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

respecto a las horas del día

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Prof

unfi

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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

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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