Cleaning Session in the Twilight Zone

Latest update June 8, 2020 Started on October 12, 2018

The aim of this mission is to conduct deep technical dives using close-circuit rebreathers to improve our knowledge about Mesophotic Coral Ecosystems (MCEs) and their importance for marine life, particularly for emblematic fish species.

Why are MCEs crucial in Ocean conservation? Let's find out! You can also follow our Instagram and Facebook pages @unseenexpeditions.

October 12, 2018
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In The Field

Throwback to our deepest dive on the project. We deployed our deepest temperature logger, at a depth of -120 metres, and we used our extra-long decompression stops on the ascent to re-deploy loggers at the -60 and -30 metres stations, after we retrieved their data the day before. These loggers will stay underwater for months, recording data at fixed intervals.
In combination with other parameters, it will allow us to better understand what is influencing wildlife at mesophotic depths.

Maximum depth: -125 metres. First decompression stop: -60 metres. Total dive time: 199 minutes, or 3h19min.

Entering the Twilight Zone is like entering a new realm, dominated by new kinds of species such as this soft coral rising from the sea floor. This image was shot at -57 meters, within the framework of our Unseen Expeditions project, "Cleaning session in the Twilight Zone", supported by grants from the National Geographic Society and Institut Français d'Indonésie.


Rigorous preparation and the completion of cautious checks at various stages before getting in the water greatly minimize the risks associated with deep diving.
Another great day of mesophotic exploration for Marc and myself on the Unseen Expeditions project, "Cleaning session in the Twilight Zone", supported by grants from the National Geographic Society and Institut Français d'Indonésie.

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Deep on the reef, branching corals and the habitat they provide to marine life are nowhere to be found. The structural complexity is however created by other organisms such as massive branching sponges, hosting high concentrations of undetermined azooxanthellate cnidarians and other animals (cf. picture below). Sea fans are also an important structural component of the Mesophotic Coral Ecosystems here in Bali, reaching sizes of sometimes more than 2 meters wide.

Photos: Branching sponge, -103m (left) and sea fan, -64m (right).

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Super glad to have had Alexis Tabbagh giving us a hand today, accompanying me to 100 meters and shooting some videos. It's been a while since we dived deep together for the last time, but today went flawless!

As a part of our project supported by the National Geographic Society and Institut Français d'Indonésie, we explored another area along the coastline for comparing the deep reef structure and biodiversity with our two survey sites. At -102m, we were greeted by an inquisitive pelagic thresher shark, Alopias pelagicus. Amazing, yet endangered, animal. Two massive tunas were also sighted deep on the reef.

Once again, a big thanks to Marc and Tekdeep Asia for the logistic on this dive. Team work is critical on this kind of project, at every levels.

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Mission accomplished! The 4 light loggers have been successfully deployed at 4 different depths on our study site. They will record the variations of light intensity at fixed intervals during many months. A big thanks to Yvonne Press who accepted to accompany me on today's deep dive and who was holding the camera, filming the logger deployment at -100 meters. As you can see on the short video clip, the visibility was amazing down there!

And of course, a special shout-out to Marc, who organised all the logistics on his day off (actually, he doesn't know what is a day off :) ).

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Really love following your expeditions. The photos and videos are great!
Hi Shaylyn, thank you for your kind words! We try to do our best :)

On March 25, I had the chance to be invited by Rili Djohani and her team from the Coral Triangle Center in Sanur, Bali, to give the first official presentation about our project "Cleaning Session in the Twilight Zone". It was the occasion to share the first results and images collected from our deep dives last month and to discuss about why those deep coral reef habitats are so important to preserve for the sake of our Oceans. Glad to see that the images presented raised excitement and awe, showing that so little is known about the Twilight Zone and that people are willing to know more about it! Another confirmation that raising awareness is crucial to impulse changes and improve conservation strategies. And that photos are sometimes more powerful than words.

