Abstract: A buoyant actuator (10) is used in apparatus (11) for harnessing wave energy in a body of water such as the ocean. The buoyant actuator (10) is deployed within the body of water (12) and is responsive to wave motion in the body of water. The buoyant actuator (10) includes a body (101) incorporating a flow path along which water can flow, and a gate means (115) for controlling flow along the flow path. The gate (115) includes closure elements configured as flaps (221) providing a barrier (222) across the flow path through the body (101). Each flap (221) is moveable into and out of a condition in which it cooperates with the other flaps (221) to provide the barrier (222). A latch mechanism (231) is provided for releasably retaining each flap (221) in the condition providing the barrier (222). The latch mechanism (231) has a magnetic coupling.