Drivers of concentrated predation in an Antarctic marginal-ice-zone food web

Benjamin T Saenz,Megan L Elrod,David G Ainley,Kendra L Daly,Erin Conlisk,Grant Ballard,Stacy L Kim

doi:10.1038/s41598-020-63875-y

Abstract

Predators impact preyscapes (3-D distribution of forage species) by consuming prey according to their abilities or by altering prey behavior as they avoid being consumed. We elucidate prey (Antarctic silverfish[Pleuragramma antarctica] and crystal krill[Euphausia chrystallorophias]) responses to predation associated with the marginal ice zone (MIZ) of the McMurdo Sound, Antarctica, polynya. Prey abundance and habitat was sampled across a 30 × 15 km area by remotely-operated vehicle, and included locations that were accessible (ice edge) or inaccessible (solid fast ice) to air-breathing predators. Prey and habitat sampling coincided with bio-logging of Adélie penguins and observations of other air-breathing predators (penguins, seals, and whales), all of which were competing for the same prey. Adélie penguins dived deeper, and more frequently, near the ice edge. Lowered abundance of krill at the ice edge indicated they were depleted or were responding to increased predation and/or higher light levels along the ice edge. Penguin diet shifted increasingly to silverfish from krill during sampling, and was correlated with the arrival of krill-eating whales. Behaviorally-mediated, high trophic transfer characterizes the McMurdo Sound MIZ, and likely other MIZs, warranting more specific consideration in food web models and conservation efforts.

Highlights

Predators impact preyscapes (3-D distribution of forage species) by consuming prey according to their abilities or by altering prey behavior as they avoid being consumed
This marginal ice zone (MIZ) exhibits trophic qualities observed in larger-scale MIZs, including high seasonal primary productivity associated with the polynya and fast ice edge[7,8,24], and large numbers of predators including penguins[5,21,37], seals[38,39], and whales[20,40,41] (Figs. 1, 2)
We evaluate the extent to which prey availability to penguins in the McMurdo Sound MIZ is driven by physical processes, and by foraging pressure through trophic competition

Summary

Introduction

Predators impact preyscapes (3-D distribution of forage species) by consuming prey according to their abilities or by altering prey behavior as they avoid being consumed. For the MIZ of the McMurdo Sound, Antarctica, polynya, we address questions of how the preyscape, i.e. 3-D prey availability and forage potential, is influenced by A) animal behaviors, predator avoidance behaviors by the prey, and predation pressure, through resource or interference competition among predators; and by B) physical characteristics of the environment This MIZ exhibits trophic qualities observed in larger-scale MIZs, including high seasonal primary productivity associated with the polynya and fast ice edge[7,8,24], and large numbers of predators including penguins[5,21,37], seals[38,39], and whales[20,40,41] We synthesize direct prey and predator observations that together constitute a natural predator-exclusion experiment in a before-and-after sequence to quantify the change in prey distribution as a consequence of predation

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Discussion

Conclusion