Tracking habitat and
resource use for Dosidicus
gigas: a stable isotope
analysis in the Northern
Humboldt Current System
15N
Juan Argüelles · Anne Lorrain · Yves Cherel · Michelle Graco · Ricardo
Tafur · Ana Alegre · Pepe Espinoza · Anatolio Taipe · Patricia Ayón ·
Arnaud Bertrand
Introduction
D. gigas diet
Stomach content:
Some limitations:
•absence or minimal amount of food in cephalopods stomach
•differences in digestibility among preys
•selectivity rejection of a potential prey
Introduction
D. Gigas habitat
22:00
20:00
18:00
16:00
14:00
12:00
10:00
8:00
6:00
4:00
2:00
0:00
Horas del día
0
Profunfidad (m)
100
200
300
400
500
600
700
800
Fluctuación de los registros del calamar gigante con
respecto a las horas del día
Introduction
Stable isotope analysis (SIA)
Stable isotopes of consumers reflect that of prey as well as
the habitat of the individual.
You are what you eat
Nitrogen isotopes typically indicate trophic position, while
carbon isotopes reflect variation in baseline producers or
habitat.
Questions:
The life history of D. gigas in Peruvian waters
is same for all individuals?
D. Gigas is a highly mobile in Peruvian
waters?
D. gigas carry out migrations along latitude or
longitude in Peruvian waters?
There is a systematic increase in trophic
position with size in Peruvian waters ?.
Data and methods (sampling on board jigging fleet)
234 D. gigas (2.2 and 98.8 cm mantle
length) obtained from 03.48°S to
18.31°S, and up to 813 km from the shelf
break from the commercial jigging fleet
and research vessels (2008-2010)
Thirty-four samples of zooplankton (2008
using a Hensen net).
LATITUDE
3421 stomachs of D. gigas (14.3 - 112.5
cm ML) collected from 05°S to 18°S,
onboard the jigging fleet from 2004 to
2009.
Micromass at
Department of
Marine Biology,
La Rochelle,
France.
LONGITUDE
Data and methods
Potential relationships between
dependent variables (δ15N and δ13C)
and independent variables (latitude,
ML, distance to shelf break were
investigated using generalized
additive models (software R)
Classification and regression trees
(CART, Brieman et al. 1984) were
used to assess the relative
importance of Year, latitude, size
(ML) and DSB on squid δ15N and
δ13C values
Results: Isotopes variability and habitat
Statistical outputs of GAMs based on mantle δ13C and δ15N values of D. gigas
Variable
Source
e.d.f
F
P
% explained
δ13C
Lat
3.768
37.780
< 2 e-16
34.40
Size
1.000
26.500
7.10 e-07
7.80
DSB
8.283
12.830
7.77 e-15
34.43
< 2 e-16
76.63
Model
δ15N
Lat
3.629
59.419
< 2 e-16
45.33
Size
8.763
9.945
3.46 e-12
28.72
DSB
2.853
7.366
4.19 e-05
6.15
< 2 e-16
82.20
Model
Results: 13C vs DSB
13C
13C
Coastal waters
(>productivity)
13C
Oceanic waters
(<productivity)
Results: 13C vs latitude
13C
(North, <5°S)
13C
7°-13°S
Results: 13C vs latitude
-14
δ13C
-16
-18
-20
Copepods
y = 0.355x - 22.89
r² = 0.655
-22
-24
0
15
10
5
Latitude (S)
Euphausiids
Copepods
D.gigas
Lineal (Copepods)
The latitudinal variation of δ13C values in D. gigas muscles and in zooplankton
samples could then be related to the upwelling off Peru and reflect latitudinal
changes in productivity
20
Results: 13C vs size
Other papers; Ruiz-Cooley (2006)
13C
Related with food web, carbon differences
in δ13C occur primarily at primary
production, with small increases with
increasing trophic level (0.4%; Post 2002)
Therefore, hypothesizing that δ13C values
only reflect changes in habitat, the
increasing trend of δ13C values with ML
would suggest that D. gigas might change
of habitat while growing.
