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Sellanes, J, Neira C, Quiroga E, Teixido N.  2010.  Diversity patterns along and across the Chilean margin: a continental slope encompassing oxygen gradients and methane seep benthic habitats. Marine Ecology-an Evolutionary Perspective. 31:111-124.   10.1111/j.1439-0485.2009.00332.x   AbstractWebsite

In the present study we review datasets available for the Chilean margin to assess the relationship between environmental (or habitat) heterogeneity and benthic diversity. Several factors, such as the presence of different water masses, including the oxygen-deficient Equatorial Sub-surface Waters (ESSW) at the continental shelf and upper slope, and the Antarctic Intermediate Waters (AIW) at mid slope depths appear to control the bathymetric distribution of benthic communities. The presence of methane seeps and an extended oxygen minimum zone (OMZ) add complexity to the benthic distribution patterns observed. All these factors generate environmental heterogeneity, which is predicted to affect the diversity patterns both along and across the Chilean continental margin. The response to these factors differs among different faunal size groups: meio-, macro-, and megafauna. Physiological adaptations to oxygen deficiency and constraints related to body size of each group seem to explain the larger-scale patterns observed, while sediment/habitat heterogeneity (e.g. at water mass boundaries, hardgrounds, biogeochemical patchiness, sediment organic content, grain size) may influence the local fauna diversity patterns.

Gooday, AJ, Bett BJ, Escobar E, Ingole B, Levin LA, Neira C, Raman AV, Sellanes J.  2010.  Habitat heterogeneity and its influence on benthic biodiversity in oxygen minimum zones. Marine Ecology-an Evolutionary Perspective. 31:125-147.   10.1111/j.1439-0485.2009.00348.x   AbstractWebsite

Oxygen minimum zones (OMZs; midwater regions with O(2) concentrations <0.5 ml l(-1)) are mid-water features that intercept continental margins at bathyal depths (100-1000 m). They are particularly well developed in the Eastern Pacific Ocean, the Arabian Sea and the Bay of Bengal. Based on analyses of data from these regions, we consider (i) how benthic habitat heterogeneity is manifested within OMZs, (ii) which aspects of this heterogeneity exert the greatest influence on alpha and beta diversity within particular OMZs and (iii) how heterogeneity associated with OMZs influences regional (gamma) diversity on continental margins. Sources of sea-floor habitat heterogeneity within OMZs include bottom-water oxygen and sulphide gradients, substratum characteristics, bacterial mats, and variations in the organic matter content of the sediment and pH. On some margins, hard grounds, formed of phosphorites, carbonates or biotic substrata, represent distinct subhabitats colonized by encrusting faunas. Most of the heterogeneity associated with OMZs, however, is created by strong sea-floor oxygen gradients, reinforced by changes in sediment characteristics and organic matter content. For the Pakistan margin, combining these parameters revealed clear environmental and faunal differences between the OMZ core and the upper and lower boundary regions. In all Pacific and Arabian Sea OMZs examined, oxygen appears to be the master driver of alpha and beta diversity in all benthic faunal groups for which data exist, as well as macrofaunal assemblage composition, particularly in the OMZ core. However, other factors, notably organic matter quantity and quality and sediment characteristics, come into play as oxygen concentrations begin to rise. The influence of OMZs on meiofaunal, macrofaunal and megafaunal regional (gamma) diversity is difficult to assess. Hypoxia is associated with a reduction in species richness in all benthic faunal groups, but there is also evidence for endemism in OMZ settings. We conclude that, on balance, OMZs probably enhance regional diversity, particularly in taxa such as Foraminifera, which are more tolerant of hypoxia than others. Over evolutionary timescales, they may promote speciation by creating strong gradients in selective pressures and barriers to gene flow.

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, [], [URL:] 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, Decraemer W, Backeljau T.  2005.  A new species of Glochinema (Epsilonematidae : Nematoda) from the oxygen minimum zone off Baja California, NE Pacific and phylogenetic relationships at species level within the family. Cahiers De Biologie Marine. 46:105-126. AbstractWebsite

Glochinema spinithorni sp. nov. is described from muddy, bathyal sediments of the oxygen minimum zone (OMZ) of the north eastern Pacific Ocean off Baja California. It is characterized by a rather large body length (over I mm), a large number of body rings (242-282), sexual dimorphism in the number and position of pharyngeal thorns near the head region, cuticular ornamentation with numerous hairy spines and two sets of stronger spines ventrally in the anterior body half, mid-sized spiral amphids, and by the number and arrangement of ambulatory setae and long spicules (over 100 mu m). The finding of a second OMZ Glochinema species with similar morphological characteristics supports the presumption that OMZs function as isolated habitats promoting endemism at low taxonomic levels. Results of phylogenetic analyses at the species level restricted to the Glochinematinae and Keratonematinae suggest that both OMZ species form a monophyletic group. An attempt was made to recognize phylogenetic relationships at species level within the family. The phylogenetic analyses were based upon a data matrix of 96 ingroup taxa and 25 characters. The results support the monophyly of the genera Leptepsilonema, Metepsilonema, Perepsilonema and Polkepsilonema (with or without Pternepsilonema).

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.

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'.