The Coral Triangle Center is an Indonesian NGO conducting major work in Indonesia and Timor Leste for conservation, capacity building of local communities and education, on various topics: plastic waste, coral reef restoration and monitoring, sustainable tourism, policy changes, etc. More info here.

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Why would cleaning stations be limited to shallow depths? These two photos, taken 102 meters beneath the surface, illustrates a suspected cleaning station composed of brocken-back shrimps, probably of Genus Lysmata. The high concentration of these critters in a small area (at least 28 individuals on the first image) surprised us at this depth and there is a good chance that this place is visited by other marine creatures to get parasites removed from their bodies. If you look closely, you can actually see the back of a fish with the dorsal fin erected (damselfish probably) in the crack in the center of the first photo.

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Travelling buddies can sometimes make an interesting and unexpected duo. Like this fish and jellyfish we recorded at 75 meters deep during one of our deep dives!

And that's a wrap! Last dive of this first part on March 5 for myself, accompanied by Claude this time, Marc being busy teaching diving. We were welcomed by two longfin bannerfish, Heniochus acuminatus, at around -50 meters on the reef slope. The fish were so inquisitive and coming close to us and also to the camera dome, that I couldn't even light them properly with the strobes! Definitely a very interesting behaviour, potentially linked to cleaning interactions.
It's now time for the team to pack everything and process all the data collected. Nyepi, the day of silence in Bali where no one is allowed to go out, is coming on March 7, so it will be a good opportunity for resting at home. Because soon we will be preparing the next steps of this fascinating project...

We will keep posting photos taken during this first part, so stay alert!

And we would like once again to thank all our partners for their amazing support!

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The first part of the project "Cleaning Session in the Twilight Zone" is coming to an end. One more "shallower" dive tomorrow for Alexis and few more CTD measurements for Indra and then it will be time for processing data and images before the next mission, later during the year! Today's dive was cold and dark but many fish were spotted on the deeper part of the reef, between -70 to -100 meters: school of jacks bombing to us, tunas, school of fusiliers... And we also had those beautiful jellies that we've encountered many times deep during our expedition.

Thanks to our friend Claude for triggering the shutter on the last photo, taken during the last minutes at the 3 meters decompression stop. It's not that often that Marc and Alexis appear on the same photo when underwater! Claude has been diving with us those last few days, meeting Marc and Alexis during their slow ascent due to long decompression stops.

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Yesterday was dedicated to the recovery of a tripod and an underwater camera that Marc and Alexis left the day before at 60 meters deep. The camera was programmed to take a photo every 5 minutes to record the activity on the reef when there was no divers. After few minutes of an anxious descent, what a relief to see that the tripod didn't move a bit and that the camera was still working, with no leak in the underwater housing! The protocol being now validated, the system will be deployed again but over 48 hours this time and at a deeper depth.

However, today Marc and Alexis were taking a break from diving, after 10 consecutive days of deep dives to 100 meters, cumulating more than 30 hours of underwater time. It's time for their body to have a rest and recover from the deep diving induced physiological and physical stress! Indra still went back on the water, together with Dr. Gede Hendrawan, for measurements of the water column and bathymetry of the project area. Team work is essential!

You can enjoy our third episode of "Cleaning Session in the Twilight Zone", with few words on the bump-head sunfish, Mola alexandrini, by sunfish expert Dr. Marianne Nyegaard.

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I got to dive with Marianne in Bali a few years back. What a great woman!
She sure is! Brilliant on so many levels!

What an interesting dive today for Marc and Alexis, while Indra was relentlessly deploying a CTD probe from the boat, down to 100m every 10 minutes... And during 3 hours! The only way to collect robust scientific data and understand the water behaviour in the area!

After two days without seeing any, we finally had the chance to spot a curious Longfin bannerfish (Heniochus acuminatus) on our potential cleaning station site (photo 1). Only one bad photo as we were following our protocol route, involving a fast descent to 100m, and this guy was hanging around at -60m.

