New light has been cast on the biodiversity inhabiting the coral reef ecosystems of the Maldives as researchers from the California Academy of Sciences lift the lid on a new species of damselfish to have been discovered and described during an exploration of the deep sea.

Described as pale with a “ghostly blue underside”, the species – Chromis abadhah – was discovered by the small team of scientists while on an expedition to explore the deep sea coral reefs of the Indian Ocean, a region they claim to be “vastly under explored” due to its inaccessibility. 

The breakthrough discovery – a species of damselfish found dwelling in the deep sea coral system – has been described by the team as a crucial step forwards in the search for better understanding of life and ecosystems within the deeper regions of the Indian Ocean, the eastern Atlantic, and the eastern Pacific. The team notes that in comparison to their shallow reef counterparts, regions such as these remain “poorly studied” yet are the potential home to “many yet to be described species.”

“Exploration of the planet’s mesophotic ecosystems has been uneven,” said Luiz A Rocha, from the California Academy of Sciences and co-lead author of the study, now published in ZooKeys. “Hawai’i and some locations in the Caribbean, the South Pacific, and the Red Sea are relatively well-known, whereas the eastern Pacific, eastern Atlantic, and Indian Ocean are largely unexplored. 

“Aiming to fill this gap through a partnership between the California Academy of Science, the Maldives Marine Research Institute, and Rolex, we conducted surveys to depths of 150 metres at 21 locations across five atolls in the Maldives, Indian Ocean where several new species of fish were discovered.”

Chromis abadhah is the first of these discoveries to be described. Recorded at eight locations spanning 180km from Faadhippolhu to Dhaalu Atoll, it is now presumed the species is widely distributed across the Maldivian Archipelago. It shares its pearly white appearance and black markings with three other species of Chromis – all of which are mesophotic, having only been recorded below 30 metres depth.

Chromis abadhah has been found to live in or near crevasses, close to populations of sea sponges, indicative – the team suggests – that this is a species popular among predators. 

Specimens of the fish were collected using hand nets and immediately transported to a field laboratory where they were photographed and tissue sampled. It was given the name ‘abadhah’, which means ‘perpetual’ in Dhivehi, the local language of the Maldives in a nod of recognition to the Rolex Perpetual Planet initiative from which the team received its funding.

The team concluded by noting that deep sea reefs do not face the same risk from rising acidity due to increasing amounts of carbon dioxide in the air as shallow reefs do, but still face other human-made hazards such as nets and ropes that fall from ships, bleaching, and pollution. All of which, noted the team, will likely present a danger to the fish that live there as well.

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