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
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)
2
Context: For fish and plankton, oxygen does matter
Depth (m)
DO (mL/L)
OMZ
(Bertrand et al., 2008, PinO)
In some cases: almost no room for fish (<10 m),
anchoveta seems to manage but what about
sardine or jack mackerel?
Ballón et al. (2011, PinO)
3
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)
4
1. Anchoveta and sardine ‘alternance’
The ‘common’ statement:
Alternance of decadal ‘cold’
anchovy (La Vieja) and ‘warm’
sardine(El Viejo) periods (Chavez
et al., 2003)
(Chavez
et al.,et2003)
(Chavez
al., 2003)
5
1. Anchoveta and sardine ‘alternance’
Paleo-ecological studies: surprises from the past
om fluxes
haet.-free)
fish scale DR
Diatom fluxes
Anchovy
(Chaet.-free)
TOC flux
anomalies
Callao
2000
1900
1800
fish
TOC flux Bones &
warm-water
Anchovy
anomalies vertebrae DR
species
Anchoveta abundant,
few sardine
Both abundant
Sardine abundant,
few anchoveta
Both scarce
1700
oceanic
mero
neritic
oceanic
mero
neritic
1600
1500
offshore
spp.
sardine
1400
Both abundant
1300
10
6
30
-3 -2 -1 0 1 2 3
Pisco 2000
0
405 80 10300 300
20
-3 -240-1 060 1 0 2 150
3
D. Gutiérrez et al. (2009)
1000
0 40
80
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)
But sardine is able to forage on macrozooplankton (Espinoza et al., 2009)
So what?
(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).
8
Low
biomass
Area
Density
(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)
High
biomass
Area
Density
Habitat selection and dynamics: some models
(see Barange et al., 2009):
Density
1. Anchoveta and sardine variability
Area
1. Anchoveta and sardine variability
-5
-10
-10
-15
However…
lat (deg. W)
First the fish, then the habitat...
CCW
M CS
SSW
SEW
STW
CAW
M RW
M ESC
-15
CCW
M CS
SSW
SEW
STW
CAW
M RW
M ESC
1996 Feb-Apr
lat (deg. W)
-5
Basin model (MacCall, 1990): when a 1995
fish Feb-Apr
population
increases it will occupy new habitat.
Horizontal distribution of anchoveta: limited by the cold
coastal waters (CCW) + mix waters, independent of its
-82
-78
-74
-70a
abundance; when the habitat range increases
during
lon (deg. S)
certain time  abundance increases (Bertrand
et al., 2004,
-82
-78
-74
-70
lon (deg. S)
2008; Swartzman et al., 2008).
lat (deg. W)
anc hov y
s ardine
-15
-10
-15
lat (deg. W)
first 'comes the habitat', then the fish...
Sardine: much more ubiquist in terms of water mass but
distribution always more offshore than -82
anchovy
(why?).
-78
-74
-70
lon (deg. S)
9
-5
anc hov y
s ardine
-10
-5
 MacCall (1990) basin theory since we observed that
-82
-78
-74
lon (deg. S)
-70
1. Anchoveta and sardine variability
Habitat-based hypothesis (Bertrand et al., 2004, 2008, 2010):
Variations in the range of habitat constrain the extensioncontraction 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)...
10
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?
Mixed
sardineAn 'horizontal' habitat-based
hypothesis
does not explain the full story
anchovy
Index of
biomass
(a)
(b)
dominance
Anchovy
dominance
and sardine
collapse
Full anchovy
era
Voir également Massé et Gerlotto,
2003)
Gutiérrez et al. (2007)
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
11
Retention-transport
See Lett et al. (2007)
and Brochier et al. (2010)
(c)
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
1. Oxygen does matter: Oxygen and pelagic fish variability
Decadal scale
A
D
15
Catches/biomass in 106 t
DO (mL L-1)
4.88
4.66
4.44
4.2
4.00
3.88
90
80
E
C
60
Z2mL/L (m)
5
0
75
50
40
Sardine
4
3
2
1
0
30
1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
13
10
85
Catches/biomass in 106 t
DOsat (%)
B
Anchovy
1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
1. Oxygen does matter: Oxygen and pelagic fish variability
Cross-shore scale
14
1. Oxygen does matter: Oxygen and pelagic fish variability
Local (1 nm) scale
Fish acoustic biomass vs. Oxygen
Period: 1983-2000
Sardine
Anchovy
Dissolved oxygen (mL.L-1)
Oxygen saturación (%)
Oxycline depth (m)
At all scales: sardine avoid areas/period with low oxygen/shallow habitat
15
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.
16
1. Oxygen does matter: Oxygen and pelagic fish variability
17
Bertrand, Chaigneau,
Peraltilla, Ledesma,
Graco, Monetti, Chavez
(2011 PLoS ONE)
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