The quest for deep sea critters

Although the recent Indian Ocean Territories expedition has been suspended, we found many fascinating deep sea animals during our 19 days at sea. Dr Ingo Burghardt, AMRI scientist on board the CSIRO research vessel Investigator, shares the latest findings.

Dr Elena Kupriyanova, Dr Frank Koehler, Alice Yan, Claire Rowe and I recently embarked with fellow researchers on the Investigating the Indian Ocean Territories (IOT) voyage. Led by Dr Tim O’Hara, the Chief Scientist from Museums Victoria, this expedition on the CSIRO research vessel (RV) Investigator departed from Darwin on the 30th of June. The aim of the expedition was to explore the seafloor across the IOT and its marine life, as very little is known about the marine biodiversity in the IOT region. During the expedition, scientists would complete multibeam mapping and collect benthic and planktonic samples from a number of IOT seamounts. Our job on board was to sort, preserve and identify the marine life collected, allowing the marine biodiversity in the region to be characterised.

During our time at sea, we were fortunate to find diverse deep sea critters in our biological sampling. I wrote about what was happening on board and wanted to share this as a snapshot in time.

14 July 2021:

After leaving the waters around Christmas Island a few days ago, we are now pretty much in the middle of nowhere. The ocean swells are getting bigger and it’s now easier to understand why there are so many structures (hooks, etc.) all over the RV Investigator to prevent things from flying around in rough seas.

Many people probably have romantic notions in mind when they think about a voyage like this but the reality is that we work 24/7, and in shifts. It feels like everything merges into one very long day. I’m working on the late shift, from 2pm to 2am which actually suits my natural biorhythm best!

Sampling is now in full swing and we are pretty busy, sometimes analysing up to three sampling sites during one shift. Sampling alternates between using the CTD (a large instrument that takes water samples from various water depths to measure oxygen, nutrients, salinity and water temperature) and using devices for biological sampling of the sea floor.

For the biological sampling we are mostly using the ‘Beam Trawl’ – a big net that is kept open by a steal beam. Occasionally we also use the ‘Sherman Sled’ as an alternative: a large and robust metal box that can cope with rough surfaces, rocks and more. So far, the Beam Trawl has delivered better results; at times the Sherman Sled only brought back some pretty ‘naked’ rocks (which made our geologist Steph happy but not we biologists).

Most of the catches are still relatively small but contain a good diversity of deep sea critters. Apart from deep sea life, the catch mainly consists of volcanic rocks and/or coral rubble which both offer a good substrate for organisms to attach to. Luckily, we’ve been spared big mud samples so far – wading through and sieving mud would be so much fun (not)!

Every catch has its own highlights, whether it’s bizarrely shaped sea cucumbers, huge sea stars, blood-red crustaceans or alien-looking fish. I’m mainly focusing on polychaete worms and squat lobsters but we haven’t come across many specimens from those groups yet.

This is my second voyage on board the RV Investigator: 2.5 years ago, I was lucky enough to participate in a journey to the seamounts south of Tasmania. But the cool temperate rough Southern Ocean is obviously a different beast compared to the tropical Indian Ocean and it’s interesting for me to see the similarities and differences in the deep sea fauna of seamounts in both very different oceans.

I was under the impression that I would see a similar diversity of deep sea animals in both areas but so far the diversity here in the Indian Ocean seems lower. Tropical waters are generally lower in nutrients than cool temperate waters so maybe that is reflected in lower deep sea diversity around seamounts? But it’s too early to tell and there are so many more ancient seamounts to be sampled soon. So perhaps that perceived pattern will change – stay tuned!

There are also some exciting relatively new techniques performed on this voyage: Katrina West from CSIRO in Hobart is taking loads of water samples from various water depths (brought up by the CTD) to investigate ‘eDNA’ (= environmental DNA). Environmental DNA can come from soil, water or other environmental sources but in this particular case we are talking about organic material (such as mucus) that is produced and released by deep sea organisms and that dissolves their traceable DNA in water.

By means of PCR assays (to be performed back on land later on) Katrina will be able to tell which organisms were present in a particular spot without even seeing it – fascinating stuff which gives us an additional insight into the diversity of deep sea habitats!

The RV Investigator was in the waters off Christmas Island and is expected to dock at Hobart on the 29th of July. The CSIRO MNF is hoping to reschedule the voyage as soon as it is able to.

Dr Ingo Burghardt, Research Associate, Marine Invertebrates, Australian Museum Research Institute.