The Experts below are selected from a list of 2409 Experts worldwide ranked by ideXlab platform

Craig R Smith - One of the best experts on this subject based on the ideXlab platform.

  • intense deposition and rapid processing of seafloor Phytodetritus in a glaciomarine fjord andvord bay antarctica
    Progress in Oceanography, 2020
    Co-Authors: Amanda F Ziegler, M Cape, Oyvind Lundesgaard, Craig R Smith
    Abstract:

    Abstract The West Antarctic Peninsula (WAP) region encompasses numerous fjords known to be hotspots of benthic biodiversity and biomass. These ecosystems are undergoing rapid climate warming and oceanographic change; consequent glacial melt and retreat may dramatically alter benthic communities and ecosystem functions in WAP fjords. In addition, there is extreme variability in seasonal productivity and phytodetrital food input to the deep shelf benthos of the WAP. Here we document the flux and utilization of Phytodetritus at 530 m depth in Andvord Bay, a WAP glaciomarine fjord, using seafloor time-lapse images spanning a 10-month period, from December 2015 to September 2016. To explore the relationship between sea-surface conditions and detrital export, we developed a color-based method to quantify seafloor Phytodetritus cover in time-lapse images, and correlated Phytodetritus cover with sea-ice cover and surface wind speed. During the most rapid period of Phytodetritus accumulation in early January 2016, approximately 3 cm of Phytodetritus was deposited on the fjord floor over six days, representing a large input of organic carbon to the benthos. The timing of this rapid export event was not related to overlying wind conditions and occurred when the fjord was ice-free. To assess the response of the megafaunal community, we measured fecal-pellet production by the dominant surface deposit-feeder, the ampharetid polychaete Amythas membranifera. The deposit-feeding rate of A. membranifera increased substantially during high seafloor Phytodetritus cover and returned to background levels for the rest of the autumn and winter. Ampharetids and mobile megafauna were observed to feed throughout the entire time-series, including beneath winter sea ice, suggesting that the delivery of Phytodetritus from surface phytoplankton blooms in spring/summer sustains these abundant populations year-round with a sediment food bank. A. membranifera can reach densities of >37 m−2 and, as a population, processes a volume equivalent to the top 1.05 cm of sediment annually. The maximum individual feeding rates measured are comparable to some temperate intertidal deposit feeders. Nonetheless, Phytodetritus on 31–73% of the seafloor was consumed by macrofauna or microbial populations not visible in time-lapse photographs, suggesting that recently deposited Phytodetritus is processed primarily by these smaller size classes. This study demonstrates the seasonal coupling and subsequent decoupling of detritivore activity in response to a massive detrital deposition event in a deep, subpolar WAP fjord. This work indicates that both megafaunal deposit feeders and smaller size classes play important roles in processing labile organic matter in WAP fjord ecosystems.

  • Seasonal dynamics of megafauna on the deep West Antarctic Peninsula shelf in response to variable phytodetrital influx.
    Royal Society open science, 2014
    Co-Authors: Paulo Y. G. Sumida, Craig R Smith, Angelo F. Bernardino, Paulo S. Polito, D. R. Vieira
    Abstract:

    The deep West Antarctic Peninsula (WAP) shelf is characterized by intense deposition of Phytodetritus during spring/summer months, while very little food material reaches the seafloor during winter. The response of the shelf benthic megafauna to this highly variable food supply is still poorly understood. In order to characterize the deposition of Phytodetritus and the megabenthic community response, we deployed a seafloor time-lapse camera at approximately 590 m depth on the mid WAP shelf west of Anvers Island for 15 months. Seafloor photographs were taken at intervals of 12 or 24 h nearly continuously from 9 December 1999 (austral winter) to 20 March 2001 (summer) and analysed for Phytodetritus deposition and megafaunal dynamics. Seafloor images indicated a marked seasonal arrival of greenish Phytodetritus, with large interannual and seasonal variability in the coverage of depositing phytodetrital particles. The surface-deposit-feeding elasipod holothurians Protelpidia murrayi and Peniagone vignoni dominated the epibenthic megafauna throughout the year, frequently constituting more than 80% of the megafaunal abundance, attaining total densities of up to 2.4 individuals m−2. Elasipod abundances were significantly higher in summer than winter. During summer periods of high phytodetrital flux, Pr. murrayi produced faecal casts at higher rates, indicating intensified population-level feeding activity. In March–June 2000, faecal casts lasted longest, suggesting lower horizontal bioturbation activity during autumn–winter. Our data indicate that the Pr. murrayi population increases its feeding rates in response to increasing amounts and/or lability of organic matter on the sediment surface. Assuming that this species feeds on the top millimetre of the sediment, we estimate that, during periods of high phytodetrital flux, the Pr. murrayi population reworks one square metre of sediment surface in approximately 287 days. We suggest that Pr. murrayi is an important species for organic-carbon recycling on the deep WAP shelf, controlling the availability of deposited labile Phytodetritus to the broader shelf benthic community.

