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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.

Levin, LA, Boesch DF, Covich A, Dahm C, Erseus C, Ewel KC, Kneib RT, Moldenke A, Palmer MA, Snelgrove P, Strayer D, Weslawski JM.  2001.  The function of marine critical transition zones and the importance of sediment biodiversity. Ecosystems. 4:430-451.   10.1007/s10021-001-0021-4   AbstractWebsite

Estuaries and coastal wetlands are critical transition zones (CTZs) that link land, freshwater habitats, and the sea. CTZs provide essential ecological functions, including decomposition, nutrient cycling, and nutrient production, as well as regulation of fluxes of nutrients, water, particles, and organisms to and from land, rivers, and the ocean. Sediment-associated biota are integral to these functions. Functional groups considered essential to CTZ processes include heterotrophic bacteria and fungi, as well as many benthic invertebrates. Key invertebrate functions include shredding, which breaks down and recycles organic matter; suspension feeding, which collects and transports sediments across the sediment-water interface; and bioturbating, which moves sediment into or out of the seabed. In addition, macrophytes regulate many aspects of nutrient, particle, and organism dynamics above- and belowground. Animals moving within or through CTZs are vectors that transport nutrients and organic matter across terrestrial, freshwater, and marine interfaces. Significant threats to biodiversity within CTZs are posed by anthropogenic influences; eutrophication, nonnutrient pollutants, species invasions, overfishing, habitat alteration, and climate change affect species richness or composition in many coastal environments. Because biotic diversity in marine CTZ sediments is inherently low whereas their functional significance is great, shifts in diversity are likely to be particularly important. Species introductions (from invasion) or loss (from overfishing or habitat alteration) provide evidence that single-species changes can have overt, sweeping effects on CTZ structure and function. Certain species may be critically important to the maintenance of ecosystem functions in CTZs even though at present there is limited empirical evidence that the number of species in CTZ sediments is critical. We hypothesized that diversity is indeed important to ecosystem function in marine CTZs because high diversity maintains positive interactions among species (facilitation and mutualism), promoting stability and resistance to invasion or other forms of disturbance. The complexity of interactions among species and feedbacks with ecosystem functions suggests that comparative (mensurative) and manipulative approaches will be required to elucidate the role of diversity in sustaining CTZ functions.

Levin, LA.  1984.  Multiple patterns of development in Streblospio benedicti Webster (Spionidae) from three coasts of North America. Biological Bulletin. 166:494-508.   10.2307/1541157   AbstractWebsite

Streblospio benedicti Webster, a small tube-dwelling polychaete common in Pacific, Gulf of Mexico, and Atlantic estuaries of North America, exhibits both lecithotrophic and planktotrophic modes of larval development. In lecithotrophic forms females produce few (9-50) large ova (100-200 μm diam.). These develop in dorsal pouches into 9-12 setiger larvae, competent to settle at release. Females of planktotrophic forms produce large broods (100-548) of small ova (70-90 μm), brood larvae in dorsal pouches or beneath dorsal branchiae, and release 3-7 setiger larvae which bear long swimming setae and feed in the plankton for 1-5 weeks before settling. Lecithotrophy is reported for S. benedicti populations on all three coasts of N. America, planktotrophy from the Atlantic and Gulf coasts only. Reproductive differences observed in the field are maintained by laboratory cultures reared under constant (20°C) conditions, though individuals from planktotrophic and lecithotrophic populations are interfertile. Developmental variations observed in the field are believed to generate different patterns of dispersal, recruitment, population growth (r), and mortality. Poicilogony, the occurrence of multiple development modes, may account for the considerable success of S. benedicti in N. America.

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.

