Sara Simmonds (Koch)

Sara Simmonds (Koch)

Former graduate student

M.S. Biology 2008


The movement of larvae among spatially separated populations, can be a driving force in the persistence of marine populations. The recent range extension of Kellet’s Whelk, Kelletia kelletii, illustrates the need to identify natal origins of larvae to understand connectivity among historic and new populations. K. kelletii ranged from Isla Asuncion, Mexico to Pt. Conception, California, but since the 1980s have been found as far north as Monterey Bay. Two possible explanations have been proposed to explain this, 1) an episodic reversal of prevailing current patterns during the spawning season, facilitating northward transport of larvae from south of Pt. Conception, or 2) warming of northern coastal waters, allowing larvae produced at northern sites to survive. The aim of Sara’s study was to use natural tags in statoliths of larval K. kelletii to determine whether northern populations are reliant on larvae from south of Pt. Conception for persistence.

Elements incorporated into larval calcified structures have been used as natural tags to estimate levels of population connectivity via larval dispersal at various scales, but never across a species’ range. To explore the use of statoliths of Kelletia kelletii as natural tags, Sara characterized the scale of spatial variation and temporal stability of embryonic statolith chemistry at 21 sites across its range (Monterey, California, USA to Isla Asuncion, Baja California, Mexico) in 2004 and 2005. Statoliths were analyzed for five element-to-calcium ratios (Mg/Ca, Sr/Ca, Ba/Ca, Ce/Ca, Pb/Ca) using laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS). Multivariate analysis of variance (MANOVA) showed that statolith chemistry was significantly different among sites and regions. Discriminant function analysis (DFA) accurately assigned 43% of statoliths to natal site and grouping sites into regions increased classification success to 70%. Statolith chemistry was not temporally stable at the site or regional level, driven mainly by fluctuations in Ce/Pb and Pb/Ca. However, pooling statoliths across years decreased the total classification success to 63%. Comparing statolith chemistry to collection site temperatures, revealed a positive relationship for Mg/Ca and a negative relationship for Sr/Ca, Ba/Ca and Pb/Ca. Results from this study suggest that K. kelletii is a model system to use natural tags in estimating population connectivity across a species’ range. Thus, statoliths could be used to test hypotheses about exchange of larvae across the biogeographic boundary, Point Conception, California, and between California, USA and Baja California, Mexico.

After graduating, Sara worked as a research associate at University of California, Santa Barbara where she collaborated with Brian Kinlan to build a Bayesian mixture model using genetics, microchemistry data, oceanography and dispersal characteristics to predict dispersal patterns across the range of Kellet’s whelk. She first-authored a paper in 2014 based upon some of this work:

Simmonds SE, Kinlan B, White CC, Paradis GL, Gaines SG, Warner RR, and DC Zacherl. 2014. Geospatial statistics strengthen ability of natural geochemical tags to estimate range-wide population connectivity in marine species. Marine Ecology Progress Series 508: 33-51.

Sara is now finishing up her Ph.D. with advisor Paul Barber at University of California, Los Angeles where she studies the population genomics and comparative phylogeography of corallivorous gastropods in the Coral Triangle.