  • trophic structure on the west antarctic peninsula shelf detritivory and benthic inertia revealed by δ13c and δ15n analysis
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2008
    Co-Authors: Sarah L. Mincks, Craig R Smith, Rachel M. Jeffreys, Paulo Y. G. Sumida
    Abstract:

    Abstract Summer bloom-derived Phytodetritus settles rapidly to the seafloor on the West Antarctic Peninsula (WAP) continental shelf, where it appears to degrade relatively slowly, forming a sediment “food bank” for benthic detritivores. We used stable carbon and nitrogen isotopes to examine sources and sinks of particulate organic material (POM) reaching the WAP shelf benthos (550–625 m depths), and to explore trophic linkages among the most abundant benthic megafauna. We measured δ 13 C and δ 15 N values in major megafaunal taxa ( n =26) and potential food sources, including suspended and sinking POM, ice algae, sediment organic carbon, Phytodetritus, and macrofaunal polychaetes. The range in δ 13 C values (>14‰) of suspended POM was considerably broader than in sedimentary POC, where little temporal variability in stable isotope signatures was observed. While benthic megafauna also exhibited a broad range of δ 13 C values, organic carbon entering the benthic food web appeared to be derived primarily from phytoplankton production, with little input from ice algae. One group of organisms, primarily deposit-feeders, appeared to rely on fresh Phytodetritus recovered from the sediments, and sediment organic material that had been reworked by sediment microbes. A second group of animals, including many mobile invertebrate and fish predators, appeared to utilize epibenthic or pelagic food resources such as zooplankton. One surface-deposit-feeding holothurian ( Protelpidia murrayi ) exhibited seasonal variability in stable isotope values of body tissue, while other surface- and subsurface-deposit-feeders showed no evidence of seasonal variability in food source or trophic position. Detritus from phytoplankton blooms appears to be the primary source of organic material for the detritivorous benthos; however, seasonal variability in the supply of this material is not mirrored in the sediments, and only to a minor degree in the benthic fauna. This pattern suggests substantial inertia in benthic–pelagic coupling, whereby the sediment ecosystem integrates long-term variability in production processes in the water column above.

  • The FOODBANCS project: Introduction and sinking fluxes of organic carbon, chlorophyll-a and Phytodetritus on the western Antarctic Peninsula continental shelf
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2008
    Co-Authors: Craig R Smith, Sarah L. Mincks, David J. Demaster
    Abstract:

    Abstract The impact of the highly seasonal Antarctic primary production cycle on shelf benthic ecosystems remains poorly evaluated. Here we describe a times-series research project on the West Antarctic Peninsula (WAP) shelf designed to evaluate the seafloor deposition, and subsequent ecological and biogeochemical impacts, of the summer phytoplankton bloom along a transect crossing the Antarctic shelf near Anvers Island. During this project, entitled Food for Benthos on the Antarctic Continental Shelf (FOODBANCS), we deployed replicate sediment traps 150–170 m above the seafloor (total water-column depth of 590 m) on the central shelf from December 1999 to March 2001, recovering trap samples every 3–4 months. In addition, we used a seafloor time-lapse camera system, as well as video surveys conducted at 3–4 months intervals, to monitor the presence and accumulation of Phytodetritus at the sediment–water interface. The fluxes of particulate organic carbon and chlorophyll-a into sediment traps (binned over 3–4 month intervals) showed patterns consistent with seasonal variability, with average summer fluxes during the first year exceeding winter fluxes by a factor of ∼2–3. However, inter-annual variability in summer fluxes was even greater than seasonal variability, with 4–10-fold differences in the flux of organic carbon and chlorophyll-a between the summer seasons of 1999–2000 and 2000–2001. Phytodetrital accumulation at the shelf floor also exhibited intense inter-annual variability, with no visible Phytodetritus from essentially December 1999 to November 2000, followed by pulsed accumulation of 1–2 cm of Phytodetritus over a ∼30,000 km2 shelf area by March 2001. Comparisons with other studies suggest that the levels of inter-annual variability we observed are typical of the Antarctic shelf over decadal time scales. We conclude that fluxes of particulate organic carbon, chlorophyll-a and Phytodetritus to WAP-shelf sediments vary intensely on seasonal to inter-annual time scales, yielding dramatic temporal variability in the flux of food for detritivores to the Antarctic shelf floor.