Levin, LA, Talley D, Thayer G.  1996.  Succession of macrobenthos in a created salt marsh. Marine Ecology-Progress Series. 141:67-82.   10.3354/meps141067   AbstractWebsite

Early succession of macrofauna was examined over several years in a created Spartina alterniflora marsh located on the Newport River Estuary, North Carolina, USA. Epifauna and infaunal community structure and composition were compared at 2 elevations in plots planted with S. alterniflora, plots left bare of vegetation and vegetated plots in a nearby natural S, alterniflora marsh. No significant successional differences were observed between vegetated and unvegetated sediments in the created marsh. The earliest stages of colonization involved recruitment by opportunistic estuarine polychaetes: Streblospio benedicti, Capitella spp, and Polydora cornuta. Capitella spp. dominated the macrofauna a month after marsh creation, but thereafter S. benedicti was the most abundant species. During the first few years, the artificial marsh retained early successional characteristics, with S, benedicti, Capitella spp. and turbellarians accounting for 75 to 95% of the total macrofauna. Fiddler crabs were common epifaunal colonists. After 4 yr, species richness increased and dominance by the early colonists diminished. Taxa lacking planktonic larvae and swimming adults were particularly slow to recover in the created marsh, but accounted for over 25% of the infauna by Year 4. Oligochaetes, which comprised over 50% of the fauna in the natural marsh, remained absent or rare in the artificial system throughout the study. Infaunal recovery appears to be more rapid in lower than upper marsh elevations. Although macrofaunal densities and species richness of sediments in the lower created marsh came to resemble those of the natural marsh within 6 mo, species composition and faunal feeding modes did not. These observations suggest there may be significant functional differences between young artificial marshes and older natural marshes. Consideration of the timing of marsh creation, marsh configuration, continuity with natural marshes, seeding of taxa with poor dispersal, and attention to species habitat requirements are recommended to accelerate infaunal colonization of created Spartina marshes.

Levin, LA, Mendoza GF, Konotchick T, Lee R.  2009.  Macrobenthos community structure and trophic relationships within active and inactive Pacific hydrothermal sediments. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:1632-1648.   10.1016/j.dsr2.2009.05.010   AbstractWebsite

Hydrothermal fluids passing through sediments create a habitat hypothesized to influence the community structure of infaunal macrobenthos. Here we characterize the density, biomass, species composition, diversity, distributions, lifestyle, and nutritional sources of macroinfauna in hydrothermal sediments in NE and SW Pacific settings, and draw comparisons in search of faunal attributes characteristic of this habitat. There is increasing likelihood that seafloor massive sulfide deposits, associated with active and inactive hydrothermal venting, will be mined commercially. This creates a growing imperative for a more thorough understanding of the structure, dynamics, and resilience of the associated sediment faunas, and has stimulated the research presented here. Macrobenthic assemblages were studied at Manus Basin (1430-1634 m, Papua New Guinea [PNG]) as a function of location (South Su vs. Solwara 1), and hydrothermal activity (active vs. inactive), and at Middle Valley (2406-2411 m, near Juan de Fuca Ridge) as a function of habitat (active clam bed, microbial mat, hot mud, inactive background sediment). The studies conducted in PNG formed part of the environmental impact assessment work for the Solwara 1 Project of Nautilus Minerals Niugini Limited. We hypothesized that hydrothermally active sites should support (a) higher densities and biomass, (b) greater dominance and lower diversity, (c) a higher fraction of deposit feeders, and (d) greater isotopic evidence for chemosynthetic food sources than inactive sites. Manus Basin macrofauna generally had low density (<1000ind.m(-2)) and low biomass (0.1-1.07gm(-2)), except for the South Su active site, which had higher density (3494ind.m(-2)) and biomass (11.94gm(-2)), greater dominance (R1D=76%), lower diversity and more spatial (between-core) homogeneity than the Solwara 1 and South Su inactive sites. Dominant taxa at Manus Basin were Spionidae (Prionospio sp.) in active sediments, and tanaids and deposit-feeding nuculanoid bivalves in active and inactive sediments. At Middle Valley, hot mud sediments supported few animals (1011 ind m(-2)) and low biomass (1.34g m(-2)), while active clam bed sediments supported a high-density (19,984indm(-2)), high-biomass (4.46gm(-2)), low-diversity assemblage comprised of largely orbiniid and syllid polychaetes. Microbial mat sediments had the most diverse assemblage (mainly orbiniid, syllid, dorvilleid, and ampharetid polychaetes) with intermediate densities (8191 ind m(-2)) and high biomass (4.23 g m(-2)). Fauna at both Manus Basin active sites had heavy delta(13)C signatures (-17 parts per thousand to -13 parts per thousand) indicative of chemosynthetic, TCA-cycle microbes at the base of the food chain. In contrast, photosynthesis and sulfide oxidation appear to fuel most of the fauna at Manus Basin inactive sites (delta(13)C = -29 parts per thousand to -20 parts per thousand) and Middle Valley active clam beds and microbial mats (delta(13)C = -36 parts per thousand to -20 parts per thousand). The two hydrothermal regions, located at opposite ends of the Pacific Ocean, supported different habitats, sharing few taxa at the generic or family level, but both exhibited elevated infaunal density and high dominance at selected sites. Subsurface-deposit feeding and bacterivory were prevalent feeding modes. Both the Manus Basin and Middle Valley assemblages exhibit significant within-region heterogeneity, apparently conferred by variations in hydrothermal activity and associaed biogenic habitats. (C) 2009 Elsevier Ltd. All rights reserved.

