Detektering av flera fiskarter i dieten hos den invasiva svartmunnade smörbulten påvisar nya trofiska interaktioner i Östersjön

The purpose of the study was to investigate round goby diet in two geographically distant areas in the Baltic Sea in two consecutive years, using two different methods. We collected round goby using fyke nets and gill nets in May and June 2018-2019 in Karlskrona in the southern Baltic Sea and on Åland in the northern Baltic Sea. The data set contains data of round goby diet, collected through both visual stomach content analysis (VSCA) and DNA metabarcoding. In VSCA, we dissected round goby and determined the prey items to the lowest possible taxonomic level, counted the individual prey/prey groups and estimated their relative proportions in each sample. In DNA metabarcoding, we used the 12S marker for detection of fish species in round goby diet, and the COI marker for an estimation of the proportions of fishes vs. invertebrates in the diet. DNA from round goby stomach samples was amplified using PCR and sequenced on the Illumina MiSeq platform. The output is then provided as number of sequences per prey species per sample, which roughly corresponds to relative biomass per prey species per sample. This makes it possible to compare approximate diet proportions between VSCA and DNA metabarcoding. We then analyzed round goby diet variation between areas and years for VSCA and metabarcoding (12S) separately with Redundancy analysis (RDA). In order to investigate how round goby environmental abundances potentially influenced round goby diet, we analyzed how the fyke net catches varied between areas, years and months. The data of round goby environmental abundances was standardized for catch per unit effort (CPUE) to make comparisons possible. We then related the fyke net catches to number of prey aggregated in prey groups in round goby diet using linear mixed models (LMM) and general linear mixed models (GLMM). To minimize the risk of drawing the wrong conclusions from the analysis of how round goby environmental abundances potentially influenced round goby diet, we also analyzed the environmental densities of ...