Trophic position of Mediterranean bluefin tuna larvae estimated by different stable isotope analyses

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1 Trophic position of Mediterranean bluefin tuna larvae estimated by different stable isotope analyses Amaya Uriarte, R. Laiz-Carrion, J. Llopiz, J.M. Quintanilla, F. Alemany and A. García

2 Introduction Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758) is a large migratory fish and an oceanic top predator, considered as an important fishery resource worldwide and key species in the pelagic ecosystems. ABF is listed as Endangered under Criterion A2 (UICN)

3 Introduction The larval phase is a vulnerable life stage critical to recruiment Recruitment processes of marine fish populations have long centered on the transition from yolk sac to exogenous feeding as one the most important factors influencing larval survival. Flexion Preflexion Postflexion

4 Introduction Trophic ecology Stable isotope analysis Stable isotopes of nitrogen 15 N/ 14 N(δ 15 N) provide a powerful tool for estimating the trophic positions in food webs

5 Introduction Measurements of the δ 15 N a consumer are enriched in successive trophic levels δ 15 N From Ménard et al., st CLIOTOP Symposium δ 15 N is an indicator of trophic position in food webs

6 Introduction Aim of the study Study of the variability of δ 15 N ( ) during the ontogenic development of BFTL Estimates the trophic position (TP) of Mediterranean bluefin tuna larvae by different stable isotopes analyses (SIA-Bulk) and amino acids (CSIA-AA) Compare analyses methods of stable isotopes (SIA-Bulk vs CSIA-AA) in bluefin tuna larvae SIA-Bulk TP δ 15 N CSIA-AA

7 Materials and Methods ATAME project Study area and sampling Surveys Bluenfin (jun-jul) Spain - Mediterranean Balearic Sea RV Socib STATION SAMPLING DISTRIBUTION

8 Materials and Methods Samples treatment Nets Bongo 90 (500µ) Bongo 20 (200µ) B-20 N2 On board Photo-SL Preserve Lab IEO-Málaga -80ºC Dry freezer Weight B-90 Depth mts Length-Weight Selection Stable Isotope Analyses CSIA-AA SIA-Bulk

9 Materials and Methods SIA-Bulk Trophic position CSIA-AA Glu Phe

10 Results y Discussion 2,0 1,5 Length-Weight Preflexion Postflexion Y=0,0097*exp (0,626*X) ) N=307 larvae DW(mg) 1,0 Flexion 0,5 0, SL(mm)

11 Results y Discussion δ 15 N-Length (mm) SIA-Bulk broodstock 16 Preflexion Postflexion YSL ) N 15 ( δ 10 8 Flexion 6 4 Post-flexion larvae SL(mm) δ 15 N pre-flexion larvae δ 15 N post-flexion larvae

12 Results y Discussion TROPHIC CSIA-AA SIA-Bulk AA SOURCE Diferent between pre and postflexion

13 Relative δ 15 N ( ) Results y Discussion 12 - Top Carnivores YSL - Eggs 9 - Carnivores 6 - Adult 3 - Omnivorous Juvenil Planktivoros Post-Larvae 1 - Larvae Amaya Uriarte et al, SIEBM2016 Trophic ecology of bluefin tuna in relative δ 15 N ( ) δ 15 N pre-flexion larvae and eggs = δ 15 N broodstock

14 Results y Discussion Trophic position Methods N # Larva Trophic position (TP) SIA-Bulk CSIA-AA pool 3.05 ± ± 0.04 ANOVA, F(2,246)= 8.16 p<0.05 No significant difference is observed in trophic position TP between stable isotope analyses

15 Results y Discussion Comparison of methods SIA for estimating trophic position TP - SIA-Bulk Require the δ 15 N identification of source food in the environment high variability, require more samples CSIA-AA Weight per sample (>4mg), require make a pool of larvae for a sample Complex and expensive analyses Less weight per sample (1-2mg) individual larva Isotopic data of environment /Compare ecosystems Simpler and economic analyses The TP is estimate from amino acids trophic (δ 15 N Glu ) and source (δ 15 N Phe ) of the larvae.

16 Conclusions 1. Differences between pre and post-flexion development stage in bluefin tuna. 2. High values of δ15n in pre-flexion larvae are origin maternal and reach steady state in flexion stage. 3. Trophic position was estimated in post-flexion larvae to avoid the maternal influence of δ 15 N. TP= was similar to reported by Laiz-Carrión et al in the Mediterranean Sea. 4. Trophic position (TP) estimated was similar with both methods (CSIA and SIA), showed that are an usefull tool to study the feeding ecology of tuna larvae

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18 16 14 Field: Preflexion Postflexion Culture: Preflexion Postflexion 12 δ 15 N ( ) SL(mm)

19 δ 13 C ( ) δ 13 C ( ) δ 15 N ( ) δ 15 N ( ) YSL Preflexion Rotifers Absorption δ 15 N: 0.5 Yolk Sac δ 13 C: Maternally Transmitted Flexion Postflexion Early juvenil Yolk sac larvae Sparus aurata δ 15 N: 12.9 δ 13 C: DPH DAH Uriarte et al Scientia Marina (in press)