Coral bleaching seen 60m deep off Northeast coast

In April this year, scientists from the Federal University of Pernambuco (UFPE) recorded the bleaching of corals 40 to 60 meters deep off Brazil’s Northeast coast. This is the first time that the phenomenon—which is caused by rising ocean temperatures and can lead to the death of these animals—has been recorded at such depths in the South Atlantic.

With the support of NGO WWF-Brasil, a scientific expedition carried out in April on an undersea mountain chain near the coast of the states of Ceará and Rio Grande do Norte recorded bleaching in populations of the species Agaricia fragilis living 60 meters deep.

The bleaching was also found to have affected all six species in the area, including the fire coral Millepora alcicornis, which had never been found living more than 40 meters deep—the mesophotic zone, where sunlight is less intense and temperatures are lower.

“We thought this species only occurred in the shallows. And we found an impressive fire coral reef on the east ridge, 50 to 43 meters deep. This could be Brazil’s largest coral reef,” said UFPE researcher Mauro Maida. “We had never seen it before, and when we did, it was bleaching.”

The other four species recorded on the northern ridges—Montastrea cavernosa, Siderastrea stellata, Meandrina brasiliensis, and the endangered Mussismilia harttii—also showed bleaching spots.

Symbiosis

Corals are marine invertebrates capable of feeding themselves, but a significant portion of their diet stems from symbiosis—a mutually beneficial relationship—with zooxanthellae algae. Through photosynthesis, the algae provide nutrients for their animal hosts.

These algae are also responsible for the colors of corals. When the sea temperature rises, however, they abandon the animals, which gives them a whitish hue. Without the nutrients provided by algae, corals can stay alive and feed on microorganisms for months, but their health is impaired, making them more susceptible to disease and death.

This year, a new wave of global bleaching is affecting several coral reefs around the world. On the northeast coast of Brazil, the phenomenon has been observed since March.

Temperature

Mauro Maida has been conducting expeditions to these northern ridges and the neighboring Fernando Noronha chain since 2016 and says that he had never observed coral bleaching in the mesophotic zone there. “The mesophotic reefs were thought to be less susceptible to global warming, but we’re seeing that it’s reached the bottom. The El Niño was so extreme it even increased temperatures at the bottom,” he noted.

Coral bleaching, he went on to say, is a worrying indicator of the global climate situation. “It’s a thermometer. And it’s so bad it’s reaching the bottom of the sea.”

Leonardo Messias, coordinator at Cepene, a research center on marine life in Brazil’s Northeast, pointed out that coral bleaching is not dissociated from natural disasters that affect people. “Climate change is a serious matter. We’re experiencing this very drastically in Rio Grande do Sul.”