It was also a sad encounter that we had at -101m, where we found a plastic bottle (photo 2). Never forget that not all your "recyclable products" actually get recycled or even disposed of properly... Even if you put them in the bin! And they will most likely end up in the oceans, where they will take hundreds of years to discompose, poisoning animals for generations. Clearly, as this photo witnesses, even the deeper parts of the reef are impacted and even if we already knew that, it's always sad to see it with our own eyes. The main solution to that problem: reducing our daily use of plastic!

Finally, our long decompression stops between 12 and 3 meters allowed us to practise for an upcoming task: deploying a ballasted tripod at -80m. So today we tested how it felt to handle the weight, in order to come up with an efficient and safe plan to deploy the heavy equipment at 80m deep in the coming days (photo 3).

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Preparation is crucial! Every morning, the team is busy setting up everything, making sure there won't be any equipment failure that would make us lose one precious day of field work or worse, that could compromise our safety. And after the day on the field, it's time for cleaning everything thoroughly and preparing for the next day. Technical diving is an amazing way to discover a whole new world, laying beneath 60 meters under the surface, however it requires to follow rigorous protocoles and equipment maintenance, before, during and after the dives.

It's already the sixth day on the field, totalising a bit more than 17 hours underwater for Marc and Alexis, who just completed their fifth 100 meters dive in a row since the beginning of the project! Big up to Indra as well who is successfully performing water parameters measurements from the boat, every 10 minutes and down to 100 meters, thanks to a CTD probe. He already collected amazing abiotic data, that will be crucial in understanding how coral reefs (shallow and deep) are influenced by water movements in the area.

Tomorrow, Dr. Gede Hendrawan will be joining the team on the boat, sharing is oceanographic knowledge and expertise.

Enjoy a selection of photos of the team getting ready and few photos brought back from the depth!

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Day 3 of our expedition. Indra successfully performed many water samplings and water parameter measurements thanks to a CTD probe deployed from the boat. The data will be analysed later, in the lab, but it already reveals interesting aspects of the water column. So far the dives are going great as well, with only light current and nice visibility. Temperature are dropping quite fast though, with a 20°C at -100m, when it was 29°C at -3m! Marc and myself could explore and chose the underwater itineraries that we will follow every time for the rest of the project on our two stations. We were also able to deploy the data loggers: one water level logger à -60m and three temperature loggers at -30, -60 and -100m. They will stay deployed for one year, recording data at fixed intervals. One more temperature logger will be deployed in the coming days at -120m and four luminosity loggers at -10, -30, -60 and -100m.
We also had nice encounters on the deeper part of the reef, where jellyfish and longfin bannerfish came to say hi!

Preparing the right breathing gas mix is crucial for this kind of deep technical dives to 100m. It requires various cautious analysis, at different stages of the preparation. Here are Marc and Indra analysing and labelling the oxygen and helium contents of dive cylinders that Alexis and Marc will bring underwater, as emergency gas, if one of their rebreathers is failing. Each of them will cary 3 cylinders of 11L in complement of their rebreathers!

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Here we are, finally in the field! And for this occasion, we released our first web episode below. First dive tomorrow, stay tuned!


Alexis Chappuis is a French marine biologist, technical scientific diver and amateur photographer. He has conducted various marine ecological studies worldwide during his career, logging hours on and under the sea. After spending more than 4 years living and working in Indonesia for an environmental consulting company, he recently co-founded the French-based non-profit organisation UNSEEN (“Underwater Scientific Exploration for Education”).

He uses close-circuit rebreathers for the exploration and study of poorly known underwater ecosystems, particularly Mesophotic Coral Ecosystems (MCEs). In 2018, he has been awarded grants from the National Geographic Society and the French Embassy in Indonesia to conduct this pioneering research project on deep reef habitats, off the North-East coast of Bali, Indonesia. Starting in February 2019, the aims will be to investigate the connectivity of these deep coral ecosystems and their roles and importance for emblematic megafauna species such as the Bump-head sunfish, Mola alexandrini.

