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Zirino, A, Elwany H, Neira C, Maicu F, Mendoza G, Levin LA.  2014.  Salinity and its variability in the Lagoon of Venice, 2000–2009. Advances in Oceanography and Limnology. 5:41-59.: Taylor & Francis   10.1080/19475721.2014.900113   Abstract

Yearly averages computed from monthly and bimonthly salinity data collected between 2000 and 2009 from 13 broadly spaced stations in the Venice Lagoon were analysed in view of 30 min data collected semi-continuously during 2009 at nine similarly located stations. Data from all stations and all years indicate that, based on yearly averages, the lagoon may be divided along its major (long) axis into three areas: 1) a northern, freshwater impacted area (S = <28 PSU) of high, tidally-caused, variability, 2) a southern, marine, zone of S >32 PSU of low, tidally-caused, variability, and 3) an intermediate zone. Salinity changes are closely associated with rainfall events, and the incoming freshwater is consistently distributed throughout the lagoon by tidal action. Much variability is simply a result of the forward and backward motion of the tides and is not caused by a salinity change in the water itself. The consistency of the 2000?2009 data and the historical (to 1961) watershed record support the hypothesis that the Venice Lagoon has been and is currently at steady-state with respect to its salinity distribution. As such, it is conducive to the development of (at least) three separate ecosystems.

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.)

Zhang, J, Gilbert D, Gooday AJ, Levin L, Naqvi SWA, Middelburg JJ, Scranton M, Ekau W, Pena A, Dewitte B.  2010.  Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development. Biogeosciences. 7:1443-1467., France: European Geosciences Union AbstractWebsite

Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including estuaries, coastal waters, upwelling areas, fjords and semi-enclosed basins, with various external forcings, ecosystem responses, feedbacks and potential impact on the sustainability of the fishery and economics. The obvious external forcings include freshwater runoff and other factors contributing to stratification, organic matter and nutrient loadings, as well as exchange between coastal and open ocean water masses. Their different interactions set up mechanisms that drive the system towards hypoxia. Coastal systems also vary in their relative susceptibility to hypoxia depending on their physical and geographic settings. It is understood that coastal hypoxia has a profound impact on the sustainability of ecosystems, which can be seen, for example, by the change in the food-web structure and system function; other influences include compression and loss of habitat, as well as changes in organism life cycles and reproduction. In most cases, the ecosystem responds to the low dissolved oxygen in non-linear ways with pronounced feedbacks to other compartments of the Earth System, including those that affect human society. Our knowledge and previous experiences illustrate that there is a need to develop new observational tools and models to support integrated research of biogeochemical dynamics and ecosystem behavior that will improve confidence in remediation management strategies for coastal hypoxia.

Zapata-Hernandez, G, Sellanes J, Thurber AR, Levin LA, Chazalon F, Linke P.  2014.  New insights on the trophic ecology of bathyal communities from the methane seep area off Concepcion, Chile (similar to 36 degrees S). Marine Ecology-an Evolutionary Perspective. 35:1-21.   10.1111/maec.12051   AbstractWebsite

Studies of the trophic structure in methane-seep habitats provide insight into the ecological function of deep-sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepcion, Chile (similar to 36 degrees S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane-derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension-feeding and deposit-feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEA(B)) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic-derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep-sea habitats in the Southeastern Pacific.

Zapata-Hernandez, G, Sellanes J, Thurber AR, Levin LA.  2014.  Trophic structure of the bathyal benthos at an area with evidence of methane seep activity off southern Chile (similar to 45 degrees S). Journal of the Marine Biological Association of the United Kingdom. 94:659-669.   10.1017/s0025315413001914   AbstractWebsite

