These observations were made during the most intense part of the El Ni n over tildeo when there may have been slight oxygenation of an otherwise anoxic basin, but oligochaete presence prior to this event is likely. The occurrence of symbiont-bearing gutless oligochaetes mainly within the upper 5 cm of the sediment column coincided with a bioturbated zone overlying distinctly laminated sediments. Our observations redefine the lower oxygen limit of macrofaunal bioturbation to much less than2 muM, and indicate a need to modify currently accepted ideas about the relationship between bioturbation and paleo-oxygen concentration.
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These results also address an ongoing debate about the lifestyles of bioturbating organisms in oxygen-poor settings. C Elsevier B. All rights reserved. These seafloor oxygen minimum zones OMZs typically occur at bathyal depths between m and m, and are major sites of carbon burial along the continental margins. Despite extreme oxygen depletion, protozoan and metazoan assemblages thrive in these environments.
Metazoan adaptations include small, thin bodies, enhanced respiratory surface area, blood pigments such as haemoglobin, biogenic structure formation for stability in soupy sediments, an increased number of pyruvate oxidoreductases, and the presence of sulphide-oxidising symbionts. The organic-rich sediments of these regions often support mats of large sulphide-oxidising bacteria Thioploca, Beggiatoa, Thiomargarita , and high-density, low-diversity metazoan assemblages. Densities of protistan and metazoan meiofauna are typically elevated in OMZs, probably due to high tolerance of hypoxia, an abundant food supply, and release from predation.
Macrofauna and megafauna often exhibit dense aggregations at OMZ edges, but depressed densities and low diversity in the OMZ core, where oxygen concentration is lowest. Agglutinated protozoans, harpacticoid copepods, and calcified invertebrates are typically less tolerant. High dominance and relatively low species richness are exhibited by foraminiferans, metazoan meiofauna, and macrofauna within OMZs.
At dissolved oxygen concentrations below 0. OMZs represent a major oceanographic boundary for many species. As they expand and contract over geological time, OMZs may influence genetic diversity and play a key role in the evolution of species at bathyal depths. These ecosystems may preview the types of adaptations, species, and processes that will prevail with increasing hypoxia over ecological and evolutionary time. However, many questions remain unanswered concerning controls on faunal standing stocks in OMZs, and the physiological, enzymatic, metabolic, reproductive and molecular adaptations that permit benthic animals to live in OMZs.
As global warming and eutrophication reduce oxygenation of the world ocean, there is a pressing need to understand the functional consequences of oxygen depletion in marine ecosystems. Oxygen minimum zones OMZs are widespread features in the most productive regions of the world ocean. A holistic view of benthic responses to OMZ conditions will improve our ability to predict ecosystem-level consequences of climatic trends that influence oxygen availability, such as global warming or ENSO-related events. Sampling took place during early January , an intense El Ni n over tildeo period associated with higher-than-normal levels of O 2 on the shelf and upper slope.
Peru slope sediments were highly heterogeneous. Deeper sites contained phosphorite crusts or pellets and exhibited greater bottom-water oxygenation and lower content and quality of organic matter. X-radiographs and Pb and Th profiles suggested the dominance of lateral transport and bioturbation over pelagic sedimentation at the mid- and lower slope sites. Macrofauna, metazoan meiofauna and foraminifera exhibited coherence of density patterns across stations, with maximal densities and for macrofauna, reduced diversity at Station A, where bottom-water oxygen concentration was lowest and sediment labile organic matter content LOC: sum of protein, carbohydrate and lipid carbon was greatest.
Metazoan and protozoan meiofaunal densities were positively correlated with sediment LOC. The taxa most tolerant of nearly anoxic, organic-rich conditions within the Peru OMZ were calcareous foraminifera, nematodes and gutless phallodrilinid symbiont-bearing oligochaetes.
Oceanography and Marine Biology: An Annual Review
Agglutinated foraminifera, harpacticoid copepods, polychaetes and many other macrofaunal taxa increased in relative abundance below the OMZ. Future sampling may determine whether the Peru margin system exhibits dynamic responses to changing ENSO-related conditions. C Elsevier Science Ltd. 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 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. Release of methane from large marine reservoirs has been linked to climate change, as a causal mechanism and a consequence of temperature changes, during the Quaternary and the Paleocene.
These inferred linkages are based primarily on variations in benthic foraminiferal stable isotope signatures. Few modem analog data exist, however, to assess the influence of methane flux on the geochemistry or faunal characteristics of benthic foraminiferal assemblages. Calcareous foraminiferal assemblages associated with Calyptogena clam bed seeps were comprised of species that are also found in organic-rich environments. Cosmopolitan, paleoceanographically important taxa were abundant; these included Uvigerina, Bolivina, Chilostomella, Globobulimina, and Nonionella.
We speculate that seep foraminifera are attracted to the availability of food at cold seeps, and require no adaptations beyond those needed for life in organic-rich, reducing environments. Oxygen isotopic values of the tests of living foraminiferal assemblages from seeps had a high range up to 0. Many living foraminiferal isotope values were within the range exhibited by the same or similar species in non-seep environments. Carbon isotopic values of fossil foraminifera found deeper in the sediments cm , however, were 4.
These results suggest that delta 13 C values of foraminiferal tests reflect methane seepage and species-specific differences in isotopic composition, and can indicate temporal variations in seep activity. A better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo-seep recognition, and improve interpretations of climatic and paleoceanographic change. C Elsevier Science B. Previous work has shown that some foraminiferal species thrive in organically enriched, oxygen-depleted environments. The papers provide a substantial update of the knowledge about this highly productive and important transitional region in the North Pacific.
Year: Harmful Algae Review paper, Harmful algal blooms and climate change: Learning from the past and present to forecast the future based on PICES and other organization sponsored workshop. Authors: M. Wells, V. Trainer, T. Smayda, B. Karlson, C. Trick, R. Kudela, A. Ishikawa, S. Bernard, A. Wulff, D. Anderson and W. Cochlan Harmful Algae , Vol. In January this article was the most frequently downloaded article in Harmful Algae in the last 90 days.
Bern achieved many scientific accomplishments during his career in fisheries and oceanography and served PICES in many different roles, sometimes simultaneously. Curchitser, K.
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Rose, S. Ito, M. Peck and M. Kishi display some of the breadth of models in use for understanding the mechanisms linking environmental forcing to biological responses in ocean systems—it is a collection that Bern would be proud of. Authors: S. Kim, A. Hollowed, M. Barange, and B. MacKenzie Oceanography, Vol. Hazen, R. Suryan, S. Bograd, Y. Watanuki and R. Wilson Mar. Drinkwater, G. Hunt, Jr. Johnson, and David L. Year: Fisheries Research Special Issue on Ecosystem-based approaches for the assessment of fisheries under data-limited situations Guest Editors: Dr.
Patricia Livingston, Dr. Gordon Kruse and Dr. Laura Richards Fish. Yamaguchi and C. Cherniawsky, M. Foreman, B. Kagan and A. Rabinovich Cont. Kawaguchi and W. Sydeman [pdf, 2. Christian, Kitack Lee, and Christopher L. Sabine J.
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Kruse, Yukimasa Ishida, E. Ted Perry, Vladimir I. Radchenko and Chang Ik Zhang Fish. Mooers and Jong-Hwan Yoon J. Systems , , Vol. Megrey, Jason S. Link and Erlend Moksness Prog.
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