Preprint volume - SIBM

Genoa
Sestri Levante
Pre-print Volume – Oral presentations
Topic 3: INTEGRATED COASTAL ZONE MANAGEMENT
Ligurian
Sea
15° E
40° N
Fig. 1 – Map of the sampling location.
Localizzazione geografica del sito di campionamento.
Sagittal otoliths were extracted under a stereomicroscope, cleaned and stored to dry.
One otolith from each pair was aged, mounted on glass slide, and ground (with 3M
Imperial lapping film) to expose the core. Otoliths were then rinsed, sonicated for 10
min in de-ionized water, and analyzed using a LA-ICPMS (laser ablation inductively
coupled plasma mass spectrometer) for 8 elements (Li, Mg, Mn, Zn, Sr, Ba, Pb and Hg;
the values of Mn and Hg were consistently below the detection limits and therefore
excluded from the data analyses). The LA-ICPMS system was calibrated using 610 and
612 glasses. Calcium was used as internal standard to take into account variation in
ablation and aerosol efficiency. Three replicates from each core were sampled by three
sequential pits vertically collected (Ruttenberg et al., 2008) using a spot size of ~28
μm. Three additional pits were collected in the juvenile region (~40-50 μm far from the
core; Cermeño et al., 2006) to assess potential differences in the microchemical
composition of the otolith related to the ontogenetic development (Elsdon &
Gillanders, 2005). Prior to analysis, samples were pre-ablated to remove any surface
contamination (laser at 50% power). The putative differences between ‘core’ and
‘juvenile’ otolith sectors, and among otoliths (using otolith × element matrices) were
analysed using two-way permutational multivariate analysis of variance
(PERMANOVA; Anderson, 2001). The sampling design consisted of 2 factors: “core”
vs “juvenile” otolith sectors (C vs J; fixed factor with 2 levels) and ‘otolith’ (Ot;
random and orthogonal). Multivariate analyses were based on dissimilarity matrices
based on Euclidean distances and log(x+1) transformed data. nMDS of centroids for
each otolith (separating cores and juvenile sectors) was used to visualize the pattern
observed (Clarke & Warwick, 2001). The SIMPROF (similarity profile) test,
associated to cluster analysis (PRIMER 6 package; Clarke & Gorley, 2006), was used
to test the null hypothesis that our set of otolith cores, not a priori divided into groups,
do not differ from each other in microchemical composition. The SIMPROF test was
run after having split anchovy samples into age groups. Otoliths corresponding to
specimens 3 (n=10) and 4 years old (n=3) were too scarce numerically and were
excluded from the statistical analyses.
Results - Otoliths of European anchovy from Sestri Levante showed different
microchemical patterns when cores were compared with juvenile otolith sectors (Fig.
2). PERMANOVA test revealed that cores and juvenile sectors were significantly
different (d.f.: 1; pseudo-F: 1766.98; P