Humans rely on the ocean for many things, including food, jobs, recreation and stabilization of Earth’s climate. But although ocean resources may seem infinite, human impacts like pollution, overfishing and climate change are creating what United Nations Secretary-General António Guterres has called an “ocean emergency.” Climate change is pushing ocean temperatures to record levels, many fisheries are overharvested, and plastic waste is accumulating in the deep sea.

These five articles from The Conversation’s archive spotlight urgent challenges for ocean conservation, and describe what researchers are doing to devise effective responses.

Invasive lionfish are aggressive predators, native to the Indo-Pacific Ocean, that feed on smaller reef fish. They have caused heavy damage in the Caribbean and Gulf of Mexico since they first appeared in the Atlantic in 1985. Now, they’ve spread south to Brazil, which has many rare endemic fish species and is behind the curve in responding.

“As one of many Brazilian scientists who warned repeatedly about a potential lionfish invasion over the past decade, I’m disheartened that my country missed the window to take early action,” wrote Charles Darwin University marine scientist Osmar J. Luiz. “Now, however, marine researchers and local communities are stepping up.”

One important control strategy was to create an interactive dashboard where anyone can report lionfish sightings. Other steps are likely to include environmental education, organized culls and genetic research to identify distinct lionfish populations and see where they’re moving. With a similar lionfish invasion underway in the Mediterranean, there’s urgent need for effective responses.

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One of the ocean’s potentially most valuable resources hasn’t been tapped yet – but that could be about to change.

Scattered across large zones of the ocean floor, manganese nodules – lumps that look like cobblestones – contain rich deposits of nickel, copper, cobalt and other metals that are newly in demand for manufacturing batteries and renewable energy components.

“A fierce debate is now playing out as a Canadian company makes plans to launch the first commercial deep sea mining operation in the Pacific Ocean,” Indiana University scholars Scott Shackelford, Christiana Ochoa, David Bosco and Kerry Krutilla warned.

Less than 10% of the deep seabed has been mapped thoroughly, and most life forms discovered there have never been seen before. Collecting materials from the ocean floor could harm these species – for example, by burying them in sediments. “We believe it would be wise to better understand this existing, fragile ecosystem better before rushing to mine it,” the authors concluded.

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