Post on 29-Jan-2016
15N
Tracking habitat and resource use for Dosidicus
gigas: a stable isotope analysis in the Northern
Humboldt Current System
Juan Argüelles · Anne Lorrain · Yves Cherel · Michelle Graco · Ricardo Tafur ·
Ana Alegre · Pepe Espinoza · Anatolio Taipe · Patricia Ayón · Arnaud Bertrand
Introduction
Some limitations:•absence or minimal amount of food in cephalopods stomach•differences in digestibility among preys•selectivity rejection of a potential prey
D. gigas diet Stomach content:
Introduction
D. Gigas habitat
Fluctuación de los registros del calamar gigante con
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Prof
unfi
dad
(m
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Introduction
Stable isotope analysis (SIA)
Stable isotopes of consumers reflect that of prey as well as the habitat of the individual.
Nitrogen isotopes typically indicate trophic position, while
carbon isotopes reflect variation in baseline producers or habitat.
You are what you eat
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 ?.
Questions:
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).
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.
LONGITUDE
LATI
TUD
E
Micromass at Department of Marine Biology, La Rochelle, France.
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
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
Model < 2 e-16 76.63
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
Model < 2 e-16 82.20
Statistical outputs of GAMs based on mantle δ13C and δ15N values of D. gigas
Results: 13C vs DSB
13C
13C 13C
Coastal waters(>productivity)
Oceanic waters(<productivity)
Results: 13C vs latitude
13C 13C
(North, <5°S) 7°-13°S
Results: 13C vs latitude
Copepodsy = 0.355x - 22.89
r² = 0.655-24
-22
-20
-18
-16
-14
0 5 10 15 20
δ13C
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
Results: 13C vs size1
3C
Other papers; Ruiz-Cooley (2006)
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
Baseline isotopic planktonDissolved inorganic nitrogen
Environmental factor (02)
Results: 15N vs latitude
Baseline isotopic planktonDissolved inorganic nitrogen
Environmental factor (02)
North…………………………………………………………………………….South
nitrates nitrates
< Oxygen deficient > Oxygen deficient
< denitrification
< 15N
> denitrification
> 15N
Euphausiidsy = 0.469x + 5.647
r² = 0.987
Copepodsy = 0.395x + 5.112
r² = 0.852
D. gigasy = 0.539x + 7.404
r² =0.6700
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δ15N
Latitude (S)Euphausids Copepods D.gigas
Lineal (Euphausids) Lineal (Copepods) Lineal (D.gigas)
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.
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.
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
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
Model < 2 e-16 76.63
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
Model < 2 e-16 82.20
Statistical outputs of GAMs based on mantle δ13C and δ15N values of D. gigas
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
Results: 15N vs size1
5N
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).
Dosidicus gigas
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 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).
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.
There is no systematic increase in trophic position with size and that latitude is the main driving factor on δ15N values off Peru
Summary
Thanks