial colonization was slower but macrofaunal colonization was faster at White Sand Swale (WSS, 585 m), where rippled foraminiferal sands migrate daily, than at Sea Pen Rim (SPR, 635 m), where the basaltic sands move infrequently. Total densities of macrofaunal colonizers at WSS were 31 and 75% of ambient after 7 wk and 6.4 mo, respectively; at SPR they were 6 and 49% of ambient, respectively. Over 3/4 of the colonists were polychaetes (predominantly hesionids and dorvilleids) and aplacophoran molluscs. Species richness of colonizers was comparable at SPR and WSS and did not differ substantially from ambient. Most of the species (91%) and individuals (95%) recovered in colonization trays were taxa present in background cores. However, only 25% of the taxa colonizing tray sediments occurred in trays at both WSS and SPR. Sessile species, carnivores and surface feeders were initially slow to appear in colonization trays, but after 6.4 mo, colonizer feeding modes, life habits and mobility patterns mirrored those in ambient sediments at WSS and SPR. Defaunated sediments were colonized by larvae, juveniles and adults at both sites. These experiments provide the first observations of infaunal colonization on seamounts, and in deep, high-energy settings. Passive bedload transport appears to be a dominant colonization mechanism in unstable foraminiferal sands at WSS. Based on the rapid recovery of infauna in trays and low diversity at WSS, we infer that disturbance is a natural feature of this site and that the ambient fauna of WSS retains features of early succession. Infaunal colonization is slower in the stable substrate at SPR, where physical disturbance may occur much less frequently.

Levin, LA, Michener RH.  2002.  Isotopic evidence for chemosynthesis-based nutrition of macrobenthos: The lightness of being at Pacific methane seeps. Limnology and Oceanography. 47:1336-1345. AbstractWebsite

The importance of chemosynthetic nutritional pathways was examined for macrofaunal invertebrates (>300 mum) from methane seeps in the Gulf of Alaska (4,413-4,443 m), on the Oregon margin (590 m), and on the northern California slope [Eel River margin] (520 m) by use of natural abundance stable isotopic data. Seep macrofauna exhibited lighter delta(13)C and delta(15)N values than those in nonseep sediments, but isotopic signatures varied among seep sites. Macrofaunal isotopic signatures indicated chemosynthetically fixed carbon sources with a significant contribution from methane-derived carbon (MDC) in macrofauna from sediments of pogonophoran fields (average delta(13)C, -46.44parts per thousand, 32%-51% MDC) and Calyptogena phaseoliformis beds (average delta(13)C, -40.89parts per thousand, 12%-40% MDC) in the Gulf of Alaska and in microbial mat sediments on the Oregon margin (average delta(13)C, -43.80parts per thousand, 20%-44% MDC). Lesser influence of MDC was noted in macrofauna from sediments of Calyptogena pacifica beds on the Oregon (average delta(13)C, -33.38parts per thousand, 0%-27% MDC) and California (delta(13)C, -25.10parts per thousand, 0%-22% MDC) margins and from California microbial mat sediments (delta(13)C, -22.23%o, 0%-5% MDC). Although most macrofauna appeared to be heterotrophic, light delta(15)N and delta(13)C values together provided evidence for chemoautotrophic symbioses in selected taxa. Carbon isotopic signatures were consistent with consumption of methane-oxidizing archaea by some dorvilleid polychaetes (delta(13)C, -90.62parts per thousand and -73.80parts per thousand) and with grazing on filamentous sulfur bacteria by gastropods and polychaetes from the Oregon and California seeps. The importance of chemosynthetic trophic pathways varies regionally and among microhabitats, taxonomic groups, and feeding guilds.

Levin, LA.  1986.  The influence of tides on larval availability in shallow waters overlying a mudflat. Bulletin of Marine Science. 39:224-233. AbstractWebsite

The plankton overlying the Kendall-Frost mudflat (Mission Bay, California) was sampled over four separate 12-h tidal cycles, two during the day and two at night, in order to identify short-term, tidally-induced variations in meroplankton abundance. In daytime samples larvae of four polychaete species and bivalve veligers exhibited a distinct bimodal abundance pattern, suggesting oscillation of a large patch of larvae in the back of Mission Bay. Physical data collected previously support this hypothesis and provide evidence for retention of larvae on or near the adult habitat. Nocturnal samples yielded less consistent, species-specific abundance patterns. Several polychaetes, bivalves and ghost shrimp exhibited peak larval abundances at dusk high tide, brachyuran zoea were released just after high tide and one polychaete exhibited a bimodal pattern similar to the daytime samples. Amphipods and harpacticoid copepods peaked in abundance at low tide. No ontogenetic differences in temporal distributions of precompetent and competent polychaete larvae were observed during the study. The mudflat meroplankton is not a well-mixed soup. Tenfold variations in larval abundance, documented for the polychaete species on an annual and seasonal basis (Levin, 1984), can also be observed at one site within a single tidal cycle. Attempts to estimate larval availability should incorporate short-term tidal and diel variability into the sampling design.