Through application of carbon (C) and nitrogen (N) stable isotope analyses, we investigated the benthic trophic structure of the upper-slope off southern Chile (similar to 45 degrees S) including a recent methane seep area discovered as part of this study. The observed fauna comprised 53 invertebrates and seven fish taxa, including remains of chemosymbiotic fauna (e.g. chemosymbiotic bivalves and siboglinid polychaetes), which are typical of methane seep environments. While in close-proximity to a seep, the heterotrophic fauna had a nutrition derived predominantly from photosynthetic sources (delta C-13 > -21 parts per thousand). The absence of chemosynthesis-based nutrition in the consumers was likely a result of using an Agassiz trawl to sample the benthos, a method that is likely to collect a mix of fauna including individuals from adjacent non-seep bathyal environments. While four trophic levels were estimated for invertebrates, the fish assemblage was positioned within the third trophic level of the food web. Differences in corrected standard ellipse area (SEA(C)), which is a proxy of the isotopic niche width, yielded differences for the demersal fish Notophycis marginata (SEA(C) = 5.1 parts per thousand) and Coelorinchus fasciatus (SEA(C) = 1.1 parts per thousand), suggesting distinct trophic behaviours. No ontogenic changes were detected in C. fasciatus regarding food sources and trophic position. The present study contributes the first basic trophic data for the bathyal area off southern Chile, including the identification of a new methane seep area, among the furthest south ever discovered. Such information provides the basis for the proper sustainable management of the benthic environments present along the vast Chilean continental margin.

Woulds, C, Andersson JH, Cowie GL, Middelburg JJ, Levin LA.  2009.  The short-term fate of organic carbon in marine sediments: Comparing the Pakistan margin to other regions. Deep Sea Research (Part II, Topical Studies in Oceanography). 56:393-402., United Kingdom: Elsevier BV   10.1016/j.dsr2.2008.10.008   AbstractWebsite

Pulse-chase experiments with isotopically labelled phytodetritus conducted across the Pakistan margin reveal that the impact of biological activities on benthic C-cycling varies markedly among sites exhibiting different seafloor conditions. In this study, patterns of biological C-processing across the Pakistan margin oxygen minimum zone (OMZ) are compared with those observed in previous tracer studies. Variations in site environmental conditions are proposed to explain the considerable variations in C-processing patterns among this and previous studies. Three categories of C-processing pattern are identified: (1) respiration dominated, where respiration accounts for >75% of biological C-processing, and uptake by metazoan macrofauna, foraminifera and bacteria are relatively minor processes. These sites tend to show several (although not necessarily all) of the properties of being cold and deep, and having low inputs of organic carbon to the sediment and relatively low-biomass metazoan macrofaunal communities; (2) active faunal uptake, where respiration accounts for <75%, and metazoan macrofaunal, foraminiferal and bacterial uptake each account for 10-25% of biological C-processing. This type is further split into metazoan macrofaunal- and foraminiferal-dominated situations, dictated by oxygen availability; and (3) metazoan macrofaunal uptake dominated, characterised by metazoan macrofaunal uptake accounting for ~50% of biological C-processing, due to unusually large biomasses of the phytodetritus-consuming animals. Total respiration rates (of added C) on the Pakistan margin fell within the range of rates measured elsewhere in the deep sea (} .1-2.8mgCm super(-) super(2)h super(-) super(1)), and seem to be dominantly controlled by seafloor temperature. Rates of metazoan macrofaunal uptake of organic matter (OM) on the Pakistan margin are larger than those in most other studies, and this is attributed to the large and active metazoan macrofaunal communities in the lower OMZ, characteristic of OMZ boundaries. Finally, biological mixing of Pakistan margin sediments was reduced compared to that observed in comparable tracer studies on other margins. This probably reflects faunal feeding and burrowing strategies consistent with low oxygen concentrations and a relatively abundant supply of sedimentary OM.

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.

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.

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.

Whitcraft, CR, Levin LA.  2007.  Regulation of benthic algal and animal communities by salt marsh plants: Impact of shading. Ecology. 88:904-917.   10.1890/05-2074   AbstractWebsite