  • Selective feeding by benthic foraminifera on Phytodetritus on the western Antarctic Peninsula shelf: evidence from fatty acid biomarker analysis
    Marine Ecology Progress Series, 2003
    Co-Authors: Stephanie B. Suhr, Andrew J. Gooday, David W. Pond, Craig R Smith
    Abstract:

    This study presents the first direct evidence, based on biochemical analysis of fresh material, that certain benthic foraminifera feed selectively on specific components of seasonally deposited Phytodetritus in their natural environment. Three abundant species of benthic foramini- fera, the calcareous species Globocassidulina subglobosa and Quinqueloculina seminula and the agglutinated species Thurammina albicans, collected after the deposition of phytoplankton bloom material at a shelf site (560 m water depth) west of the Antarctic Peninsula in March 2001, showed significant differences in their fatty acid profiles compared to the surrounding Phytodetritus. Fur- thermore, the 2 calcareous species contained significantly higher amounts of polyunsaturated fatty acids (PUFAs) than were found in their presumptive phytodetrital food source, indicating that the foraminifera discriminate between, and selectively feed on, the different components of the deposited material. Possible implications for the benthic food web are discussed.

Jefferson T Turner - One of the best experts on this subject based on the ideXlab platform.

  • zooplankton fecal pellets marine snow Phytodetritus and the ocean s biological pump
    Progress in Oceanography, 2015
    Co-Authors: Jefferson T Turner
    Abstract:

    Abstract The “biological pump” is the process by which photosynthetically-produced organic matter in the ocean descends from the surface layer to depth by a combination of sinking particles, advection or vertical mixing of dissolved organic matter, and transport by animals. Particulate organic matter that is exported downward from the euphotic zone is composed of combinations of fecal pellets from zooplankton and fish, organic aggregates known as “marine snow” and Phytodetritus from sinking phytoplankton. Previous reviews by Turner and Ferrante (1979) and Turner (2002) focused on publications that appeared through late 2001. Since that time, studies of the biological pump have continued, and there have been >300 papers on vertical export flux using sediment traps, large-volume filtration systems and other techniques from throughout the global ocean. This review will focus primarily on recent studies that have appeared since 2001. Major topics covered in this review are (1) an overview of the biological pump, and its efficiency and variability, and the role of dissolved organic carbon in the biological pump; (2) zooplankton fecal pellets, including the contribution of zooplankton fecal pellets to export flux, epipelagic retention of zooplankton fecal pellets due to zooplankton activities, zooplankton vertical migration and fecal pellet repackaging, microbial ecology of fecal pellets, sinking velocities of fecal pellets and aggregates, ballasting of sinking particles by mineral contents, phytoplankton cysts, intact cells and harmful algae toxins in fecal pellets, importance of fecal pellets from various types of zooplankton, and the role of zooplankton fecal pellets in picoplankton export; (3) marine snow, including the origins, abundance, and distributions of marine snow, particles and organisms associated with marine snow, consumption and fragmentation of marine snow by animals, pathogens associated with marine snow; (4) Phytodetritus, including pulsed export of Phytodetritus, Phytodetritus from Phaeocystis spp., picoplankton in Phytodetritus, the summer export pulse (SEP) of Phytodetritus in the subtropical North Pacific, benthic community responses to Phytodetritus; (5) other components of the biological pump, including fish fecal pellets and fish-mediated export, sinking carcasses of animals and macrophytes, feces from marine mammals, transparent exopolymer particles (TEP); (6) the biological pump and climate, including origins of the biological pump, the biological pump and glacial/interglacial cycles, the biological pump and contemporary climate variations, and the biological pump and anthropogenic climate change. The review concludes with potential future modifications in the biological pump due to climate change.

