Deciphering Eurasian otter (Lutra lutra L.) and seal (Phoca vitulina L.; Halichoerus grypus F.) diet: Metabarcoding tailored for fresh and saltwater fish species

Abstract

Long‐lived top predators shape biodiversity structure in their ecosystems and predator–prey interactions are critical in decoding how communities function. Studies on the foraging ecology of seals and Eurasian otters in Western Europe are outdated and most studies solely performed traditional hard part analysis. Molecular metabarcoding can be used as an innovative noninvasive diet analysis tool, which has proven efficient and complementary to hard part analysis, however, lacking application in the wider North Sea area. In this study, DNA from digesta, collected between 2014–2020, were used to identify fish species in the diet of 47 Eurasian otters, 54 harbour seals and 21 grey seals by applying a next‐generation metabarcoding approach. A newly designed 16S rRNA primer, providing the best coverage of >130 local marine and freshwater fish species, was used to amplify prey DNA from seal scats and otter gut content sampled from the North Sea and regional freshwater bodies. Frequent fish species included tench, ninespine stickleback and white bream in otters; hooknose and common roach in grey seals and Pleuronectidae and sand gobies in harbour seals. Bipartite network analysis showed a strong overlap of harbour and grey seal diets. Otter diet intersected with both seal species in terms of freshwater species. This study provides new knowledge about dietary composition and community assemblage of fish prey in otters and seals in the North Sea and regional freshwaters, and a new molecular tool to elucidate predator–prey interactions and interspecies competition in complex and changing ecosystems under pressure from anthropogenic activities.

Heartworms in Halichoerus grypus: first records of Acanthocheilonema spirocauda (Onchocercidae; Filarioidea) in 2 grey seals from the North Sea

“…Heartworms are common in harbour seals and frequently infect individuals found stranded along the German North-and Baltic Sea coasts (Claussen et al, 1991;Lehnert et al, 2007Lehnert et al, , 2015 and adjacent waters (Lunneryd, 1992). However, they were so far not reported from grey seals which share their habitat, diet preferences and haul-outs with harbour seals (Brasseur, 2017;Damseaux et al, 2021;Boyi et al, 2022). The insect seal louse Echinophthirius (E.) horridus infects both harbour and grey seals and occur regularly on both species throughout the study area (Zimmermann and Nebel, 1975;Lehnert et al, 2015) and in adjacent waters (Thompson et al, 1998;Morick et al, 2009).…”

“…Heartworms are common in harbour seals and frequently infect individuals found stranded along the German North- and Baltic Sea coasts (Claussen et al ., 1991; Lehnert et al ., 2007, 2015) and adjacent waters (Lunneryd, 1992). However, they were so far not reported from grey seals which share their habitat, diet preferences and haul-outs with harbour seals (Brasseur, 2017; Damseaux et al ., 2021; Boyi et al ., 2022). The insect seal louse Echinophthirius ( E .)…”

Insights into Ecological & Evolutionary Processes via Community Metabarcoding

“…Ando et al (2022) used fecal DNA metabarcoding from 7 species of ducks (329 samples) to show strong niche partitioning of plant diet across species but opportunistic foraging when invertebrates were the available food source. Likewise, Boyi et al (2022) examined niche overlap in a co-occurring predators in the North Sea. Using a new 16S primer to metabarcode gut contents, they showed that the composition of fish prey in the diet of the Eurasian otter overlaps that of both harbour and grey seal diets, highlighting the possibility of interspecies competition where these species sharing foraging ground.…”