Plant cover is a fundamental feature of many coastal marine and terrestrial systems and controls the structure of associated animal communities. Both natural and human-mediated changes in plant cover influence abiotic sediment properties and thus have cascading impacts on the biotic community. Using clipping ( structural) and light ( shading) manipulations in two salt marsh vegetation zones ( one dominated by Spartina foliosa and one by Salicornia virginica), we tested whether these plant species exert influence on abiotic environmental factors and examined the mechanisms by which these changes regulate the biotic community. In an unshaded ( plant and shade removal) treatment, marsh soils exhibited harsher physical properties, a microalgal community composition shift toward increased diatom dominance, and altered macrofaunal community composition with lower species richness, a larger proportion of insect larvae, and a smaller proportion of annelids, crustaceans, and oligochaetes compared to shaded ( plant removal, shade mimic) and control treatment plots. Overall, the shaded treatment plots were similar to the controls. Plant cover removal also resulted in parallel shifts in microalgal and macrofaunal isotopic signatures of the most dynamic species. This suggests that animal responses are seen mainly among microalgae grazers and may be mediated by plant modi. cation of microalgae. Results of these experiments demonstrate how light reduction by the vascular plant canopy can control salt marsh sediment communities in an arid climate. This research facilitates understanding of sequential consequences of changing salt marsh plant cover associated with climate or sea level change, habitat degradation, marsh restoration, or plant invasion.

Whitcraft, CR, Levin LA, Talley D, Crooks JA.  2008.  Utilization of invasive tamarisk by salt marsh consumers. Oecologia. 158:259-272.   10.1007/s00442-008-1144-5   AbstractWebsite

Plant invasions of coastal wetlands are rapidly changing the structure and function of these systems globally. Alteration of litter dynamics represents one of the fundamental impacts of an invasive plant on salt marsh ecosystems. Tamarisk species (Tamarix spp.), which extensively invade terrestrial and riparian habitats, have been demonstrated to enter food webs in these ecosystems. However, the trophic impacts of the relatively new invasion of tamarisk into marine ecosystem have not been assessed. We evaluated the trophic consequences of invasion by tamarisk for detrital food chains in the Tijuana River National Estuarine Research Reserve salt marsh using litter dynamics techniques and stable isotope enrichment experiments. The observations of a short residence time for tamarisk combined with relatively low C:N values indicate that tamarisk is a relatively available and labile food source. With an isotopic ((15)N) enrichment of tamarisk, we demonstrated that numerous macroinvertebrate taxonomic and trophic groups, both within and on the sediment, utilized (15)N derived from labeled tamarisk detritus. Infaunal invertebrate species that took up no or limited (15)N from labeled tamarisk (A. californica, enchytraeid oligochaetes, coleoptera larvae) occurred in lower abundance in the tamarisk-invaded environment. In contrast, species that utilized significant (15)N from the labeled tamarisk, such as psychodid insects, an exotic amphipod, and an oniscid isopod, either did not change or occurred in higher abundance. Our research supports the hypothesis that invasive species can alter the trophic structure of an environment through addition of detritus and can also potentially impact higher trophic levels by shifting dominance within the invertebrate community to species not widely consumed.

Vandover, CL, Smith CR, Ardron J, Dunn D, Gjerde K, Levin L, Smith S, Dinard Workshop C.  2012.  Designating networks of chemosynthetic ecosystem reserves in the deep sea. Marine Policy. 36:378-381.   10.1016/j.marpol.2011.07.002   AbstractWebsite

From the moment of their discovery, chemosynthetic ecosystems in the deep sea have held intrinsic scientific value. At the same time that the scientific community is studying chemosynthetic ecosystems other sectors are either engaged in, or planning for, activities that may adversely impact these ecosystems. There is a need and opportunity now to develop conservation strategies for networks of chemosynthetic ecosystem reserves in national and international waters through collaboration among concerned stakeholders. (C) 2011 Elsevier Ltd. All rights reserved.

Thurber, AR, Levin LA, Rowden AA, Sommer S, Linke P, Kroger K.  2013.  Microbes, macrofauna, and methane: A novel seep community fueled by aerobic methanotrophy. Limnology and Oceanography. 58:1640-1656.   10.4319/lo.2013.58.5.1640   AbstractWebsite