Levin, LA, Gage J, Lamont P, Cammidge L, Patience A, Martin C.  1997.  Infaunal community structure in a low-oxygen organic rich habitat on the Oman Continental Slope, NW Arabian Sea. The responses of marine organisms to their environments : Proceedings of the 30th European Marine Biology Symposium, University of Southampton, Southampton, United Kingdom. ( Hawkins LE, Hutchinson S, Jensen AC, Sheader M, Williams JA, Eds.).:223-230., Southampton: Southampton Oceanography Centre, University of Southampton Abstract
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Levin, LA.  1991.  Interactions between metazoans and large, agglutinating protozoans: implications for the community structure of deep-sea benthos. American Zoologist. 31:886-900. AbstractWebsite

Large, agglutinating protozoans belonging to the Foraminiferida (suborder Astrorhizina) and the Xenophyophorea are conspicuous, often dominant faunal elements in the deep sea. A review of known and suspected interactions between these forms and metazoans reveals a potentially significant role for the protozoans in structuring deep-sea metazoan assemblages. Direct interactions include provision to metazoans of (a) hard or stable substratum, (b) refuge from predators or physical disturbance, and (c) access to enhanced dietary resources. In some instances, rhizopod tests may provide a nursery function. Xenophyophore modification of flow regimes, particle flux, bottom skin friction and sediment characteristics appear likely and are believed to account for altered composition and abundance of meiofauna and macrofauna in the vicinity of rhizopod tests. Some analogous interactions are observed between metazoans and biogenic sediment structures in shallow water. However, metazoan-rhizopod associations are hypothesized to be more highly developed and complex in the deep sea than are comparable shallow-water associations, due to rhizopod abilities to enhance scarce food resources and to low rates of disturbance in much of the deep sea. Agglutinating rhizopods appear to be a significant source of heterogeneity on the deep-sea floor and large tests often represent 'hotspots' of metazoan activity. As such, they are hypothesized to have contributed to the origin and maintenance of metazoan diversity in the deep sea by providing distinct microenvironments in which species can specialize.

Levin, LA, Neira C, Grosholz ED.  2006.  Invasive cordgrass modifies wetland trophic function. Ecology. 87:419-432.   10.1890/04-1752   AbstractWebsite

Vascular plants strongly control belowground environments in most ecosystems. Invasion by vascular plants in coastal wetlands, and by cordgrasses (Spartina spp.) in particular, are increasing in incidence globally, with dramatic ecosystem-level consequences. We examined the trophic consequences of' invasion by a Spartina hybrid (S. alterniflora X S. foliosa) in San Francisco Bay (USA) by documenting differences in biomass and trophic structure of benthic communities between sediments invaded by Spartina and uninvaded sediments. We found the invaded system shifted from all algae-bascd to a detritus-based food web. We then tested for a relationship between diet and tolerance to invasion, hypothesizing that species that consume Spartina detritus are more likely to inhabit invaded sediments than those that consume surface algae. Infaunal diets were initially examined with natural abundance stable isotope analyses and application of mixing models, but these yielded an ambiguous picture of food sources. Therefore, we conducted isotopic enrichment experiments by providing N-15-labeled Spartina detritus both on and below the sediment surface in areas that either contained Spartina or were unvegetated. Capitellid and nereid polychaetes, and oligochaetes, groups shown to persist following Spartina invasion of San Francisco Bay tidal flats, took up N-15 from labeled native and invasive Spartina detritus. In contrast, We found that amphipods, bivalves, and other taxa less tolerant to invasion consumed primarily surficial algae, based oil C-13 enrichment experiments. Habitat (Spartina vs. unvegetated patches) and location of' detritus (on or within sediments) did not affect N-15 uptake from cletritus. Our investigations support a "trophic shift" model for ecosystem response to wetland plant invasion and preview loss of key trophic support for fishes and migratory birds by shifting dominance to species not widely consumed by species at higher trophic levels.

Levin, LA, Thomas CL.  1989.  The influence of hydrodynamic regime on infaunal assemblages inhabiting carbonate sediments on central Pacific seamounts. Deep-Sea Research Part a-Oceanographic Research Papers. 36:1897-&.   10.1016/0198-0149(89)90117-9   AbstractWebsite