  • Zooplankton fecal pellets, marine snow, Phytodetritus and the ocean’s biological pump
    Progress in Oceanography, 2015
    Co-Authors: Jefferson T Turner
    Abstract:

    Abstract The “biological pump” is the process by which photosynthetically-produced organic matter in the ocean descends from the surface layer to depth by a combination of sinking particles, advection or vertical mixing of dissolved organic matter, and transport by animals. Particulate organic matter that is exported downward from the euphotic zone is composed of combinations of fecal pellets from zooplankton and fish, organic aggregates known as “marine snow” and Phytodetritus from sinking phytoplankton. Previous reviews by Turner and Ferrante (1979) and Turner (2002) focused on publications that appeared through late 2001. Since that time, studies of the biological pump have continued, and there have been >300 papers on vertical export flux using sediment traps, large-volume filtration systems and other techniques from throughout the global ocean. This review will focus primarily on recent studies that have appeared since 2001. Major topics covered in this review are (1) an overview of the biological pump, and its efficiency and variability, and the role of dissolved organic carbon in the biological pump; (2) zooplankton fecal pellets, including the contribution of zooplankton fecal pellets to export flux, epipelagic retention of zooplankton fecal pellets due to zooplankton activities, zooplankton vertical migration and fecal pellet repackaging, microbial ecology of fecal pellets, sinking velocities of fecal pellets and aggregates, ballasting of sinking particles by mineral contents, phytoplankton cysts, intact cells and harmful algae toxins in fecal pellets, importance of fecal pellets from various types of zooplankton, and the role of zooplankton fecal pellets in picoplankton export; (3) marine snow, including the origins, abundance, and distributions of marine snow, particles and organisms associated with marine snow, consumption and fragmentation of marine snow by animals, pathogens associated with marine snow; (4) Phytodetritus, including pulsed export of Phytodetritus, Phytodetritus from Phaeocystis spp., picoplankton in Phytodetritus, the summer export pulse (SEP) of Phytodetritus in the subtropical North Pacific, benthic community responses to Phytodetritus; (5) other components of the biological pump, including fish fecal pellets and fish-mediated export, sinking carcasses of animals and macrophytes, feces from marine mammals, transparent exopolymer particles (TEP); (6) the biological pump and climate, including origins of the biological pump, the biological pump and glacial/interglacial cycles, the biological pump and contemporary climate variations, and the biological pump and anthropogenic climate change. The review concludes with potential future modifications in the biological pump due to climate change.

Ursula Witte - One of the best experts on this subject based on the ideXlab platform.

  • Carbon and Nitrogen Uptake of Calcareous Benthic Foraminifera along a Depth-Related Oxygen Gradient in the OMZ of the Arabian Sea
    Frontiers in microbiology, 2016
    Co-Authors: Annekatrin J. Enge, Julia Wukovits, Wolfgang Wanek, Margarete Watzka, Ursula Witte, William Ross Hunter, Petra Heinz
    Abstract:

    Foraminifera are an important faunal element of the benthos in oxygen-depleted settings such as Oxygen Minimum Zones (OMZs) where they can play a relevant role in the processing of Phytodetritus. We investigated the uptake of Phytodetritus (labeled with 13C and 15N) by cal-careous foraminifera in the 0-1 cm sediment horizon under different oxygen concentrations within the OMZ in the eastern Arabian Sea. The in situ tracer experiments were carried out along a depth transect on the Indian margin over a period of 4 to 10 days. The uptake of phy-todetrital carbon within 4 days by all investigated species shows that Phytodetritus is a rele-vant food source for foraminifera in OMZ sediments. The decrease of total carbon uptake from 540 to 1100 m suggests a higher demand for carbon by species in the low-oxygen core region of the OMZ or less food competition with macrofauna. Especially Uvigerinids showed high uptake of phytodetrital carbon at the lowest oxygenated site. Variation in the ratio of phytodetrital carbon to nitrogen between species and sites indicates that foraminiferal carbon and nitrogen use can be decoupled and different nutritional demands are found between spe-cies. Lower ratio of phytodetrital carbon and nitrogen at 540 m could hint for greater demand or storage of food-based nitrogen, ingestion or hosting of bacteria under almost anoxic condi-tions. Shifts in the foraminiferal assemblage structure (controlled by oxygen or food availabil-ity) and in the presence of other benthic organisms account for observed changes in the pro-cessing of Phytodetritus in the different OMZ habitats. Foraminifera dominate the short-term processing of Phytodetritus in the OMZ core but are less important in the lower OMZ bounda-ry region of the Indian margin as biological interactions and species distribution of foraminif-era change with depth and oxygen levels.