During the discovery and description of seven New Zealand methane seep sites, an infaunal assemblage dominated by ampharetid polychaetes was found in association with high seabed methane emission. This ampharetid-bed assemblage had a mean density of 57,000 +/- 7800 macrofaunal individuals m(-2) and a maximum wet biomass of 274 g m(-2), both being among the greatest recorded from deep-sea methane seeps. We investigated these questions: Does the species assemblage present within these ampharetid beds form a distinct seep community on the New Zealand margin? and What type of chemoautotrophic microbes fuel this heterotrophic community? Unlike the other macro-infaunal assemblages, the ampharetid-bed assemblage composition was homogeneous, independent of location. Based on a mixing model of species-specific mass and isotopic composition, combined with published respiration measurements, we estimated that this community consumes 29-90 mmol C m(-2) d(-1) of methane-fueled biomass; this is > 290 times the carbon fixed by anaerobic methane oxidizers in these ampharetid beds. A fatty acid biomarker approach supported the finding that this community, unlike those previously known, consumes primarily aerobic methanotrophic bacteria. Due to the novel microbial fueling and high methane flux rates, New Zealand's ampharetid beds provide a model system to study the influence of metazoan grazing on microbially mediated biogeochemical cycles, including those that involve greenhouse gas emissions.

Thurber, AR, Kroger K, Neira C, Wiklund H, Levin LA.  2010.  Stable isotope signatures and methane use by New Zealand cold seep benthos. Marine Geology. 272:260-269.   10.1016/j.margeo.2009.06.001   AbstractWebsite

The carbon isotopic composition of seep faunal tissue represents a time-integrated view of the interaction between biology and the biogeochemical gradients within the environment. Here we provide an initial description of carbon and nitrogen stable isotope signatures of dominant symbiont-bearing megafauna and heterotrophic mega- and macrofauna from 10 methane-seep sites on the continental margin of the North Island of New Zealand (662-1201 m water depth). Isotopic signatures suggest that sulfide oxidation supports symbiont-bearing taxa including solemyid and vesicomyid bivalves, and methanotrophic symbionts are present in the seep mussel Bathymodiolus sp Multiple species of Frenulata (Siboglinidae) are present and have a range of isotopic values that are indicative of both thiotroph- and methanotroph-based nutrition. Isotopic composition of the tubeworm Lamellibrachia sp. varied by 23 3 parts per thousand among individuals although there was no consistent difference among sites Variation in methane use by heterotrophic fauna appears to reflect the availability of hard vs. soft substrate, macrofauna on hard substrates had high delta(13)C signatures, reflecting consumption of photosynthetic-derived organic matter Two unique, biotic assemblages were discovered to be fueled largely by methane: a hard-substrate, multi-phyla sponge-associated community (inhabiting the sponge Pseudosuberites sp) and a soft-sediment assemblage dominated by ampharetid polychaetes Isotope signatures yield estimates of 38-100% and 6-100% methane-derived carbon in sponge associates and ampharetid-bed macrofauna. respectively. These estimates are comparable to those made for deeper methane seeps at the Florida Escarpment (3290 m) and Kodiak. Alaska seeps (4445 m) The overall high use of methane as a carbon source by both symbiont-bearing and heterotrophic fauna suggests that New Zealand methane seeps are an ideal model system to study the interaction among metazoans, bacteria, archaea, and their resulting effect on methane cycles. (C) 2009 Elsevier B V All rights reserved

Thurber, AR, Levin LA, Orphan VJ, Marlow JJ.  2012.  Archaea in metazoan diets: implications for food webs and biogeochemical cycling. ISME Journal. 6:1602-1612.   10.1038/ismej.2012.16   AbstractWebsite

Although the importance of trophic linkages, including 'top-down forcing', on energy flow and ecosystem productivity is recognized, the influence of metazoan grazing on Archaea and the biogeochemical processes that they mediate is unknown. Here, we test if: (1) Archaea provide a food source sufficient to allow metazoan fauna to complete their life cycle; (2) neutral lipid biomarkers (including crocetane) can be used to identify Archaea consumers; and (3) archaeal aggregates are a dietary source for methane seep metazoans. In the laboratory, we demonstrated that a dorvilleid polychaete, Ophryotrocha labronica, can complete its life cycle on two strains of Euryarchaeota with the same growth rate as when fed bacterial and eukaryotic food. Archaea were therefore confirmed as a digestible and nutritious food source sufficient to sustain metazoan populations. Both strains of Euryarchaeota used as food sources had unique lipids that were not incorporated into O. labronica tissues. At methane seeps, sulfate-reducing bacteria that form aggregations and live syntrophically with anaerobic-methane oxidizing Archaea contain isotopically and structurally unique fatty acids (FAs). These biomarkers were incorporated into tissues of an endolithofaunal dorvilleid polychaete species from Costa Rica (mean bulk delta C-13 = -92 +/- 4 parts per thousand; polar lipids -116 parts per thousand) documenting consumption of archaeal-bacterial aggregates. FA composition of additional soft-sediment methane seep species from Oregon and California provided evidence that consumption of archaeal-bacterial aggregates is widespread at methane seeps. This work is the first to show that Archaea are consumed by heterotrophic metazoans, a trophic process we coin as 'archivory'. The ISME Journal (2012) 6, 1602-1612; doi:10.1038/ismej.2012.16; published online 8 March 2012

