Table 1.
Biomass of tested brown algae and their specific extract yield.
Table 2.
Blast identification and percentage similarity of bacterial 16S rDNA sequences.
Fig 1.
Log response ratios (LogRR) of bacterial growth of strains 1–6 (a-f) in response to different concentrations of crude and surface extracts of Sargassum fusiforme (S.f.), Sargassum horneri (S.h.), native (nat.) and invasive (inv.) Sargassum muticum (S.m.), Fucus vesiculosus (F.v.) and the antibiotic positive control (AB; gentamicin or penicilin; 100 μg/ml). Circle–natural concentrations, square– 2-times natural concentrated extracts. Asterisks indicate significant differences between treatments and solvent control (ANOVA, Tukey post-hoc test p < 0.05).
Table 3.
Anti-QS and growth inhibitiory activity of Chromobacterium violaceum by algal extracts.
Fig 2.
Antidiatom activity of algal extracts.
Effect of crude (black) and surface (grey) extracts of S. fusiforme (S.f.), S. horneri (S.h.), native and invasive S. muticum (S.m. (nat.) and (inv.)), and F. vesiculosus (F.v.) on cell densities (mean ± SD, n = 6) of the diatom C. closterium after 7 days. Extracts were tested at the natural concentrations. Methanol was used as the control (C). Significant differences (p < 0.05) are indicated by different letters (upper- and lower case letters for crude and surface extracts, respectively) above the bars (according to Kruskal–Wallis test with the Dunn′s multiple post-hoc comparison test).
Fig 3.
Growth inhibitory activity of algal extracts on Cylindrotheca closterium.
Effect of different concentrations (1-, 0.5-, 0.1-, 0.05-, and 0.01-times natural concentration) of crude and surface extracts of S. fusiforme, the native (nat) and invasive (inv) S. muticum (S. m.) and surface extracts of S. horneri and F. vesiculosus on the density of the diatom Cylindrotheca closterium after 1 and 7 days. The data are the mean + SD, n = 6. Colour gradient from black to white represents different concentrations of extracts. Significant density differences compared to controls are indicated by asterisks above the bars (* p ≤ 0.05, ** p ≤ 0.01, ***p ≤ 0.001, Kruskal–Wallis test).
Fig 4.
Anti-larval activity of algal extracts.
Percentage of settled, swimming and dead bryozoan larvae of B. neritina. Larvae were exposed to 0.2-times natural concentrated crude- (black) and surface extracts (grey) of S. fusiforme (S.f.), S. horneri (S.h.) the native and invasive S. muticum (S.m. (nat.) and S.m. (inv.)) and solvent controls (C). Larvae were counted 3, 6, and 24 h after the start of the experiment. The data are the mean + SD, n = 10. Significant differences (p < 0.05) of crude (capital letters) and surface extracts (lowercase letters) compared to the controls are indicated by different letters above the bars (Kruskal–Wallis test with Dunn′s multiple comparisons post hoc test).
Fig 5.
Anti-zygote activity of algal extracts.
Effect of different concentrations (1-, 0.5-, 0.1-times natural concentrations) of crude and surface extracts of S. fusiforme, S. horneri, the native and invasive S. muticum (S.m.) and solvent controls (C) on F. vesiculosus zygote settlement. Data are the mean ± SD, n = 6. Settlement rates were scored 1, 2, 4 and 7 days after the start. Significant settlement differences compared to controls are indicated by asterisks above the bars (* p ≤ 0.05, ** p ≤ 0.01, ***p ≤ 0.001, ANOVA).
Fig 6.
Tissue phlorotannin content (means + SD; n = 3) in Sargassum spp. from Japan (white bars; S. muticum (SM (nat), S. fusiforme (SF), S. horneri (SH)) and S. muticum (SM (inv.) and F. vesiculosus (FV) from the North Sea (black bars). Different letters above the bars indicate significant differences between tissue concentrations (ANOVA, Tukey post hoc test, p < 0.05).
Fig 7.
Summary of the results of the experiments comparing the chemical defence of the invasive and native S. muticum, Sargassum spp. from Japan, and the brown alga F. vesiculosus from the North Sea.
The antibacterial activity is presented as the percent of inhibited bacterial strains and MIC-values are provided for inhibition of QS (X-times natural concentration, ‘-’ = no inhibition). The settlement inhibitory activity is presented as both, the MIC inhibiting diatom (C. closterium) growth and bryozoan (B. neritina) larval settlement (‘+’ = settlement inhibition after 24h; ‘-’ = no settlement inhibition; n.c. = not conducted). Algal zygote settlement inhibition is presented as the MIC inhibiting F. vesiculosus zygote settlement (as X-times natural concentration [x N]). The amount of phlorotannins in algal tissues is represented as the proportion of total phenolic content (TPC) per algal dry weight (dw).