  It is advocated that the superembedding approach is a generic covariant
method for the description of superbranes as models of (partial) spontaneous
supersymmetry breaking. As an illustration we construct (in the framework of
superembeddings) an n=1, d=3 worldvolume superfield action for a supermembrane
propagating in N=1, D=4,5,7 and 11-dimensional supergravity backgrounds. We
then show how in the case of an N=1, D=4 target superspace gauge fixing local
worldvolume superdiffeomorphisms in the covariant supermembrane action results
in an effective N=2, d=3 supersymmetric field theory with N=2 supersymmetry
being spontaneously broken down to N=1. The broken part of N=2, d=3
supersymmetry is nonlinearly realized when acting on Goldstone N=1, d=3
superfields, which describe physical degrees of freedom of the model. As an
introduction to the formalism, the procedure of getting effective field
theories with partially broken supersymmetry by gauge fixing covariant
superbrane actions is also demonstrated with a simpler example of a massive
N=2, D=2 superparticle.