Levin, LA, Zhu J, Creed E.  1991.  The genetic basis of life history characters in a polychaete exhibiting planktotrophy and lecithotrophy. Evolution. 45:380-397.   10.2307/2409672   AbstractWebsite

The polychaete Streblospio benedicti is unusual in that several field populations consist of individuals that exhibit either planktotrophic or lecithotrophic larval development. Planktotrophy in this species involves production of many small ova that develop into feeding larvae with a two- to three-week planktonic period. Lecithotrophy involves production of fewer, larger ova that develop into nonfeeding larvae that are brooded longer and have a brief planktonic stage. Reciprocal matings were performed to investigate genetic variance components and the correlation structure of life-history traits associated with planktotrophy and lecithotrophy. Our objective was to better understand persistence of this developmental dichotomy in Streblospio benedicti, and among marine invertebrates in general. Substantial additive genetic variation (75-98% of total) was detected for the following characters at first reproduction: female length; position of the first gametogenic setiger and first brood pouch; ovum diameter; three traits related to fecundity (numbers of ova per ovary, larvae per brood pouch, and larvae per brood); median larval planktonic period and the presence of larval swimming setae; but not for total number of brood pouches; larval length; larval feeding; and larval survivorship. Based on the unusual geographic distribution of development modes in this species, we hypothesize that the developmental traits have evolved in allopatry and have only recently come into contact in North Carolina. The high additive contribution to variance observed for many traits may be inflated due to (a) nonrandom breeding in nature, and (b) examination of only one component of an age-structured population at one time. Nuclear interaction variance and maternal variance accounted for 84% of the total variation in larval survivorship. This observation supports other empirical studies and theoretical predictions that nonadditive components of variance will increase in importance in individual traits that are most closely tied to fitness. A network of life-history trait correlations was observed that defines distinct planktotrophic and lecithotrophic trait complexes. Negative genetic correlations were present between fecundity and egg size, between fecundity and position of the first gametes, and between larval survivorship and median planktonic period. Positive genetic correlations were detected between fecundity and female size at first reproduction and between planktonic period and the presence of swimming setae. Intergenerational product-moment correlations were negative for larval length and fecundity, planktonic period and egg size, female size and larval survivorship, and fecundity and larval survivorship. If the genetic correlation structure observed in the laboratory persists in the field, it may constrain responses of individual characters to directional selection, and indirectly perpetuate the dichotomies associated with planktotrophy and lecithotrophy.

Levin, LA, Gooday A.  2003.  The Deep Atlantic Ocean. Ecosystems of the deep oceans. ( Tyler PA, Ed.).:111-178., Amsterdam ; New York: Elsevier Abstract
Levin, LA, Caswell H, Depatra KD, Creed EL.  1987.  Demographic consequences of larval development mode: planktotrophy vs. lecithotrophy in Streblospio benedicti. Ecology. 68:1877-1886.   10.2307/1939879   AbstractWebsite

