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Mengerink, KJ, Vandover CL, Ardron J, Baker M, Escobar-Briones E, Gjerde K, Koslow J, Ramirez-Llodra E, Lara-Lopez A, Squires D, Sutton T, Sweetman A, Levin LA.  2014.  A Call For Deep-Ocean Stewardship. Science. 344:696-698.
Frieder, CA, Gonzalez JP, Bockmon EE, Navarro MO, Levin LA.  2014.  Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae? Global Change Biology. 20:754-764.   10.1111/gcb.12485   AbstractWebsite

Natural variation and changing climate in coastal oceans subject meroplanktonic organisms to broad ranges of pH and oxygen ([O2 ]) levels. In controlled-laboratory experiments we explored the interactive effects of pH, [O2 ], and semidiurnal pH fluctuations on the survivorship, development, and size of early life stages of two mytilid mussels, Mytilus californianus and M. galloprovincialis. Survivorship of larvae was unaffected by low pH, low [O2 ], or semidiurnal fluctuations for both mytilid species. Low pH (<7.6) resulted in delayed transition from the trochophore to veliger stage, but this effect of low pH was absent when incorporating semidiurnal fluctuations in both species. Also at low pH, larval shells were smaller and had greater variance; this effect was absent when semidiurnal fluctuations of 0.3 units were incorporated at low pH for M. galloprovincialis but not for M. californianus. Low [O2 ] in combination with low pH had no effect on larval development and size, indicating that early life stages of mytilid mussels are largely tolerant to a broad range of [O2 ] reflective of their environment (80-260 μmol kg(-1) ). The role of pH variability should be recognized as an important feature in coastal oceans that has the capacity to modulate the effects of ocean acidification on biological responses.

Basak, C, Rathburn AE, Perez ME, Martin JB, Kluesner JW, Levin LA, De Deckker P, Gieskes JM, Abriani M.  2009.  Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin. Marine Micropaleontology. 70:89-101.   10.1016/j.marmicro.2008.11.002   AbstractWebsite

Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modem environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in (13)C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera (Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera (Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Delta delta(13)C value, defined as foraminiferal delta(13)C values minus estimated ambient delta(13)C values from the Aleutian Margin, is 0.97 parts per thousand higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry. (C) 2008 Elsevier B.V. All rights reserved.

Marlow, JJ, Steele JA, Ziebis W, Thurber AR, Levin LA, Orphan VJ.  2014.  Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea. Nature Communications. 5   10.1038/ncomms6094   AbstractWebsite

The atmospheric flux of methane from the oceans is largely mitigated through microbially mediated sulphate-coupled methane oxidation, resulting in the precipitation of authigenic carbonates. Deep-sea carbonates are common around active and palaeo-methane seepage, and have primarily been viewed as passive recorders of methane oxidation; their role as active and unique microbial habitats capable of continued methane consumption has not been examined. Here we show that seep-associated carbonates harbour active microbial communities, serving as dynamic methane sinks. Microbial aggregate abundance within the carbonate interior exceeds that of seep sediments, and molecular diversity surveys reveal methanotrophic communities within protolithic nodules and well-lithified carbonate pavements. Aggregations of microbial cells within the carbonate matrix actively oxidize methane as indicated by stable isotope FISH-nanoSIMS experiments and (CH4)-C-14 radiotracer rate measurements. Carbonate-hosted methanotrophy extends the known ecological niche of these important methane consumers and represents a previously unrecognized methane sink that warrants consideration in global methane budgets.

Grosholz, ED, Levin LA, Tyler C, Neira C.  2009.  Changes in community structure and ecosystem function following Spartina alterniflora invasion of Pacific estuaries. Human impacts on salt marshes : a global perspective. ( Silliman BR, Grosholz E, Bertness MD, Eds.).:23-40., Berkeley: University of California Press Abstract
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.

