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2014
Larkin, KE, Gooday AJ, Woulds C, Jeffreys RM, Schwartz M, Cowie G, Whitcraft C, Levin L, Dick JR, Pond DW.  2014.  Uptake of algal carbon and the likely synthesis of an "essential" fatty acid by Uvigerina ex. gr. semiornata (Foraminifera) within the Pakistan margin oxygen minimum zone: evidence from fatty acid biomarker and C-13 tracer experiments. Biogeosciences. 11:3729-3738.   10.5194/bg-11-3729-2014   AbstractWebsite

Foraminifera are an important component of benthic communities in oxygen-depleted settings, where they potentially play a significant role in the processing of organic matter. We tracked the uptake of a C-13-labelled algal food source into individual fatty acids in the benthic foraminiferal species Uvigerina ex. gr. semiornata from the Arabian Sea oxygen minimum zone (OMZ). The tracer experiments were conducted on the Pakistan margin during the late/post monsoon period (August-October 2003). A monoculture of the diatom Thalassiosira weisflogii was C-13-labelled and used to simulate a pulse of phytoplankton in two complementary experiments. A lander system was used for in situ incubations at 140m water depth and for 2.5 days in duration. Shipboard laboratory incubations of cores collected at 140 m incorporated an oxystat system to maintain ambient dissolved oxygen concentrations and were terminated after 5 days. Uptake of diatoms was rapid, with a high incorporation of diatom fatty acids into foraminifera after similar to 2 days in both experiments. Ingestion of the diatom food source was indicated by the increase over time in the quantity of diatom biomarker fatty acids in the foraminifera and by the high percentage of C-13 in many of the fatty acids present at the endpoint of both in situ and laboratory-based experiments. These results indicate that U. ex. gr. semiornata rapidly ingested the diatom food source and that these foraminifera will play an important role in the short-term cycling of organic matter within this OMZ environment. The presence of 18:1(n-7) in the experimental foraminifera suggested that U. ex. gr. semiornata also consumed non-labelled bacterial food items. In addition, levels of 20:4(n-6), a PUFA only present in low amounts in the diatom food, increased dramatically in the foraminifera during both the in situ and shipboard experiments, possibly because it was synthesised de novo. This "essential fatty acid" is often abundant in benthic fauna, yet its origins and function have remained unclear. If U. ex. gr. semiornata is capable of de novo synthesis of 20:4(n-6), then it represents a potentially major source of this dietary nutrient in benthic food webs.

2013
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.

Levin, LA, McGregor AL, Mendoza GF, Woulds C, Cross P, Witte U, Gooday AJ, Cowie G, Kitazato H.  2013.  Macrofaunal colonization across the Indian margin oxygen minimum zone. Biogeosciences. 10:7161-7177.   10.5194/bg-10-7161-2013   AbstractWebsite

