Genetically engineered marine algae can be just as useful as fresh water algae for producing biofuels, researchers in California say.

Biologists at the University of California, San Diego, said the yield of petroleum-like compounds from genetically modified saltwater algae could match that of fresh water varieties.

The ability to genetically transform marine algae into a biofuel crop is important, they said, because it expands the types of environments in which algae can be grown for biofuels.

Algal biofuels can be produced in the ocean, in the brackish water of tide lands or even on agricultural land on which crops can no longer be grown because of high salt content in the soil, they said.

"The algal community has worked on fresh water species of algae for 40 years," UCSD researcher Stephen Mayfield said.

"What our research shows is that we can achieve in marine species exactly what we've already done in fresh water species.

"There are about 10 million acres of land across the United States where crops can no longer be grown that could be used to produce algae for biofuels. Marine species of algae tend to tolerate a range of salt environments, but many fresh water species don't do the reverse."

Using marine algae could help make algal biofuels a viable transportation fuel in the future, researchers said.

"And once you can use ocean water, you are no longer limited by the constraints associated with fresh water," Mayfield said. "Ocean water is simply not a limited resource on this planet."