Middelburg, JJ, Levin LA.  2009.  Coastal hypoxia and sediment biogeochemistry. Biogeosciences. 6:1273-1293. AbstractWebsite

The intensity, duration and frequency of coastal hypoxia (oxygen concentration < 63 mu M) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry. Changes in bottom-water oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accumulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. Bottom-water oxygen levels also affect the organisms involved in organic matter processing with the contribution of metazoans decreasing as oxygen levels drop. Hypoxia has a significant effect on benthic animals with the consequences that ecosystem functions related to macrofauna such as bio-irrigation and bioturbation are significantly affected by hypoxia as well. Since many microbes and microbial-mediated biogeochemical processes depend on animal-induced transport processes (e.g. re-oxidation of particulate reduced sulphur and denitrification), there are indirect hypoxia effects on biogeochemistry via the benthos. Severe long-lasting hypoxia and anoxia may result in the accumulation of reduced compounds in sediments and elimination of macrobenthic communities with the consequences that biogeochemical properties during trajectories of decreasing and increasing oxygen may be different (hysteresis) with consequences for coastal ecosystem dynamics.

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.

Bowden, DA, Rowden AA, Thurber AR, Baco AR, Levin LA, Smith CR.  2013.  Cold seep epifaunal communities on the Hikurangi Margin, New Zealand: Composition, succession, and vulnerability to human activities. Plos One. 8   10.1371/journal.pone.0076869   AbstractWebsite

Cold seep communities with distinctive chemoautotrophic fauna occur where hydrocarbon-rich fluids escape from the seabed. We describe community composition, population densities, spatial extent, and within-region variability of epifaunal communities at methane-rich cold seep sites on the Hikurangi Margin, New Zealand. Using data from towed camera transects, we match observations to information about the probable life-history characteristics of the principal fauna to develop a hypothetical succession sequence for the Hikurangi seep communities, from the onset of fluid flux to senescence. New Zealand seep communities exhibit taxa characteristic of seeps in other regions, including predominance of large siboglinid tubeworms, vesicomyid clams, and bathymodiolin mussels. Some aspects appear to be novel; however, particularly the association of dense populations of ampharetid polychaetes with high-sulphide, high-methane flux, soft-sediment microhabitats. The common occurrence of these ampharetids suggests they play a role in conditioning sulphide-rich sediments at the sediment-water interface, thus facilitating settlement of clam and tubeworm taxa which dominate space during later successional stages. The seep sites are subject to disturbance from bottom trawling at present and potentially from gas hydrate extraction in future. The likely life-history characteristics of the dominant megafauna suggest that while ampharetids, clams, and mussels exploit ephemeral resources through rapid growth and reproduction, lamellibrachid tubeworm populations may persist potentially for centuries. The potential consequences of gas hydrate extraction cannot be fully assessed until extraction methods and target localities are defined but any long-term modification of fluid flow to seep sites would have consequences for all chemoautotrophic fauna.

Pasulka, AL, Goffredi SK, Tavormina PL, Dawson KS, Levin LA, Rouse GW, Orphan VJ.  2017.  Colonial tube-dwelling ciliates influence methane cycling and microbial diversity within methane seep ecosystems. Frontiers in Marine Science. 3   10.3389/fmars.2016.00276   Abstract

