Abstract
Diet studies provide base understanding of trophic structure and are a valuable initial step for many fields of marine ecology, including conservation and fisheries biology. Considerable complexity in marine trophic structure can exist due to the presence of highly mobile species with long life spans. Mobula rays are highly mobile, large, planktivorous elasmobranchs that are frequently caught either directly or as bycatch in fisheries, which, combined with their conservative life history strategy, makes their populations susceptible to decline in intensely fished regions. Effective management of these iconic and vulnerable species requires an understanding of the diets that sustain them, which can be difficult to determine using conventional sampling methods. We use three DNA metabarcode assays to identify 44 distinct taxa from the stomachs (n = 101) of four sympatric Mobula ray species (Mobula birostris, Mobula tarapacana, Mobula japanica, and Mobula thurstoni) caught over 3 years (2013–2015) in a direct fishery off Bohol in the Philippines. The diversity and incidence of bony fishes observed in ray diets were unprecedented. Nevertheless, rays showed dietary overlap, with krill (Euphausia) dominating their diet. Our results provide a more detailed assessment of sympatric ray diets than was previously described and reveal the complexity that can exist in food webs at critical foraging habitats.
Highlights
Diet studies provide basic knowledge of a species’ diet composition, its trophic position, and the links between predator and prey in the food web
Operational Taxonomic Units (OTUs) were resolved to genus, family, or higher, for 16S Fish or 16S Crustacea primer assays based on the percent similarity to taxa alignments; we provide a summary of maximum bit scores and identities for the most closely matched species to provide transparency in OTU clustering (Table 4)
In our case, where we study the diet of four closely related sympatric species, biases are very likely to be consistent among the four ray species, so it is reasonable to infer that all of them eat a similar proportion of Euphausia and have a low level of dependence on nonkrill items
Summary
Diet studies provide basic knowledge of a species’ diet composition, its trophic position, and the links between predator and prey in the food web. DNA metabarcoding studies have revealed insights into the dietary composition of endangered sea lions (Berry et al, 2017), exploited marine fishes (Berry et al, 2015), planktivorous fishes (Albaina, Aguirre, Abad, Santos, & Estonba, 2016) and have even been used to investigate dietary niche partitioning by large African herbivores (Kartzinel et al, 2015) These DNA‐based approaches have the potential to extend our current understanding of Mobula prey items and trophic interactions, especially when multiple DNA markers are combined with conventional methods (Nielsen et al, 2017; Pompanon et al, 2012). We identified taxa to the lowest resolution, determined the frequency of occurrence for each taxon, tested for prey differences between years, investigated dietary overlap in potential prey between species, and estimated the dietary proportions of these potential prey items
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