Thorrold, SR, Zacherl DC, Levin LA.  2007.  Population connectivity and larval dispersal using geochemical signatures in calcified structures. Oceanography. 20:80-89.   AbstractWebsite

The importance of larval dispersal to the population dynamics and biogeography of marine organisms has been recognized for almost a century (Hjort, 1914; Thorson, 1950). More recently, theoretical studies have highlighted the role that connectivity may play in determining the resilience of marine populations (Hastings and Botsford, 2006). Effective spatial management of marine capture fisheries, including the design of marine reserve networks, also requires an understanding of population connectivity (Sale et al., 2005). However, remarkably few empirical estimates of larval dispersal or population connectivity in ocean environments exist.

Thornhill, DJ, Struck TH, Ebbe B, Lee RW, Mendoza GF, Levin LA, Halanych KM.  2012.  Adaptive radiation in extremophilic Dorvilleidae (Annelida): diversification of a single colonizer or multiple independent lineages? Ecology and Evolution. 2:1958-1970.   10.1002/ece3.314   AbstractWebsite

Metazoan inhabitants of extreme environments typically evolved from forms found in less extreme habitats. Understanding the prevalence with which animals move into and ultimately thrive in extreme environments is critical to elucidating how complex life adapts to extreme conditions. Methane seep sediments along the Oregon and California margins have low oxygen and very high hydrogen sulfide levels, rendering them inhospitable to many life forms. Nonetheless, several closely related lineages of dorvilleid annelids, including members of Ophryotrocha, Parougia, and Exallopus, thrive at these sites in association with bacterial mats and vesicomyid clam beds. These organisms are ideal for examining adaptive radiations in extreme environments. Did dorvilleid annelids invade these extreme environments once and then diversify? Alternatively, did multiple independent lineages adapt to seep conditions? To address these questions, we examined the evolutionary history of methane-seep dorvilleids using 16S and Cyt b genes in an ecological context. Our results indicate that dorvilleids invaded these extreme habitats at least four times, implying preadaptation to life at seeps. Additionally, we recovered considerably more dorvilleid diversity than is currently recognized. A total of 3 major clades (designated "Ophryotrocha,""Mixed Genera" and "Parougia") and 12 terminal lineages or species were encountered. Two of these lineages represented a known species, Parougia oregonensis, whereas the remaining 10 lineages were newly discovered species. Certain lineages exhibited affinity to geography, habitat, sediment depth, and/or diet, suggesting that dorvilleids at methane seeps radiated via specialization and resource partitioning.

Thistle, D, Levin LA.  1998.  The effect of experimentally increased near-bottom flow on metazoan meiofauna at a deep-sea site, with comparison data on macrofauna. Deep-Sea Research Part I-Oceanographic Research Papers. 45:625-+.   10.1016/s0967-0637(97)00101-5   AbstractWebsite

It has been argued that strong near-bottom hows affect macrofauna and meiofauna in the deep sea, but the evidence comes largely from studies that compared sites separated geographically by hundreds to thousands of kilometers and in depth by hundreds of meters. In this paper, the results of the first experimental investigation of the effects of strong near-bottom flow on deep-sea metazoan meiofauna are presented. At a site (32 degrees 27.581' N, 127 degrees 47.839' W) at 583 m depth on the Fieberling Guyot summit plain, the submersible Alvin emplaced weirs designed to increase the near-bottom flow locally. After 6.5 weeks, sediments in the weirs and unmanipulated locations in the vicinity were sampled. The abundances of nematodes, harpacticoid copepods, ostracods, and kinorhynchs, considered collectively and as individual taxa, were significantly lower in the weir samples than in the background samples. Parallel responses were observed in total macrofaunal and mollusk abundances. Proportional declines in kinorhynchs and mollusks were observed as well. These results suggest that strong near-bottom flow can reduce the abundance of meiofauna and macrofauna in the deep sea and alter assemblage composition. (C) 1998 Elsevier Science Ltd. All rights reserved.

