A lobsterman, a seaweed farmer and a surfer called for an end to offshore oil drilling Wednesday, and to spills such as the BP America disaster that’s spewing millions of gallons into the Gulf of Mexico. The demonstrators spoke during a gathering of about 30 people at East End Beach in Portland, organized by the Sierra Club, a national environmental organization. A half-dozen people then stood up on paddleboards to symbolize standing up against offshore drilling. “We are blowing it,” said Nanci Boutet, owner of Aquaholics Surf Shop in Kennebunk. Paul Dobbins of Ocean Approved, a sea kelp growing operation in Casco Bay, said the oil spill shows why it is time to stop using fossil fuels and turn to biofuels, wind and other renewable energy sources. “An oil spill would kill our crops and put our co-workers’ jobs in jeopardy,” said Dobbins.