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AK, S, LA L, HT R, C S.  2013.  Faunal trophic structure at hydrothermal vents on the southern Mohn’s Ridge, Arctic Ocean. Marine Ecology Progress Series. 473:115-131.   10.3354/meps10050   AbstractWebsite

We explore the trophic ecology of heterotrophic fauna associated with a high temperature (HT) vent, 2 low temperature vents, a ‘near-HT vent’ habitat and a non-vent site situated at upper bathyal depths on the southern Mohn’s Ridge in the Arctic Ocean. Only a single taxon (the gastropod Pseudosetia griegi) was found at the high temperature vent habitat. Their mean δ13C values were significantly lighter than conspecifics from a low temperature vent habitat within the same vent field, reflecting the incorporation of sulfide oxidizing bacteria into the biomass of the animals. The majority of fauna from the low temperature, near-HT, and non-vent habitats had isotopic signatures indicative of assimilation of photosynthetic material. However, we found remarkably diverse isotopic compositions among the fauna sampled here, with a small sub-set of fauna at each site possessing C and N isotopic signatures indicative of incorporation of chemosynthetic production. Moreover, when isotopic signatures of similar taxa were compared from the same sample, δ13C signatures suggested a high degree of trophic complexity can exist over relatively small spatial scales at vent habitats on the southern Mohn’s Ridge. The high contribution of photosynthetic food material to faunal diets and variability in food types may result from the upper bathyal venting depth and sedimentary nature of the vents. We hypothesize that the upper bathyal depth of active venting may lead to iron enhancement of surface photosynthetic production, especially in high nutrient areas, which ultimately sinks to the seabed where it is incorporated by fauna around the vents.

Andersson, JH, Woulds C, Schwartz M, Cowie GL, Levin LA, Soetaert K, Middelburg JJ.  2008.  Short-term fate of phytodetritus in sediments across the Arabian Sea oxygen minimum zone. Biogeosciences. 5:43-53. AbstractWebsite

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 (similar to 100-1100 m). Phytodetritus sedimentation events were simulated by adding similar to 44 mmol (13)C-labelled algal material per m(2) 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.

Arntz, WE, Gallardo VA, Gutierrez D, Isla E, Levin LA, Mendo J, Neira C, Rowe GT, Tarazona J, Wolff M.  2006.  El Niño 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.

Askarizadeh, A, Rippy MA, Fletcher TD, Feldman DL, Peng J, Bowler P, Mehring AS, Winfrey BK, Vrugt JA, AghaKouchak A, Jiang SC, Sanders BF, Levin LA, Taylor S, Grant SB.  2015.  From rain tanks to catchments: Use of low-impact development to address hydrologic symptoms of the urban stream syndrome. Environmental Science & Technology. 49:11264-11280.   10.1021/acs.est.5b01635   AbstractWebsite

Catchment urbanization perturbs the water and sediment budgets of streams, degrades stream health and function, and causes a constellation of flow, water quality, and ecological symptoms collectively known as the urban stream syndrome. Low-impact development (LID) technologies address the hydrologic symptoms of the urban stream syndrome by mimicking natural flow paths and restoring a natural water balance. Over annual time scales, the volumes of stormwater that should be infiltrated and harvested can be estimated from a catchment-scale water-balance given local climate conditions and preurban land cover. For all but the wettest regions of the world, a much larger volume of stormwater runoff should be harvested than infiltrated to maintain stream hydrology in a preurban state. Efforts to prevent or reverse hydrologic symptoms associated with the urban stream syndrome will therefore require: (1) selecting the right mix of LID technologies that provide regionally tailored ratios of stormwater harvesting and infiltration; (2) integrating these LID technologies into next-generation drainage systems; (3) maximizing potential cobenefits including water supply augmentation, flood protection, improved water quality, and urban amenities; and (4) long-term hydrologic monitoring to evaluate the efficacy of LID interventions.