Happening Here in Heron: Checklist of black coral species descriptions of undescribed species, and conservation of biodiversity. Oh my!

Danielle Simmons Prize

Antipatharians | Taxonomy | Phylogenetics

Happening Here in Heron: Checklist of black coral species, descriptions of undescribed species, and conservation of biodiversity. Oh my!

By Jeremy Horowitz James Cook University

Black corals have been on Earth for over 400 million years and they provide food and shelter for a wide range of fish and invertebrates. Like many coral groups, black coral populations are threatened, particularly in areas where they are harvested for the jewellery industry. However, little is known about the distributions of black coral species, which is required to conserve black coral populations.

Focusing mainly on the Great Barrier Reef (GBR) and Coral Sea, I collected and identified black coral species to update their ranges. I found that black coral diversity varied between reefs, but it was not clear what drives these variations. Next, I wanted to understand what enables or restricts black corals from occurring on a given reef. Answering this knowledge gap can help to build a model that predicts where different black coral species occur.

I was awarded the Australian Coral Reef Society Danielle Simmons award to describe black coral assemblages around Heron Island, an area where very few black coral species had been recorded. Teaming up with Project Phoenix, I documented and collected black corals on diverse habitats and compared the collection locations and coral morphologies to various abiotic features to understand what limits black corals from flourishing in the region.

I spent one week diving around Heron Island, which confirmed that black corals were rare compared to other parts of the GBR. Specimens collected were identified species based on morphological characteristics, including the colonies overall shape and size, polyp (feeding mouth) and tentacle shapes and sizes, and skeletal spine characteristics, which are small (<1 mm in height) features found all along the skeleton and can differ in shape and size between closely related species. A scanning electron microscope was needed to view the spine characteristics. I also identified the abiotic characteristics at each collection site including depth, habitat type, and current strength. I compared the data from Heron to equivalent data collected from previous trips to other sites on the GBR to determine which abiotic characteristics are common where black coral diversities are high or low.

Branched and unbranched species were found on the protected (leeward) side of the island, only unbranched species were found in habitats with moderate protection from the open ocean and no black

“Black coral diversity is low in Heron Island because it is a high energy environment, and generally, wave action can predict black coral biodiversity in shallow-water environments.”

Above: Black coral from the Coral Sea. © Image courtesy of Schmidt Ocean Institute

corals were found on the exposed (windward) side of the island.

The more protection from oceanic swell and crashing waves on shallow-water environments, the greater the black coral diversity. This can be explained by branched species having larger surface areas and a greater likelihood of being broken in high energy environments. The reefs of the Capricorn-Bunker group in the far southern GBR are all located on the outer-shelf, with little protection from the open ocean. In contrast, black coral diversity was much higher on more protected, mid-shelf reefs. Our findings suggest that black coral diversity is low in Heron Island because it is a high energy environment, and generally, wave action can predict black coral biodiversity in shallow-water environments.

Acknowledgements

This work would not be possible without the Australian Coral Reef Society, James Cook University, and the Centre of Excellence for Coral Reef Studies, my JCU supervisors Dr. Tom Bridge, Dr. Peter Cowman, Prof. Julian Caley, and Prof. Bob Pressey. Lastly, none of this work would be possible without my best friend, wife, and turtle expert, Kristina Pahang.

Top right: Author Jeremy Horowitz imaging a whip-black coral. © Hanaka Mera

Bottom right: Divers Tom Bridge, Hanaka Mera, and Jeremy Horowitz heading out to sea to collect black corals. © Andrew Baird

PhD students Chris Hemingson and Pauline Narvaez, and Dr. Renato Morais herd fsh toward a barrier net. © Victor Huertas