Abstract
The three-spined stickleback (Gasterosteus aculeatus L., hereafter ‘stickleback’) is a common mesopredatory fish in marine, coastal and freshwater areas. In large parts of the Baltic Sea, stickleback densities have increased >10-fold during the last decades, and it is now one of the dominating fish species both in terms of biomass and effects on lower trophic levels. Still, relatively little is known about its diet—knowledge which is essential to understand the increasing role sticklebacks play in the ecosystem. Fish diet analyses typically rely on visual identification of stomach contents, a labour-intensive method that is made difficult by prey digestion and requires expert taxonomic knowledge. However, advances in DNA-based metabarcoding methods promise a simultaneous identification of most prey items, even from semi-digested tissue. Here, we studied the diet of stickleback from the western Baltic Sea coast using both DNA metabarcoding and visual analysis of stomach contents. Using the cytochrome oxidase (CO1) marker we identified 120 prey taxa in the diet, belonging to 15 phyla, 83 genera and 84 species. Compared to previous studies, this is an unusually high prey diversity. Chironomids, cladocerans and harpacticoids were dominating prey items. Large sticklebacks were found to feed more on benthic prey, such as amphipods, gastropods and isopods. DNA metabarcoding gave much higher taxonomic resolution (median rank genus) than visual analysis (median rank order), and many taxa identified using barcoding could not have been identified visually. However, a few taxa identified by visual inspection were not revealed by barcoding. In summary, our results suggest that the three-spined stickleback feeds on a wide variety of both pelagic and benthic organisms, indicating that the strong increase in stickleback populations may affect many parts of the Baltic Sea coastal ecosystem.
Highlights
The three–spined stickleback (Gasterosteus aculeatus L., hereafter ‘stickleback’) is a common mesopredatory fish of high ecological interest, widespread all over the northern hemisphere in various habitats including coastal seas, estuaries, freshwater lakes and streams [1]
We addressed three questions: 1) what do sticklebacks eat in coastal areas, 2) how does stickleback diet depend on its body size, and 3) how do visual and DNA-based methods compare in terms of prey identification from stomach content
A broad range of phyla were found, but Arthropoda dominated by far (Fig 2). Given that this is the first barcodingbased study of Baltic Sea stickleback diet, we provide the whole list of taxa found (S1 Table)
Summary
The three–spined stickleback (Gasterosteus aculeatus L., hereafter ‘stickleback’) is a common mesopredatory fish of high ecological interest, widespread all over the northern hemisphere in various habitats including coastal seas, estuaries, freshwater lakes and streams [1]. Knowledge on the role of sticklebacks in aquatic food webs is, rather limited, especially in coastal and marine areas. To better understand the ecological role of sticklebacks, their feeding patterns and diet preferences need to be described, as feeding behaviour may affect community composition and food web functions. In the brackish Baltic Sea, stickleback abundance has increased more than 10-fold during the last decade [5]. The increasing abundances of sticklebacks, in combination with their central role in ecosystem functioning, points to the need for more detailed knowledge on stickleback diets
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