Thistle, D, Levin LA, Gooday AJ, Pfannkuche O, Lambshead PJD.  1999.  Physical reworking by near-bottom flow alters the metazoan meiofauna of Fieberling Guyot (northeast Pacific). Deep-Sea Research Part I-Oceanographic Research Papers. 46:2041-2052.   10.1016/s0967-0637(99)00040-0   AbstractWebsite

Although much of the deep sea is physically tranquil, some regions experience near-bottom flows that rework the surficial sediment. During periods of physical reworking, animals in the reworked layer risk being suspended, which can have both positive and negative effects. Reworking can also change the sediment in ecologically important ways, so the fauna of reworked sites should differ from that of quiescent locations. We combined data from two reworked, bathyal sites on the summit of Fieberling Guyot (32 degrees 27.631'N, 127 degrees 49.489'W; 32 degrees 27.581'N, 127 degrees 47.839'W) and compared the results with those of more tranquil sites. We tested for differences in the following parameters, which seemed likely to be sensitive to the direct or indirect effects of reworking: (1) the vertical distribution of the meiofauna in the sea bed, (2) the relative abundance of surface-living harpacticoids, (3) the proportion of the fauna consisting of interstitial harpacticoids, (4) the ratio of harpacticoids to nematodes. We found that the vertical distributions of harpacticoid copepods, ostracods, and kinorhynchs were deeper on Fieberling. In addition, the relative abundance of surface-living harpacticoids was less, the proportion of interstitial harpacticoids was greater, and the ratio of harpacticoids to nematodes was greater on Fieberling. These differences between Fieberling and the comparison sites suggest that physical reworking affects deep-sea meiofauna and indicate the nature of some of the effects. (C) 1999 Elsevier Science Ltd. AII rights reserved.

Tegner, MJ, Levin LA.  1982.  Do sea urchins and abalones compete in California kelp forest communities? Echinoderms, proceedings of the International Conference, Tampa Bay. ( Lawrence JM, Ed.).:265-271., RotterdamSalem, NH: A.A. Balkema ;Distributed in USA & Canada by MBS Abstract
Tegner, MJ, Levin LA.  1983.  Spiny lobsters and sea urchins: Analysis of a predator-prey interaction. Journal of Experimental Marine Biology and Ecology. 73:125-150.   10.1016/0022-0981(83)90079-5   AbstractWebsite

Spiny lobsters, Panulirus interruptus (Randall), are important predators of two species of sea urchins, Strongylocentrotus franciscanus (A. Agassiz) and S. purpuratus (Stimpson), which are major herbivores in southern California kelp forest communities. Aquarium experiments indicate that spiny lobsters strongly prefer S. purpuratus over S. franciscanus of comparable test diameter, probably accounting for the higher number of S. purpuratus mortalities observed in the field. Juvenile S. franciscanus (< 60 mm test diameter, TD) are preferred over larger conspecifics, but the smallest S. franciscanus (< 30 mm TD) are protected by association with the adult urchin spine canopy. Mid-sized S. franciscanus too large to fit under the spine canopy are subject to intense predation. All sizes of P. interruptus tested showed a notable reluctance to attack large S. franciscanus (> 90 mm TD) when offered a range of sizes, although the larger lobsters are capable of handling the largest urchins. Relative movement, spine length, test thickness, and gonad weights of sea urchins were examined to evaluate the factors affecting the lobsters' choice of prey, and behavioral responses to lobsters were assessed to determine urchin availability to these predators. The handling problems associated with the long spines of larger S. franciscanus appear to be the major considerations in prey choice despite the much greater potential energy gain from these urchins. Thus predation by spiny lobsters appears to be sufficient to explain the bimodal size-frequency distribution typical of S. franciscanus populations in areas where these predators are common. Heavy fishing pressure on spiny lobsters during this century probably resulted in the release of sea urchin populations and contributed to episodes of destructive urchin grazing observed in the 1950's and subsequent years.

