Behind the science:

Lower mesophotic coral communities (60-125 m depth) of the Northern...

   2018, May 22
Posted by Veronica Radice

An interview with:
Pim Bongaerts
California Academy of Sciences  (United States of America)
Interview keywords
Study location

“Lower mesophotic coral communities of the Northern Great Barrier Reef and Coral Sea”

What was the most challenging aspect of your study (can be anything from field, lab to analysis)?

Definitely the biggest challenge was having to study these lower mesophotic communities "remotely" using a ROV. The very strict scientific diving regulations in Australia - which are largely based on the commercial/off-shore industry - make it logistically impracticable to conduct any research dives below 30-40 m. We therefore used two Seabotix ROVs to overcome these restrictions, but obviously also had to face the associated challenge of conducting research with a little grabber and no peripheral vision. That certainly made surveys and specimen collections much more challenging than what we had anticipated. The great advantage of the ROVs was that we could stay productive throughout the day, as it allowed us to "stay at depth" during the 3-hour surface intervals that we needed between our regular dives (that we spent looking at coral communities at 40 m depth). Another major challenge was accessing the outer shelf edge reefs of the Great Barrier Reef and outer atolls, which are remote and often difficult to access due to large swells. Accessing these requires a liveaboard vessel, but there are no guarantees that the weather will be favourable for the time period that you book, which means that sometimes you get stuck in the shallow Great Barrier Reef lagoon (as we did).

What was the most memorable moment in undertaking this study?

We ended up spending a fair bit of time at sea for these surveys, with a total of around two months on the boat spread across four different expeditions (2012-2014). During this time, we had countless memorable wildlife encounters, particularly in the Far Northern Great Barrier, where the ROV raised great curiosity with the local sharks. We came across countless grey reef and silvertip sharks, and the occasional hammerhead and (baby) tiger shark. One particularly memorable event was a very rough crossing out to Osprey Reef in the Coral Sea, where our boat started to take on a fair bit of water due to a leak - that was definitely scary, but it luckily got resolved on time by the crew!

Our live-a-board (MV Reef Connections) for the first three expeditions: large enough to host a research team, but small enough to be anchored on the reef for ROV deployment (C) XL Catlin Seaview Survey - The Ocean Agency
David Whillas recovering temperature loggers with the ROV, with Pim Bongaerts and Paul Muir looking on (C) Global Change Institute

What was your favorite research site in this study and why?

I think Osprey Reef is still one of my favourites, and one where we ended up spending quite a bit of time. Admittedly as we got stuck there because of the weather, but that turned into a great opportunity to study this reef in-depth and establish permanent sites for long-term monitoring. Osprey Reef is a submerged atoll offshore in the Coral Sea, and David Attenborough dedicated an episode for his BBC Great Barrier Reef series to it entitled "The Perfect Reef". Technically this reef is not part of the Great Barrier Reef, and unfortunately it continues to receive rather poor protection from the Australian Government despite the ecological uniqueness of this isolated reef. Sadly, the reef got badly impacted by the 2016 mass bleaching event, and we could hardly recognise our sites during out latest revisit (2017).

Other than your co-authors, with whom would you like to share credit for this work?

I must say that we were blessed with a fantastic team of people during our time at sea. Besides those listed as authors (Norbert Englebert, Paul Muir and Kyra Hay), we had David Whillas (our ROV tech), Jaap Barendrecht (our logistics tech) and Linda Tonk (shallow-water sampling) with us for most of the time, and who were absolutely instrumental to getting this work done. Also, a specific mention for Joe Lepore from the Waitt Foundation, for getting us anchored in spots and conditions we never thought to be possible. Then there were of course the crews and numerous others that all contributed to making this work possible (check out the long list in the acknowledgements!).

ROV on the way down to survey the mesophotic communities of Osprey Reef (sampling basket where specimens were placed into barely visible in the right corner) (C) XL Catlin Seaview Survey - The Ocean Agency
The team: Norbert Englebert, Kyra Hay, Paul Muir, David Whillas and Pim Bongaerts (C) Global Change Institute

Any important lessons learned (through mistakes, experience or methodological advances)?

Learning to operate the ROV was a greatly rewarding experience, although with a steep learning curve! Before embarking on the expeditions, three of us (me, Norbert and Paul) completed the ADAS ROV Pilot Course (video example from the course), taught in a quarry in remote South Australia. The course was taught by David Whillas, and our "natural abilities" of getting entangled underwater and stirring up the sediment soon led to him giving us the endearing (?), collective nickname of "muppets"! Luckily, we had David along on most of the trips, so he could intervene when we got ourselves (once again) into a tricky situation. The one expedition he was not on the boat, we actually managed to "sample the benthos" with all 6 thrusters, rendering the ROV completely stuck and helpless at depth. A bit stressful at the time, as while trying to rescue the ROV, a film crew had just radioed in saying they were about to arrive to come film "the scientists in action". The major lesson learned though, was that having dedicated techs (such as David and Jaap) was crucial on these kinds of expeditions, as there are constantly issues to be fixed and problems to be solved.

Can we expect any follow-up on this work?

This study was led by Norbert Englebert, and was part of the "Deep Reef " project that we conducted as part of the XL Catlin Seaview Survey. During the Great Barrier Reef and Coral Sea expeditions associated with this project, we managed to collect data for a wide range of different projects. There are several notes and papers already published (Bongaerts et al. 2013, Englebert et al. 2014, Muir et al. 2015, Hernandez-Agreda et al. 2016), and quite a few more that are close to being submitted and that we are quite excited about. This includes population genomics and microbial assessments of our focal species (Pachyseris speciosa, Acropora aculeus and Seriatopora hystrix), a phylogenomic study of mesophotic Leptoseris, new species descriptions and an overall synthesis of mesophotic scleractinian coral biodiversity in the region, and an assessment of our first five years of temperature and benthic monitoring. Other than that, I am hopeful that we can soon revisit these areas, but with the support for decompression diving and closed-circuit rebreathers, so that we can begin to study these lower mesophotic depths in more depth.

Paul Muir and Norbert Englebert during the ADAS ROV Course in South Australia (C) Pim Bongaerts - Global Change Institute
Retrieving the ROV after getting all the thrusters entangled at depth (C) Steve Lindfield

Featured article:

Lower mesophotic coral communities (60-125 m depth) of the Northern Great Barrier Reef and Coral Sea | article
Englebert N, Bongaerts P, Muir PR, Hay KB, Pichon M, Hoegh-Guldberg O (2017)
PLoS ONE 12:e0170336