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Neira, C, Gad G, Arroyo NL, Decraemer W.  2001.  Glochinema bathyperuvensis sp. n. (Nematoda, Epsilonematidae): A new species from Peruvian bathyal sediments, SE Pacific Ocean. Contributions to Zoology. 70:147-159. AbstractWebsite

Glochinema bathyperuvensis sp. n., the first record of Epsilonematidae from bathyal muddy sediments of the oxygen minimum zone (OMZ) off Callao, Peru (eastern Pacific Ocean) is described. The new species belongs to the subfamily Glochinematinae and is characterized by the possession of more than 8 pairs of subdorsal thorns asymmetrically arranged and a single dorsal one in the pharyngeal region, as well as by the presence of ten to thirteen blade-like cuticular protrusions forming a latero-dorsal palisade around the posterior head region and anterior cervical region, In addition, G. bathyperuvensis is characterized by its large size, more than 240 cuticular annules, provided with an extremely dense,hairy'' body ornamentation and, four rows of ambulatory setae: two inner subventral ones with 8 to 9 setae in males, and 5 to 6 setac in females, and two outer subventral rows composed each of 9-12 ambulatory setae followed by a large number of modified somatic setae. The dense hairy body spines, the large number of modified somatic setae, its dominant occurrence exclusive in oxygen-depleted, organic-rich soupy surface sediments indicate an adaptation to the stressed OMZ habitat conditions.

Levin, L, Gutierrez D, Rathburn A, Neira C, Sellanes J, Munoz P, Gallardo V, Salamanca M.  2002.  Benthic processes on the Peru margin: a transect across the oxygen minimum zone during the 1997-98 El Nino. Progress in Oceanography. 53:1-27.   10.1016/s0079-6611(02)00022-8   AbstractWebsite

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. Four stations off Callao, Peru (-12'S, Station A, 305 m; Station B, 562 m; Station C, 830 nu and Station D, 1210 m) were sampled to examine the influence of the low bottom-water oxygen concentration and high organic-matter availability within the OMZ (O(2) < 0.5 ml L(-1)) on sediments, benthic communities, and bioturbation. Sampling took place during early January 1998, 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. Sediment total organic carbon content exceeded 16%, lamination was present below 6 cm depth, and filamentous sulfur bacteria (Thioploca spp.) were present at Station A, (305 m, 0, < 0.02 ml L(-1)). Deeper sites contained phosphorite crusts or pellets and exhibited greater bottom-water oxygenation and lower content and quality of organic matter. X-radiographs and (210)Pb and (234)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. Agglutinated foraminifera, harpacticoid copepods, polychaetes and many other macrofaunal taxa increased in relative abundance below the OMZ. During the study (midpoint of the 1997-98 El Ni (n) over tildeo), the upper OMZ boundary exhibited a significant deepening (to 190 m) relative to 'normal', non-El Ni (n) over tildeo conditions (< 100 m), possibly causing a mild, transient oxygenation over the upper slope (200-300 m) and reduction of the organic particle flux to the seabed. Future sampling may determine whether the Peru margin system exhibits dynamic responses to changing ENSO-related conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.

Sellanes, J, Neira C, Quiroga E.  2003.  Composition, structure and energy flux of the meiobenthos off central Chile. Revista Chilena De Historia Natural. 76:401-415.   10.4067S0716-078X2003000300006.   AbstractWebsite

