Marine officials say the growing green crab population is the number one threat to Maine’s $15-million soft-clam industry. Volunteers were pulling traps Wednesday in dozens of coastal towns for a Department of Marine Resources survey to gauge the abundance of the invasive crabs, which threaten clams, mussels, and other shellfish. The survey will be used to raise public awareness and help towns develop plans to control the predators. At a press conference in Freeport, clam digger Chad Coffin said that if the crabs are unchecked, there might not be a viable clam-digging industry in a couple of years. The increase in the crab population has coincided with the increase in ocean temperatures in recent years.