The research, published in Frontiers of Biogeography, was led by Dr. Maria "Duda" Santos of the UH Manoa Hawaii Institute of Marine Biology ToBo Lab and the University of the Ryukyus. The project began with what Santos described as an underwater sense of deja vu during her first dive in Okinawa, Japan, after years of studying zoantharians in her native Brazil. "During my first dive in Okinawa, I was surrounded by a multitude of species I had never seen in my homeland of Brazil. But then I saw the zoantharians. They looked exactly like the ones back home the same colors, shapes, and sizes. It was striking," she recalls.
In most reef animal groups, the Indo Pacific hosts roughly an order of magnitude more species than the Atlantic, and lineages separated by continents typically diverge genetically and morphologically over evolutionary timescales. The new study shows that zoantharians do not follow this pattern. Despite being separated by millions of years and continental barriers, many Atlantic and Indo Pacific zoantharian lineages display only narrow genetic divergence and remain remarkably similar in appearance, behavior, and ecological roles.
The authors suggest that zoantharians may be among the ocean's most capable long distance travelers. A key factor appears to be an extended larval phase in which zoantharian larvae can remain viable in open water for more than 100 days, dramatically increasing their potential dispersal range across currents that connect distant regions. This "epic" larval duration allows larvae to cross ocean basins that would normally isolate populations of other reef organisms.
In addition to their long lived larvae, zoantharians may use rafting to bridge the Atlantic Indo Pacific divide. By attaching to floating debris, natural flotsam, or other mobile substrates, colonies can hitchhike across large stretches of ocean that would otherwise act as barriers. Once they reach new coastlines and reef systems, their ability to establish and persist helps maintain connectivity between far flung populations.
The study also points to an unusually slow evolutionary rate as another piece of the puzzle. Zoantharian lineages appear to accumulate genetic changes more slowly than many other reef animals, which means that even populations isolated for long periods can still look and function like close siblings. This combination of high dispersal potential and slow genomic change helps explain why Atlantic and Indo Pacific zoantharians remain so similar despite their geographic separation.
These traits have important consequences for how reefs may change under accelerating climate stress. Traditional framework building stony corals are increasingly vulnerable to warming, acidification, and pollution, leading to degradation and loss of coral dominated habitats in many regions. "In habitats impacted by stress, some zoantharian species can outcompete stony corals. 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," says Santos.
As zoantharians colonize disturbed or warming reefs, they can occupy ecological niches vacated by declining stony corals, alter habitat structure, and reshape local biodiversity patterns. The team notes that these changes are not inherently negative but represent a fundamental reorganization of reef ecosystems. Documenting which zoantharian species occur where, and how they respond to environmental change, will therefore be critical for anticipating the emerging biogeography of tropical and temperate seas.
The project brought together researchers from Hawaii, Okinawa, Russia, Brazil, Hong Kong, Taiwan, and Indonesia, reflecting the global scale of both zoantharian distributions and the questions at stake. By compiling DNA sequences and occurrence records from locations spanning Mexico to the Philippines, the study produced the first global atlas focused on this often overlooked group of hexacorals. The resulting map captures both tropical and temperate provinces and highlights distinct community assemblages even where genetic differentiation between ocean basins remains weak.
This atlas serves as a baseline for tracking how zoantharian ranges shift as oceans continue to warm and human pressures on coastal ecosystems intensify. Because zoantharians can thrive in environments where classic reef builders struggle, they may become increasingly prominent in future reefscapes, especially in regions repeatedly affected by bleaching, storms, or pollution. The authors emphasize that management and conservation planning will need to consider these dynamics as part of a broader reevaluation of what constitutes a healthy or typical reef under changing climatic conditions.
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