Fig 1.
(A) Map of study area: Spiekeroog, East Frisian Islands, Germany, North Sea. (B) Salt marsh zonation: upper salt marsh (USM, >35 cm above MHWL), lower salt marsh (LSM, 0–35 cm above MHWL) and pioneer zone (PZ, below MHWL) from the land to the sea in relation to shore height and frequency of inundations (USM: 35–70 times a year, LSM: 150–250 times a year, PZ: inundations twice a day).
Fig 2.
(A) Soil mesofauna community structure: canonical correspondence analysis (CCA) based on the density of 86 soil animal taxa (log-transformed) along the studied salt marsh gradient: upper salt marsh (USM), lower salt marsh (LSM) and pioneer zones (PZ). For full species names see Table A in S1 File. Eigenvalues of axis 1 = 0.6610 and axis 2 = 0.3214. (B) Discriminant function analysis (DFA) of soil invertebrate community of the three salt marsh zones: USM, LSM and PZ; ellipses represent confidence ranges at p < 0.05.
Fig 3.
(A) Density and (B) diversity of soil mesofauna species at the upper salt marsh (USM), lower salt marsh (LSM) and pioneer zone (PZ). Boxplots represent mean (red line) and median (black line) of density and diversity. Different letters represent significant differences between zones (Tukey’s HSD test, p < 0.05).
Fig 4.
(A) δ15N signatures of all soil mesofauna species in the upper salt marsh (USM), lower salt marsh (LSM) and pioneer zone (PZ). Boxplots represent mean (red line) and median (black line) of δ15N signatures; different letters represent significant differences between zones (Tukey’s HSD; p < 0.05). (B) δ13C and δ15N stable isotope values (means with standard deviation) of dominant mesofauna species: Collembola (orange squares), Mesostigmata (blue squares) and Oribatida (green squares). Black dashed horizontal lines represent estimated trophic level boundaries with each trophic level spanning 3.4‰ δ15N: I = primary decomposers, II = secondary decomposers, III = first order predators, and IV = second order predators. Number of replicates are included in parentheses; see Table C in S1 File for full species names.
Fig 5.
(A) δ13C signatures of basal food resources in the three salt marsh zones: upper salt marsh (USM), lower salt marsh (LSM) and pioneer zones (PZ). Boxplots represent mean (red line) and median (black line) of δ13C signatures; different letters represent significant differences between vegetation zones (Tukey’s HSD, p < 0.05). (B) Pie charts represent mean percentages of potential food resources [C3 plants/algae, C4 plants/algae and organic material (OM) containing C3 and/or C4 plants/algae] of Collembola and Oribatida species along the salt marsh gradient.