This paper examines the demographic consequences of planktotrophic and lecithotrophic development in an estuarine polychaete. Two strains of Streblospio benedicti (Spionidae) were reared in the laboratory from birth through death at 20⚬C and salinity 34 per mille. Survivorship and reproductive data were collected weekly and were used to construct life tables and population projection matrices for each development mode. Planktotrophic females reproduced earlier, and had higher fecundity and a shorter generation time than lecithotrophic females, but also exhibited higher mortality early in life. Despite the apparently opportunistic nature of the planktotrophic life history traits, the finite rate of increase (λ) in the lecithotrophic strain (1.319 wk-1) exceeded that of the planktotrophic strain (1.205 wk-1). Net reproductive rate (R0) was also higher for the lecithotrophs (93.4) than for the planktotrophs (17.6) Peak reproductive values were attained earlier in planktotrophs than in lecithotrophs. Sensitivity analyses indicate that λ is most sensitive to changes in larval and juvenile survivorship, and that the differences in λ were almost completely determined by life table differences during the first 15 wk of life. The potential population growth rates obtained in this study agree well with those estimated for other opportunistic polychaete species such as Capitella sp. I and Polydora ligni. Under uniform conditions the two strains of S. benedicti achieved similar growth rates with very different life history traits. We hypothesize that each combination of traits may be adaptive under different circumstances in the field.

Levin, LA, Gage JD, Martin C, Lamont PA.  2000.  Macrobenthic community structure within and beneath the oxygen minimum zone, NW Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:189-226.   10.1016/s0967-0645(99)00103-4   AbstractWebsite

Investigations of macrobenthos were carried out within and beneath the oxygen minimum zone (OMZ, < 0.5 ml l(-1)) during Fall 1994 on the Oman margin, NW Arabian Sea. Six stations (400, 700, 850, 1000, 1250 and 3400m) were characterized with respect to macrofaunal abundance, biomass, body size, taxonomic composition, diversity and lifestyles, and the relation of these parameters to environmental conditions. The OMZ (400-1000 m) was dominated by a dense (5818-19,183 ind m(-2)), soft-bodied assemblage consisting largely (86-99%) of surface-feeding polychaetes, Spionids and cirratulids dominated at the 400- and 700-m stations, paraonids and ampharetids at the 850- and 1000-m stations. Molluscs and most crustaceans were common only below the OMZ ( greater than or equal to 1250 m); a species of the amphipod Ampelisca was abundant within the OMZ, however. Both density and biomass were elevated within the OMZ relative to stations below but body size did not differ significantly among stations. The lower OMZ boundary (0.5 ml l(-1)) was not a zone of enhanced macrofaunal standing stock, as originally hypothesized. However, abundance maxima at 700-850m may reflect an oxygen threshold (0.15-0.20 ml l(-1)) above which macrofauna take advantage of organically enriched sediments. Incidence of burrowing and subsurface-deposit feeding increased below the OMZ, Species richness (E[S(100)]), diversity (H') and evenness (J') were lower and dominance (R1D) was higher within than beneath the OMZ. Within-station (between-boxcore) faunal heterogeneity increased markedly below the OMZ. Surface sediment pigment concentrations and oxygen together explained 96-99% of the variance in measures of E[S(100)], H' and J' across the transect; grain size and % TOC did not yield significant regressions. Pigments, assumed to reflect food availability and possibly oxygen effects on organic matter preservation, were negatively correlated with species richness and evenness, and positively correlated with dominance. The reverse was true for water depth. Macrobenthic patterns of calcification and lifestyle within the Oman margin OMZ (0.13-0.3 mi l(-1)) match the dysaerobic biofacies of paleo-environmental reconstruction models. (C) 1999 Elsevier Science Ltd. All rights reserved.

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

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

Levin, LA, Ziebis W, Mendoza GF, Bertics VJ, Washington T, Gonzalez J, Thurber AR, Ebbed B, Lee RW.  2013.  Ecological release and niche partitioning under stress: Lessons from dorvilleid polychaetes in sulfidic sediments at methane seeps. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 92:214-233.   10.1016/j.dsr2.2013.02.006   AbstractWebsite

