  We examine the nature of the collective excitations in a strongly anisotropic
system of bosons interacting via Coulomb interaction. Such a system has often
been used in the past to model the effects of quantum and classical phase
fluctuations on the superfluid density of underdoped cuprates. Depending on the
anisotropy and the effective strength of the interaction we find four different
regimes for the temperature dependence of the superfluid density. Coulomb
interaction in underdoped cuprates is argued to be effectively short-ranged,
and of order of unity in appropriately defined units.