There is a growing need to understand the ability of bathyal assemblages to recover from disturbance and oxygen stress, as human activities and expanding oxygen minimum zones increasingly affect deep continental margins. The effects of a pronounced oxygen minimum zone (OMZ) on slope benthic community structure have been studied on every major upwelling margin; however, little is known about the dynamics or resilience of these benthic populations. To examine the influence of oxygen and phytodetritus on shortterm settlement patterns, we conducted colonization experiments at 3 depths on the West Indian continental margin. Four colonization trays were deployed at each depth for 4 days at 542 and 802 m (transect 1-16 degrees 58 ' N) and for 9 days at 817 and 1147 m (transect 2-17 degrees 31 ' N). Oxygen concentrations ranged from 0.9 mu M (0.02 mLL(-1)) at 542 m to 22 mu M (0.5 mLL(-1) ) at 1147 m. All trays contained local defaunated sediments; half of the trays at each depth also contained C-13/N-15-labeled phytodetritus mixed into the sediments. Sediment cores were collected between 535 m and 1140 m from 2 cross-margin transects for analysis of ambient (source) macrofaunal (> 300 mu m) densities and composition. Ambient macrofaunal densities ranged from 0 ind m(-2) (at 535-542 m) to 7400 ind m(-2), with maximum values on both transects at 700-800 m. Macrofaunal colonizer densities ranged from 0 ind m(-2) at 542 m, where oxygen was lowest, to average values of 142 ind m(-2) at 800 m, and 3074 ind m(-2) at 1147 m, where oxygen concentration was highest. These were equal to 4.3 and 151% of the ambient community at 800 m and 1147 m, respectively. Community structure of settlers showed no response to the presence of phytodetritus. Increasing depth and oxygen concentration, however, significantly influenced the community composition and abundance of colonizing macrofauna. Polychaetes constituted 92.4% of the total colonizers, followed by crustaceans (4.2%), mollusks (2.5%), and echinoderms (0.8%). The majority of colonizers were found at 1147 m; 88.5% of these were Capitella sp., although they were rare in the ambient community. Colonists at 800 and 1147 m also included ampharetid, spionid, syllid, lumbrinerid, cirratulid, cossurid and sabellid polychaetes. Consumption of C-13/N-15-labeled phytodetritus was observed for macrofaunal foraminifera (too large to be colonizers) at the 542 and 802/817 m sites, and by metazoan macrofauna mainly at the deepest, better oxygenated sites. Calcareous foraminifera (Uvigerina, Hoeglundina sp.), capitellid polychaetes and cumaceans were among the major phytodetritus consumers. These preliminary experiments suggest that bottom-water oxygen concentrations may strongly influence ecosystem services on continental margins, as reflected in rates of colonization by benthos and colonizer processing of carbon following disturbance. They may also provide a window into future patterns of settlement on the continental slope as the world's oxygen minimum zones expand.

2012
Guilini, K, Levin LA, Vanreusel A.  2012.  Cold seep and oxygen minimum zone associated sources of margin heterogeneity affect benthic assemblages, diversity and nutrition at the Cascadian margin (NE Pacific Ocean). Progress in Oceanography. 96:77-92.   10.1016/j.pocean.2011.10.003   AbstractWebsite

Hydrate Ridge (HR), located on the northeastern Pacific margin off Oregon, is characterized by the presence of outcropping hydrates and active methane seepage. Additionally, permanent low oxygen conditions overlay the benthic realm. This study evaluated the relative influence of both seepage and oxygen minima as sources of habitat heterogeneity and potential stress-inducing features on the bathyal metazoan benthos (primarily nematodes) at three different seep and non-seep HR locations, exposed to decreasing bottom-water oxygen concentrations with increasing water depth. The nematode seep communities at HR exhibited low diversity with dominance of only one or two genera (Daptonema and Metadesmolaimus), elevated average individual biomass and delta C-13 evidence for strong dependance on chemosynthesis-derived carbon, resembling deep-sea seeps worldwide. Although the HR seep habitats harbored a distinct nematode community like in other known seep communities, they differed from deep-sea seeps in well-oxygenated waters based on that they shared the dominant genera with the surrounding non-seep sediments overlain by oxygen-deficient bottom water. The homogenizing effect of the oxygen minimum zone on the seep nematode assemblages and surrounding sediments was constant with increasing water depth and concomitant greater oxygen-deficiency, resulting in a loss of habitat heterogeneity. (C) 2011 Elsevier Ltd. All rights reserved.

Hunter, WR, Levin LA, Kitazato H, Witte U.  2012.  Macrobenthic assemblage structure and organismal stoichiometry control faunal processing of particulate organic carbon and nitrogen in oxygen minimum zone sediments. Biogeosciences. 9:993-1006.   10.5194/bg-9-993-2012   AbstractWebsite