Talley, TS, Levin LA.  2001.  Modification of sediments and macrofauna by an invasive marsh plant. Biological Invasions. 3:51-68.   10.1023/A:1011453003168   AbstractWebsite

Invasive grasses have recently altered salt marsh ecosystems throughout the northern hemisphere. On the eastern seaboard of the USA, Phragmites australis has invaded both brackish and salt marsh habitats. Phragmites australis influence on sediments and fauna was investigated along a salinity and invasion-age gradient in marshes of the lower Connecticut River estuary. Typical salinities were about 19-4 ppt in Site I, 9-10 ppt in Site II and 5-7 ppt in Site III. Strongest effects were evident in the least saline settings (II and III) where Phragmites has been present the longest and exists in monoculture. Limited influence was evident in the most saline region (I) where Phragmites and native salt marsh plants co-occur. The vegetation within Phragmites stands in tidal regions of the Connecticut River generally exhibits taller, but less dense shoots, higher above-ground biomass, and lower below-ground biomass than does the un-invaded marsh flora. There were lower sediment organic content, greater litter accumulation and higher sediment chlorophyll a concentrations in Phragmites-invaded than un-invaded marsh habitat. Epifaunal gastropods (Succinea wilsoni and Stagnicola catascopium) were less abundant in habitats where Phragmites had invaded than in un-invaded marsh habitat. Macro-infaunal densities were lower in the Phragmites-invaded than un-invaded habitats at the two least saline sites (II and III). Phragmites stands supported more podurid insects, sabellid polychaetes, and peracarid crustaceans, fewer arachnids, midges, tubificid and enchytraeid oligochaetes, and greater habitat-wide taxon richness as measured by rarefaction, than did the uninvaded stands. The magnitude and significance of the compositional differences varied with season and with site; differences were generally greatest at the oldest, least saline sites (II and III) and during May, when faunal densities were higher than in September. However, experimental design and the 1-year study period precluded clear separation of salinity, age, and seasonal effects. Although structural effects of Phragmites on salt marsh faunas are evident, further investigation is required to determine the consequences of these effects for ecosystem function.

Talley, TS, Levin LA.  1999.  Macrofaunal succession and community structure in Salicornia marshes of southern California. Estuarine Coastal and Shelf Science. 49:713-731.   10.1006/ecss.1999.0553   AbstractWebsite

Lack of basic understanding of ecosystem structure and function forms a major impediment to successful conservation of coastal ecosystems. This paper provides a description of the fauna and examines faunal succession in Salicornia-vegetated sediments of southern California. Environmental attributes (vegetation and sediment properties) and macrofaunal (animals greater than or equal to 0.3 mm) community structure were examined in sediments of five natural, southern California Salicornia spp. marshes (Tijuana Estuary, San Diego Bay, Mission Bay, Upper Newport Bay and Anaheim Bay) and in created Salicornia marshes 16 months to 10 years in age, located within four of the bays. Oligochaetes and insects were the dominant taxa in both natural (71 to 98% of total fauna) and created (91 to 97%) marshes. In San Diego, Newport and Anaheim Bays, macrofaunal densities were generally higher in the created marshes (88 000 to 290 000 ind m(-2)) than in their natural counterparts (26 000 to 50 000 ind m(-2)). In the youngest system, Mission Bay, the reverse was true (natural: 113 000 vs created: 28 000 ind m-2). Similar species numbers were recorded from the created and adjacent natural marshes. Insects, especially chironomids, dolichopodids, and heleids, as well as the naidid oligochaete, Paranais litoralis, characterize early successional stages. Enchytraeid and tubificid oligochaetes reflect later succession evident in natural and older created marshes. Sediment organic matter (both combustible and below-ground plant biomass) was the environmental variable most commonly associated with densities of various macrofaunal taxa. These relationships were generally negative in the natural marshes and positive in the created marshes. Within-bay comparisons of macrofauna from natural Salicornia- vs Spartina-vegetated habitat in San Diego and Mission Bays revealed lower macrofaunal density (San Diego Bay only), proportionally fewer oligochaetes and more insects, and no differences in species richness in the Salicornia habitat. The oldest created Salicornia marsh (San Diego Bay) exhibited an assemblage intermediate in composition between those of the natural Salicornia- and Spartina-vegetated marshes. These results suggest: (a) faunal recovery following Salicornia marsh creation can require 10 or more years, (b) high macrofaunal variability among bays requires marsh creation reference site selection from within the same bay, and (c) Spartina-based research should not be used for Salicornia marsh management decisions. (C) 1999 Academic Press.

