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Oxygen, a fundamental property regulating pelagic ecosystem structure in the coastal southeastern tropical Pacific Bertrand A., Chaigneau A., Peraltilla.

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Presentation on theme: "Oxygen, a fundamental property regulating pelagic ecosystem structure in the coastal southeastern tropical Pacific Bertrand A., Chaigneau A., Peraltilla."— Presentation transcript:

1 Oxygen, a fundamental property regulating pelagic ecosystem structure in the coastal southeastern tropical Pacific Bertrand A., Chaigneau A., Peraltilla S., Ledesma J., Graco M., Monetti F. & Chavez F.P. O2O2

2 Global expansion of Oxygen Minimum Zones (OMZ) (e.g. Stramma et al., 2008) DePol-Holz et al. (2007) The Humboldt Current system presents a very intense and shallow OMZ 2 Context

3 3 (Bertrand et al., 2008, PinO) Context: For fish and plankton, oxygen does matter In some cases: almost no room for fish (<10 m), anchoveta seems to manage but what about sardine or jack mackerel? Depth (m) OMZ DO (mL/L) Ballón et al. (2011, PinO)

4 Fish need both food and oxygen, the latter might be more difficult to obtain than the former (Pauly, 2010) 4 Context: For fish and plankton, oxygen does matter

5 The ‘common’ statement: Alternance of decadal ‘cold’ anchovy (La Vieja) and ‘warm’ sardine(El Viejo) periods (Chavez et al., 2003) 5 (Chavez et al., 2003) 1. Anchoveta and sardine ‘alternance’ 5

6 6 Paleo-ecological studies: surprises from the past D. Gutiérrez et al. (2009) Both abundant Both scarce Anchoveta abundant, few sardine Sardine abundant, few anchoveta Both abundant 1. Anchoveta and sardine ‘alternance’

7 1. Anchoveta and sardine variability Ayón et al. (2011) Anchovy is more abundant when macrozooplankton dominate while sardine is more abundant when small zooplankton is abundant But sardine is able to forage on macrozooplankton (Espinoza et al., 2009) So what?

8 1. Anchoveta and sardine variability 8 Density Area High biomass Low biomass (i) Constant density model: density stays constant and the area covered by the stock varies with abundance (Iles and Sinclair, 1982; Hilborn and Walters, 1992) Habitat selection and dynamics: some models (see Barange et al., 2009): (ii) Proportional model, where the area occupied stays constant and local density varies proportionally to abundance (Houghton, 1987; Myers and Stokes, 1989; Hilborn and Walters, 1992; Petitgas, 1997) Density Area (iii) Basin model, where density and area vary with abundance (MacCall, 1990). Density Area

9 1. Anchoveta and sardine variability Basin model (MacCall, 1990): when a fish population increases it will occupy new habitat. First the fish, then the habitat... Horizontal distribution of anchoveta: limited by the cold coastal waters (CCW) + mix waters, independent of its abundance; when the habitat range increases during a certain time  abundance increases (Bertrand et al., 2004, 2008; Swartzman et al., 2008). However…  MacCall (1990) basin theory since we observed that first 'comes the habitat', then the fish... Sardine: much more ubiquist in terms of water mass but distribution always more offshore than anchovy (why?). 9

10 Habitat-based hypothesis (Bertrand et al., 2004, 2008, 2010) : Variations in the range of habitat constrain the extension- contraction of fish distribution and determine their abundance if favourable or unfavourable conditions last long enough to influence their population dynamics. First the habitat, then the fish (bottom-up process) Anchoveta and sardine variability 10

11 Intermediate period Strong upwelling period Habitat-based hypothesis 11 Weak upwelling period Retention-transport See Lett et al. (2007) and Brochier et al. (2010) Sardine is ubiquitous relative to water masses: why sardine do not distribute closer to the coast? An 'horizontal' habitat-based hypothesis does not explain the full story Gutiérrez et al. (2007)

12 1. Anchoveta and sardine variability An 'horizontal' habitat-based hypothesis fits well the anchovy but does not explain the full story for sardine Sardine is ubiquitous relative to water masses: why sardine does not distribute closer to the coast? Does vertical (and oxygen) matter? 12

13 1. Oxygen does matter: Oxygen and pelagic fish variability Decadal scale 13

14 1. Oxygen does matter: Oxygen and pelagic fish variability Cross-shore scale 14

15 1. Oxygen does matter: Oxygen and pelagic fish variability Local (1 nm) scale Sardine Anchovy Dissolved oxygen (mL.L -1 )Oxygen saturación (%)Oxycline depth (m) 15 Fish acoustic biomass vs. Oxygen Period: At all scales: sardine avoid areas/period with low oxygen/shallow habitat

16 1. Oxygen does matter: Oxygen and pelagic fish variability Oxygen, prey and foraging capabilities Anchoveta: gets most of its energy by direct biting on macrozoopk. Filter feeding on small zoopk: very expensive (O 2 ) relative to biting. Macrozoopk. more abundant in high upwelling-low oxygen periods. 16 Sardine: filter-feeding on small pk. energetically much cheaper. Small pk. more abundant in low upwelling-high oxygen periods.

17 1. Oxygen does matter: Oxygen and pelagic fish variability 17 Bertrand, Chaigneau, Peraltilla, Ledesma, Graco, Monetti, Chavez (2011 PLoS ONE)

18 Oxygen, a fundamental property regulating pelagic ecosystem structure in the coastal southeastern tropical Pacific Bertrand A., Chaigneau A., Peraltilla S., Ledesma J., Graco M., Monetti F. & Chavez F.P. O2O2


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