Seamount effect on circulation and distribution of ocean taxa in the vicinity of La Pérouse, a shallow seamount in the southwestern Indian Ocean

Type Article
Date 2020-06
Language English
Author(s) Marsac Francis1, 2, Annasawmy Pavanee1, 2, Noyon Margaux3, Demarcq Herve1, 2, Soria Marc1, 2, Rabearisoa Njaratiana1, 2, Bach Pascal2, 4, Cherel Yves6, Grelet Jacques7, Romanov Evgeny5
Affiliation(s) 1 : MARBEC, Univ Montpellier, CNRS, Ifremer, IRD, Sète, France
2 : Institut de Recherche pour le Développement (IRD), Sète, France
3 : UK-SA NRF/DST Bilateral Research Chair: Ocean Sciences & Marine Food Security, Nelson Mandela University, Port Elizabeth, South Africa
4 : MARBEC, Univ Montpellier, CNRS, Ifremer, IRD, Victoria, Seychelles
5 : CAP RUN – CITEB, Le Port, Île de La Réunion, France
6 : Centre D’Etudes Biologiques de Chizé (CEBC), UMR 7372 CNRS-La Rochelle Université, Villiers-en-Bois, France
7 : IMAGO, IRD Bretagne, Technopole de Brest Iroise, Plouzané, France
Source Deep-sea Research Part Ii-topical Studies In Oceanography (0967-0645) (Elsevier BV), 2020-06 , Vol. 176 , P. 104806 (18p.)
DOI 10.1016/j.dsr2.2020.104806
WOS© Times Cited 1
Keyword(s) Bathymetry, Mesoscale eddies, L-ADCP, Mesozooplankton, Micronekton, Stomach contents, Pelagic longline fisheries
Abstract

The La Pérouse seamount (60 m depth) has so far been poorly studied despite it being a short distance (160 km) from Réunion Island. As part of the MADRidge project, a multidisciplinary cruise was conducted to evaluate the effect of this shallow seamount on the local hydrology and ecology. Current measurements, temperature and chlorophyll-a profiles, and mesozooplankton and micronekton samples were collected between the summit and 35 km away. Micronekton data were supplemented with stomach content of pelagic top predators as well as fisheries statistics from the domestic longline fleet operating from Réunion. Vertical current profiles revealed distinct patterns between the offshore and seamount-flanked stations, giving evidence of topographical induced flow instabilities, notably on its leeward side (west) relative to the east flank. Distinct patterns in temperature and chlorophyll-a vertical profiles suggest the formation of convergent and divergent circulation cells as a result of the irregular and crescent-like summit topography. Spatial differences in zooplankton abundance were detected with higher biovolumes on the leeward flank. The overall acoustic backscatter for micronekton over the summit was weaker than offshore, but highly concentrated in the upper layer. Albacore tuna and swordfish dominate the longline catch west of Réunion, seemingly in association with a deep (900 m) topographic feature. Yet the largest catch is not directly associated with La Pérouse which would be too shallow for top predators to aggregate around in the long term. Enhanced levels of phytoplankton or zooplankton enrichment at La Pérouse were not demonstrated in this study, nor was there notable diversity of micronekton species. This might explain the relatively limited importance of this seamount to the tuna fisheries in this region.

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Marsac Francis, Annasawmy Pavanee, Noyon Margaux, Demarcq Herve, Soria Marc, Rabearisoa Njaratiana, Bach Pascal, Cherel Yves, Grelet Jacques, Romanov Evgeny (2020). Seamount effect on circulation and distribution of ocean taxa in the vicinity of La Pérouse, a shallow seamount in the southwestern Indian Ocean. Deep-sea Research Part Ii-topical Studies In Oceanography, 176, 104806 (18p.). Publisher's official version : https://doi.org/10.1016/j.dsr2.2020.104806 , Open Access version : https://archimer.ifremer.fr/doc/00631/74286/