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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. . O 2. Context.

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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.

O2

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Context

Global expansion of Oxygen Minimum Zones (OMZ) (e.g. Stramma et al., 2008)

The Humboldt Current system presents a very intense and shallow OMZ

DePol-Holz et al. (2007)

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Context: For fish and plankton, oxygen does matter

DO (mL/L)

Depth (m)

OMZ

In some cases: almost no room for fish (<10 m), anchoveta seems to manage but what about sardine or jack mackerel?

(Bertrand et al., 2008, PinO)

Ballón et al. (2011, PinO)

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Context: For fish and plankton, oxygen does matter

Fish need both food and oxygen, the latter might be more difficult to obtain than the former (Pauly, 2010)

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1. Anchoveta and sardine ‘alternance’

(Chavez et al., 2003)

The ‘common’ statement:

Alternance of decadal ‘cold’ anchovy (La Vieja) and ‘warm’ sardine(El Viejo) periods (Chavez et al., 2003)

(Chavez et al., 2003)

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1. Anchoveta and sardine ‘alternance’

Paleo-ecological studies: surprises from the past

Anchoveta abundant, few sardine

Both abundant

Sardine abundant,

few anchoveta

Both scarce

Both abundant

D. Gutiérrez et al. (2009)

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1. Anchoveta and sardine variability

Anchovy is more abundant when macrozooplankton dominate while sardine is more abundant when small zooplankton is abundant

Ayón et al. (2011)

Butsardineisabletoforageonmacrozooplankton (Espinoza et al., 2009)

So what?

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1.Anchoveta and sardine variability

Habitat selection and dynamics: some models

(see Barange et al., 2009):

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)

Density

Density

Density

Area

Area

Area

(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)

(iii) Basin model, where density and area vary with abundance (MacCall, 1990).

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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...

However…

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).

 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?).

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1. Anchoveta and sardine variability

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)...

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Habitat-based hypothesis

Weak upwelling period

Intermediate period

Strong upwelling period

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

Retention-transport

See Lett et al. (2007)

and Brochier et al. (2010)

Gutiérrez et al. (2007)

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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?

Doesvertical (and oxygen) matter?

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1. Oxygen does matter: Oxygen and pelagic fish variability

Fish acoustic biomass vs. Oxygen

Period: 1983-2000

Local (1 nm) scale

Dissolved oxygen (mL.L-1)

Oxygen saturación (%)

Oxycline depth (m)

Sardine

At all scales: sardine avoid areas/period with low oxygen/shallow habitat

Anchovy

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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 (O2) relative to biting.

Macrozoopk. more abundant in high upwelling-low oxygen periods.

Sardine: filter-feeding on small pk. energetically much cheaper. Small pk. more abundant in low upwelling-high oxygen periods.

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1. Oxygendoesmatter: Oxygenand pelagicfishvariability

Bertrand, Chaigneau, Peraltilla, Ledesma, Graco, Monetti, Chavez (2011 PLoS ONE)

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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.

O2