In a variety of marine ecosystems, microbial eukaryotes play important ecological roles; however, our knowledge of their importance in deep-sea methane seep ecosystems is limited. Microbial eukaryotes have the potential to influence microbial community composition and diversity by creating habitat heterogeneity, and may contribute to carbon cycling through grazing or symbiotic associations with microorganisms. In this study, we characterized the distribution, substrate variability and ecology of a particular group of microbial eukaryotes, known as folliculinid ciliates, at methane seeps along the eastern Pacific margin. Folliculinid ciliates were recently recognized as an abundant and ecologically important component of hydrothermal vent ecosystems, but their ecology in methane seeps has not been examined. Folliculinid ciliates inhabited methane seeps from Costa Rica to Oregon, suggesting a broad distribution in the eastern Pacific. Using phylogenetic analyses of the 18S rRNA gene, two different species of folliculinid were identified. Folliculinids occupied a range of physical substrates, including authigenic carbonate rocks, shells of dead vesicomyid clams, polychaete tubes and gastropod shells. Molecular analysis of folliculinid associated microorganisms (16S rRNA and particulate methane monooxygenase) revealed that these ciliates not only influence overall microbial diversity, but also and have a specific relationship with bacteria in the ‘Deep sea-2’ methanotroph clade. Natural δ13C isotope signatures of folliculinids (-35‰) and their 13C-enrichment patterns in shipboard 13CH4 stable isotope-probing experiments indicated these ciliates and their associated microbes are involved in cycling methane-derived carbon. Folliculinids were significantly enriched in 13C after the addition of 13CH4 over short-term (3-8 day) incubations. Together, these results suggest that folliculinid ciliates represent a previously overlooked contributor to the ecology and biogeochemical cycling of deep-sea methane seep ecosystems.

Burkett, AM, Rathburn AE, Perez ME, Levin LA, Martin JB.  2016.  Colonization of over a thousand Cibicidoides wuellerstorfi (foraminifera: Schwager, 1866) on artificial substrates in seep and adjacent off-seep locations in dysoxic, deep-sea environments. Deep-Sea Research Part I-Oceanographic Research Papers. 117:39-50.   10.1016/j.dsr.2016.08.011   AbstractWebsite

After-1 yr on the seafloor at water depths of similar to 700 m on Hydrate Ridge in the Pacific, eight colonization experiments composed primarily of a plastic mesh cube (from here on refered to as SEA(3), for Seafloor Epibenthic Attachment Cubes) were colonized by 1076 Cibicidoides wuellerstorfi on similar to 1841 cm(2) of experimental substrate. This species is typically considered an indicator of well-oxygenated conditions, and recruitment of such large numbers in bottom waters with low dissolved oxygen availability (0.24-0.37 mL/L) indicate that this taxon may not be as limited by oxygen as previously thought. Clues about substrate preferences were evident from the distribution, or lack thereof, of individuals among plastic mesh, coated steel frame, wooden dowels and reflective tape. Abundance, individual size distributions within cage populations and isotopic biogeochemistry of living foraminifera colonizing experimental substrates were compared between active seep and adjacent off seep experiment locations, revealing potential differences between these environments. Few studies have examined foraminiferal colonization of hard substrates in the deep-sea and to our knowledge no previous study has compared foraminiferal colonization of active seep and off-seep substrates from the same region. This study provides initial results of recruitment, colonization, geochemical and morphological aspects of the paleoceanographically significant species, C. wuellerstorfi, from dynamic deep-sea environments. Further experimental deployments of SEA(3)s will provide a means to assess relatively unknown ecologic dynamics of important foraminiferal deep-sea species.

Moseman, SM, Levin LA, Currin C, Forder C.  2004.  Colonization, succession, and nutrition of macrobenthic assemblages in a restored wetland at Tijuana Estuary, California. Estuarine Coastal and Shelf Science. 60:755-770.   10.1016/j.ecss.2004.03.013   AbstractWebsite

