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�鶹��ýscientists discover marine creatures bending the laws of evolution

Caption: Close view of Palythoa grandiflora. Credit: Marcelo Visentini Kitahara

Polyps of Parazoanthus swiftii growing attached to a sponge. Credit: Marcelo Visentini Kitahara

Zoantharian colony in a reef ecosystem in South Brazil. Credit: Marcelo Visentini Kitahara

A group of colorful hexacorals (aquatic organisms  in the group of stony corals and anemones), known as "zoantharians" is defying the traditional laws of evolution by remaining virtually identical across the Atlantic and Indo-Pacific oceans, according to a led by researchers at the University of Hawaiʻi at Mānoa. 

The study, led by Maria “Duda” Santos of �鶹��ýMānoa’s (HIMB) ToBo Lab and the University of the Ryukyus, began with a moment of "déjà vu" underwater. 

"During my first dive in Okinawa, I was surrounded by a multitude of species I had never seen in my homeland of Brazil," said Santos. "But then I saw the zoantharians. They looked exactly like the ones back home—the same colors, shapes and sizes. It was striking."

While the Indo-Pacific typically hosts 10 times the species diversity of the Atlantic for most reef animals, this research found that the genetic and morphological divergence between oceans for these creatures is surprisingly narrow.

By combining DNA data and records from Mexico to the Philippines, the team has provided the first-ever global "atlas" for a group of animals that has remained in the shadows for decades. This map of the past and present provides a vital baseline for monitoring how marine life will navigate climate change.

Secrets of the ultimate travelers

The researchers suggest that zoantharians may be the ultimate oceanic travelers. Their secret likely lies in high dispersal via an "epic" larval phase, where young zoantharians can survive in open water for more than 100 days, paired with an ability to "raft" across ocean basins by hitchhiking on floating objects. In addition, an unusually slow evolutionary rate appears to keep distant populations looking and acting like siblings, even after long time of separation.

As climate change stresses traditional stony corals, zoantharians are increasingly moving in to fill the void. 

"In some habitats impacted by stress, some zoantharian species can outcompete stony corals," said Santos. "We are seeing 'phase shifts' where reefs once dominated by corals are being taken over by zoantharians. Understanding how they spread helps us forecast what the reefs of the future will look like."

This study represents an international effort, uniting a team from Hawaiʻi, Okinawa, Russia, Brazil, Hong Kong, Taiwan and Indonesia.