A fully coupled ecosystem model to predict the foraging ecology of apex predators in the California Current

Abstract

MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Vol. 556: 273–285, 2016 doi: 10.3354/meps11849 Published September 8 A fully coupled ecosystem model to predict the foraging ecology of apex predators in the California Current J. Fiechter 1, *, L. A. Huckstadt 2 , K. A. Rose 3 , D. P. Costa 2 Institute of Marine Sciences, University of California Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA Department of Oceanography and Coastal Sciences, Louisiana State University, 1002-Y Energy, Coast & Environment Building, Baton Rouge, LA 70803, USA ABSTRACT: Results from a fully coupled end-to-end ecosystem model for the California Current Large Marine Ecosystem are used to describe the impact of environmental variability and prey availability on the foraging ecology of its most abundant apex predator, the California sea lion Zalophus californianus. The ecosystem model consists of a biogeochemical submodel embedded in a regional ocean circulation submodel, both coupled with a multi-species individual-based sub- model for forage fish (sardine and anchovy) and California sea lions. Sardine and anchovy are explicitly represented in the model as they are commonly found in the diet of sea lions and exhibit significant interannual and decadal variability in population abundances that reflect variations in their environment and lower trophic level prey. Output from a 20 yr run (1989−2008) of the model demonstrates how different physical and biological processes control habitat utilization and forag- ing success of California sea lions on interannual time scales, with the dominant modes of variabil- ity linked to sardine abundance and coastal upwelling intensity. The results also illustrate how variability in environmental conditions, forage fish distribution, and prey assemblage affect sea lion feeding success. While specifically focusing on the foraging ecology of sea lions, the modeling framework has the ability to provide a more complete understanding of the physical and biologi- cal mechanisms impacting trophic interactions in the California Current, or other regions where similar fully coupled ecosystem models may be implemented. KEY WORDS: Ecosystem model · Foraging ecology · California Current · Upwelling · Sea lions · Marine predators · Zalophus californianus Resale or republication not permitted without written consent of the publisher Determining the relationships between environ- mental variability, prey field dynamics, and the foraging ecology of marine mammals and other apex predators has been an on-going research topic for several decades (Fiedler et al. 1998). However, re - cent pro gress in animal tagging has shed new light on the mechanisms through which changing environmental conditions may impact the habitat selection of pelagic predators (Block et al. 2011, Irvine et al. 2014). Such information is critical to identify the underlying physical and biological processes that control the foraging and migratory behavior of higher trophic level species (Weise et al. 2006, Bailey et al. 2009). Understanding the linkages among environmental variability, prey availability, and predator distribution should ulti- mately lead to a better characterization of biologi- cal ‘hot spots’ in the ocean and how these hot spots may respond to changing climate conditions (Pala- cios et al. 2006). *Corresponding author: fiechter@ucsc.edu © Inter-Research 2016 · www.int-res.com INTRODUCTION