  We present a study of galaxy mergers and the influence of environment in the
Abell 901/902 supercluster at z~0.165. We use HST ACS F606W data from the
STAGES survey, COMBO-17, Spitzer 24um, and XMM-Newton X-ray data. Our analysis
utilizes both a visual classification system, and quantitative CAS parameters
to identify systems which show evidence of a recent or ongoing merger of mass
ratio >1/10. Our results are: (1) After visual classification and minimizing
the contamination from false projection pairs, we find that the merger fraction
f_merge is 0.023+/-0.007. The estimated fractions of likely major mergers,
likely minor mergers, and ambiguous cases are 0.01+/-0.004, 0.006+/-0.003, and
0.007+/-0.003, respectively. (2) The mergers lie outside the cluster core of
radius R < 0.25 Mpc: the lack of mergers in the core is likely due to the large
galaxy velocity dispersion in the core. Mergers populate the region (0.25 Mpc <
R <= 2 Mpc) between the core and outskirt. In this region, the estimated
frequency of mergers is similar to those seen at typical group overdensities.
This suggests ongoing growth of the clusters via accretion of group and field
galaxies. (3) We compare our observed merger fraction with those reported in
other clusters and groups out to z~0.4. Existing data points on the merger
fraction for L<= L* galaxies in clusters allow for a range of evolutionary
scenarios. (4) The fraction of mergers, which lie on the blue cloud is
80%+/-18% versus 34%+/-7% for non-interacting galaxies, implying that
interacting galaxies are preferentially blue. (5) The average SFR, based on UV
or UV+IR data, is enhanced by a factor of ~1.5 to 2 in mergers compared to
non-interacting galaxies. However, mergers in the clusters contribute only a
small fraction (between 10% and 15%) of the total SFR density.(Abridged)

Cosmology and Nongalactic Astrophysics