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We analysed carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios of organisms and biogenic tissues from Comau Fjord (southern Chile) to characterise benthic food webs and spatial isotope variability in this ecosystem. These values were intended to serve as a baseline for detecting anthropogenic impacts on Patagonian marine fjord ecosystems in later studies. Benthic macroalgae and invertebrate suspension feeders were primarily considered, with some supplementary data from cyanobacteria, plankton, fish, and coastal vertebrates. Six depth transects typified the lateral salinity gradients from the innermost part of the fjord to its mouth, as well as the vertical density gradients caused by freshwater inflow. Carbon isotope signatures indicated predominant consumption of either CO 2 or HCO 3 -for benthic macroalgal. All CO 2 users belonged to rhodophytes. The δ 15N values of benthic macrophytes decreased with decreasing salinity, both vertically and along the fjord axis. This implies the influence of 15 N-poor terrestrial dissolved inorganic nitrogen (DIN) at these sites. Enhanced influence of freshwater influx also lowered N contents and increased C/N ratios in algal tissues. Exceptionally high macroalgae δ Mar Ecol Prog Ser 428: [89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104] 2011 2007, van Ofwegen et al. 2006, Esteves et al. 2007, Sinniger & Häussermann 2009). The driving forces behind these patterns are not yet fully understood (Fernandez et al. 2000, Escribano et al. 2003. Possible environmental factors affecting biodiversity are specific physical and chemical gradients or highly dynamic nutrient and organic matter fluxes. However, few oceanographic data are available (e.g. Pickard 1971, Silva et al. 1995, Strub et al. 1998). An understanding of the functioning of the Chilean fjord ecosystem is a prerequisite in order to assess the consequences of the intensified exploitation of marine resources and of rapidly expanding aquaculture, the latter adding additional nutrient sources to benthic ecosystems. In addition to species inventories, a deeper understanding of the biogeochemical cycles in Patagonian fjords is the basis for environmental monitoring.Stable isotope methods are frequently applied to characterise marine food webs (Minagawa & Wada 1984, Schoeninger & DeNiro 1984, Bergmann et al. 2009, Steinarsdóttir et al. 2009). The nitrogen and carbon isotopic compositions of natural samples are given as delta values (δ), representing the isotope ratio of the heavy to the light isotope (‰) relative to an international standard and is defined as: δ y X = (R sample / R standard -1) × 1000, with R being the ratio of the heavier to the lighter isotope ( The carbon isotope composition (δ 13 C) of an organism can be used to distinguish isotopically different sources in food webs (DeNiro & Epstein 1978). Minor δ 13 C differences of 0 to 1 ‰ are observed between animals and their food (Peterson & Fry 1987). Thus, the much larger carbon isotope discrepancies between certain groups of prim...

B fRACT T he response of deep-sea benthic foraminifera to a simulated sedimentation event was assessed in a shipboard microcosm by using transmission electron microscopy, organic carbon, adenosine nucleotide, ETS assays and live observations. A rapid activation of foraminiferal metabolism was detected with an incrca e in ETS activity and a distinct decrease in AMP to build up A TP. Based on this phy iological-awakening reaction, food was gathered by pseudopodia] activity and ingested in high quantities. Three days after feeding, high quality food was found in the digestion vacuoles leading to an increase of 89% in individual organic carbon contents. During the following six days, this food was converted into biomass as lipids and other reserve compounds were built up. After ten days, digestion vacuoles contained degraded matter onJy. The final shift in individual biomass was 16.9 % in comparison to the initial population.

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