Publications

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2011
Fodrie, FJ, Becker BJ, Levin LA, Gruenthal K, McMillan PA.  2011.  Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels. Journal of Sea Research. 65:141-150.   10.1016/j.seares.2010.09.001   AbstractWebsite

The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels (Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78-87% of all cases. Settlement varied between 2 and 27 settlers grambyssus(-1) week(-1) at 510 and HI, and both sites were characterized by 2-3 weeks with "high" settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between "high" and "low" settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations. (C) 2010 Elsevier B.V. All rights reserved.

2008
Fodrie, FJ, Levin LA.  2008.  Linking juvenile habitat utilization to population dynamics of California halibut. Limnology and Oceanography. 53:799-812.   10.4319/lo.2008.53.2.0799   AbstractWebsite

We investigated the nursery role of four coastal ecosystems for the California halibut (Paralichthys californicus) using the following metrics: (1) contribution in producing the fish that advance to older age classes, (2) connectivity of coastal systems resulting from migration of fish from juvenile to subadult habitats, and (3) effect of nursery habitat usage and availability on subadult population size, specifically evaluating the concentration hypothesis. Potential nurseries were grouped using a robust classification scheme that segregated exposed, bay, lagoon, and estuarine environments. Assignment of nursery origins for individual subadult fish via elemental fingerprinting indicated that exposed coasts, bays, lagoons, and estuaries contributed 31%, 65%, 1%, and 3% of advancing juvenile halibut during 2003, versus 49%, 33%, 16%, and 2% during 2004, respectively. These results were remarkably similar to "expected'' nursery contributions derived from field surveys, suggesting that in this system juvenile distributions were a good indicator of unit-area productivity of juvenile habitats and that density-dependent mechanisms during the juvenile phase did not regulate recruitment pulses. Elemental fingerprinting also demonstrated that individuals egressing from bays did not migrate far from their nursery origins (, 10 km), resulting in reduced connectivity along the 110-km study region over the timescale of approximately one generation. Consequently, we observed considerably higher subadult densities at sites near large bays, while populations distant from large bays appeared to be more influenced by nursery habitat limitation. Over large (similar to 100 km) scales, the location and availability of nursery habitat alternatives had significant effects on the population dynamics of an important member of the ichthyofaunal community of southern California.

2007
Thorrold, SR, Zacherl DC, Levin LA.  2007.  Population connectivity and larval dispersal using geochemical signatures in calcified structures. Oceanography. 20:80-89.   dx.doi.org/10.5670/oceanog.2007.31   AbstractWebsite

The importance of larval dispersal to the population dynamics and biogeography of marine organisms has been recognized for almost a century (Hjort, 1914; Thorson, 1950). More recently, theoretical studies have highlighted the role that connectivity may play in determining the resilience of marine populations (Hastings and Botsford, 2006). Effective spatial management of marine capture fisheries, including the design of marine reserve networks, also requires an understanding of population connectivity (Sale et al., 2005). However, remarkably few empirical estimates of larval dispersal or population connectivity in ocean environments exist.