The Indian Ocean Expedition of the Monaco Explorations

by Francis Marsac, mission leader of the Saya de Malha project

S.A. Agulhas II, Indian Ocean Expedition @Nicolas Mathys

The Monaco Explorations (ME) have organized a major 2-month campaign in the south-western Indian Ocean, in October and November 2022, by chartering the South African oceanographic vessel S.A. Agulhas II. The ship left Cape Town (South Africa) at the beginning of October and made a first stop in Mauritius, before undertaking a circumnavigation of the region passing through Reunion Island, Aldabra and Mahé in the Seychelles, the Saya de Malha bank, St Brandon, before returning to Mauritius where almost the entire scientific team disembarked. The ship then left for Cape Town, which it reached at the end of November, thus completing a journey of 10,000 nautical miles (18,500 km). The expedition mobilized 150 participants of 20 different nationalities: scientists, young researchers and students, filmmakers and photographers, artists and communicators.

A multidisciplinary expedition on the Saya de Malha Bank

It was a multidisciplinary expedition, articulated around 8 projects and an on-board school of 20 students of Master level. The main project of this expedition concerned the large Saya de Malha Bank (40,000 km²), for a holistic study of its ecosystem with a particular emphasis on the benthic biodiversity in invertebrates, sponges and plants. This bank is included in a joint management area of 400,000 km² between Mauritius and Seychelles created in the framework of the extension of the continental shelf of these two states. This legal status, provided for in the United Nations Convention on the Law of the Sea, gives the two states full sovereignty over the seabed, the subsoil and their dependent resources. There is a need for scientific data to inform the marine spatial planning being developed in this area, and this part of the ME campaign was designed with a "Science for Governance" objective.

The Saya de Malha project took place over 2 weeks, from November 2 to 17, 2022. Measurements of the physico-chemical and biological properties of the water column (25 hydrological and plankton harvesting stations) and collections of benthic fauna and flora were conducted on the shelf, along its slopes and in the deep sea. Sampling of benthic biodiversity was carried out through 11 dives by professional divers, 46 trawls and other bottom operations by towed gears (from 70 to 1100 m depth), and 12 dives by a remotely operated vehicle (ROV).

Map with the limits of the joint Mauritius-Seychelles maritime area. Source: CSMZAE, Mauritius

Click on the map to enlarge it

Deck sorting table @ Francis Marsac_IRD_Explorations de Monaco

Promising preliminary results

The results were as expected, with the collection of 300 to 400 species of molluscs, 250 species of crustaceans and about 100 species of plants. The taxonomic inventory is in progress, but already, on board, three specimens were confirmed as new, undescribed species (a crab Ethusidae, a shrimp Stenopidae and a gastropod Lamellarinae). Given the richness of the collection, many new identifications can be expected. The endemism concerning molluscs could be 20% on Saya de Malha. A characteristic of the benthic fauna of Saya is the very small size of the organisms that dominate the collections, often molluscs less than 2 mm. Species described in the early 20th century or in the late 1980s have been "rediscovered", such as Conus primus and the clam Tridacna rosewaterii.

The identification of the collected specimens will take several years. However, as early as September 2023, a workshop gathering the best taxonomic experts in the world will be organized in France, and we can expect significant progress towards a better appreciation of the benthic biodiversity of Saya de Malha.

Shrimp Stenopidae @ Laure Corbari_MNHN_Monaco Explorations

Gastéropode Lamellarinae @ MNHN_Monaco Explorations

Crab Ethusidae @ Laure Corbari_MNHN_Monaco Explorations

DIDEM training on board the ship

In addition to this work, training sessions were organized on board the ship to explain the articulation between natural sciences and public decision in the governance of marine areas by recalling the provisions of the International Law of the Sea. This was accompanied by complete training materials and simple framing articles that will soon be available in the project's resources tab. These sessions were an opportunity to exchange in a multidisciplinary way with Mauritian and Seychellois scientists, bringing together skills to clarify the possibilities of administering emblematic areas such as seamounts and underwater structures, which form national or high seas and deep seabed natural heritage, for which new protections are to be considered

Developments in the 21st Century Law of the Sea. How many nautical miles away are we from the environmentalist inflection? by Florence GALLETTI, S.A. Agulhas II, 14 November 2022

Florence Galletti giving an on-board training @ IRD_Monaco Explorations

Strengthening links between countries

Finally, this campaign was an extraordinary opportunity for students and some young scientists to be trained in the work of an oceanographic campaign. It also strengthened the links between Seychellois and Mauritian scientists, who ended up on common workshops. The expedition contributed to the establishment of a regional team ready to be deployed on other missions, especially those concerning the joint management area between the two states.