Modes of colonization, the successional trajectory, and trophic recovery of a macrofaunal community were analyzed over 19 months in the Friendship marsh, a 20-acre restored wetland in Tijuana Estuary, California. Traditional techniques for quantifying macrofaunal communities were combined with emerging stable isotopic approaches for evaluation of trophic recovery, making comparisons with a nearby natural Spartina foliosa habitat. Life history-based predictions successfully identified major colonization modes, although most taxa employed a variety of tactics for colonizing the restored marsh. The presence of S.foliosa did not seem to affect macrofaunal colonization or succession at the scale of this study. However, soil organic matter content in the restored marsh was positively correlated with insect densities, and high initial salinities may have limited the success of early colonists. Total macrofaunal densities recovered to natural marsh levels after 14 months and diversity, measured as species richness and the Shannon index (H'), was comparable to the natural marsh by 19 months. Some compositional disparities between the natural and created communities persisted after 19 months, including lower percentages of surface-feeding polychaetes (Polydora spp.) and higher percentages of dipteran insects and turbellarians in the Friendship marsh. As surficial structural similarity of infaunal communities between the Friendship and natural habitat was achieved, isotopic analyses revealed a simultaneous trajectory towards recovery of trophic structure. Enriched delta(13)C signatures of benthic microalgae and infauna, observed in the restored marsh shortly after establishment compared to natural Spartina habitat, recovered after 19 months. However, the depletion in delta(15)N signatures of macrofauna in the Friendship marsh indicated consumption of microalgae, particularly nitrogen-fixing cyanobacteria, while macroalgae and Spartina made a larger contribution to macrofaunal diets in the natural habitat. Future successional studies must continue to develop and employ novel combinations of techniques for evaluating structural and functional recovery of disturbed and created habitats. (C) 2004 Elsevier Ltd. All rights reserved.

Zirino, A, Neira C, Maicu F, Levin LA.  2013.  Comments on and implications of a steady-state in coastal marine ecosystems. Chemistry & Ecology. 29:86-99.   10.1080/02757540.2012.696613   AbstractWebsite

Coastal ecosystems can be thought of as being established by a number of physico-geochemical drivers, e.g. geochemistry and bathymetry of the basins, climate, tidal and freshwater flows, natural and anthropogenic inputs of nutrients and toxins, all of which exert an influence on the resulting communities of organisms. Depending on the interactions among the major drivers, ecosystems may occur on both large and small scales and be basin-wide or within basins. For individual and separate ecosystems to exist with some permanence in time, e.g. reach a steady-state, they also have to be ‘defended’. Defences are mechanisms that counter changes to maintain the status quo. We argue, and present evidence to support the notion, that the defence mechanisms are inextricably tied to primary production and the biogeochemical cycling of organic matter and provide buffers that mitigate potentially adverse impacts by trace toxins. Colloid pumping, production of complexing ligands and sulfide formation are some of the mechanisms that control trace substances. Current methods for assessing ecosystems do not address the issue of steady-state, nor do they take account of defence activities, e.g. buffering. Therefore, they cannot assess the ‘robustness’ of ecosystems or their ability to resist change, for good or bad. Also, defence mechanisms may, for a time, mask future potentially serious impacts, suggesting that monitoring efforts with limited budgets should consider the measurement of the inputs into ecosystems as well as the immediate or short-term result of the inputs. [ABSTRACT FROM PUBLISHER]Copyright of Chemistry & Ecology is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Levin, LA, Mendoza GF.  2007.  Community structure and nutrition of deep methane-seep macrobenthos from the North Pacific (Aleutian) Margin and the Gulf of Mexico (Florida Escarpment). Marine Ecology-an Evolutionary Perspective. 28:131-151.   10.1111/j.1439-0485.2006.00131.x   AbstractWebsite

Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200-3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep-water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow-seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane-derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 +/- 11,618 ind(.)m(2)), the lowest in the Florida pogonophoran fields (926 +/- 132 ind(.)m(2)), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non-seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (> 60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H') was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non-seep sediments. Community composition differences between seep and non-seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep VC and delta N-15 signatures were lighter for seep than non-seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest delta C-13 values (average of species' means) were observed at the Florida escarpment (-42.87 parts per thousand). We estimated that on average animal tissues had up to 55% methane-derived carbon in Florida mats, 3144% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9-23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific 613C variation (> 307.0) between patch types. Overall we found few characteristic communities or features common to the three deep-water seeps (> 3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon.