The Arabian Sea oxygen minimum zone (OMZ) impinges on the western Indian continental margin between 150 and 1500 m, causing gradients in oxygen availability and sediment geochemistry at the sea floor. Oxygen availability and sediment geochemistry are important factors structuring macrofaunal assemblages in marine sediments. However, relationships between macrofaunal assemblage structure and sea-floor carbon and nitrogen cycling are poorly understood. We conducted in situ C-13:N-15 tracer experiments in the OMZ core (540 m [O-2] = 0.35 mu mol l(-1)) and lower OMZ boundary (800-1100 m, [O-2] = 2.2-15.0 mu mol l(-1)) to investigate how macrofaunal assemblage structure, affected by different oxygen levels, and C:N coupling influence the fate of particulate organic matter. No macrofauna were present in the OMZ core. Within the OMZ boundary, relatively high abundance and biomass resulted in the highest macrofaunal assimilation of particulate organic carbon (POC) and nitrogen (PON) at the lower oxygen 800 m stations ([O-2] = 2.2-2.36 mu mol l(-1)). At these stations the numerically dominant cirratulid polychaetes exhibited greatest POC and PON uptake. By contrast, at the higher oxygen 1100 m station ([O-2] = 15.0 mu mol l(-1)) macrofaunal C and N assimilation was lower, with POC assimilation dominated by one large solitary ascidian. Macrofaunal POC and PON assimilation were influenced by changes in oxygen availability, and significantly correlated to differences in macrofaunal assemblage structure between stations. However, macrofaunal feeding responses were ultimately characterised by preferential organic nitrogen assimilation, relative to their internal C:N budgets.

2009
Gooday, AJ, Levin LA, da Silva AA, Bett BJ, Cowie GL, Dissard D, Gage JD, Hughes DJ, Jeffreys R, Lamont PA, Larkin KE, Murty SJ, Schumacher S, Whitcraft C, Woulds C.  2009.  Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:488-502.   10.1016/j.dsr2.2008.10.003   AbstractWebsite

The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150-1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140-1850 m water depth) across the OMZ during the 2003 intermonsoon (March-May) and late/post-monsoon (August-October) seasons. All groups exhibited some drop in abundance in the OMZ core (250-500 m water depth; O(2): 0.10-0.13 mL L(-1) = 4.46-5.80 mu M) but to differing degrees. Densities of foraminiferans >63 mu m were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 mu m were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O(2) <0.14-0.15 mLL(-1) = 6.25-6.69 mu M) but were represented by a huge, ophiuroid-dominated abundance peak at 1000 m (O(2) similar to 0.15-0.18 mLL(-1) = 6.69-8.03 mu M). Gromiid protists were confined largely to depths below 1150 m (O(2) > 0.2 mLL(-1) = 8.92 mu M). The progressively deeper abundance peaks for foraminiferans (> 63 mu m), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136-300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mLL(-1)( = 5.80 mu M). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna, and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side. (C) 2008 Published by Elsevier Ltd.

Hughes, DJ, Lamont PA, Levin LA, Packer M, Feeley K, Gage JD.  2009.  Macrofaunal communities and sediment structure across the Pakistan margin Oxygen Minimum Zone, North-East Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:434-448.   10.1016/j.dsr2.2008.05.030   AbstractWebsite

Benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect (depths 140, 300, 940, 1200, 1850 m) through the Pakistan margin Oxygen Minimum Zone (OMZ) during the 2003 intermonsoon (March-May) and late-post-monsoon (August-October) periods. Objectives were to compare patterns with those described from other OMZs, particularly the Oman margin of the Arabian Sea, in order to assess the relative influence of bottom-water oxygenation and sediment organic content on macrofaunal standing stock and community structure. Macrofaunal density was highest at the 140-m station subject to monsoon-driven shoaling of the OMZ, but there was no elevation of density at the lower OMZ boundary (1200 m). Numbers was extremely low in the OMZ core (300 m) and were not readily explicable from the environmental data. There was no consistent depth-related trend in macrofaunal biomass. Macrofaunal densities were consistently lower than found off Oman but there was less contrast in biomass. A significant post-monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa. Polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from Oman. Cirratulidae and Spionidae were major components of the polychaete fauna at most stations but Acrocirridae, Ampharetidae, Amphinomidae and Cossuridae were more important at 940 m. Polychaete assemblages at each station were almost completely distinct at the species level. Polychaete species richness was positively correlated with bottom-water dissolved oxygen and negatively correlated with sediment TOC, C:N ratio and total phytopigments. Community dominance showed the opposite pattern. The strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects. The strongly laminated sediments in the OMZ core contrasted with the homogeneous, heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition. In general, data from the Oman margin were weak predictors of patterns seen off Pakistan, and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in OMZs. (C) 2008 Elsevier Ltd. All rights reserved.

