Marine predators and phytoplankton: how elephant seals use the recurrent Kerguelen plume

• Published in: Marine Ecology Progress Series
• Main Authors: O’toole, Malcolm, Guinet, Christophe, Lea, Ma, Hindell, Mark A.
• Other Authors: Institute for Marine and Antarctic Studies Hobart (IMAS), University of Tasmania Hobart, Australia (UTAS), Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Antarctic Climate and Ecosystems CRC - Australia, Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2017
• Subjects: Mirounga leonina; Foraging strategy; Prey encounter events; Dive behaviour; Kerguelen phytoplankton plume; Prey access; [SDE]Environmental Sciences; Kerguelen; Kerguelen Islands; Elephant Seals
• Online Access: https://hal.science/hal-01636338; https://doi.org/10.3354/meps12312

International audience Predators feeding in a highly dynamic environment have evolved strategies to re -spond to patchy resource distribution. However, studying these ecological interactions is challengingin the marine environment, as both predators and elements in their environment are oftenhighly mobile and difficult to monitor. We used sensors deployed on female southern elephantseals Mirounga leonina to collect data as they foraged hundreds of metres below a large recurrentphytoplankton plume east of the Kerguelen Islands (49° 15’ S, 69° 10’ E). Data collected by animalbornelight sensors were used to reconstruct phytoplankton patterns encountered by the seals.Prey encounter events (PEEs) recorded by seal-borne accelerometers below the euphotic zonewere compared with phytoplankton estimates at 2 scales: mesoscale (10s to 100s km) and smallscale (inter-dive). These analyses were performed on data recorded during daylight hours only,and did not include data at night due to the sensitivity threshold of the light sensors. Our resultsshowed that elephant seals moved through alternating patches of high- and low-density phytoplankton,but the timing and locations of these bloom patches were different between the upperand lower euphotic layers. Seals recorded more PEEs and shallower dives below high-densitypatches of phytoplankton. We propose that phytoplankton density at the mesoscale facilitatesprey aggregation (direct effect). However, phytoplankton density between dives (small scale)likely facilitates vertical access to prey via the shading effect of phytoplankton (indirect effect).Our study shows how a deep-diving marine predator may use its environment to maximise netenergy intake, and we demonstrate its resilience in a highly dynamic ecosystem.