Page 1 - Thunnus_2020

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open Growth-related trophic changes of

Thunnus thynnus as evidenced by

stable nitrogen isotopic values in

the f rst dorsal spine

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paola Rumolo 1 ✉ , Angelo Bonanno , Simona Genovese , teresa Romeo ,
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Salvatore Mazzola , Gualtiero Basilone , Serena Gherardi , pietro Battaglia ,
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franco Andaloro & Marco Barra 1
The bluef n tuna, Thunnus thynnus, is a highly migratory and long-living f sh at the top of the pelagic
food web. As top predator, it plays a key role in the stability of marine food webs by exerting top-down
control on its prey. The diet composition of bluef n tuna varies in relation to its growth, seasons and
migratory patterns, making it dif cult to evaluate spatial and temporal ef ects. This latter aspect is
further complicated to be determined during the f rst months of life, when T. thynnus specimens have a
rapid growth rate leading to changes in the trophic status. in this study, the potential collagen-related
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ef ects on δ n and δ c values were evaluated on the whole spine of adult tuna specimens collected in
the central Mediterranean Sea. Obtained results showed non-signif cant dif erences between extracted
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and non-extracted collagen samples for δ n in whole spine, allowing adopting the isotopic analysis
both for annuli in the spine section of adults and for younger specimens, whose spine size does not
permit the collagen extraction. Specif cally, isotopic analysis of whole spine of the young of the year
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specimens, showed a rapid change in δ n values with length, following an exponential model. for
older specimens, δ N values were higher and varied around a plateau, likely due to a higher specif city
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in the choice of prey and/or to change in the geographical location. Such variability was also mirrored
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in annuli of spines sections of adult tunas. As far as δ c values are concerned, a strong collagen-related
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ef ect was evidenced, likely highlighting the inf uence of lipids. Consequently, δ c analysis may be used
only on adult specimens where collagen extraction is possible. this research also showed how isotopic
analysis of both whole sample and sequence of annuli in the cross-section of dorsal spine might produce
isotopic prof les useful to detect specif c trophic dynamics along the bluef n tuna growth.
In recent years, stable nitrogen and carbon isotopes analyses (δ N and δ C), performed on less metabolically
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active tissues, such as scale, otoliths, spines and bones, allowed to investigate several aspects of animal’s feeding
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habits, habitat use and migration (e.g. ). However, there are dif erent isotopic approaches for estimating diet
and movement patterns of multiple taxa using inert tissues. For instance, the collagen extracted from whole bone
of an animal can provide an integration of stable isotopes from multiple years with a general interpretation of its
trophic behavior during the entire lifetime 2,7–11 . T e analysis in single layers in some hard structures, such as teeth
and humerus (with each layer representing a dif erent interval of animal’s life), provides a time series of isotopic
data, useful for reconstructing an animal’s foraging ecology over time 7,12–20 . It is important to single out that some
methods need large amount of sample in order to remove lipids and other contaminants (e.g. collagen extraction),
thus preventing their use for samples characterized by small dimensions ; other methods require a greater ef -
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ciency and accuracy in the determination and in the selection of individual annual growth layer from the tissue
section (e.g. skeletochronology method) 14–16 .
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1 CNR-ISMAR, Calata Porta di Massa (Interno Porto di Napoli), Naples, Italy. CNR-IAS, Torretta Granitola, Campobello
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di Mazara (TP), Italy. Stazione Zoologica Anton Dohrn, Centro Interdipartimentale della Sicilia, Milazzo (ME), Italy.
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4 Istituto Superiore per la Protezione e la Ricerca Ambientale, ISPRA, Milazzo (ME), Italy. e-mail: paola.rumolo@
cnr.it
Scientific RepoRtS | (2020) 10:9899 | https://doi.org/10.1038/s41598-020-66566-w 1