## 4 Discussion
### Implications for Shorebirds and Benthic Invertebrates  
This intertidal cartography was made with a focus on identifying and quantifying habitat units of importance to shorebirds and their prey. As such, all seven habitat types are characterized by biotic and abiotic traits differentially important to shorebird species. Rock habitats are scarce in the Bijagos Archipelago and mainly border the coasts of the islands. They are nonetheless important intertidal habitats to some shorebird species such as the Common Sandpiper _Actitis hypoleucos_ and Ruddy Turnstone _Arenaria interpres_[57]. Hard structures in the sediment, such as dead shell beds, may increase the substrate resistance, consequently decreasing the available space for some benthic invertebrates [56] and rendering the sediment inaccessible to probing shorebirds. However, in temperate intertidal areas, Ruddy Turnstones were reported to occur only in areas with >30% of dead shell cover [54] and Whimbrels _Numenius phaeopus_ were also observed using dead oyster banks (author's pers. obs.). Macroalgae, which cover ca. 12% of the intertidal surface of the Bijagos Archipelago, may differentially affect the foraging behaviour and success of different shorebird species. Some visual foragers such as Grey Plovers _Pluvialis squatarola_ have been reported to have had their foraging area reduced by macroalgae mats [58], while tactile forager species can actually benefit from macroalgae habitats, as they promote prey variability across the intertidal landscape and may additionally reduce competition from larger shorebird species [58].  
Fiddler crabs occupy a quarter of the intertidal area and have been reported to be a main player in habitat partitioning in the Bijagos Archipelago for benthic invertebrate and shorebird communities [25]. This crab acts both as a key prey for certain shorebird species, such as Whimbrels _Numenius phaeopus_, Grey Plovers, and Redshanks _Tringa totanus_[7; 116],and as a regulator, likely limiting the occurrence and biomass of most harvestable macroinvertebrates, namely bivalves, polychaetes, gastropods, and other crustaceans [25]. Hence, shorebird communities are clearly segregated between areas with and without fiddler crabs, and in our map, bare sediment areas will support markedly different (and also more abundant and richer) shorebird and benthic invertebrate communities compared to the FCB areas. In fact, the ability to map the FCB habitats at the scale of the entire Bijagos Archipelago with good accuracy is one of the important contributions of this work, and to the best of our knowledge, this is the first time the distribution of fiddler crabs has been mapped with remote sensing. This opens a promising scope regarding the assessment of the spatial extent of its influence on the intertidal ecosystem through time.  
Sediments with higher mud content will be potentially more attractive to certain shorebird species, as has been shown in different areas for Red Knots _Calidris canutus_[62], Grey Plovers [54], and Curlew Sandpipers _Calidris ferruginea_[116], while others will prefer sandy sediments, with less mud content, such as Sanderlings _Calidris alba_ and Kentish Plovers _Charardius alexandrinus_[54,116]. This confirms that knowledge on the distribution of these intertidal habitats and ecosystem engineers is of great importance in understanding and predicting the distribution, foraging ecology, and community composition of the shorebird assemblages in the Bijagos Archipelago.