Organisms inhabiting methane seep sediments are exposed to stress in the form of high levels of hydrogen sulfide, which result mainly from sulfate reduction coupled to anaerobic methane oxidation. Dorvilleidae (Polychaeta) have successfully invaded this ecosystem, and multiple species in divergent genetic clades co-occur at high densities. At methane seeps in the NE Pacific off California and Oregon, the genera Ophryotrocha, Parougia and Exallopus are especially well represented. To test the hypothesis that dorvilleid coexistence is facilitated by niche partitioning through sulfide tolerance and trophic patterns, we examined dorvilleid species-specific patterns of occurrence and nutrition at methane seeps off Eel R. [ER] on the Californian continental slope and at Hydrate Ridge [HR] on the Oregon continental slope, and in two habitats (clam bed and microbial mat) characterized by lower and higher hydrogen sulfide levels, respectively. Microelectrode measurements of hydrogen sulfide enabled characterization of environmental sulfide levels for species sampled in background sediment cores and in colonization trays. Dorvilleids tolerated H2S levels from 10 mu M to over 2.6 mM, with the majority of species inhabiting sediments with similar environmental H2S concentrations (median 85-100 mu M). Dorvilleid species richness was greater at HR than ER, but did not differ between clam bed and microbial mat habitats. Species distribution patterns reflected preferences for ER clam bed (lower sulfide levels), ER mat and HR clam bed (moderate sulfide levels), or HR mat (very high sulfide levels). Nutritional patterns, including trophic diversity and functional similarity, were examined using community stable isotope metrics based on delta N-15 and delta C-13. Within each region, dorvilleid species exhibited multiple trophic strategies. Co-existing congeners typically exhibited distinct isotope signatures, suggesting trophic partitioning. Trophic diversity and delta N-15 range for whole assemblages (measured by Total Hull Area and Standard Elliptical Area using species averages) and functional redundancy or species packing (measured as distance to nearest neighbor) among species and individuals were generally higher at ER, where sulfide levels were lower than at HR. In contrast, average trophic diversity among individuals within a species was greater at HR than ER. In colonization experiments involving agar-based manipulations of sulfide in tray sediments that mimicked clam bed and mat conditions, dorvilleids comprised 68% and 48% of colonists at ER and HR, respectively. Dorvilleid species richness was higher in trays that were initially more sulfidic. However, habitat exerted stronger influence on the composition of colonizing dorvilleids than did sulfide additions. In the NE Pacific, regional, habitat and vertical (down-core) variation in hydrogen sulfide creates complex environmental heterogeneity at methane seeps, promoting high diversity of stress-tolerant taxa such as dorvilleid polychaetes. (C) 2013 Elsevier Ltd. All rights reserved.

Levin, LA, Bridges TS.  1995.  Pattern and diversity in reproduction and development. Ecology of marine invertebrate larvae. ( McEdward LR, Ed.).:1-48., Boca Raton: CRC Press Abstract
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, Childers SE, Smith CR.  1991.  Epibenthic, agglutinating foraminiferans in the Santa Catalina Basin and their response to disturbance. Deep-Sea Research Part a-Oceanographic Research Papers. 38:465-483.   10.1016/0198-0149(91)90047-j   AbstractWebsite

There are five common species of large (0.5-6 cm long) epibenthic, agglutinating foraminiferans in the Santa Catalina Basin (1200-1350 m). This paper describes their basic ecology and response to mound disturbance. Combined, the five species attain mean densities of 200-300 individuals per m2 and their protoplasm has an average biomass of 199.5 mg m-2. Individual species occur at densities ranging from 7 to 100 m-2, and each species has a different population size structure. Protoplasm comprises < 2% of test volumes. Analysis of excess Th-234 revealed no indication of particle sequestering within tests, and acridine orange direct counts of bacteria provided no evidence of microbial gardening or enhancement associated with tests. Twenty-five per cent of tests examined had metazoan associates; approximately half of these were polychaetes. Experiments were carried out to investigate the response of the epibenthic foraminiferal assemblage to disturbance from large, biogenic mounds, a common feature on the Santa Catalina Basin floor. Three branched forms, Pelosina cf. arborescens, P. cf. cylindrica and a mud-walled astrorhizinid, were most abundant on background sediments, less common on natural mounds and absent from artificially-created mounds exposed for 10.5 months. Two spherical species, Oryctoderma sp. and a different mud-walled astrorhizinid, were present at similar densities on artificial mounds (9.5-10.5 months old), natural mounds and undisturbed sediments, but Oryctoderma sp. attained largest sizes on mounds. These two species appear to be opportunistic taxa that can colonize and grow rapidly on mound sediments. This study suggests that disturbance, in this case that by sediment mound builders, is an important source of spatial heterogeneity in deep-water foraminiferal communities. Where sediment mounds occur, foraminiferal assemblages will experience disequilibrium dynamics.