Talley, TS, Crooks JA, Levin LA.  2001.  Habitat utilization and alteration by the invasive burrowing isopod, Sphaeroma quoyanum, in California salt marshes. Marine Biology. 138:561-573.   10.1007/s002270000472   AbstractWebsite

In recent years the pace of exotic species introduction and invasion has accelerated, particularly in estuaries and wetlands. Species invasions may affect coastal ecosystems in many ways. Alteration of sedimentary environments, through structure formation and burrowing, has particularly dramatic effects on coastal habitats. This study examines modification of channel bank and marsh edge habitat by the burrowing Australasian isopod Sphaeroma quoyanum Milne Edwards, in created and natural salt marshes of San Diego Bay and San Francisco Bay. Abundance and distribution patterns of this isopod species, its relationships with habitat characteristics, and its effects on sediment properties and bank erosion were examined seasonally, and in several marsh microhabitats. Mean isopod densities were 1541 and 2936 individuals per 0.25 m(2) in San Francisco Bay, and 361 and 1153 individuals per 0.25 m(2) in San Diego Bay study sites during December and July 1998, respectively. This isopod forms dense, anastomosing burrow networks. S. quoyanum densities did not differ as a function of location within creeks or location in natural versus created marshes. Burrows, which are on average 6 mm wide and 2 cm long, were associated with firm sediments containing high detrital biomass. Although erosion is a natural process along salt marsh banks, enclosure experiments demonstrated that isopod activities can enhance sediment loss from banks. In areas infested with S. quoyanum, losses may exceed 100 cm of marsh edge per year. The effects of habitat alteration by this invading species are likely to increase in severity in the coastal zone as these ecosystems become degraded.

Sweetman, AK, Thurber AR, Smith CR, Levin LA, Mora C, Wei CL, Gooday AJ, Jones DOB, Rex M, Yasuhara M, Ingels J, Ruhl HA, Frieder CA, Danovaro R, Wurzberg L, Baco A, Grupe BM, Pasulka A, Meyer KS, Dunlop KM, Henry LA, Roberts JM.  2017.  Major impacts of climate change on deep-sea benthic ecosystems. Elementa-Science of the Anthropocene. 5:1-23.   10.1525/elementa.203   AbstractWebsite

The deep sea encompasses the largest ecosystems on Earth. Although poorly known, deep seafloor ecosystems provide services that are vitally important to the entire ocean and biosphere. Rising atmospheric greenhouse gases are bringing about significant changes in the environmental properties of the ocean realm in terms of water column oxygenation, temperature, pH and food supply, with concomitant impacts on deep-sea ecosystems. Projections suggest that abyssal (3000-6000 m) ocean temperatures could increase by 1 degrees C over the next 84 years, while abyssal seafloor habitats under areas of deep-water formation may experience reductions in water column oxygen concentrations by as much as 0.03 mL L-1 by 2100. Bathyal depths (200-3000 m) worldwide will undergo the most significant reductions in pH in all oceans by the year 2100 (0.29 to 0.37 pH units). O-2 concentrations will also decline in the bathyal NE Pacific and Southern Oceans, with losses up to 3.7% or more, especially at intermediate depths. Another important environmental parameter, the flux of particulate organic matter to the seafloor, is likely to decline significantly in most oceans, most notably in the abyssal and bathyal Indian Ocean where it is predicted to decrease by 40-55% by the end of the century. Unfortunately, how these major changes will affect deep-seafloor ecosystems is, in some cases, very poorly understood. In this paper, we provide a detailed overview of the impacts of these changing environmental parameters on deep-seafloor ecosystems that will most likely be seen by 2100 in continental margin, abyssal and polar settings. We also consider how these changes may combine with other anthropogenic stressors (e.g., fishing, mineral mining, oil and gas extraction) to further impact deep-seafloor ecosystems and discuss the possible societal implications.