Gov. John Baldacci declared an economic emergency Friday as a result of red tide, following the lead of his Massachusetts counterpart in seeking federal relief funds.

Throughout New England, shellfish beds remain closed in response to the worst red tide outbreak in decades, and scientists predict it could be a month or more before shellfish recover.

“This says to me that the difficulties facing the shellfish industry now will continue and the economic impacts will grow,” Baldacci said in a statement released Friday in which he called for regional cooperation.

Red tide is caused by a microscopic plankton called Alexandrium, which in high enough concentrations can cause seawater to take on a reddish tinge. The toxic plankton doesn’t hurt shellfish, but filter feeders such as clams, mussels and oysters take the organisms into their bodies. Shrimp, lobsters and crabs are not affected by the blooms.

When people or animals eat infected shellfish, they can become seriously ill. In rare cases, they can die of suffocation from paralytic shellfish poisoning, or PSP.

No one has died of PSP in Maine in the 50 years that the state has been monitoring red tide blooms.

Shellfish dealers said this week they already are seeing red tide’s impact in the form of price spikes and consumer fear. Much of Maine’s coast is closed to shellfishing, and consumers are avoiding the clams and mussels that are being harvested from areas north and east of the blooms.

Massachusetts Gov. Mitt Romney declared a state of emergency Thursday, citing losses of $3 million per week if the red tide lingers. Baldacci’s office had no economic figures to report Friday, but, Department of Marine Resources statistics place the value of Maine’s clam industry in excess of $15 million annually.