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

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

Levin, LA, Creed EL.  1986.  Effect of temperature and food availability on reproductive responses of Streblospio benedicti (Polychaeta: Spionidae) with planktotrophic or lecithotrophic development. Marine Biology. 92:103-113.   10.1007/bf00392752   AbstractWebsite

Streblospio benedicti (Webster) from Tar Landing North Carolina (NC), USA with either planktotrophic or lecithotrophic development were reared under two food levels and three temperature regimes (two mimicking seasonal cycles in NC and one at constant 20°C). During the eight-month experiment no females switched reproductive mode and no significant differences in survivorship or reproductive activity were observed between reproductive types. However, reproductive activity and fecundity-related parameters were subject to influence by food and temperature. Survivorship, body size, and larval production was greater in winter-spring than summer-fall regimes. Higher food levels produced increased survivorship, reproductive activity and egg production in adults with lecithotrophic development but no change in those with planktotrophic development. Body size, egg size, egg number, numbers of larvae per brood pouch, and brood size were strongly correlated in female S. benedicti and most correlation coefficients were similar (or identical) in individuals having planktotrophic and lecithotrophic development. A comparison of egg size and brood size in females from Tar Landing suggests that individuals with the two forms of development package offspring differently but expend approximately equivalent reproductive effort. Larval trophic mode is best viewed as a genetic polymorphism in S. benedicti. Individuals with planktotrophic and lecithotrophic development exhibit similar reproductive responses to environmental variation and there is no evidence for speciation.

Levin, LA, Mengerink K, Gjerde KM, Rowden AA, Vandover CL, Clark MR, Ramirez-Llodra E, Currie B, Smith CR, Sato KN, Gallo N, Sweetman AK, Lily H, Armstrong CW, Brider J.  2016.  Defining "serious harm" to the marine environment in the context of deep-seabed mining. Marine Policy. 74:245-259.   10.1016/j.marpol.2016.09.032   AbstractWebsite

Increasing interest in deep-seabed mining has raised many questions surrounding its potential environmental impacts and how to assess the impacts' significance. Under the United Nations Convention on the Law of the Sea (UNCLOS), the International Seabed Authority (ISA) is charged with ensuring effective protection of the marine environment as part of its responsibilities for managing mining in seabed areas beyond national jurisdiction (the Area) on behalf of humankind. This paper examines the international legal context for protection of the marine environment and defining the significant adverse change that can cause "serious harm", a term used in the ISA Mining Code to indicate a level of harm that strong actions must be taken to avoid. It examines the thresholds and indicators that can reflect significant adverse change and considers the specific vulnerability of the four ecosystems associated with the minerals targeted for mining: (1) manganese (polymetallic) nodules, (2) seafloor massive (polymetallic) sulphides, (3) cobalt-rich (polymetallic) crusts and (4) phosphorites. The distributions and ecological setting, probable mining approaches and the potential environmental impacts of mining are examined for abyssal polymetallic nodule provinces, hydrothermal vents, seamounts and phosphorite-rich continental margins. Discussion focuses on the special features of the marine environment that affect the significance of the predicted environmental impacts and suggests actions that will advance understanding of these impacts.

Levin, LA, Gage JD.  1998.  Relationships between oxygen, organic matter and the diversity of bathyal macrofauna. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 45:129-163.   10.1016/s0967-0645(97)00085-4   AbstractWebsite