The better we know, the better we can preserve. From this belief, Alexis’ work is to raise awareness on the importance, but also the vulnerabilities, of these poorly-known MCEs. He hopes that this project will shed light on those elusive, yet crucial, environments and will open new research and conservation perspectives. One of them would be to include deep coral ecosystems in future marine protected areas, in order to fight more efficiently the current dramatic erosion of marine biodiversity and improve the global coral reef and coastal ecosystems resilience.

Alexis is the project leader on this expedition and is working closely with his Indonesian counter-part, Dr. I Gede Hendrawan, and with Dr. Marianne Nyegaard for the scientific aspects. He will also be involved in every deep dive with Marc Crane and in charge of documenting the deep reef habitats and fish behaviours observed at those depths.

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Originally from England’s South coast, Marc Crane has been a professional scuba diver since 1996, when he passed his instructor rating while on a gap year in Kenya. Having worked in the industry in a variety of destinations for the last 2 decades, he has witnessed the human impacts on the marine environment globally. After coming to Indonesia for the first time in 2010, he quickly developed an interest in deep reef exploration and research. He is an active deep Mixed Gas CCR instructor, trainer for SSI and TDI, as well as IANTD. When not teaching, you will find him hanging around at -100m.

Thanks to his high level of knowledge and understanding of deep technical diving and its effects on the human physiology, Marc will be in charge of the diving logistic and safety during this challenging project. Working at those depth is adding more risks to the dive itself, therefore it is important to plan everything carefully and properly before getting in the water. It is also crucial to have reliable team members that you know and trust.

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Dr. Marianne Nyegaard is an ocean sunfish researcher, avid scuba diver and ocean lover. She recently finished her PhD on sunfishes across Indonesia, Australia and New Zealand. During her PhD she spent three consecutive sunfish seasons on Nusa Lembongan, studying the seasonal Bali sunfish phenomenon with the aim to understand the relationship between the influx of sunfish and the large-scale oceanographic features influencing the Lombok Strait. During this time, she started the citizen science project “Bali Mola ID Catalogue”, and later co-founded the “Match My Mola” project.

She was the recipient of a prestigious Endeavor Primer Ministers scholarship, allowing her to take time out from her PhD to satellite tag Bali sunfish and uncover their movements during the Bali sunfish season. Her venture of working across three countries also led to the discovery of a new species of sunfish – the first new sunfish species to be described in over 180 years – which she named the Hoodwinker sunfish (Mola tecta) to commemorate its long history of hiding from scientific discovery and recognition. Her taxonomic and genetic work on the ocean sunfishes also led to the clarification that the sunfish most commonly encountered off Bali is Mola alexandrini and not, as widely believed, Mola mola.

Marianne is currently based in Auckland, New Zealand, where she is looking at a local sunfish hot spot she found during the PhD, where plenty of “Bali molas” visit the productive waters off the North Island of New Zealand. She continues to publish on sunfishes, and is excited to discover what the “Cleaning Session in the Twilight Zone” project will uncover and teach us about the deep waters off Bali. It is important to note that her extensive sunfish knowledge and precious advices helped us design the project from the beginning and even though she won’t be joining us on the field (unfortunately), she will be involved during data analysis and later communication.

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[ENG] To whom does this blurry dark silhouette belong?
In approximately a month from now, our exciting deep reef exploration project will start in Indonesia, with a very special quest... Thanks to all our partners who are making this possible. Stay tuned and share with your network!

[FR] À qui appartient cette silhouette sombre et floue? Dans environ un mois à partir de maintenant, notre passionnant projet d'exploration de récifs profonds va débuter en Indonésie, avec une quête très spéciale... Merci à tous nos partenaires qui rendent ce travail possible. Restez connectés et partagez avec votre réseau !


