Abstract
Studies of the diet, feeding habits and trophic activity of top marine predators are essential for understanding their trophodynamics. The main direct method used for such studies thus far has been morphological inventories of stomach contents. This approach presents limitations such as missing gelatinous prey, which are usually digested too quickly to be detectable. Here, we analysed the stomachs of 48 Atlantic bluefin tuna (Thunnus thynnus, approximately 15 to 60 kg, including juveniles and adult fishes) collected from the Mediterranean Sea through the metabarcoding of two gene regions (cytochrome c oxidase subunit I (COI) and the ribosomal 18S-V1V2 region). The identified prey taxa and their relative read abundances (RRAs) estimated using COI results were in line with the findings of morphologically based inventories simultaneously performed on the same set of tuna samples. In both cases (and with the same rankings), the prey taxa included anchovy (Engraulis encrasicolus, here detected in more than 80% of samples, RRA = 43%), sardine (Sardina pilchardus, also approximately 80%, RRA = 30%), sprat (Sprattus sprattus, approximately 66%, RRA = 8%), mackerel (Scomber colias, approximately 44%, RRA = 7%) and cephalopods (approximately 15%, RRA = 1.4%). Another striking result was the detection, based on 18S (with which vertebrates were detected as the most abundant group, RRA = 61.6%), of a high prevalence and diversity of gelatinous organisms (RRA = 27.1%), including cnidarians (6.7%), salps (11.7%), and ctenophores (8.7%), the latter increasing with the size of the predator. These results thus support the hypothesis of the role of gelatinous prey in the diet of Atlantic bluefin tuna, suggesting that this species is even more generalist and opportunistic than previously thought. This study further confirms that DNA metabarcoding can be a powerful tool for assessing the diet and trophodynamics of top marine predators.
Highlights
Large pelagic fishes are top predators that contribute to the stability and persistence of marine ecosystems through top-down control (Estes et al, 2011; Hughes et al, 2013).How to cite this article Günther B, Fromentin J-M, Metral L, Arnaud-Haond S. 2021
Following the recommendation of Deagle et al (2019) to conduct species-by-species comparative studies when working with stomach contents, our comparative analysis showed reasonable congruence between the morphological inventories and relative read abundances (RRAs) based on the c oxidase subunit I (COI) metabarcoding of stomach contents, at least for vertebrate prey
The results obtained from the 18S metabarcoding of stomach contents highlighted a high diversity of gelatinous taxa in the Atlantic bluefin tuna (ABFT) diet, which was stable across years; the importance of these taxa seemed to increase with ABFT weight and, likely with age
Summary
Large pelagic fishes are top predators that contribute to the stability and persistence of marine ecosystems through top-down control (Estes et al, 2011; Hughes et al, 2013).How to cite this article Günther B, Fromentin J-M, Metral L, Arnaud-Haond S. 2021. Large pelagic fishes are top predators that contribute to the stability and persistence of marine ecosystems through top-down control (Estes et al, 2011; Hughes et al, 2013). How to cite this article Günther B, Fromentin J-M, Metral L, Arnaud-Haond S. Information about their ecological niche and trophic dynamics, or ‘‘trophodynamics’’ (the spatial and temporal dynamics of trophic interactions, (Lindeman, 1942; Young et al, 2015), provides insight into essential elements of their basic biology. It is increasingly necessary to understand and forecast the cascading effects of environmental and anthropogenic changes on the marine ecosystems to which they contribute (Myers et al, 2007; Casini et al, 2012)
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