Levin, LA, Liu KK, Emeis KC, Breitburg DL, Cloern J, Deutsch C, Giani M, Goffart A, Hofmann EE, Lachkar Z, Limburg K, Liu SM, Montes E, Naqvi W, Ragueneau O, Rabouille C, Sarkar SK, Swaney DP, Wassman P, Wishner KF.  2015.  Comparative biogeochemistry-ecosystem-human interactions on dynamic continental margins. Journal of Marine Systems. 141:3-17.   10.1016/j.jmarsys.2014.04.016   AbstractWebsite

The oceans' continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO2-induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins, (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO2-induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services. These include primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins. (C) 2014 Elsevier BM. All rights reserved.

Bernardino, AF, Levin LA, Thurber AR, Smith CR.  2012.  Comparative composition, diversity and trophic ecology of sediment macrofauna at vents, seeps and organic falls. Plos One. 7   10.1371/journal.pone.0033515   AbstractWebsite

Sediments associated with hydrothermal venting, methane seepage and large organic falls such as whale, wood and plant detritus create deep-sea networks of soft-sediment habitats fueled, at least in part, by the oxidation of reduced chemicals. Biological studies at deep-sea vents, seeps and organic falls have looked at macrofaunal taxa, but there has yet to be a systematic comparison of the community-level attributes of sediment macrobenthos in various reducing ecosystems. Here we review key similarities and differences in the sediment-dwelling assemblages of each system with the goals of (1) generating a predictive framework for the exploration and study of newly identified reducing habitats, and (2) identifying taxa and communities that overlap across ecosystems. We show that deep-sea seep, vent and organic-fall sediments are highly heterogeneous. They sustain different geochemical and microbial processes that are reflected in a complex mosaic of habitats inhabited by a mixture of specialist (heterotrophic and symbiont-associated) and background fauna. Community-level comparisons reveal that vent, seep and organic-fall macrofauna are very distinct in terms of composition at the family level, although they share many dominant taxa among these highly sulphidic habitats. Stress gradients are good predictors of macrofaunal diversity at some sites, but habitat heterogeneity and facilitation often modify community structure. The biogeochemical differences across ecosystems and within habitats result in wide differences in organic utilization (i.e., food sources) and in the prevalence of chemosynthesis-derived nutrition. In the Pacific, vents, seeps and organic-falls exhibit distinct macrofaunal assemblages at broad-scales contributing to beta diversity. This has important implications for the conservation of reducing ecosystems, which face growing threats from human activities.

Becker, BJ, Levin LA, Fodrie FJ, McMillan PA.  2007.  Complex larval connectivity patterns among marine invertebrate populations. Proceedings of the National Academy of Sciences of the United States of America. 104:3267-3272.   10.1073/pnas.0611651104   AbstractWebsite

Based on the belief that marine larvae, which can spend days to months in the planktonic stage, could be transported considerable distances by ocean currents, it has long been assumed that populations of coastal species with a planktonic larval stage are demographically open and highly "connected." Such assumptions about the connectivity of coastal populations govern approaches to managing marine resources and shape our fundamental understanding of population dynamics and evolution, yet are rarely tested directly due to the small size and high mortality of marine larvae in a physically complex environment. Here, we document a successful application of elemental fingerprinting as a tracking tool to determine sources of settled invertebrates and show that coastal mussel larvae, previously thought to be highly dispersed, can be retained within 20-30 km of their natal origin. We compare two closely related and co-occurring species, Mytilus californianus and Mytilus galloprovincialis, and determine that, despite expected similarities, they exhibit substantially different connectivity patterns. Our use of an in situ larval culturing technique overcomes the previous challenge of applying microchemical tracking methods to species with completely planktonic development. The exchange of larvae and resulting connectivities among marine populations have fundamental consequences for the evolution and ecology of species and for the management of coastal resources.

