14 May, 2024

Carl Nasman Washington DC The surfaces of the oceans are getting hotter day by day. That has implications almost everywhere, from inland food supplies that need reliable rainfall, to coastal cities finding themselves in the paths of ever more powerful hurricanes. It's changing the game for life in the ocean too. This week, we take a look just below the surface, where a painstaking battle is going on for Florida's coral reefs. This reef, one of the largest in the world, has not escaped record bleaching of recent years. In a race against time and heat, scientists in Florida are more determined than ever to save a diverse and much-loved ecosystem. Also in this edition, a living fossil captured on camera and the forgotten pioneer of the wind turbine.

CLIMATE CONVERSATION  How to save corals from heat Divers tend to corals painstakingly grown in their nursery. Credit: Coral Restoration Foundation It was an underwater evacuation. ‌ Last summer, a team of scuba divers descended to the sea floor off the coast of the US state of Florida. Navigating a forest of metal poles resembling TV antennae, the divers collected spiky staghorn and elkhorn corals dangling from the posts, placed them delicately in crates and ascended with the precious cargo.

The corals were transported to safety in cooler waters. Credit: Coral Restoration Foundation The underwater nursery was designed to be a breeding ground to help restore the state's reef – the third largest in the world. ‌ But in the summer of 2023, simmering sea temperatures ranging up to 101F (38C) led to the reef's worst ever mass bleaching event. The corals died rapidly, including about half of the stock being raised by the Coral Restoration Foundation. The scientists' evacuation programme managed to bring a substantial proportion of their nursery to safety in cooler water tanks on shore. ‌ Corals along the greater reef itself were not as lucky. ‌ "For some of the species – these iconic reef-building pieces like the branching corals, the elk and the star coral – at some locations, it was locally an extinction," Phanor Montoya-Maya, Coral Restoration Foundation's restoration programme manager, told me in a recent interview.

Buying time Last summer's bleaching may have been the worst in Florida's history, but experts are bracing for more of the same in coming years. In the past 12 months, the average world ocean temperature has broken records for the time of year every single day. Read BBC News' analysis of the extraordinary data. ‌ Despite the bleak picture, the Coral Restoration Foundation is scrambling to adapt its plans for saving Florida's reef. ‌ "Restoration has a role here to avoid some species reaching extinction," says Montoya-Maya. "We need to continue buying time." Tougher corals Last week, the organisation's divers once again descended into the shallow waters off the Florida Keys, this time "outplanting" new corals at damaged reef sites. ‌ Part of the foundation's new strategy involves finding the hardiest coral. Early restoration efforts focused on fast-growing varieties like staghorn coral to restore Florida's reef, which has already experienced a 90% decline since the 1980s. Staghorn and elkhorn corals, which have a branching structure, also host a large array of other species, giving them additional appeal in restoration efforts. ‌ But it turns out that staghorns are also very heat sensitive, which meant much of the previously restored corals died off last summer. ‌ This summer, the Coral Restoration Foundation will be turning to slower growing boulder coral, which appears to survive better in nurseries and on reefs. ‌ "Now we […] are planting certain species to mimic what survived the bleaching event and continue adding those species to the reef." Keeping cool In another strategy, the group is moving its nurseries into deeper waters where temperatures are slightly lower. It's also planning to experiment with what it calls "shading structures" to partially block the Sun's warming rays. ‌ With climate change warming the oceans at unexpectedly fast rates, survival is not guaranteed. But Montoya-Maya says it's still worth the effort. ‌ "I would argue that if it wasn't for the work that we've been doing for the last 15, 20 years, some of these species may have already died," he says. "It gives me hope: seeing that [the reef] is still alive, and that a lot of people now are paying attention to the stress and the challenge that coral reefs are facing." ‌ Read more about what record ocean warming means for the planet.