Little is known about the processes shaping population structure in saltmarshes. It is expected that the sea should act as a powerful agent of dispersal. Yet, in contrast, import of external propagules into a saltmarsh is thought to be small. To determine the level of connectivity between saltmarsh ecosystems at a macro-geographical scale, we characterised and compared the population structure of two polyploid saltmarsh species, Puccinellia maritima and Triglochin maritima based on a seascape genetics approach. A discriminant analysis of principal components highlighted a genetic structure for both species arranged according to a regional pattern. Subsequent analysis based on isolation by distance and isolation by resistance frameworks indicated a strong role of coastal sediment transport processes in delimiting regional structure in P. maritima while additional overland propagule dispersal was indicated for T. maritima. The identification and comparison of regional genetic structure and likely determining factors presented here allows us to understand the biogeographical units along the UK coast, between which barriers to connectivity occur not only at the species level but at the ecosystem scale. This information is valuable in plant conservation and community ecology and in the management and restoration of saltmarsh ecosystems.

#### Mantel test script

R script permitting to compute Mantel tests

Mantel.R

#### Ordination (NMDS) script

R script permitting to compute and plot a Nonmetric Multidimensional Scaling (NMDS) ordination

Ordination.R

#### Puccinellia maritima population assignment to DAPC regions (K=4)

Puccinellia maritima input file for the implementation of the AMOVA

P_4clusters.txt

#### Puccinellia maritima population assignment to DAPC regions (K=5)

Puccinellia maritima input file for the implementation of the AMOVA

P_5clusters.txt

#### Puccinellia maritima population assignment to DAPC regions (K=6)

Puccinellia maritima input file for the implementation of the AMOVA

P_6clusters.txt

#### Puccinellia maritima AMOVA script

R script permitting to compute AMOVA for Puccinellia maritima

P_amova.R

#### Puccinellia maritima samples assignment to population of origin

Puccinellia maritima input file for the implementation of the AMOVA

P_Populationdata.txt

#### Puccinellia maritima DAPC script

R script permitting to compute DAPC for Puccinellia maritima

P_Script DAPC.R

#### Coastal distance between Puccinellia maritima populations

Matrix showing coastal distance between Puccinellia maritima populations

Pdistcoast.txt

#### Puccinellia maritima microsatellite dataset

Individuals are in row, microsatellite alleles in columns. Microsatellite alleles are coded as present or absent (1/0) in each individuals. NA for missing data.

Pglobalpopgenbin.txt

#### Pairwise effective resistance between Puccinellia maritima population (TIDE model)

Matrix of pairwise effective resistance (TIDE model) between Puccinellia maritima population inferred using the software Circuitscape. This matrix is inputted in R for Mantel test.

Pres_100_linear_buffer.txt

#### Pairwise effective resistance between Puccinellia maritima population (SEDCELLS model)

Matrix of pairwise effective resistance (SEDCELLS model) between Puccinellia maritima population inferred using the software Circuitscape. This matrix is inputted in R for Mantel test.

Pres_100_sedcells_buffer.txt

#### Pairwise effective resistance between Puccinellia maritima population (TIDE_SEDCELLS model)

Matrix of pairwise effective resistance (TIDE_SEDCELLS model) between Puccinellia maritima population inferred using the software Circuitscape. This matrix is inputted in R for Mantel test.

Pres_100_sedcells_linear_buffer.txt

#### Triglochin maritima population assignment to DAPC regions (K=4)

Triglochin maritima input file for the implementation of the AMOVA

T_4 clusters.txt

#### Triglochin maritima population assignment to DAPC regions (K=5)

Triglochin maritima input file for the implementation of the AMOVA

T_5 clusters.txt

#### Triglochin maritima population assignment to DAPC regions (K=6)

Triglochin maritima input file for the implementation of the AMOVA

T_6 clusters.txt

#### Triglochin maritima AMOVA script

R script permitting to compute AMOVA for Triglochin maritima

T_amova.R

#### Triglochin maritima samples assignment to population of origin

Triglochin maritima input file for the implementation of the AMOVA

T_Populationdata.txt

#### Triglochin maritima DAPC script

R script permitting to compute DAPC for Triglochin maritima

T_Script DAPC.R

#### Coastal distance between Triglochin maritima populations

Matrix showing coastal distance between Triglochin maritima populations

Tdistcoast.txt

#### Triglochin maritima microsatellite dataset

Individuals are in row, microsatellite alleles in columns. Microsatellite alleles are coded as present or absent (1/0) in each individuals. NA for missing data.

Tglobalpopgenbin.txt

#### Pairwise effective resistance between Triglochin maritima population (TIDE model)

Matrix of pairwise effective resistance (TIDE model) between Triglochin maritima population inferred using the software Circuitscape. This matrix is inputted in R for Mantel test.

Tres_100_linear_buffer.txt

#### Pairwise effective resistance between Triglochin maritima population (SEDCELLS model)

Matrix of pairwise effective resistance (SEDCELLS model) between Triglochin maritima population inferred using the software Circuitscape. This matrix is inputted in R for Mantel test.

Tres_100_sedcells_buffer.txt

#### Pairwise effective resistance between Triglochin maritima population (TIDE_SEDCELLS model)

Matrix of pairwise effective resistance (TIDE_SEDCELLS model) between Triglochin maritima population inferred using the software Circuitscape. This matrix is inputted in R for Mantel test.

Tres_100_sedcells_linear_buffer.txt