Changes in otolith microchemistry over a protracted spawning season influence assignment of natal origin

Abstract

Our understanding of the role dispersal plays in marine population dynamics is incomplete. One method used to quantify movement among populations is otolith microchemistry. A challenge with this method is gaining an understanding of the spatial and temporal variability of microchemistry that occurs over the course of a protracted spawning season. High-resolution sampling was used to explore the variability of elemental fingerprints of Hypsypops rubicundus at 6 rocky reefs spanning the southern California (USA) coastline from 3 June to 2 September 2008. Otolith microchemistry of 1101 larval fish and 72 juveniles was analyzed using a laser ablation inductively coupled plasma mass spectrometer. Within-reef elemental fingerprints were more similar than among-reef elemental fingerprints. The primary elements enabling discrimination among reefs and their relative contribution (%) to the elemental fingerprint of each reef were U (47%), Pb (31%), Ba (14%), Mg (9%), and Sr (1%). The 2 elements with the most consistent shifts in elemental chemistry from the onset to cessation of the spawning season were Ba (decreased across all study sites) and U (increased across all study sites). More than a third of the time (34%), the elemental fingerprint of a given reef was indistinguishable from the elemental fingerprint of a different reef later in the spawning season. When natal origins of juveniles were classified using microchemical data spanning the entire spawning season, the number of source populations and number of individuals predicted to have originated from actual source populations were underestimated. Researchers must utilize natural history information together with otolith microchemistry data to ensure that the natal origin of juveniles is assigned using data that account for both spatial and temporal changes in reef-specific elemental fingerprints. © Inter-Research 2011.