  • Sediment community responses to marine vs. terrigenous organic matter in a submarine canyon
    Biogeosciences, 2013
    Co-Authors: William Ross Hunter, Alan J. Jamieson, Veerle A.i. Huvenne, Ursula Witte
    Abstract:

    The Whittard Canyon is a branching submarine canyon on the Celtic continental margin, which may act as a conduit for sediment and organic matter (OM) transport from the European continental slope to the abyssal sea floor. In situ stable-isotope labelling experiments were conducted in the eastern and western branches of the Whittard Canyon, testing short-term (3–7 days) responses of sediment communities to deposition of nitrogen-rich marine ( Thalassiosira weissflogii ) and nitrogen-poor terrigenous ( Triticum aestivum ) Phytodetritus. 13 C and 15 N labels were traced into faunal biomass and bulk sediments, and the 13 C label traced into bacterial polar lipid fatty acids (PLFAs). Isotopic labels penetrated to 5 cm sediment depth, with no differences between stations or experimental treatments (substrate or time). Macrofaunal assemblage structure differed between the eastern and western canyon branches. Following deposition of marine Phytodetritus, no changes in macrofaunal feeding activity were observed between the eastern and western branches, with little change between 3 and 7 days. Macrofaunal C and N uptake was substantially lower following deposition of terrigenous Phytodetritus with feeding activity governed by a strong N demand. Bacterial C uptake was greatest in the western branch of the Whittard Canyon, but feeding activity decreased between 3 and 7 days. Bacterial processing of marine and terrigenous OM were similar to the macrofauna in surficial (0–1 cm) sediments. However, in deeper sediments bacteria utilised greater proportions of terrigenous OM. Bacterial biomass decreased following Phytodetritus deposition and was negatively correlated to macrofaunal feeding activity. Consequently, this study suggests that macrofaunal–bacterial interactions influence benthic C cycling in the Whittard Canyon, resulting in differential fates for marine and terrigenous OM.

  • Food quality determines sediment community responses to marine vs. terrigenous organic matter in a submarine canyon
    2012
    Co-Authors: William Ross Hunter, Alan J. Jamieson, Veerle A.i. Huvenne, Ursula Witte
    Abstract:

    Abstract. The Whittard canyon is a branching submarine canyon on the Celtic continental margin, which may act as a conduit for sediment and organic matter (OM) transport from the European continental slope to the abyssal sea floor. In situ stable-isotope labelling experiments were conducted in the eastern and western branches of the Whittard canyon testing short term (3–7 day) responses of sediment communities to deposition of nitrogen-rich marine (Thallassiosira weissflogii) and nitrogen-poor terrigenous (Triticum aestivum) Phytodetritus. 13C and 15N labels were traced into faunal biomass and bulk sediments, and the 13C label traced into bacterial polar lipid fatty acids (PLFAs). Isotopic labels penetrated to 5 cm sediment depth, with no differences between stations or experimental treatments (substrate or time). Macrofaunal assemblage structure differed between the eastern and western canyon branches. Following deposition of marine Phytodetritus, no changes in macrofaunal feeding activity were observed between the eastern and western branches, with little change between 3 and 7 days. Macrofaunal C and N uptake was substantially lower following deposition of terrigenous Phytodetritus with feeding activity governed by a strong N demand. Bacterial C uptake was greatest, in the western branch of the Whittard canyon, but feeding activity decreased between 3 and 7 days. Bacterial processing of marine and terrigenous OM were similar to the macrofauna in surficial (0–1 cm) sediments. However, in deeper sediments bacteria utilised greater proportions of terrigenous OM. Bacterial biomass decreased following Phytodetritus deposition and was negatively correlated to macrofaunal feeding activity. Consequently, this study suggests that macrofaunal-bacterial interactions influence benthic C cycling in the Whittard canyon, resulting in differential fates for marine and terrigenous OM.

  • Retarded response by macrofauna-size foraminifera to Phytodetritus in a deep Norwegian Fjord
    The Journal of Foraminiferal Research, 2009
    Co-Authors: Andrew K. Sweetman, Olaf Pfannkuche, Stefan Sommer, Ursula Witte
    Abstract:

