Case study
Inventory and detection of elasmobranchii at La Réunion
The Mascareignes Archipelago is one of the main hotspots of biodiversity in the Indian Ocean. Little is known about Elasmobranchii, which are cartilaginous fishes such as sharks and rays, thus limiting conservation mesures to be set up. In order to complete the taxonomic data obtained by classic inventories from the Observatory of Elasmobranchii of the Mascareignes Archipelago (MAEO), the ARBRE association (Research Agency for Biodiversity at La Réunion) called on ARGALY to obtain the most exhaustive information as possible thanks to the environmental DNA method.
ARGALY's mission:
Optimize a non-invasive, reproducible and standardized protocol for the environmental monitoring of sharks and rays around La Réunion.
To answer these technical questions, water and sediment samples were collected on three stations around the island Réunion. The sediments were sampled on the ocean floor, and water filtrations were performed with 0.45µm Waterra capsules, on the surface and in the water column. Shark tissue samples served as positive controls.
Parcelle non infestée - Zone vierge de toute EEE utilisée comme témoin négatif
Parcelle émergente - Observations de rares plants précoces d'EEE
Parcelle peu infestée - Quelques plantes invasives visibles
Parcelle infestée (A) - Observations régulières d'astéracées invasives, soumises à une fauche en octobre 2023
Parcelle infestée (B) - Observations régulières d'astéracées invasives, soumises à un arrachage en octobre 2023
Sampling methodology
Sampling methodology
Localization of sampling stations for the eDNA taxonomic analyses around La Réunion.
After extraction of the DNA contained in the samples, three genetic markers of elasmobranchii were tested for the PCR amplification and metabarcoding inventory : Shark_miniCOI (Fields and al. 2015), Elas01 (Miya and al. 2015) et Elas02 (Taberlet and al. 2018). Simultaneously, six specific primer pairs were conceived or optimized in silico then tested in vitro for the qPCR detection of four shark species and two ray species, selected according to their status on the threatened species red list settled by the International Union for the Conservation of Nature (UICN).
To answer these technical questions, water and sediment samples were collected on three stations around the island Réunion. The sediments were sampled on the ocean floor, and water filtrations were performed with 0.45µm Waterra capsules, on the surface and in the water column. Shark tissue samples served as positive controls.
Localization of sampling stations for the eDNA taxonomic analyses around La Réunion.
To answer these technical questions, water and sediment samples were collected on three stations around the island Réunion. The sediments were sampled on the ocean floor, and water filtrations were performed with 0.45µm Waterra capsules, on the surface and in the water column. Shark tissue samples served as positive controls.
Study conclusion
The eDNA tool confirms and completes the data obtained from the MAEO program: the majority of visually observed species were detected by eDNA and some species that were invisible during diving or by cameras are identified thanks to eDNA. This project, in collaboration with ARGALY,therefore provided an eDNA expertise for the monitoring of rays and sharks at La Réunion to participate to a better knowledge of elasmobranchii biodiversity in the Mascareignes Archipelago. It is thus paving the way for the implementation of preservation actions .
