  We conducted a panoramic spectroscopic campaign with MOSCA at the Calar Alto
observatory. We acquired spectra of more than 500 objects. Approximately 150 of
these spectra were of galaxies that are members of six different clusters,
which differ in intrinsic X-ray luminosity. The wavelength range allows us to
quantify the star formation activity by using the OII and the Halpha lines.
This activity is examined in terms of the large-scale environment expressed by
the clustercentric distance of the galaxies as well as on local scales given by
the spatial galaxy densities. A global suppression of star-formation is
detected in the outskirts of clusters, at about 3Rvir. Galaxies with ongoing
star-formation have similar activity, regardless of the environment. Therefore,
the decline of the star-formation activity inside the investigated clusters is
driven mainly by the significant change in the fraction of active versus
passive populations. This suggests that the suppression of the star-formation
activity occurs on short timescales. We detect a significant population of red
star-forming galaxies whose colors are consistent with the red-sequence of
passive galaxies. They appear to be in an intermediate evolutionary stage
between active and passive types. Since a suppression of star-formation
activity is measured at large clustercentric distances and low projected
densities, purely cluster-specific phenomena cannot fully explain the observed
trends. Therefore, as suggested by other studies, group preprocessing may play
an important role in transforming galaxies before they enter into the cluster
environment. Since models predict that a significant fraction of galaxies
observed in the outskirts may have already transversed through the cluster
center, the effects of ram-pressure stripping cannot be neglected. (ABRIDGED)