    Due to the scarcity of information concerning the role that large foraminifera play in deep-sea carbon cycling, the response of a foraminiferal community (>250 pm) to a simulated Phytodetritus sedimentation event was assessed over two weeks using sediment cores collected from a deep-fjord environment. Sediment cores were collected from similar to 700 in water depth in the Korsfjorden, western Norway, and incubated ex situ with 1 9 C-org m(2) of labile C-13-labeled Skeletonema costatum for 2, 7, and 14 days. We selectively picked (without prior staining) cytoplasm-containing foraminifera and found the foraminiferal community to be largely dominated (91%) by the deep-dwelling species Globobulimina turgida and Melonis barleeanum, as well as the shallow infaunal species 1 Hyalinea balthica. None of the >250 mu m, cytoplasm-containing fraction was involved in carbon uptake during the first 7 days. After 14 days, 3% of the foraminiferal samples possessed delta C-13 signatures indicative of carbon uptake, but the uptake was confined to the surface-living (0-2 cm) G. turgida. Foraminifera contributed 2.4% to faunal carbon uptake (foraminifera plus macrofauna) after 14 days, despite making up 24% of the combined biomass. Both the dominance of deep-infaunal species, such as G. turgida and M. barleeanum (68%), which are known to prefer degraded over more labile material, together with their large size, which often makes foraminifera respond slower to Phytodetritus deposition than the more abundant, smaller-size foraminifera, are possible reasons for the retarded response observed. Overall, results from this investigation highlight that the response of large-size foraminifera to Phytodetritus deposition is very slow. In addition, the results presented provide evidence that the foraminiferal response is most likely driven by differences in foraminiferal community composition and structure, with large, deep-infaunal species showing slower reactions to Phytodetritus deposition compared to smaller foraminifera, metazoan meiofauna, and macrofauna.

  • macrofaunal response to Phytodetritus in a bathyal norwegian fjord
    Deep Sea Research Part I: Oceanographic Research Papers, 2008
    Co-Authors: Andrew K. Sweetman, Ursula Witte
    Abstract:

    Abstract The continental margin (rise and shelf) constitutes approximately 1/10th of the surface area of the oceans, but 80–90% of all sedimentary organic matter (OM) is remineralised here. Recent evidence has suggested that macrofauna may play an important role in organic matter remineralisation in deep-sea continental margin sediments, and the deep fjords of western Norway provide a relatively easily accessible opportunity for detailed studies of continental margin macrofaunal communities and their role in C-cycling. We examined the macrofaunal community and assessed its response to a simulated OM pulse in a fjord environment using pulse-chase tracer experiments. In each experiment, 1 g Corg m−2 of 13C-labelled Skeletonema costatum was deposited onto intact sediment cores collected from 688 m water depth and incubated ex situ for 2, 7 and 14 d. Macrofaunal abundance and biomass were comparable to those of other deep-sea continental margin sediments of similar depths, but in contrast to previous fjord studies, the macrofaunal community was numerically dominated by ostracods. Tracer experiments revealed highest uptake of tracer after 7 and 14 d compared to 2 d. Of the seven deposit feeding polychaete families, only the Paraonidae and Cirratulidae—together with the largely carnivorous Lumbrineridae—showed a significant response to our labelled C-source. The lack of response by the majority of deposit feeders and the unexpected feeding mode of the Lumbrineridae may be attributable to species—rather than family specific feeding—ecologies or ontogenetic changes in diet/feeding mode. Total macrofaunal C-turnover was much lower than recorded in the deep Sognefjord in a 3 d feeding experiment, and is possibly a result of (1) distinct differences in macrofaunal community composition between sites, with a predominantly sub-surface-feeding macrofaunal assemblage being found in this study as opposed to a surface-feeding community in the Sognefjord, or (2) variations in OM supply and demand. Overall, this investigation highlights the importance of ecological information at the species level for a detailed understanding of macrofaunal C-cycling and early diagenesis in marine sediments.

Paulo Y. G. Sumida - One of the best experts on this subject based on the ideXlab platform.

  • Seasonal dynamics of megafauna on the deep West Antarctic Peninsula shelf in response to variable phytodetrital influx.
    Royal Society open science, 2014
    Co-Authors: Paulo Y. G. Sumida, Craig R Smith, Angelo F. Bernardino, Paulo S. Polito, D. R. Vieira
    Abstract:

    The deep West Antarctic Peninsula (WAP) shelf is characterized by intense deposition of Phytodetritus during spring/summer months, while very little food material reaches the seafloor during winter. The response of the shelf benthic megafauna to this highly variable food supply is still poorly understood. In order to characterize the deposition of Phytodetritus and the megabenthic community response, we deployed a seafloor time-lapse camera at approximately 590 m depth on the mid WAP shelf west of Anvers Island for 15 months. Seafloor photographs were taken at intervals of 12 or 24 h nearly continuously from 9 December 1999 (austral winter) to 20 March 2001 (summer) and analysed for Phytodetritus deposition and megafaunal dynamics. Seafloor images indicated a marked seasonal arrival of greenish Phytodetritus, with large interannual and seasonal variability in the coverage of depositing phytodetrital particles. The surface-deposit-feeding elasipod holothurians Protelpidia murrayi and Peniagone vignoni dominated the epibenthic megafauna throughout the year, frequently constituting more than 80% of the megafaunal abundance, attaining total densities of up to 2.4 individuals m−2. Elasipod abundances were significantly higher in summer than winter. During summer periods of high phytodetrital flux, Pr. murrayi produced faecal casts at higher rates, indicating intensified population-level feeding activity. In March–June 2000, faecal casts lasted longest, suggesting lower horizontal bioturbation activity during autumn–winter. Our data indicate that the Pr. murrayi population increases its feeding rates in response to increasing amounts and/or lability of organic matter on the sediment surface. Assuming that this species feeds on the top millimetre of the sediment, we estimate that, during periods of high phytodetrital flux, the Pr. murrayi population reworks one square metre of sediment surface in approximately 287 days. We suggest that Pr. murrayi is an important species for organic-carbon recycling on the deep WAP shelf, controlling the availability of deposited labile Phytodetritus to the broader shelf benthic community.