The general objective of this study was to determine the structure of metazoan meiofauna (at a high taxonomic level) and to estimate its role in the energy flux of the benthic sub-system off Concepcion, Chile (similar to36degrees30' S). Samples were collected in May and November 1997 and May 1998 at five sites located at the: inner Bay of Concepcion (28 m), bay-mouth (35 m), inner-shelf (64 m), mid-shelf (88 in) and outer-shelf (120 m). The study period coincided with the El Nino 1997-1998 (EN) event. The diversity of the meiobenthos was low, but density and biomass were moderate to high compared with average values reported for muddy sub-littoral environments elsewhere. Nematodes were the dominant group, with over 95 % (10(3)-10(4) ind 10 cm(-2)) of the total density, followed by copepods and polychaetes. Highest densities and biomasses were always found at the bay-mouth, followed by the inner-bay and the inner-shelf, while the lowest values occurred at the mid- and outer-shelf. Off Concepcion, the meiofauna plays an important role in the energy flux through the benthic sub-system. Indeed, the meiofauna could be converting to biomass and remineralizing in the inner-bay and bay-mouth up to 36 and 45 %, respectively, of the organic carbon reaching the sediments from the water column.

Gutierrez, D, Gallardo VA, Mayor S, Neira C, Vasquez C, Sellanes J, Rivas M, Soto A, Carrasco F, Baltazar M.  2000.  Effects of dissolved oxygen and fresh organic matter on the bioturbation potential of macrofauna in sublittoral sediments off Central Chile during the 1997/1998 El Nino. Marine Ecology-Progress Series. 202:81-99.   10.3354/meps202081   AbstractWebsite

A study off Concepcion, central Chile, during the 1997/1998 El Nino (EN) revealed that the concentration of dissolved oxygen and the organic content and quality of the sediment control the vertical distribution of macrofauna in the sediment and bioturbation potential. The study area, characterized by organic-rich, silty sediments, lies within the most intense upwelling center off the coast of Chile, and is subject to the seasonal influx of hypoxic subsurface waters. Five stations (28 to 120 m depth) were sampled seasonally. The vertical distribution and integrated biomass and abundance of macrofauna (> 0.5 mm) were determined, as well as the dissolved oxygen content of the bottom water (BWDO) and sediment parameters such as total organic carbon (TOC), the C/N ratio, sulphide content, chi a content, and the thickness of the oxidized zone. Chi a proved to be a good indicator of fresh (high-quality) organic matter. Major components contributing to variation in the macrofauna feeding guilds, bioturbation categories, and their vertical position in the sediment were: (1) the relative bioturbation potential (contribution of bioturbating taxa to the assemblage) and (2) the vertical distribution and ratio of surface-to subsurface deposit-feeders. Higher levels of BWDO and a lower quality of organic matter at the sediment surface tended to provide better conditions for potentially strong bioturbators, while lower BWDO levels and higher-quality organic matter were accompanied by the dominance of tube-dwelling, surface-defecating land hence weakly bioturbating) species. Higher TOC levels and lower-quality organic matter at the surface resulted in deeper vertical distributions of animals and a higher relative abundance of subsurface deposit-feeders. During the study period, BWDO levels increased, while the total organic carbon and the quality of organic matter decreased. These conditions encouraged the vertical penetration of macrofauna into the sediment column and the relatively larger contribution of stronger bioturbators to the assemblage. The most drastic changes in faunal lifestyles and vertical distribution during the 1997/1998 EN were observed within the Bay of Concepcion, an area usually characterized by sulphidic sediments under the conditions of severe seasonal hypoxia or anoxia obtaining during 'normal' (i.e. non-EN) years; and in the deepest shelf site, which usually experiences permanent hypoxia because of the influence of the 'oxygen minimum zone'.

Arntz, WE, Gallardo VA, Gutierrez D, Isla E, Levin LA, Mendo J, Neira C, Rowe GT, Tarazona J, Wolff M.  2006.  El NiƱo and similar perturbation effects on the benthos of the Humboldt, California, and Benguela Current upwelling ecosystems. Advances in Geosciences. 6:243-265.: European Geosciences Union, c/o E.O.S.T. 5, rue Rene Descartes Strasbourg Cedex 67084 France, [mailto:egu.production@copernicus.org], [URL:http://www.copernicus.org/EGU] AbstractWebsite

