A shark bit a paddleboard while a man was on it Wednesday off the coast of Cape Cod, forcing officials to close a popular beach.The incident happened in 3 feet of water, about 50 to 75 yards south of Marconi Beach, according to the Cape Cod National Seashore.The bite did not cause an injury, but the 69-year-old paddleboarder suffered a leg injury when he fell into the water, according to officials at the Cape Cod National Seashore.There were reports of several seals in the water at the time.On Monday, several Cape Cod beaches were closed after a shark attacked a seal near the shore of Nauset Beach.Swimming was prohibited for a time Monday afternoon at Ballston Beach, Longnook Beach, Coast Guard Beach, Head of the Meadow Beach and Nauset Beach because of shark activity.On Sunday, Coast Guard Beach in Eastham was closed to swimming for an hour due to a shark sighting.