However, the high variability of δ13C by size
in our work suggests that D. gigas’
juveniles and adults distribute over a
large range of habitats
Results: 15N vs latitude
Increasing trend (8‰; 3°S-18°S)
Ruiz-Cooley (2006) (6‰; 40°N-0°N)
Takai (2000) (6‰; Japan – Perú)
If the δ15N of animal tissues are used as an
indicator of trophic position in marine food webs,
variation in δ15N values in consumers may not only
result from the trophic level at which they feed,
but also from changes at the base of the food web
Results: 15N vs latitude
Environmental factor (02)
Dissolved inorganic nitrogen
Baseline isotopic plankton
Results: 15N vs latitude
Environmental factor (02)
Dissolved inorganic nitrogen
Baseline isotopic plankton
North…………………………………………………………………………….South
nitrates
< Oxygen deficient
< denitrification
< 15N
nitrates
> Oxygen deficient
> denitrification
> 15N
Results:Latitudinal variation of δ15N values of zooplankton and D. gigas
in Peruvian waters
A similar trend in D. gigas and
zooplankton suggests that
baseline isotopic values are
also the main drivers of δ15N
values in jumbo squid
muscles.
25
20
δ15N
15
As the slopes did not differ
significantly between
zooplankton nd jumbo squid we
hypothesize that squids of a
same size have a similar
trophic position whatever the
latitude.
10
5
D. gigas
y = 0.539x + 7.404
r² =0.670
Euphausiids
y = 0.469x + 5.647
r² = 0.987
Copepods
y = 0.395x + 5.112
r² = 0.852
0
0
5
10
15
Latitude (S)
Euphausids
Copepods
D.gigas
Lineal (Euphausids)
Lineal (Copepods)
Lineal (D.gigas)
20
At the population level, the very
high variability in both δ13C and
δ15N values at a given DSB or
latitude illustrates that squids
in a given area may come
from different places and
therefore have different life
histories in terms of habitats.
Results: Isotopes variability and diet
Statistical outputs of GAMs based on mantle δ13C and δ15N values of D. gigas
Variable
Source
e.d.f
F
P
% explained
δ13C
Lat
3.768
37.780
< 2 e-16
34.40
Size
1.000
26.500
7.10 e-07
7.80
DSB
8.283
12.830
7.77 e-15
34.43
< 2 e-16
76.63
Model
δ15N
Lat
3.629
59.419
< 2 e-16
45.33
Size
8.763
9.945
3.46 e-12
28.72
DSB
2.853
7.366
4.19 e-05
6.15
< 2 e-16
82.20
Model
Results: 15N vs size
Increasing trend  Ruiz-Cooley (2006)
15N
High variability …..opportunistic foraging strategies
High variability suggest that during ontogeny
squid of different size can prey over same
resources
Results: 15N vs size
15N
Increasing trend  Ruiz-Cooley (2006)
High variability …..opportunistic foraging strategies
High variability suggest that during ontogeny
squid of different size can prey over same
resources
Number of prey species, stomach analyzed and percentage weight of principals prey groups of D.
gigas by mantle length range and latitude
Results: Isotopes variability and diet
This study confirms that D. gigas is a highly opportunistic species with a wide trophic niche
(from euphausiids to cephalopods and fish).
Summary
Results showed a very high variability in both
δ13C and δ15N values at a given DSB, latitude
or size which illustrates that squids captured
in a given area may have very different
life histories.
The increasing trend of
δ13C values with mantle
length, and the strong
relation between δ13C
values and distance to
shelf break suggest that D.
gigas migrate from
oceanic to coastal
waters, changing its
foraging areas between
juvenile and adults,
although no significant
diet shift seems to
occur.
The similar latitudinal trend of
isotope values of zooplankton
and D. gigas in the study area
suggests that D. gigas is a
relatively resident species at
the scale of its tissue
turnover (i.e., a few weeks).
Dosidicus gigas
There is no systematic
increase in trophic
position with size and
that latitude is the main
driving factor on δ15N
values off Peru
Thanks