Evaluating chemical signatures in a coastal upwelling region to reconstruct water mass associations of settlement-stage rockfishes

Abstract

Vol. 550: 191–206, 2016 doi: 10.3354/meps11704 MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published May 25 O PEN A CCESS Evaluating chemical signatures in a coastal upwelling region to reconstruct water mass associations of settlement-stage rockfishes Sarah G. Wheeler 1, *, Ann D. Russell 2 , Jennifer S. Fehrenbacher 2 , Steven G. Morgan 3 Graduate Group in Ecology at the University of California at Davis and San Diego State University, 5500 Campanile Dr, San Diego, California 92184-4614, USA University of California, Davis, One Shields Ave, Davis, California 95616, USA Bodega Marine Laboratory, University of California, Davis, 2099 Westside Dr, Bodega Bay, California 94923-0247, USA ABSTRACT: Characterizing the behavior of larvae prior to settlement is integral to understanding population dynamics because coastal oceanography may facilitate or limit settlement. Otolith microchemistry can be used to determine patterns of fish movement, although there is a limited understanding of how this tool can be applied in coastal marine systems. Our goal in this study was to evaluate the application of otolith microchemistry to characterize water mass associations of settlement-stage marine fish in a coastal upwelling region using a 3-step approach. First, we characterized seawater chemistry of coastal water mass types across multiple years, finding differ- ences in the chemical signatures of strong upwelling, weak upwelling, and relaxation events. Sec- ond, we experimentally determined the effect of temperature on the partitioning of trace elements in otoliths for 2 rockfishes (Sebastes spp.) to find that the effect of temperature on otolith partition coefficients was element- and species-specific. Finally, we compared coeval changes in seawater and otolith chemistry of settlement-stage rockfishes that were exposed to naturally variable con- ditions over an upwelling-relaxation cycle. We subsequently evaluate whether laser ablation inductively coupled plasma mass spectrometry effectively measures otolith chemistry over eco- logically relevant time scales. We discovered that elemental concentrations in otoliths respond rapidly to changes in seawater chemistry and reflect equivalent proportional changes. This study provides evidence that elemental signatures are valuable tools for reconstructing larval histories of marine fish in coastal upwelling regions. KEY WORDS: Barium · Laser ablation · Inductively coupled plasma mass spectrometry · ICP-MS · Otolith · Seawater INTRODUCTION The elemental compositions of seawater and fish otoliths have numerous applications to ecological research and fisheries management (Campana 1999, Campana & Thorrold 2001, Thorrold et al. 2007, Els- don et al. 2008). Otolith chemistry research capital- izes on differences in the chemical composition of environments to reconstruct fish movements, and heterogeneity in trace elements in freshwater and *Corresponding author: sarahgracewheeler@gmail.com estuarine environments has led to a substantial body of research in these systems (Campana & Thorrold 2001, Gillanders 2005, Elsdon & Gillanders 2006). The validation and application of chemical tags in marine fishes is relatively understudied (Sturrock et al. 2012). However, chemical gradients between near shore and offshore environments and water masses have revealed fish cross-shelf movements (Kingsford et al. 2009), larval dispersal or migrations (Swearer et al. 1999, Hamilton et al. 2008), and settle- © The authors 2016. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com