Levin, LA, Whitcraft CR, Mendoza GF, Gonzalez JP, Cowie G.  2009.  Oxygen and organic matter thresholds for benthic faunal activity on the Pakistan margin oxygen minimum zone (700-1100 m). Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:449-471.   10.1016/j.dsr2.2008.05.032   AbstractWebsite

A transition from fully laminated to highly bioturbated sediments on continental margins is thought to derive from increased animal activity associated with increasing bottom-water oxygen concentration. We examined faunal community responses to oxygen and organic matter gradients across the lower oxygen minimum zone (OMZ) on the bathyal Pakistan margin, where sediments grade from fully laminated sediment at 700m (0.12 mLL(-1) O(2) [5 mu M]) to highly bioturbated sediment at 1100 m (0.23 mLL(-1) O(2) [10 mu M]). High-resolution sampling of the seafloor (every 50 m water depth) was conducted along a single transect during inter- and post-monsoon periods in 2003 to address (a) the existence of oxygen thresholds regulating macrofaunal abundance, composition, diversity and lifestyles, (b) the interactive effects of organic matter quantity and quality, (c) associated community effects on sediment structure, and (d) potential seasonality in these processes. Macrofaunal biomass and bioturbation depth were positively correlated with organic matter availability, which peaked at 850-950 m (3.39-3.53% Org. Q. In contrast, macrofaunal diversity (HI), dominance (RID), and burrow number exhibited threshold responses at oxygen concentrations of 0.12-0.20 mLL(-1) [5-9 mu M]), with few animals and highly laminated sediments present below this concentration and most taxa present in fully bioturbated sediments above it. The highly mobile, burrowing amphinomid polychaete Linopherus sp. exhibited almost complete dominance and high density at 750-850 m (0.12-0.14 mLL(-1) O(2) [5-6 mu M]), but despite its activity, sediment laminae remained faintly visible. Formation of permanent burrows and detritivory were dominant macrofaunal lifestyles within the OMZ, allowing laminae to persist at surprisingly high animal density and biomass. Results reflect a shift from organic matter to oxygen regulation of body size and biogenic structures following the monsoon. This study suggests that for assemblages evolving under permanent severe hypoxia, food availability remains a significant determinant of animal abundance and biogenic structure depth. Oxygen influences patterns of diversity and dominance and interacts with organic matter to generate abrupt faunal transitions on the Pakistan margin. (C) 2008 Elsevier Ltd. All rights reserved.

2007
Woulds, C, Cowie GL, Levin LA, Andersson JH, Middelburg JJ, Vandewiele S, Lamont PA, Larkin KE, Gooday AJ, Schumacher S, Whitcraft C, Jeffreys RM, Schwartz M.  2007.  Oxygen as a control on seafloor biological communities and their roles in sedimentary carbon cycling. Limnology and Oceanography. 52:1698-1709.   10.4319/lo.2007.52.4.1698   AbstractWebsite

C-13 tracer experiments were conducted at sites spanning the steep oxygen, organic matter, and biological community gradients across the Arabian Sea oxygen minimum zone, in order to quantify the role that benthic fauna play in the short-term processing of organic matter (OM) and to determine how this varies among different environments. Metazoan macrofauna and macrofauna-sized foraminiferans took up as much as 56 +/- 13 mg of added C m(-2) (685 mg C m(-2) added) over 2-5 d, and at some sites this uptake was similar in magnitude to bacterial uptake and/or total respiration. Bottom-water dissolved oxygen concentrations exerted a strong control over metazoan macrofaunal OM processing. At oxygen concentrations > 7 mu mol L-1 (0.16 ml L-1), metazoan macrofauna were able to take advantage of abundant OM and to dominate OM uptake, while OM processing at O-2 concentrations of 5.0 mu mol L-1 (0.11 ml L-1) was dominated instead by (macrofaunal) foraminiferans. This led us to propose the hypothesis that oxygen controls the relative dominance of metazoan macrofauna and foraminifera in a threshold manner, with the threshold lying between 5 and 7 mu mol L-1 (0.11 to 0.16 ml L-1). Large metazoan macrofaunal biomass and high natural concentrations of OM were also associated with rapid processing of fresh OM by the benthic community. Where they were present, the polychaete Linopherus sp. and the calcareous foraminiferan Uvigerina ex gr. semiornata, dominated the uptake of OM above and below, respectively, the proposed threshold concentrations of bottom-water oxygen.

