Green cells whirl around a red-light chamber, propelled by a blade through bubbling water. These little seaweed cells, called gametophytes, will develop into a strain of fast-growing kelp — part of what was once a government-funded initiative to develop sustainable biofuels for American transport.

Electricity from solar and wind energy can power cars, however ships and aircraft largely run on liquid fuels made with a large percentage of oil or gasoline. When burned, those emit carbon dioxide, a greenhouse gas that causes global warming. Biofuel, refined from organic material like plants or algae, is a potential option to change the fuel makeup.

One kind of biofuel comes from kelp.…