Eleven-year-old Gabriel Coleman and his friends Maarten and Merel dug through driftwood piled on the shoreline under the Dumbarton Bridge, doggedly on the hunt for pieces of plastic and other debris to fill their white trash bags. “With teamwork-makes-the-dream-work, we’ve been finding big pieces and small pieces all over,” Gabriel proudly explained. The trio from Newark was among thousands of volunteers who turned out Saturday for the 39th annual California Coastal Cleanup at 695 beaches,