Temporary and reversible underwater adhesion is crucial for robotic systems performing object pickup, locomotion, and attaching in confined environments. We propose a starfish-inspired tube foot consisted of a soft hydrogel mouth and a rigid stem. The device is fabricated by combining two cylindrical components with distinct mechanical properties. As the hydrogel swells, the straight hydrogel cylinder transforms into a soft, cupped pad that spreads on contact, enabling strong surface adhesion. During detachment, vacuum formation within the tube generates effective underwater adhesion. The artificial tube feet exhibit high adhesion hysteresis, stimuli-responsive autonomous release, and rapid detachment via integrated pneumatic actuation, enabling underwater robotic rock manipulation.