  We study quantum effects due to a Dirac field in 2+1 dimensions, confined to
a spatial region with a non-trivial boundary, and minimally coupled to an
Abelian gauge field. To that end, we apply a path-integral representation,
which is applied to the evaluation of the Casimir energy and to the study of
the contribution of the boundary modes to the effective action when an external
gauge field is present. We also implement a large-mass expansion, deriving
results which are, in principle, valid for any geometry. We compare them with
their counterparts obtained from the large-mass `bosonized' effective theory.