Springer, AE, Stevens LE, Anderson DE, Partnell RA, Kreamer DK, Levin LA, Flora S.  2008.  A comprehensive springs classification system. Integrating geomorphic, hydrogeochemical, and ecological criteria. Aridland springs in North America: ecology and conservation. ( Stevens LE, Meretsky VJ, Eds.).:49-75., Tucson: University of Arizona Press and the Arizona-Sonora Desert Museum Abstract
Fodrie, FJ, Becker BJ, Levin LA, Gruenthal K, McMillan PA.  2011.  Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels. Journal of Sea Research. 65:141-150.   10.1016/j.seares.2010.09.001   AbstractWebsite

The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels (Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78-87% of all cases. Settlement varied between 2 and 27 settlers grambyssus(-1) week(-1) at 510 and HI, and both sites were characterized by 2-3 weeks with "high" settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between "high" and "low" settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations. (C) 2010 Elsevier B.V. All rights reserved.

Dibacco, C, Levin LA, Sala E.  2006.  Connectivity in marine systems: the importance of larval and spore dispersal. Connectivity Conservation. ( Crooks KR, Sanjayan A, Eds.).:157-183., Cambridge: Cambridge University Press Abstract
Hartmann, AC, Levin LA.  2012.  Conservation concerns in the deep. Science. 336:668-669. AbstractWebsite
Levin, LA, Leithold EL, Gross TF, Huggett CL, Dibacco C.  1994.  Contrasting effects of substrate mobility on infaunal assemblages inhabiting two high-energy settings on Fieberling Guyot. Journal of Marine Research. 52:489-522.   10.1357/0022240943077028   AbstractWebsite

The influence of seamount-intensified flows on the structure of infaunal assemblages was examined at two sand-covered sites located 2.3 km apart atop the summit plain of Fieberling Guyot (32-degrees 27.6'N 127-degrees 48.0'W). Both sites experience strong, tidal bottom currents with flows exceeding 20 cm/ s on a daily basis (4 mab). Estimates of shear velocity (u*) did not differ significantly between the two sites. However, differences in sediment composition and density produced different sediment transport regimes at the two sites. At Sea Pen Rim (SPR), located on the NW perimeter (635 m), sedimentary particles were composed primarily of basaltic sands that experienced negligible transport during the study period. At White Sand Swale (WSS, 580 m), a narrow valley enclosed on three sides by basalt outcrops, sediments were composed almost entirely of foraminiferal sands that moved daily. Sediment organic content and microbial abundances were similar at the two sites. Infauna (> 300 mum) had higher densities at WSS (1870/m2) than SPR (1489/m2), but lower expected species richness. Although the 2 sites shared nearly 50% of identified species, peracarid crustaceans, echinoderms, sponges, and bryozoans were proportionally more important in the stable substrates of SPR, while turbellarians, bivalves, and aplacophorans were better represented in the shifting sands of WSS. The infauna of WSS lived deeper in the sediment column (> 50% below 2 cm) than that of SPR (> 50% in the upper 1 cm), at least partly because the majority (83%) at WSS were subsurface burrowers with motile lifestyles. Tube-building and epifaunal lifestyles were more common at SPR than WSS, as were surface-deposit and filter-feeding modes. Fences and weirs were deployed at the study sites for 6.5-wk and 6-mo periods to manipulate bottom stress. Changes in faunal patterns within weirs at WSS reinforced our conjecture that contrasting sediment transport regimes explain between-site differences in community structure. Fence effects varied with deployment period and site. Topographic features on Fieberling Guyot produce heterogeneous sedimentary settings characterized by different transport regimes. Our results suggest that substrate mobility exerts primary control over infaunal community structure at the two high-energy sites.

