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I'm Christopher Intagliata. The way we sample much of the world's oceans, to see what's living down there, is pretty basic: Ask fishermen.Or just stick a net down there, and examine what we catch. Neither method is ideal. Because you basically catch the fish and kill them.Philip Francis Thomsen, a biologist at the Natural History Museum of Denmark. Another drawback, he says, is you can't do it everywhere.If the bottom is too soft, or too rocky, or there's a coral reef, you don't want to use this invasive method above sensitive habitat.So Thomsen and his team investigated an alternative, that's been used in freshwater with some success: they sampled the diversity and abundance of marine life using something called environmental DNA, or eDNA.