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

Malcolm O’toole (1) , Christophe Guinet (2) , Ma Lea (1, 3) , Mark A. Hindell (1, 3)

1 IMAS - Institute for Marine and Antarctic Studies [Hobart]
2 CEBC - Centre d'Études Biologiques de Chizé - UMR 7372
3 Antarctic Climate and Ecosystems CRC - Australia

Predators feeding in a highly dynamic environment have evolved strategies to re - spond to patchy resource distribution. However, studying these ecological interactions is challenging in the marine environment, as both predators and elements in their environment are often highly mobile and difficult to monitor. We used sensors deployed on female southern elephant seals Mirounga leonina to collect data as they foraged hundreds of metres below a large recurrent phytoplankton plume east of the Kerguelen Islands (49° 15’ S, 69° 10’ E). Data collected by animalborne light sensors were used to reconstruct phytoplankton patterns encountered by the seals. Prey encounter events (PEEs) recorded by seal-borne accelerometers below the euphotic zone were compared with phytoplankton estimates at 2 scales: mesoscale (10s to 100s km) and small scale (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 results showed 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 upper and lower euphotic layers. Seals recorded more PEEs and shallower dives below high-density patches of phytoplankton. We propose that phytoplankton density at the mesoscale facilitates prey 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 net energy intake, and we demonstrate its resilience in a highly dynamic ecosystem.

Mots clés: Mirounga leonina; Foraging strategy; Prey encounter events; Dive behaviour; Kerguelen phytoplankton plume; Prey access

Domaines: Sciences de l'environnement

Malcolm O’toole, Christophe Guinet, Ma Lea, Mark A. Hindell. Marine predators and phytoplankton: how elephant seals use the recurrent Kerguelen plume. Marine Ecology Progress Series, 2017, 581, pp.215 - 227. ⟨10.3354/meps12312⟩. ⟨hal-01636338⟩