2004
Helly, JJ, Levin LA.  2004.  Global distribution of naturally occurring marine hypoxia on continental margins. Deep-Sea Research Part I-Oceanographic Research Papers. 51:1159-1168.   10.1016/j.dsr.2004.03.009   AbstractWebsite

Hypoxia in the ocean influences biogeochemical cycling of elements, the distribution of marine species and the economic well being of many coastal countries. Previous delineations of hypoxic environments focus on those in enclosed seas where hypoxia may be exacerbated by anthropogenically induced eutrophication. Permanently hypoxic water masses in the open ocean, referred to as oxygen minimum zones, impinge on a much larger seafloor surface area along continental margins of the eastern Pacific, Indian and western Atlantic Oceans. We provide the first global quantification of naturally hypoxic continental margin floor by determining upper and lower oxygen minimum zone depth boundaries from hydrographic data and computing the area between the isobaths using seafloor topography. This approach reveals that there are over one million km(2) of permanently hypoxic shelf and bathyal sea floor, where dissolved oxygen is <0.5ml l(-1); over half (59%) occurs in the northern Indian Ocean. We also document strong variation in the intensity, vertical position and thickness of the OMZ as a function of latitude in the eastern Pacific Ocean and as a function of longitude in the northern Indian Ocean. Seafloor OMZs are regions of low biodiversity and are inhospitable to most commercially valuable marine resources, but support a fascinating array of protozoan and metazoan adaptations to hypoxic conditions. (C) 2004 Elsevier Ltd. All rights reserved.

2003
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.

2002
Shankle, AM, Goericke R, Franks PJS, Levin LA.  2002.  Chlorin distribution and degradation in sediments within and below the Arabian Sea oxygen minimum zone. Deep-Sea Research Part I-Oceanographic Research Papers. 49:953-969.   10.1016/s0967-0637(01)00077-2   AbstractWebsite

The concentration of chlorophylla degradation products, i.e. chlorins, preserved in deep-sea sediments is a function of the amount of primary production input and the rate at which it is subsequently degraded. Sedimentary chlorins can be used as a proxy for paleoproductivity; however, our understanding of the factors controlling their preservation is limited. To study the effects of changes in export of primary production from the euphotic zone and of differences in depositional conditions on chlorin concentration in marine sediments, chlorins were analyzed by high pressure liquid chromatography from sediments taken within and below the oxygen minimum zone on the Oman margin in the Arabian Sea. Among five stations at water depths between 400 and 1250 m, variation in chlorin concentration in surface sediments (0-0.5 cm) was significantly related to water depth (used here as a proxy for chlorin fluxes to the sediments) and bottom-water oxygen concentration; the more important control on chlorin concentration of surficial sediments measured in this study is the amount of chlorins reaching the sediment. Chlorins decayed exponentially downcore (0-20 cm). The degradation of sedimentary chlorins was better described by a model in which chlorins decayed at different rates within and below the sediment mixed layer. The degradation rates within the mixed layer were 0.0280 +/- 0.0385 yr(-1) (t(1/2) = 73 yr). Below the mixed layer, degradation rates were one to two orders of magnitude less, ranging from 0.0022 +/- 0.0025 yr(-1) (t(1/2) = 680 yr). Many stations had subsurface chlorin concentration peaks between 6 and 10 cm depth. The most likely explanation for these peaks is a period of increased deposition of chlorins in the past. This could result from changes in local depositional environment or a more general increase in surface production resulting in an increased sedimentation of chlorins to the sediments 500-1000 years ago. Chlorins are a useful indicator of the magnitude of chlorin deposition; however their usage as indicators of paleoproductivity is more complicated. (C) 2002 Elsevier Science Ltd. All rights reserved.

