Our time at sea: Discovering the biodiversity of the Indian Ocean Territories

A team of scientists from the Australian Museum, CSIRO, Museums Victoria Research Institute and Western Australian Museum have recently completed their voyage on CSIRO’s research vessel (RV) Investigator. Find out how this expedition helped uncover secrets of the deep seamounts of the Indian Ocean Territories (IOT).

What is a seamount?

A seamount is an undersea mountain, typically formed by an extinct volcano arising from the seafloor. There are numerous deep seamounts around the Indian Ocean Territories (IOT). However, until now, have been completely unexplored, despite some reaching heights of 4,000 metres above the seafloor and up to 70 kilometres in diameter. To put this in perspective, Australia’s Mount Kosciuszko sits at only 2,200 m height (albeit above sea level), making some of these seamounts the largest mountains in Australian territory. The geological structures of deep seamounts provide a unique habitat for marine life, making them rich in biodiversity. Located around Christmas and Cocos (Keeling) Islands, it is incredible that these seamounts have never been mapped or explored. So, a team from the Australian Museum joined scientists from around Australia on CSIRO’s research vessel (RV) Investigator to map and sample life on these seamounts and create baseline data for this unknown environment.

Why do we collect?

Collecting specimens during an expedition is vital, not only in documenting the overall biodiversity of an area (for example, describing species new to science in the IOT) but also in informing decisions around future conservation management. Additionally, having these specimens stored in museum collections allows for future scientific research; whether researchers need to study species morphology or genetics (as both are collected at a singular point in time), or help in addressing taxonomic concerns, and queries around extinction rates or climate change. Museum specimens provide invaluable data from a range of locations over time – yet so much is still unknown.

How do you collect?

Our voyage was able to provide this baseline data for deep seamounts within the IOT. However, we faced a challenge. How do you collect animals from these seamounts, the base of which can reach 5,000 m depth? We deployed beam trawls or Sherman epibenthic sleds off the rear of the ship and down to the depths below. These devices were towed along the seafloor, collecting animals in their path, before slowly being brought to the surface and on board the ship. The process of collecting the deep-sea animals and bringing them aboard allows the scientists to be hands-on and carefully study the animals, including identifying the animals to species, and extracting DNA to determine how species may be related to each other. And what an amazing array of animals were found!

What did we find?

The scientists on board the RV Investigator specialised in different animal groups, including marine worms, crustaceans, sea stars, fishes, and even slimy sea cucumbers. My specialty is jellyfish, and during this voyage we collected a total of 16 individuals that covered at least 3 different families. The most exciting jellyfish from this voyage belongs to the genus Atolla, which is typically found in the open ocean at depths below 100m, so you would never find it while swimming or washed up on the beach. Some other incredible marine invertebrates that were collected include squat lobsters (Munidopsidae), blind lobsters (Polychelidae), sea stars (Asteroidea) and even a couple of unusual sea cucumbers commonly called “sea pigs” (Elasipodida). Additionally, we collected a wide range of fishes including coffin fish (Chaunax sp.), the scary lizard fish (Bathysaurus mollis), and tripod fish (Bathypterois sp.) that can stand above the seafloor perched on their thin stilt-like fins. It seemed that each deep-sea creature that came up was slightly more unusual than the one collected before it.

Finally, on this trip we mapped the seafloor in 3D, allowing us to study the seamounts including their width, depth, and geological structures. Although previous surveys had captured some depth mapping, this was the first detailed deep-sea bathymetry map of the area. This was done through a high-tech sonar system that allowed CSIRO's Geophysical Survey and Mapping (GSM) team to create incredible images of two main seamounts. This included the seamount that the Cocos (Keeling) Islands sit on top of, and Muirfield Seamount, appropriately named after the ship that ran aground on the shallowest point of the seamount at only 16m depth. Knowing the bathymetry of these seamounts informs the locals of Cocos (Keeling) Islands about their environment, but more significantly gives us a very detailed information about these seamounts, both located within two of Australia’s newest marine parks.

Fly through video of Muirfield seamount (CSIRO).

Fly through video of seamounts Cocos (Keeling) (CSIRO).

As AMRI scientists on board the RV Investigator, we were honoured to be part of the voyage to the unknown and help solve some of the biodiversity mysteries of the seamounts belonging to the IOT. The specimens collected as part of this voyage have been dispersed between museum collections around Australia and will be vital for marine research both now and in the future.

Dr Claire Rowe, Technical Officer, Marine Invertebrates, Australian Museum.