We investigated the following hypotheses for deep seamounts in the central Pacific Ocean: (1) infaunal and microbial abundances are elevated in regions of current intensification, (2) infaunal lifestyles reflect variation in hydrodynamic conditions and (3) bioturbation is more intense in high-energy regimes. Our studies were carried out at three sites: the northwest perimeter of the Horizon Guyot sediment cap (1840 m), which is characterized by strong bottom currents and rippled foraminiferan sands, and the central summits of Horizon Guyot (1480 m) and Magellan Rise (3150 m), whose sediments are unrippled and finer grained. Contrary to our first hypothesis, the high-energy, Horizon perimeter sediments exhibited lower biological activity than the summit sites, as reflected in lower organic nitrogen (0.011% vs. 0.015–0.017%), higher C/N ratios (19 vs 11), lower bacterial counts (1.21 vs 2.03−2.15 × 108ml−1) and lower macrofaunal abundances (255 vs 388–829 m−2). Sediment organic carbon values (0.14–0.19%) and meiofaunal abundances (2866–5150 m−2) did not differ significantly among the three sites.Infaunal life habits varied among sites but sediment mixing did not. Macrofauna were found deeper in rippled perimeter sediments than in the cap sediments. Sessility and surface-feeding modes dominated among polychaetes at the higher-energy Horizon perimeter, while motility and subsurface feeding were common in the quieter, finer-grained regimes. Significant sediment mixing takes place on 100-year time scales a all three sites, probably a result of large, infaunal bioturbators at the cap sites and physical sediment instability at the perimeter site. Excess 210Pb exhibited moderately high inventories (38–59 dpm cm−2) and deep penetration (15 cm). Estimated mixing coefficients (Db) ranged from 0.6 to 3.0 cm2y−1 at the three sites. Our findings indicate that hydrodynamic differences can lead to greater variation in sediment and faunal characteristics on a single seamount than are found in similar regimes on different seamounts.Comparison of the Horizon Guyot and Magellan Rise data to comparable data from eastern Pacific seamounts, reveals lower organic carbon content, microbial abundance, macrofaunal densities, and subsurface deposit feeder representation, in central than eastern Pacific seamount sediments.

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Neira, C, Levin LA, Grosholz ED, Mendoza G.  2007.  Influence of invasive Spartina growth stages on associated macrofaunal communities. Biological Invasions. 9:975-993.   10.1007/s10530-007-9097-x   AbstractWebsite

In coastal wetlands, invasive plants often act as ecosystem engineers altering flow, light and sediments which, in turn, can affect benthic animal communities. However, the degree of influence of the engineer will vary significantly as it grows, matures and senesces, and surprisingly little is known about how the influence of an ecosystem engineer varies with ontogeny. We address this issue on the tidal flats of San Francisco Bay where hybrid Spartina (foliosa x alterniflora) invaded 30 years ago. The invasion has altered the physico-chemical properties of the sediment habitat, which we predicted should cause changes in macrofaunal community structure and function. Through mensurative and manipulative approaches we investigated the influence of different growth stages of hybrid Spartina on macrobenthos and the underlying mechanisms. Cross-elevation sampling transects were established covering 5 zones (or stages) of the invasion, running from the tidal flat (pre-invasion) to an unvegetated dieback zone. Additionally, we experimentally removed aboveground plant structure in the mature (inner) marsh to mimic the 'unvegetated areas'. Our results revealed four distinct faunal assemblages, which reflected Spartina-induced changes in the corresponding habitat properties along an elevation gradient: a pre-invaded tidal flat, a leading edge of immature invasion, a center of mature invasion, and a senescing dieback area. These stages of hybrid Spartina invasion were accompanied by a substantial reduction in macrofaunal species richness and an increase in dominance, as well as a strong shift in feeding modes, from surface microalgal feeders to subsurface detritus/Spartina feeders (mainly tubificid oligochaetes and capitellid polychaetes). Knowledge of the varying influence of plant invaders on the sediment ecosystem during different phases of invasion is critical for management of coastal wetlands.

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Wishner, K, Levin L, Gowing M, Mullineaux L.  1990.  Involvement of the oxygen minimum in benthic zonation on a deep seamount. Nature. 346:57-59.   10.1038/346057a0   AbstractWebsite

Low oxygen concentration in the seawater column reduces the abundance of midwater consumer populations1,2, which can enhance the supply of undegraded organic matter reaching the benthos. Low oxygen concentration in the water at the bottom can exclude most tolerant species from benthic habitats3–5. The interception of the seafloor with pronounced oxygen-minimum zones can produce steep gradients in benthic assemblages. We now present evidence for this interaction on Volcano 7, an oceanic seamount penetrating the oxygen-minimum zone in the eastern tropical Pacific. Submersible observations revealed only a few benthic species at the summit (730–750 m), where oxygen levels were lowest. Just tens of metres below, megafaunal and macrofaunal abundances were extremely high. Sediment organic carbon, a benthic food indicator, was unusually high. We hypothesize that a dynamic low-oxygen interface physiologically restricts benthos on the upper summit, that the enriched sediment is a result of reduced consumption and degradation of sinking material in the oxygen-minimum zone, and that this high benthic food level supports the unusually high benthic abundance. Sharp benthic zonation associated with oxygen concentrations may also be preserved in the palaeoceanographic record4,6.