When Brazilian researcher Dr Maria 'Duda' Santos went scuba diving in Okinawa, Japan, she was surprised. Everywhere she looked, she saw species that were totally different to the marine life back home – but she also saw something very familiar: the zoantharians looked identical to the ones she knew from Brazil.
Zoantharians are anemone-like animals often found in coral reefs. The tentacles that surround their mouth can make them look like tiny underwater flowers.
“Each polyp will use the tentacles to capture plankton prey in the water column,” says Santos, who is a researcher at Hawaiʻi Institute of Marine Biology, University of Hawaiʻi at Mānoa. “The meals ingested are then shared between all individuals of the colony.”
The waters of the Indo-Pacific are typically much more diverse than the Atlantic. "There are over 10 times more species of reef fishes and stony corals in the Indo-Pacific, compared to the Atlantic Ocean,” she says. “You would expect to see entirely different groups of reef animals in each ocean.”
So, it was strange to see such striking similarities between the zoantharians of Brazil and Okinawa.
This head-scratching moment led to Santos leading a scientific study – now published in Frontiers of Biogeography – that reveals that these coral-like creatures are going against the grain and that populations far apart in different ocean basins can look and behave like close relatives.
The study was the result of collaboration between scientists around the world. They looked at DNA records from Mexico to the Philippines to study the global biogeography of zoantharians for the first time.
“Biogeography is the science that studies how species are distributed across the geographical space and geological time,” she says. “For example, which regions of the world have the highest diversity? Which processes lead to biodiversity hotspots?”
Their work uncovered why zoantharians might look and act so similar even in habitats many miles apart. The scientists believe that the animals’ slow evolutionary rate plays a part as well as the fact that they may be "the ultimate oceanic travellers".
When zoantharians spawn, the larvae are spread widely across the ocean. The young can survive for more than 100 days, catching a ride on floating debris to hitchhike across immense distances – even across entire ocean basins.
Understanding how these animals spread across the ocean is important, says Santos: "By revealing biogeographical patterns, we better support the monitoring and conservation of marine organisms.”
Top image: Zoantharians . Credit: Hawai'i Institute of Marine Biology, University of Hawaiʻi at Mānoa
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