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Colorful new corals bedeck the busy waters off Hong Kong, study shows

The bright-orange Tubastraea dendroida is named for its unique tree-like branching shape.

The bright-orange Tubastraea dendroida is named for its unique tree-like branching shape. Image courtesy of Yiu et al. (2022).

  • Scientists have found three new species of sun corals off Sung Kong and Waglan islands in the eastern waters of Hong Kong.
  • The discovery of these orange, violet and green corals brings the number of known species in the Tubastraea genus from seven to 10.
  • Sun coral species don’t build reefs or host symbiotic algae, but instead live in deeper waters and eat by capturing zooplankton from seawater with their tentacles.
  • The discovery “reveals how little we know about marine diversity, and how many undescribed species are still awaiting our discovery,” one of the scientists said.

In the eastern waters off Hong Kong, a group of scientists searching for coral-eating nudibranchs stumbled upon a colorful surprise: three new species of sun corals. These orange, purple and green corals belong to the genus Tubastraea, bringing the known members of this coral group from seven species to 10.

“Given that corals are one of the best-studied marine animals, our study reveals how little we know about marine diversity, and how many undescribed species are still awaiting our discovery,” said Qiu Jianwen, a professor at Hong Kong Baptist University who, along with master’s student Yiu King-fung, found the corals.

The sun coral Tubastraea chloromura. (Left) Close-up of a corallite with extended tentacles. (Right) Close-up of the skeleton of a corallite. Image courtesy of Yiu et al. (2022).

Descriptions of the new corals, found around the Sung Kong and Waglan islands have been published in the journal Zoological Studies.

Unlike the colorful corals most people are familiar with, sun coral species don’t build reefs or host symbiotic algae. Instead, they live in deeper waters (10 to 30 meters, or 33-98 feet, below the water’s surface) and eat by capturing zooplankton from seawater with their tentacles.

The bright-orange Tubastraea dendroida is named for its unique tree-like branching shape. Tubastraea chloromura draws its name from its olive-green skeletal wall, with “chloro” meaning green and “murus” meaning wall. And Tubastraea violacea, so named for its violet color, may have color variants, such as a yellow variant in the South Pacific, according to DNA analyses.

Named for its violet color, Tubastraea violacea may have color variants, such as a yellow variant, in the South Pacific. Image courtesy of Yiu et al. (2022).

This discovery comes after eight years of surveying and research related to coral health in Hong Kong by Qiu and colleagues. The team is examining the impact of sea urchins, coral-eating nudibranchs, and coral bleaching on coral reefs around Hong Kong.

Last year, Qui and his team discovered a new sun coral species in the genus Tubastraea and two new species of nudibranchs in the genus Phestilla. The last time a new coral species was found in Hong Kong was more than 20 years earlier.

Qiu says these discoveries are encouraging and “provides strong evidence of the high marine biodiversity in Hong Kong waters … It also inspires us to further explore the diversity of marine animals, study their functions and ecosystem services, and protect them from potential human disturbances.”

Qiu Jianwen (right) and Yiu King-fung (left) introducing the new coral species. Image courtesy of Qiu Jianwen.

Banner image: The bright-orange Tubastraea dendroida is named for its unique tree-like branching shape. Image courtesy of Yiu et al. (2022).

Citation:

Yiu, S. K., & Qiu, J. (2022). Three new species of the sun coral genus Tubastraea (Scleractinia: Dendrophylliidae) from Hong Kong, China. Zoological Studies22.