The interlayer Josephson coupling in the vortex-liquid phase of Bi2Sr2CaCu2O8+δ with columnar defects is studied by means of the Josephson plasma resonance. At high temperatures well above the Bose-glass melting line, double resonance peaks appear as a function of the magnetic field in a narrow temperature range deep within the vortex-liquid state. This indicates that two types of vortex liquid, the well-coupled and the decoupled pancake vortex liquids, appear in the irradiated crystals. The pancake vortices tend to align and couple with increasing magnetic field when it approaches approximately one-third of the matching field. From the angular and frequency dependences of the resonance, we estimate the c-axis correlation length of the pancake vortices quantitatively. © 1999 ThAmerican Physical Society.