Sargassum, a brown macroalgae found in the Atlantic’s Sargasso Sea, has become a threat to coastal ecosystems and communities across the Gulf of Mexico due to an explosion in numbers since 2011. Researchers believe that farm and sewage runoff, as well as climate change, may be driving the now 5,000-mile-wide “Great Atlantic Sargassum Belt.” Despite the threat posed to coral reefs and tourism-dependent livelihoods, there are various possible applications for sargassum, including syrup, bricks, and even jet fuel. Carbonwave, a Boston- and Puerto Rico-based startup, has raised $5 million to use sargassum in fertilizer, cosmetics, and faux leather. Backed by ESG-themed investment firms Natixis and Viridios Capital, as well as ocean-focused VC Katapult, Carbonwave aims to scale production of its seaweed-based emulsifier for cosmetics. The company claims that its sargassum fertilizer “reduces the need of” climate change-driving nitrogen fertilizer. Carbonwave uses a proprietary extraction process that involves pressing the seaweed and removing the arsenic to create liquid fertilizer, while the leftover pulp forms the basis for the emulsifier and fake leather. The startup is part of a wave of companies seeking to turn algae into environmentally friendlier products.