To a certain degree, Eastern Boundary Current (EBC) ecosystems are similar: Cold bottom water from moderate depths, rich in nutrients, is transported to the euphotic zone by a combination of trade winds, Coriolis force and Ekman transport. The resultant high primary production fuels a rich secondary production in the upper pelagic and nearshore zones, but where O sub(2) exchange is restricted, it creates oxygen minimum zones (OMZs) at shelf and upper slope (Humboldt and Benguela Current) or slope depths (California Current). These hypoxic zones host a specifically adapted, small macro- and meiofauna together with giant sulphur bacteria that use nitrate to oxydise H sub(2)S. In all EBC, small polychaetes, large nematodes and other opportunistic benthic species have adapted to the hypoxic conditions and co-exist with sulphur bacteria, which seem to be particularly dominant off Peru and Chile. However, a massive reduction of macrobenthos occurs in the core of the OMZ. In the Humboldt Current area the OMZ ranges between <100 and about 600 m, with decreasing thickness in a poleward direction. The OMZ merges into better oxygenated zones towards the deep sea, where large cold-water mega- and macrofauna occupy a dominant role as in the nearshore strip. The Benguela Current OMZ has a similar upper limit but remains shallower. It also hosts giant sulphur bacteria but little is known about the benthic fauna. However, sulphur eruptions and intense hypoxia might preclude the coexistence of significant mega- und macrobenthos. Conversely, off North America the upper limit of the OMZ is considerably deeper (e.g., 500-600 m off California and Oregon), and the lower boundary may exceed 1000m. The properties described are valid for very cold and cold (La Nina and "normal") ENSO conditions with effective upwelling of nutrient-rich bottom water. During warm (El Nino) episodes, warm water masses of low oxygen concentration from oceanic and equatorial regions enter the upwelling zones, bringing a variety of (sub)tropical immigrants. The autochthonous benthic fauna emigrates to deeper water or poleward, or suffers mortality. However, some local macrofaunal species experience important population proliferations, presumably due to improved oxygenation (in the southern hemisphere), higher temperature tolerance, reduced competition or the capability to use different food. Both these negative and positive effects of el Nino influence local artisanal fisheries and the livelihood of coastal populations. In the Humboldt Current system the hypoxic seafloor at outer shelf depths receives important flushing from the equatorial zone, causing havoc on the sulphur bacteria mats and immediate recolonisation of the sediments by mega- and macrofauna. Conversely, off California, the intruding equatorial water masses appear to have lower oxygen than ambient waters, and may cause oxygen deficiency at upper slope depths. Effects of this change have not been studied in detail, although shrimp and other taxa appear to alter their distribution on the continental margin. Other properties and reactions of the two Pacific EBC benthic ecosystems to el Nino seem to differ, too, as does the overall impact of major episodes (e.g., 1982/1983(1984) vs. 1997/1998). The relation of the "Benguela Nino" to ENSO seems unclear although many Pacific- Atlantic ocean and atmosphere teleconnections have been described. Warm, low- oxygen equatorial water seems to be transported into the upwelling area by similar mechanisms as in the Pacific, but most major impacts on the eukaryotic biota obviously come from other, independent perturbations such as an extreme eutrophication of the sediments ensuing in sulphidic eruptions and toxic algal blooms. Similarities and differences of the Humboldt and California Current benthic ecosystems are discussed with particular reference to ENSO impacts since 1972/73. Where there are data available, the authors include the Benguela Current ecosystem as another important, non-Pacific EBC, which also suffers from the effects of hypoxia.