Dr. Hendrawan is a researcher and lecturer in the Department of Marine Sciences, Faculty of marine sciences and Fisheries, Udayana University, Bali.

His main field of expertise is on coastal and marine environments. Since 2005, he has published several papers related to coastal environment, its dynamic, seawater exchange, seawater circulation, coastal sedimentation and particle movement in the seawater. Beside his publications, he also received several grants for independent and team research. His research funds were notably dedicated to the study of socio-biophysics of coastal areas in Bali and of fisheries resources for fisheries sustainability in Karangasem regency, Bali. Dr. Hendrawan is active as one of the scientific experts for Bali Province Government, particularly on the following topics: 1) Formulating the zonation plan for coastal area and small islands in Bali, 2) Formulating the zonation and management plan for marine protected area in Karangasem regency-Bali, and 3) Study for Ocean health index (OHI+) pilot project in Bali.

Thanks to his level of expertise in coastal environment, the crucial inputs he will bring to this project - especially regarding physical oceanography - and his interests and involvement in conservation plans on the island of Bali, Dr. Hendrawan will be a keystone local counterpart in this work.

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We are now going to introduce each team member of the upcoming project, starting by Gede Indra Putra Pratama.

He is a student of the Marine Sciences Study Program, Faculty of Marine Sciences and Fisheries, Udayana University, Bali, Indonesia. Indra is now compiling research which is a requirement to obtain a bachelor's degree. During his education as a science student, he was involved in various projects and developed strong scientific skills: (1) Deputy Governor Student in the Executive Board of the Faculty of Marine Sciences and Fisheries, Udayana University 2017; (2) Leader of the Marine Debris Guard, Udayana Community 2018; (3) 2nd Champion and Best Poster of National Scientific Writing Competition, SBMP Diponegoro University 2016; (4) Finalists of Outstanding Students (Mahasiswa Berprestasi) of Udayana University Selection 2018; (5) Speaker of Citizen Science Networking and Ocean Plastic Waste Survey with WWF Indonesia in Wakatobi and Makassar on 28th - 30th June, 2018; (6) Research Members of the Coastal and Marine Environment Study Group (Coordinator Dr. Hendrawan), specifically dealing with Marine Debris problems on the coast of Bali throughout 2018; (7) Has obtained an Open Water Diver license from the International Association of Diving School (ADS International).

On the field, Indra will be in charge of measuring water column abiotic parameters, such as temperature, conductivity and depth by deploying a CTD probe from the boat. He will also assist the diving team during the shallow water deployment of light and temperature loggers. Back in the lab, he will analyse the oceanographic data collected for modelling purposes and be involved in various tasks, like the writing of articles and during communication events.

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The training continues for the deep diving team, who just completed 6 days of mesophotic reef exploration on the northeast coast of Bali, Indonesia. The team was diving at depth of 60 to 100 metres, using Close Circuit Rebreathers and totalising hours of decompression time.

Deep diving is very challenging and involves many risks which are crucial to identify and minimise with a proper training and a good understanding of the technical, but also the physiological aspects of diving. Those risks are increased when you have to conduct a task underwater, even the simplest one: taking photos, deploying or recovering equipment, counting fish, etc. Therefore, it is necessary to not be overloaded with too many of them, by splitting the work among the team. Each diver must clearly know his job before immersion. This is why pre-dive planning and good communication within the team are extremely important. Divers also need to be rigorous while preparing their equipment and to follow the dive plan as closely as possible. At those depth, there is very little room for mistake.

However, all the rigour and time spent for preparation were worth it: amazing encounters down the reef slope and plenty of new photos to document the deep reefs of Indonesia, for our exciting upcoming project. Cannot wait for the next underwater session!

Photos: Various MCEs landscapes and Marc Crane observing a big barrel sponge during the long and mandatory decompression stops, following a 100 metres dive.