Levin, LA, Bridges TS.  1994.  Control and consequences of alternative developmental modes in a poecilogonous polychaete. American Zoologist. 34:323-332. AbstractWebsite

The poecilogonous polychaete Streblospio benedicti (Webster) exhibits both planktotrophic and lecithotrophic modes of larval development. The alternative trophic modes are associated with differences in age and size at maturation, offspring number, size and energetic investment, larval planktonic period, morphology and survivorship. This paper reviews a decade of research into the control and consequences of the traits associated with planktotrophy and lecithotrophy in S. benedicti. The dominant control on reproductive and developmental characters is genetic. Significant additive genetic variance has been detected for egg diameter, fecundity, larval planktonic period and aspects of larval morphology. However, environmental factors such as temperature, food quality and photoperiod, and intrinsic factors such as maternal age, exert considerable influence on non-trophic developmental traits (e.g., offspring number, size and energy content). Demographic consequences of development mode are reviewed for field and laboratory demes of S. benedicti dominated by individuals exhibiting either planktotrophy or lecithotrophy. Similar population size structure, fluctuations in abundance, P:B ratios, and estimated population growth rates are achieved through trade-offs between survivorship and fecundity. Development mode may best be viewed as a complex set of traits that are intimately linked developmentally and evolutionarily to other aspects of an organism's life history. Greater insight into the control and consequences of development mode should result from further investigation of these linkages.

Levin, LA, Huggett CL, Wishner KF.  1991.  Control of deep-sea benthic community structure by oxygen and organic-matter gradients in the eastern Pacific Ocean. Journal of Marine Research. 49:763-800.   10.1357/002224091784995756   AbstractWebsite

At boundaries of oxygen minimum zones (OMZs), bathyal faunas experience steep gradients in oxygen and organic-matter availability. The present study compares changes in microbial, meiofaunal, macrofaunal and megafaunal benthic assemblages along these gradients on Volcano 7, a 2.3-km high seamount in the eastern tropical Pacific. Faunal tolerance to dysaerobic (low oxygen) conditions varies with organism size; microbial and meiofaunal abundances are less affected than macro- and megafaunal abundances. At the exceedingly low concentrations (< 0.1 ml/1) encountered on the upper summit of Volcano 7, oxygen appears to exert primary control over abundance, composition and diversity of macrofauna, overriding other factors such as food availability and sediment grain size. When oxygen concentration is sufficient, food availability in sediments (indicated by the presence of labile material such as chlorophyll a) is highly correlated with meiofaunal and macrofaunal abundance. Four distinct physical zones were identified on Volcano 7: (1) the coarse-grained upper summit zone (730-770 m) where near-bottom oxygen concentrations were usually lowest (often < 0.1 ml/1) and organic-matter (% organic carbon and chlorophyll a) availability was high, (2) the coarse-grained lower summit (770-1000 m) where near-bottom oxygen concentrations were usually slightly higher (0.11 to 0.16 ml/1) and organic-matter availability remained high, (3) the coarse-grained flank (1000-2000 m) where oxygen concentration was intermediate (0.7-0.9 ml/1) and sediment organic-matter content was very low, and (4) the finer-grained base (2000-3500 m) where oxygen values exceeded 2.5 ml/1, sediment organic carbon was moderate, and chlorophyll a was low. Abundances of larger forms (megafauna and macrofauna) were severely reduced on the upper summit, but attained high values (2.25/m2 and 8,457/m2 respectively) just tens of meters below. The smaller forms (bacteria and meiofauna) attained peak abundances on the low-oxygen upper summit, however, abundances of harpacticoid copepods were greatly reduced on the upper and lower summit, presumably due to oxygen limitation. Macrofaunal abundance and diversity patterns along the Volcano 7 oxygen/enrichment gradient resembled those typically observed along shallow-water gradients of organic pollution. Low densities of a few soft-bodied, low-oxygen tolerant species resided on the upper summit, a high-density, low-diversity assemblage inhabited the lower summit, and low-density, high-diversity assemblages occupied the flank and base sediments. The infaunal communities on Volcano 7 support the idea that OMZ boundaries are regions of enhanced biological activity. Modern faunal distributions and biogenic structures at OMZ boundaries may be useful in reconstructing oxygenation histories of ancient marine basins.