Neira, C, Sellanes J, Soto A, Gutierrez D, Gallardo VA.  2001.  Meiofauna and sedimentary organic matter off Central Chile: response to changes caused by the 1997-1998 El Nino. Oceanologica Acta. 24:313-328.   10.1016/s0399-1784(01)01149-5   AbstractWebsite

Quantitative surveys of metazoan meiofauna were carried out in an upwelling region off Central Chile (36 degreesS). During May 1997 and May 1998, coinciding with the onset and end of Fl Nino, five benthic stations (respectively 27, 34, 64, 88, and 120 m depth), from the middle of Concepcion Bay to the edge of the adjacent continental shelf, were sampled. The sedimentary organic matter biopolymeric fraction (proteins, carbohydrates and lipids) and chloroplastic pigments were also assessed. Total meiofauna abundance and biomass increased significantly between sampling dates at the mid-bay and inner shelf sites, from 1474 +/- 354 to 5035 +/- 291 individuals 10 cm(-2) and from 2618 +/- 332 to 5241 +/- 903 individuals 10 cm(-2), respectively. The relative importance of copepods in the top 2 cm increased at all sites (except in the bay mouth). During May 1998, meiofauna, especially nematodes, penetrated deeper in the bay, as well as in the inner and middle shelf sediments. Changes observed in meiobenthos structure among sites and periods were attributed to the higher oxygenation of bottom waters during the summer of 1998 (i.e. El Nino conditions). This was most evident at sites such as the mid bay, where during non-EI Nino years, oxygen-deficient conditions prevail. A decrease of organic matter quantity and quality, related to low primary productivity conditions in 1998 (El Nino), apparently caused few changes in meiofauna structure. A positive correlation between Thioploca and the meiofauna biomass was observed in May 1997, whereas in May 1998 no relationship was found. (C) 2001 Ifremer/CNRS/LRD/Editions scientifiques et medicales Elsevier SAS.

Neira, C, Sellanes J, Levin LA, Arntz WE.  2001.  Meiofaunal distributions on the Peru margin: relationship to oxygen and organic matter availability. Deep-Sea Research Part I-Oceanographic Research Papers. 48:2453-2472.   10.1016/s0967-0637(01)00018-8   AbstractWebsite

A quantitative study of metazoan meiofauna was carried out on bathyal sediments (305, 562, 830 and 1210 m) along a transect within and beneath the oxygen minimum zone (OMZ) in the southeastern Pacific off Callao, Peru (12 degreesS). Meiobenthos densities ranged from 1517 (upper slope, middle of OMZ) to 440-548 ind. 10cm(-2) (lower slope stations, beneath the OMZ). Nematodes were the numerically dominant meiofaunal taxon at every station, followed by copepods and nauplii. Increasing bottom-water oxygen concentration and decreasing organic matter availability downslope were correlated with observed changes in meiofaunal abundance. The 300-m site, located in the middle of the OMZ, differed significantly in meiofaunal abundance, dominance, and in vertical distribution pattern from the deeper sites. At 305 m, nematodes amounted to over 99% of total meiofauna; about 70% of nematodes were found in the 2-5 cm. interval. At the deeper sites, about 50% were restricted to the top I cm. The importance of copepods and nauplii increased consistently with depth, reaching similar to 12% of the total meiofauna at the deepest site. The observation of high nematode abundances at oxygen concentrations <0.02mll(-1) supports the hypothesis that densities are enhanced by an indirect positive effect of low oxygen involving (a) reduction of predators and competitors and (b) preservation of organic matter leading to high food availability and quality. Food input and quality, represented here by chloroplastic pigment equivalents (CPE) and sedimentary labile organic compounds (protein, carbohydrates and lipids), were strongly, positively correlated with nematode abundance. By way of contrast, oxygen exhibited a strong negative correlation, overriding food availability, with abundance of other meiofauna such as copepods and nauplii. These taxa were absent at the 300-m site. The high correlation of labile organic matter (C-LOM, sum of carbon contents in lipids, proteins and carbohydrates) with CPE (Pearson's r = 0.99, p <0.01) suggests that most of the sedimentary organic material sampled was of phytodetrital origin. The fraction of sediment organic carbon potentially available to benthic. heterotrophs, measured as C-LOM/Total organic carbon, was on average 17% at all stations. Thus, a residual, refractory fraction, constitutes the major portion of organic matter at the studied bathyal sites. (C) 2001 Elsevier Science Ltd. All rights reserved.