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To increase the chances of success and the scientific interests of an expedition, it is important to develop a trustful relationship with a local collaborator. Not only it is an amazing occasion for sharing knowledge with local experts and students, but it is also a matter of joining forces to achieve a common goal. Local collaborators usually have a very valuable and extensive experience of the field in their own country. Therefore, they are key players in every expedition, thanks to their scientific and technical expertise. Involving students is also a great way for capacity building and long-term impacts: the knowledge gathered during the project needs to be valued and transferred long after the end of the mission and education is the perfect way to keep it alive. For this project, we team up with the Department of Marine Sciences from the Faculty of Marine Sciences and Fisheries of Universitas Udayana in Bali, Indonesia.

But planning an expedition is also about making sure that each team member has all the proper permits to conduct the work in the destination country. Not doing so could be a violation of the country’s laws and lead to serious sanctions, including jail time! Some topics are more sensitive than others and it is always important to know about the country’s regulations before launching anything. Here again, a local partner is a serious help. Our team spent some time preparing the required documents in order to comply with the local rules. It is not the most interesting part of our project, but it is still a crucial aspect that shouldn’t be ignored.

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Expedition Background

Mesophotic Coral Ecosystems (MCEs) are composed of a community of light-dependent corals and other organisms typically occurring at depths between 30 to 150 m. Mainly due to the difficulty of accessing these depths, MCEs are greatly under-studied, as are their associated fish assemblages, including the role these deep-water habitats potentially plays in providing larger fish with opportunities for cleaner fish interactions. For the past two years, we have made a number of unique observations along the northeastern coast of Bali, Indonesia, during technical exploration dives into the twilight zone, between depths of 60 to 100 m. Here, emblematic fish like sharks, jacks, tunas and ocean sunfish (Mola alexandrini) are regularly encountered. Some of them are seen being cleaned by various species of reef fish. Indeed, based on opportunistic observations, some of these large fish appear to engage in cleaner fish interactions in certain, very specific areas of the deep-water reefs. Despite all existing technology and oceanographic expeditions, such deep reef observations are still relatively rare worldwide and not well documented, further highlighting our poor understanding of MCEs and their associated fish assemblages. A tantalising question is: do deep "cleaning stations" exist and are they purposely visited by certain species of fish and perhaps even the same individuals, over time? Answering this may have important consequences, notably in terms of conservation.

Therefore, we will conduct multiple deep dives between 60 to 100+ meters to investigate the ecological roles of MCEs. In order to access safely those depth, Close-Circuit Rebreathers (CCRs) mixed gas diving will be used. The objectives are to document those deep reef habitats thanks to photography and video and also to deploy temperature and light loggers for abiotic parameters monitoring along a depth gradient. This should allow us to better understand some structural and functional aspects of MCEs, vertical connectivity between deep and shallow reefs, but also some specific fish behaviours such as cleaning interactions. Images documenting these habitats will also help raising awareness among general public and decision makers, as both general awareness and scientific knowledge are crucial points for a better conservation of our Oceans.

Photo: _Huge seafan deep on the reef slope. Indonesia, -69m.


Hi Haresh! Thank you for your interest in our expedition. Unfortunately our small team is already full for this pilot project... But there might be other expeditions in the future. So stay tuned and share our work, that is also a great way to help us!

Hi Alexis! Happy to follow your project! I've been working on corals in Palau Bangka (North Sulawesi) and it is amazing! Now I'm working on black corals in the Mediterranean Sea, but I miss the Indonesian Coral Triangle!

Hey Giovanni, thanks for your interest in our project! I am also following yours and I have to say that black corals are so amazing... We can find many of them during our deep dives here in Indonesia and they are so beautiful. Too bad they are poached for jewellery... That's why it's always a concern wether to disclose or not their location. I didn't know you could find so many in the Mediterranean as well! Keep up the good work to preserve these amazing animals and maybe we can find a way to collaborate one day!

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