The relationships of environmental factors with measures of macrobenthic community diversity were examined for the total fauna, and for polychaetes only, from 40 bathyal stations in the North Atlantic, eastern Pacific and Indian Oceans (154-3400 m). Stepwise multiple regression revealed that depth, latitude, sediment organic-carbon content and bottom-water oxygen concentration are significant factors that together explained 52-87% of the variation in macrobenthic species richness (E[s(100)]), the Shannon-Wiener index (H'), dominance (D), and evenness (J'). Percent sand and percent clay were not significant factors. After removal of depth and latitudinal effects, oxygen and organic-carbon concentrations combined accounted for 47, 67, 52 and 32% of residual variation in macrobenthic E(s(100)), H', D, and J', respectively. Organic carbon exhibited a stronger relationship than oxygen to measures of community evenness, and appeared to have more explanatory power for polychaetes than total macrobenthos. When only stations with oxygen < 1mll(-1) were considered, oxygen concentration became the dominant parameter after depth. Results suggest existence of an oxygen threshold ( < 0.45 mi l(-1)), above which oxygen effects on macrobenthic diversity are minor relative to organic matter influence, but below which oxygen becomes a critical factor. Our regression results lead us to hypothesize that for bathyal faunas, oxygen at low concentrations has more influence on species richness, while organic carbon regulates the distribution of individuals among species (community evenness). Examination of rarefaction curves for Indo-Pacific stations reveals that total macrobenthos, polychaetes, crustaceans and molluscs all exhibit reduced species richness within oxygen minimum zones (OMZs). However, representation under conditions of hypoxia varies among taxa, with polychaetes being most tolerant. Molluscs and crustaceans often (but not always) exhibit few individuals and species in OMZs, and sometimes disappear altogether, contributing to reduced macrobenthic diversity and elevated dominance in these settings. The linear negative relationship observed between bathyal species richness and sediment organic-carbon content (used here as a proxy for food availability) may represent the right side (more productive half) of the hump-shaped, diversity-productivity curve reported in other systems. These analyses suggest then are potentially strong influences of organic matter and oxygen on the diversity and composition of bathyal macrobenthos, especially in the Indo-Pacific Ocean. (C) 1998 Elsevier Science Ltd. All rights reserved.

Levin, LA, Orphan VJ, Rouse GW, Rathburn AE, Ussler W, Cook GS, Goffredi SK, Perez EM, Waren A, Grupe BM, Chadwick G, Strickrott B.  2012.  A hydrothermal seep on the Costa Rica margin: middle ground in a continuum of reducing ecosystems. Proceedings of the Royal Society B-Biological Sciences. 279:2580-2588.   10.1098/rspb.2012.0205   AbstractWebsite

Upon their initial discovery, hydrothermal vents and methane seeps were considered to be related but distinct ecosystems, with different distributions, geomorphology, temperatures, geochemical properties and mostly different species. However, subsequently discovered vents and seep systems have blurred this distinction. Here, we report on a composite, hydrothermal seep ecosystem at a subducting seamount on the convergent Costa Rica margin that represents an intermediate between vent and seep ecosystems. Diffuse flow of shimmering, warm fluids with high methane concentrations supports a mixture of microbes, animal species, assemblages and trophic pathways with vent and seep affinities. Their coexistence reinforces the continuity of reducing environments and exemplifies a setting conducive to interactive evolution of vent and seep biota.

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.  2006.  Recent progress in understanding larval dispersal: new directions and digressions. Integrative and Comparative Biology. 46:282-297.   10.1093/icb/024   AbstractWebsite

Larvae have been difficult to study because their small size limits our ability to understand their behavior and the conditions they experience. Questions about larval transport focus largely on (a) where they go [dispersal] and (b) where they come from [connectivity]. Mechanisms of transport have been intensively studied in recent decades. As our ability to identify larval sources develops, the consequences of connectivity are garnering more consideration. Attention to transport and connectivity issues has increased dramatically in the past decade, fueled by changing motivations that now include management of fisheries resources, understanding of the spread of invasive species, conservation through the design of marine reserves, and prediction of climate-change effects. Current progress involves both technological advances and the integration of disciplines and approaches. This review focuses on insights gained from physical modeling, chemical tracking, and genetic approaches. I consider how new findings are motivating paradigm shifts concerning (1) life-history consequences; (2) the openness of marine populations, self-recruitment, and population connectivity; (3) the role of behavior; and (4) the significance of variability in space and time. A challenge for the future will be to integrate methods that address dispersal on short (intragenerational) timescales such as elemental fingerprinting and numerical simulations with those that reflect longer timescales such as gene flow estimates and demographic modeling. Recognition and treatment of the continuum between ecological and evolutionary timescales will be necessary to advance the mechanistic understanding of larval and population dynamics.

