Publications

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2014
Frieder, CA, Gonzalez JP, Levin LA.  2014.  Uranium in larval shells as a barometer of molluscan ocean acidification exposure. Environmental Science & Technology. 48:6401-6408.   10.1021/es500514j   AbstractWebsite

As the ocean undergoes acidification, marine organisms will become increasingly exposed to reduced pH, yet variability in many coastal settings complicates our ability to accurately estimate pH exposure for those organisms that are difficult to track. Here we present shell-based geochemical proxies that reflect pH exposure from laboratory and field settings in larvae of the mussels Mytilus californianus and M. galloprovincialis. Laboratory-based proxies were generated from shells precipitated at pH 7.51 to 8.04. U/Ca, Sr/Ca, and multielemental signatures represented as principal components varied with pH for both species. Of these, U/Ca was the best predictor of pH and did not vary with larval size, with semidiumal pH fluctuations, or with oxygen concentration. Field applications of U/Ca were tested with mussel larvae reared in situ at both known and unknown conditions. Larval shells precipitated in a region of greater upwelling had higher U/Ca, and these U/Ca values corresponded well with the laboratory-derived U/Ca-pH proxy. Retention of the larval shell after settlement in molluscs allows use of this geochemical proxy to assess ocean acidification effects on marine populations.

2010
Stramma, L, Schmidtko S, Levin LA, Johnson GC.  2010.  Ocean oxygen minima expansions and their biological impacts. Deep-Sea Research Part I-Oceanographic Research Papers. 57:587-595.   10.1016/j.dsr.2010.01.005   AbstractWebsite

Climate models with biogeochemical components predict declines in oceanic dissolved oxygen with global warming. In coastal regimes oxygen deficits represent acute ecosystem perturbations Here, we estimate dissolved oxygen differences across the global tropical and subtropical oceans within the oxygen minimum zone (200-700-dbar depth) between 1960-1974 (an early period with reliable data) and 1990-2008 (a recent period capturing ocean response to planetary warming) In most regions of the tropical Pacific. Atlantic, and Indian Oceans the oxygen content in the 200-700-dbar layer has declined. Furthermore, at 200 dbar, the area with O(2) < 70 mu mol kg(-1) where some large mobile macro-organisms are unable to abide, has increased by 4.5 million km(2) The tropical low oxygen zones have expanded horizontally and vertically Subsurface oxygen has decreased adjacent to most continental shelves However, oxygen has increased in sonic regions in the subtropical gyres at the depths analyzed According to literature discussed below, fishing pressure is strong in the open ocean, which may make it difficult to isolate the impact of declining oxygen on fisheries At shallower depths we predict habitat compression will occur for hypoxia-intolerant taxa, with eventual loss of biodiversity. Should past trends in observed oxygen differences continue into the future, shifts in animal distributions and changes in ecosystem structure could accelerate (C) 2010 Elsevier Ltd. All rights reserved

2002
Davis, JLD, Levin LA.  2002.  Importance of pre-recruitment life-history stages to population dynamics of the woolly sculpin Clinocottus analis. Marine Ecology-Progress Series. 234:229-246.   10.3354/meps234229   AbstractWebsite

The relative influence of pre- versus post-recruitment life-history events on population size has been the subject of much recent debate. In the marine realm, much work has focused on intertidal invertebrates and on tropical reef fishes, with mixed results. We addressed this problem for a temperate intertidal fish, Clinocottus analis. Our main goal was to determine which life-history stage was most responsible for temporal changes in population size from 1996 to 2000 at 2 sites in San Diego, California, both seasonally and during the 1997 to 1998 El Nino Southern Oscillation (ENSO) event. We approached the problem using cohort analysis and matrix population modeling. Recruitment pulses were evident in population size structure for up to a year, unobscured by post-recruitment mortality, which was not density-dependent, Recruitment was not correlated to spawning adult biomass of 3 mo earlier, suggesting that egg, larval, or early post-settlement processes during those 3 mo determined the magnitude of recruitment, and ultimately, population size. Stage-structured population projection matrices were constructed to compare population growth rates and sensitivities among seasons and between climate periods (El Nino and non-El Nino), Elasticity (prospective) and decomposition (retrospective) analyses of these matrices indicated that the vital rates to which population growth rate (lambda) was theoretically most sensitive were not necessarily those responsible for observed temporal differences in lambda. Although, was most sensitive to juvenile growth and adult survivorship, fertility (which in this model included fecundity and egg, larval, and early post-settlement survivorship), in addition to juvenile growth, drove observed seasonal differences in lambda C. andlis population size decreased during the 1997 to 1998 El Nino event due to a decrease in recruitment, a decrease in batch fecundity (hydrated eggs per female) and, at 1 site, changes in juvenile survivorship, Results of the study emphasize the power of early life-history events to structure C. analis populations on both seasonal and longer timescales.