2001
Neira, C, Sellanes J, Levin LA, Arntz WE.  2001.  Meiofaunal distributions on the Peru margin: relationship to oxygen and organic matter availability. Deep-Sea Research Part I-Oceanographic Research Papers. 48:2453-2472.   10.1016/s0967-0637(01)00018-8   AbstractWebsite

A quantitative study of metazoan meiofauna was carried out on bathyal sediments (305, 562, 830 and 1210 m) along a transect within and beneath the oxygen minimum zone (OMZ) in the southeastern Pacific off Callao, Peru (12 degreesS). Meiobenthos densities ranged from 1517 (upper slope, middle of OMZ) to 440-548 ind. 10cm(-2) (lower slope stations, beneath the OMZ). Nematodes were the numerically dominant meiofaunal taxon at every station, followed by copepods and nauplii. Increasing bottom-water oxygen concentration and decreasing organic matter availability downslope were correlated with observed changes in meiofaunal abundance. The 300-m site, located in the middle of the OMZ, differed significantly in meiofaunal abundance, dominance, and in vertical distribution pattern from the deeper sites. At 305 m, nematodes amounted to over 99% of total meiofauna; about 70% of nematodes were found in the 2-5 cm. interval. At the deeper sites, about 50% were restricted to the top I cm. The importance of copepods and nauplii increased consistently with depth, reaching similar to 12% of the total meiofauna at the deepest site. The observation of high nematode abundances at oxygen concentrations <0.02mll(-1) supports the hypothesis that densities are enhanced by an indirect positive effect of low oxygen involving (a) reduction of predators and competitors and (b) preservation of organic matter leading to high food availability and quality. Food input and quality, represented here by chloroplastic pigment equivalents (CPE) and sedimentary labile organic compounds (protein, carbohydrates and lipids), were strongly, positively correlated with nematode abundance. By way of contrast, oxygen exhibited a strong negative correlation, overriding food availability, with abundance of other meiofauna such as copepods and nauplii. These taxa were absent at the 300-m site. The high correlation of labile organic matter (C-LOM, sum of carbon contents in lipids, proteins and carbohydrates) with CPE (Pearson's r = 0.99, p <0.01) suggests that most of the sedimentary organic material sampled was of phytodetrital origin. The fraction of sediment organic carbon potentially available to benthic. heterotrophs, measured as C-LOM/Total organic carbon, was on average 17% at all stations. Thus, a residual, refractory fraction, constitutes the major portion of organic matter at the studied bathyal sites. (C) 2001 Elsevier Science Ltd. All rights reserved.

Gooday, AJ, Hughes JA, Levin LA.  2001.  The foraminiferan macrofauna from three North Carolina (USA) slope sites with contrasting carbon flux: a comparison with the metazoan macrofauna. Deep-Sea Research Part I-Oceanographic Research Papers. 48:1709-1739.   10.1016/s0967-0637(00)00098-4   AbstractWebsite

