Former U.S. Rep. Joe Kennedy said he has decided against running for the Senate seat that was held by his late uncle, Edward Kennedy.

“I have profound respect for those who choose to advance the causes of social and economic justice in elective office,” Kennedy said in a statement today. “I have decided that the best way for me to contribute to those causes is by continuing my work at Citizens Energy Corporation,” he said, referring to the nonprofit energy company he founded.

The death of Sen. Kennedy last month has triggered a battle over a seat that has been held for almost 55 of the past 57 years by a member of his family. Joe Kennedy, 56, son of the late Sen. Robert F. Kennedy, topped the field of potential candidates in a March  poll.

“Everyone else was waiting to see what Kennedy was going to do,” political scientist Jeffrey Berry of Tufts University in Medford, Massachusetts, said in a telephone interview with Bloomberg News. “I expect four or five more to get in with Kennedy gone.”

Massachusetts Attorney General Martha Coakley, who declared her candidacy on Sept. 3, is now the frontrunner, Berry said, “But she’s going to have a crowd.”

Coakley trailed Kennedy in the March favorability survey, garnering 56 percent versus Kennedy’s 67 percent