Levin, LA.  1990.  A review of methods for labeling and tracking marine invertebrate larvae. Ophelia. 32:115-144.   10.1080/00785236.1990.10422028   AbstractWebsite

Methods for marking invertebrate larvae for use in dispersal studies include staining, tagging with calcium replacements, radiotracers and rare elements, and use of genetic, morphological, and parasite markers. The mark, release and recapture method provides a valuable approach to the study of larval movements but has been attempted only rarely, in part because of difficulties with larval recovery. Methodological and instrumentational advances may improve the feasibility of release and recovery efforts. Additional approaches to tracking larvae include visual tracking, use of isolated or point sources, Lagrangian and Eulerian methods, energetic calculations, hydro-graphic modeling and simulations. Recent emphases on physical transport mechanisms, and on the interrelationship of behavior and passive transport can be considered in the context of tracking methods. Newly-developed and recently-conceived techniques offer promise of considerable advance in our understanding of larval dispersal phenomena.

Levin, LA, Etter RJ, Rex MA, Gooday AJ, Smith CR, Pineda J, Stuart CT, Hessler RR, Pawson D.  2001.  Environmental influences on regional deep-sea species diversity. Annual Review of Ecology and Systematics. 32:51-93.   10.1146/annurev.ecolsys.32.081501.114002   AbstractWebsite

Most of our knowledge of biodiversity and its causes in the deep-sea benthos derives from regional-scale sampling studies of the macrofauna. Improved sampling methods and the expansion of investigations into a wide variety of habitats have revolutionized our understanding of the deep sea. Local species diversity shows clear geographic variation on spatial scales of 100-1000 km. Recent sampling programs have revealed unexpected complexity in community structure at the landscape level that is associated with large-scale oceanographic processes and their environmental consequences. We review the relationships between variation in local species diversity and the regional-scale phenomena of boundary constraints, gradients of productivity, sediment heterogeneity, oxygen availability, hydrodynamic regimes, and catastrophic physical disturbance. We present a conceptual model of how these interdependent environmental factors shape regional-scale variation in local diversity. Local communities in the deep sea may be composed of species that exist as metapopulations whose regional distribution depends on a balance among global-scale, landscape-scale, and small-scale dynamics. Environmental gradients may form geographic patterns of diversity by influencing local processes such as predation, resource partitioning, competitive exclusion, and facilitation that determine species coexistence. The measurement of deep-sea species diversity remains a vital issue in comparing geographic patterns and evaluating their potential causes. Recent assessments of diversity using species accumulation curves with randomly pooled samples confirm the often-disputed claim that the deep sea supports higher diversity than the continental shelf. However, more intensive quantitative sampling is required to fully characterize the diversity of deep-sea sediments, the most extensive habitat on Earth. Once considered to be constant, spatially uniform, and isolated, deep-sea sediments are now recognized as a dynamic, richly textured environment that is inextricably linked to the global biosphere. Regional studies of the last two decades provide the empirical background necessary to formulate and test specific hypotheses of causality by controlled sampling designs and experimental approaches.

Levin, LA, Smith CR.  1984.  Response of background fauna to disturbance and enrichment in the deep sea: a sediment tray experiment. Deep-Sea Research Part a-Oceanographic Research Papers. 31:1277-&.   10.1016/0198-0149(84)90001-3   AbstractWebsite

Free-vehicle sediment trays were deployed on the floor of the Santa Catalina Basin (1300 m) to study the response of deep-sea infauna to defaunation and algal enrichment. We recovered three trays that had been filled with frozen basin sediment: one otherwise untreated, one enriched with 20 g of powdered Macrocystis pyrifera (kelp) and containing oxidized sediment, and one kelp-enriched and anoxic. After 4.7 months on the basin floor, macrofaunal density in the unenriched tray was 10% () of that in the surrounding sea floor. Most colonists belonged to species dominant in the background basin community. Juveniles and mature individuals were present, suggesting short maturation times or post-larval dispersal ability in some species. The kelp-enriched (oxidized) tray contained a single macrofaunal mite (Arachnida:Acarina), suggesting avoidance of kelp-enriched sediment by available colonists. The anoxic, kelp-enriched tray contained two dorvilleid polychaetes apparently adapted to high sulphide environments.As in other deep-sea studies, we obtained slower colonization of sediment trays than in shallow water experiments. The primary tray respondents, however, were dominants of the background community, in contrast to previous deep-sea experiments. The findings are consistent with the hypothesis that disturbance is important to the ecology of the dominant species in the Santa Catalina Basin.