Food supply exerts a strong influence on benthic faunal abundance and community structure. Here, we compare community-level responses of macrofaunal foraminiferans and metazoans ( > 300 mum fraction) in relation to a gradient of organic carbon flux [Site III > II > I] along the 850 m contour on the North Carolina slope. Foraminiferan density, species richness E(S(100)), and dominance were positively correlated with organic carbon flux;. Foraminiferans were more abundant at Site III, displayed lower diversity and higher dominance, and tended to live deeper in the sediment column than at either Sites I or II. The Site I fauna was dominated by agglutinated taxa (mainly simple monothalamous forms and hormosinaceans) and included large epifaunal species, some of which projected from the sediment surface and probably fed on fresh phytodetritus. Hormosinaceans and monothalamous taxa also were abundant at Site II, although large epifaunal taxa were not present. The Site III fauna was dominated by calcareous tare. The most abundant species was Globobulimina auriculata, an infaunal, low-oxygen tolerant, deposit feeder with a calcareous test sometimes obscured by an agglutinated cyst. Plate-like or flattened fragments of small xenophyophore species occurred at Site I, an unusually shallow record for this taxon and the first from the North Carolina margin. Most of these fragments were dead. Xenophyophores were not present at Sites II and III. The metazoan macrofauna exhibited trends in density, diversity, dominance and vertical distribution within the sediment that parallel those of the foraminiferans and were correlated with between-site differences in food availability. However, metazoans were 4.5-6.5 times less abundant than the foraminiferans, were more diverse, exhibited lower dominance and (at least at Sites I and III) tended to penetrate the sediment less deeply, These differences suggest that foraminiferans, considered as a group, are more opportunistic than metazoans, tolerate oxygen depletion better, and have population dynamics that are more closely coupled to organic matter inputs than those of metazoans. Foraminiferan diversity trends are even more similar to those of the polychaetes at these sites, suggesting that there are ecological parallels between the two taxa despite their fundamental phylogenetic and structural differences. Foraminiferans are a ubiquitous yet frequently overlooked component of the macrofauna on continental margins that experience a broad range of organic input regimes. They deserve to be considered more often in macrofaunal studies addressing interactions between organisms and their environments. (C) 2001 Elsevier Science Ltd. All rights reserved.

1995
Wishner, KF, Ashjian CJ, Gelfman C, Gowing MM, Kann L, Levin LA, Mullineaux LS, Saltzman J.  1995.  Pelagic and benthic ecology of the lower interface of the Eastern Tropical Pacific oxygen minimum zone. Deep-Sea Research Part I-Oceanographic Research Papers. 42:93-115.   10.1016/0967-0637(94)00021-j   AbstractWebsite

The distributions of pelagic and benthic fauna were examined in relation to the lower boundary of the oxygen minimum zone (OMZ) on and near Volcano 7, a seamount that penetrates this feature in the Eastern Tropical Pacific. Although the broad, pronounced OMZ in this region is an effective barrier for most zooplankton, zooplankton abundances, zooplankton feeding rates, and ambient suspended particulate organic carbon (POC) peaked sharply in the lower OMZ (about 740-800 m), in association with the minimum oxygen concentration and the increasing oxygen levels just below it. Zooplankton in the lower OMZ were also larger in size, and the pelagic community included some very abundant, possibly opportunistic, species. Elevated POC and scatter in the light transmission data suggested the existence of a thin, particle-rich, and carbon-rich pelagic layer at the base of the OMZ. Gut contents of planktonic detritivores implied opportunistic ingestion of bacterial aggregates, possibly from this layer. Benthic megafaunal abundances on the seamount, which extended up to 730 m, peaked at about 800 m. There was a consistent vertical progression in the depth of first occurrence of different megafaunal taxa in this depth range, similar to intertidal zonation. Although the vertical gradients of temperature, salinity, and oxygen were gradual at the lower OMZ interface (in contrast to the upper OMZ interface at the thermocline), temporal variability in oxygen levels due to internal wave-induced vertical excursions of the OMZ may produce the distinct zonation in the benthic fauna. The characteristics of the lower OMZ interface result from biological interactions with the chemical and organic matter gradients of the OMZ. Most zooplankton are probably excluded physiologically from pronounced OMZs. The zooplankton abundance peak at the lower interface of the OMZ occurs where oxygen becomes sufficiently high to permit the zooplankton to utilize the high concentrations of organic particles that have descended through the OMZ relatively unaltered because of low metazoan abundance. A similar scenario applies to megabenthic distributions. Plankton layers and a potential short food chain (bacteria to zooplankton) at OMZ interfaces suggest intense utilization and modification of organic material, localized within a thin midwater depth zone. This could be a potentially significant filter for organic material sinking to the deep-sea floor.