  • trophic structure on the west antarctic peninsula shelf detritivory and benthic inertia revealed by δ13c and δ15n analysis
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2008
    Co-Authors: Sarah L. Mincks, Craig R Smith, Rachel M. Jeffreys, Paulo Y. G. Sumida
    Abstract:

    Abstract Summer bloom-derived Phytodetritus settles rapidly to the seafloor on the West Antarctic Peninsula (WAP) continental shelf, where it appears to degrade relatively slowly, forming a sediment “food bank” for benthic detritivores. We used stable carbon and nitrogen isotopes to examine sources and sinks of particulate organic material (POM) reaching the WAP shelf benthos (550–625 m depths), and to explore trophic linkages among the most abundant benthic megafauna. We measured δ 13 C and δ 15 N values in major megafaunal taxa ( n =26) and potential food sources, including suspended and sinking POM, ice algae, sediment organic carbon, Phytodetritus, and macrofaunal polychaetes. The range in δ 13 C values (>14‰) of suspended POM was considerably broader than in sedimentary POC, where little temporal variability in stable isotope signatures was observed. While benthic megafauna also exhibited a broad range of δ 13 C values, organic carbon entering the benthic food web appeared to be derived primarily from phytoplankton production, with little input from ice algae. One group of organisms, primarily deposit-feeders, appeared to rely on fresh Phytodetritus recovered from the sediments, and sediment organic material that had been reworked by sediment microbes. A second group of animals, including many mobile invertebrate and fish predators, appeared to utilize epibenthic or pelagic food resources such as zooplankton. One surface-deposit-feeding holothurian ( Protelpidia murrayi ) exhibited seasonal variability in stable isotope values of body tissue, while other surface- and subsurface-deposit-feeders showed no evidence of seasonal variability in food source or trophic position. Detritus from phytoplankton blooms appears to be the primary source of organic material for the detritivorous benthos; however, seasonal variability in the supply of this material is not mirrored in the sediments, and only to a minor degree in the benthic fauna. This pattern suggests substantial inertia in benthic–pelagic coupling, whereby the sediment ecosystem integrates long-term variability in production processes in the water column above.

Jack J. Middelburg - One of the best experts on this subject based on the ideXlab platform.

  • Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone
    Biogeosciences, 2013
    Co-Authors: L. Pozzato, Karline Soetaert, Leon Moodley, D. Van Oevelen, Jack J. Middelburg
    Abstract:

    The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as Phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for Phytodetritus.

  • Sink or link? The bacterial role in benthic carbon cycling in the Arabian sea oxygen minimum zone
    2013
    Co-Authors: L. Pozzato, Karline Soetaert, Leon Moodley, D. Van Oevelen, Jack J. Middelburg
    Abstract:

    Abstract. The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic aquatic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea Oxygen Minimum Zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as Phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient in these sediments. Moreover, metazoans directly consume labile particulate organic matter resources and thus compete with bacteria for Phytodetritus.

  • Carbon processing at the deep-sea floor of the Arabian Sea oxygen minimum zone: A tracer approach
    Journal of Sea Research, 2013
    Co-Authors: L. Pozzato, Karline Soetaert, Dick Van Oevelen, Leon Moodley, Jack J. Middelburg
    Abstract:

