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| Abstract Submission No. | ABS-2022-06-0017 |
| Title of Abstract | Physical environment and ecological interactions at La Perouse Seamount |
| Authors | Francis Marsac*, Pavanee Annasawmy, Margaux Noyon, Evgeny Romanov |
| Organisation | IRD |
| Address | SFA, Espace Building, Po Box 449 Victoria, Mahe, Seychelles Pincode: 249 Mobile: 2482587678 E-mail: francis.marsac@ird.fr |
| Country | Seychelles |
| Presentation | Oral |
| Abstract | La Pérouse seamount is located in the Mascarene Basin at a relatively short distance (160 km) from Reunion Island. A research cruise was organized in September 2016 to investigate bio-physical interactions in the framework of a shallow-seamounts project. La Pérouse seamount was selected with regards to its shallow depth (60 m) and pelagic fishing occurring in the area. At distances ranging from 1 to 20 km from the summit, we investigated the vertical structure of the current, temperature and chlorophyll-a concentration and sampled mesozooplankton with Bongo nets and micronekton by acoustics and midwater trawls. Local circulation revealed evidences of disturbance, with implications on temperature and chlorophyll-a distribution in the water column around the seamount. Alternating convergent and divergent cells driving these dynamics were suggested in relation to the irregular and crescent-like shape of the seamount. Spatial differences in zooplankton abundance were observed with some variable patchiness of higher concentration on the leeward flank. The vertical dynamics of micronekton and the aggregation effect along the seamount slopes and summit are likely to promote favorable foraging conditions for seamount-associated demersal and pelagic predators. Albacore tuna and swordfish are two species dominating longline catches west of Reunion Island in association with underwater shoals, however only partially associated to La Pérouse seamount, as other deeper topographic features also exist in the area. We cannot demonstrate any remarkable phytoplankton or zooplankton enrichment at La Pérouse, neither a notable high diversity of micronekton species or demersal fish species, although estimates for the latter are similar to that of seamounts in other oceanic regions. |