Principal scaling relations between M_HI, M_∗, and SFR in the Coma supercluster covered by ALFALFA. Blue: Def_HI ≤ 0.2; red: Def_HI ≥ 0.2 compared to the Def_HI ≤ 0.3 in the Local Supercluster (grey, Paper II). Symbols are assigned according to the morphology: spirals (Sa-Sdm): squares; Irr-BCD: triangles; AGN: asterisks. Top-left panel: the M_HI versus M_∗ relation The diagonal lines represent the limiting sensitivity of ALFALFA (computed for a mean incl = 45°) at the distance of Virgo (gray dotted) and of Coma (black dashed). The shallow sensitivity of ALFALFA limits significantly the detection of galaxies at the distance of Coma, in particular with decreasing stellar mass. Top-right panel: the HI gas fraction (M_HI/M_∗) versus M_∗. Bottom-left panel: the relation between the SFR and the stellar mass. Bottom-right panel: the specific star formation rate versus stellar mass.