    We have elucidated the trophic interactions in the foodweb of sediments from and close to the oxygen minimum zone (OMZ) of the Arabian Sea. Sediment cores from inside (885 m depth) and outside (1791 m depth) the OMZ were manipulated onboard by adding 13C-enriched Phytodetritus. The incorporation of Phytodetritus by the benthic community was quantified after incubating for 7 days. To assess the effect of bottom-water oxygenation on the processing of organic matter, the oxygen concentration in the overlying water of the incubated cores was also manipulated. Biomass values inside and outside the OMZ were comparable for bacteria (1068 and 1276 mg C m− 2) and macrofauna (2528 and 3263 mg C m− 2), but not for meiofauna (63 and 1338 mg C m− 2). Uptake values in percentage of total added tracer were 0.8 and 0.5% for bacteria suboxic and oxic treatments inside the OMZ, and 0.5 and 1.2% for suboxic and oxic treatments outside the OMZ. Macrofauna uptake accounted for 17.4 and 4.4% in the suboxic and oxic treatments inside the OMZ, and only for 0.1% and 1.3% respectively outside the OMZ. Respiration accounted for 13% of total tracer added inside the OMZ for both treatments, 4.6 and 6.8% for oxic and suboxic treatments outside the OMZ, respectively. Our results show that Phytodetritus is most efficiently processed at in situ oxygen conditions, that foraminifera and bacteria remain active both under elevated and lowered bottom-water oxygen levels and that macrofauna was present in high abundance and showed high tracer uptake.

  • Importance of Phytodetritus and microphytobenthos for heterotrophs in a shallow subtidal sandy sediment
    Marine Ecology Progress Series, 2012
    Co-Authors: Victor Evrard, Markus Huettel, Perran L. M. Cook, Karline Soetaert, Carlo H. R. Heip, Jack J. Middelburg
    Abstract:

    The relative importance of allochthonous Phytodetritus deposition and autochthonous microphytobenthos (MPB) production for benthic consumers in an organic carbon (C-org)-poor sandy sediment was assessed using a C-13-stable isotope natural abundance study combined with a dual C-13-tracer addition approach. In a first experiment (Expt 1), a set of sediment cores received a pulse of C-13-labelled Phytodetritus and the fate of that organic matter was followed in the benthic food web (bacteria, meiofauna and macrofauna) over a period of 72 h. In a second experiment (Expt 2), the MPB present in a set of sediment cores was labelled with C-13-bicarbonate and the fate of labelled MPB was followed the same way over a period of 96 h. Natural C-13 abundances of sources and consumers revealed that the benthic food web likely relied primarily on MPB. In particular, diatoms contributed at least 40% to the diet of 12 out of the 16 taxonomic groups identified. The dual approach revealed the complexity of the trophic interactions and gave evidence for resource partitioning between 2 species of harpacticoid copepods. Both C-13-tracer addition experiments showed a fast transfer of label to most heterotrophs. Bacteria, which comprised the largest fraction of the heterotroph biomass, incorporated more C-13 than other consumers. Meiofauna had similar relative incorporations in both experiments and likely relied equally on benthic and pelagic inputs. Macrofauna relied significantly more on MPB. In both experiments, most of the C-13-label that was incorporated by heterotrophs was respired. While Phytodetritus-derived C-org consumed by heterotrophs was 41 mg C m(-2), MPB-derived was at least one order of magnitude higher. The benthic community growth efficiency in Expt 2 (40%) was higher than that of Expt 1 (25%), confirming the pivotal role of MPB.

  • Short-term fate of Phytodetritus in sediments across the Arabian Sea Oxygen Minimum Zone
    Biogeosciences, 2008
    Co-Authors: J. H. Andersson, Karline Soetaert, C. Woulds, M. Schwartz, G. L. Cowie, L. A. Levin, Jack J. Middelburg
    Abstract:

    The short-term fate of Phytodetritus was investigated across the Pakistan margin of the Arabian Sea at water depths ranging from 140 to 1850 m, encompassing the oxygen minimum zone (~100?1100 m). Phytodetritus sedimentation events were simulated by adding ~44 mmol 13C-labelled algal material per m2 to surface sediments in retrieved cores. Cores were incubated in the dark, at in situ temperature and oxygen concentrations. Overlying waters were sampled periodically, and cores were recovered and sampled (for organisms and sediments) after durations of two and five days. The labelled carbon was subsequently traced into bacterial lipids, foraminiferan and macrofaunal biomass, and dissolved organic and inorganic pools. The majority of the label (20 to 100%) was in most cases left unprocessed in the sediment at the surface. The largest pool of processed carbon was found to be respiration (0 to 25% of added carbon), recovered as dissolved inorganic carbon. Both temperature and oxygen were found to influence the rate of respiration. Macrofaunal influence was most pronounced at the lower part of the oxygen minimum zone where it contributed 11% to the processing of Phytodetritus.