Management and conservation can be greatly informed by considering explicitly how environmental factors influence population genetic structure. Using simulated larval dispersal estimates based on ocean current observations, we demonstrate how explicit consideration of frequency of exchange of larvae among sites via ocean advection can fundamentally change the interpretation of empirical population genetic structuring as compared with conventional spatial genetic analyses. Both frequency of larval exchange and empirical genetic difference were uncorrelated with Euclidean distance between sites. When transformed into relative oceanographic distances and integrated into a genetic isolation-by-distance framework, however, the frequency of larval exchange explained nearly 50 per cent of the variance in empirical genetic differences among sites over scales of tens of kilometres. Explanatory power was strongest when we considered effects of multiple generations of larval dispersal via intermediary locations on the long-term probability of exchange between sites. Our results uncover meaningful spatial patterning to population genetic structuring that corresponds with ocean circulation. This study advances our ability to interpret population structure from complex genetic data characteristic of high gene flow species, validates recent advances in oceanographic approaches for assessing larval dispersal and represents a novel approach to characterize population connectivity at small spatial scales germane to conservation and fisheries management.

Aim The development of accurate models predicting species range shifts in response to climate change requires studies on the population biology of species whose distributional limits are in the process of shifting. We examine the population biology of an example system using the recent northward range expansion of the marine neogastropod Kelletia kelletii (Forbes, 1852).Location This is a marine coastal shelf neogastropod species whose range extends from Isla Asuncion (Baja California, Mexico) to Monterey (CA, USA). Research sites spanned the extent of the range.Methods We examine abundance distributions and size frequency distributions of K. kelletii for evidence of factors determining historic and contemporary distributional patterns. Population studies were supplemented by historic and contemporary hydrographic data, including seawater temperature data from California Cooperative Oceanic Fisheries Investigations (CalCOFI ) and National Data Buoy Center (NDBC), and seawater circulation data. ResultsThe structure of recently established populations varied dramatically from that of historic populations. Markedly low densities and irregular size frequency distributions characterized recently established populations and suggested only occasionally successful recruitment. The point of transition between historic and recently established populations also corresponded to the location of a gradient in seawater temperature and the confluence of two major oceanic currents. The accumulated data suggest that temperature and/or barriers to dispersal could have set both contemporary patterns in population structure as well as the former northern range limit.Main conclusions Early life stages play a critical role in determining distributional patterns of K. kelletii. Dispersal barriers and temperature limitation are two plausible mechanisms that could determine both contemporary and historic distributional patterns. Future studies on this species should attempt to tease apart the relative importance of these factors in maintaining the populations at the northern edge of the range.

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.Direct and definitive estimates of larval dispersal in the ocean require the ability to track microscopic larvae of benthic invertebrates and fishes through the pelagic environment, from spawning locations to recruitment sites. Most marine species with pelagic larvae spawn millions of propagules that are released and then subjected to significant advection, diffusion, and mortality in vast volumes of seawater, making traditional mark-recapture approaches extremely difficult (Levin, 2006). However, ecologists have embraced recent developments in probe-based mass spectrometry to examine the chemistry of calcified structures in marine invertebrates and fishes that can be used as artificial or natural tags of natal origins. These geochemical tags are revealing fascinating data on larval dispersal that are challenging widely held paradigms concerning the spatial scale of demographic connectivity in ocean ecosystems. B y S i M o N r . t h o r r o l d ,

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Trace elements in larval hard parts may serve as useful tags of natal origin in invertebrate population studies. Using field-collected encapsulated veliger larvae of the marine gastropod Kelletia kelletii, this study examined the extent of spatial and temporal variation in the elemental composition of larval parts formed at the natal source. For both protoconchs and statoliths, results of multivariate analyses of variance (MANOVA) indicated that the elemental compositions show significant among-site and among-region differences. Linear discriminant-function analysis (DFA) correctly classified 89% of protoconchs and 80% of statoliths to their region of formation. However, there were significant interannual differences in elemental composition for statoliths at 2 sites and for protoconchs at 3 sites over a 3 yr period. Despite within-site interannual differences, the elemental compositions of hard parts formed during different years resembled one another to such a degree that a DFA generated with a single year's data could correctly predict the region of formation for 83.9% of statoliths and 82.5% of protoconchs formed in other years. A comparison of magnesium (Mg), strontium (Sr) and barium (Ba) incorporation patterns with per-site temperature profiles indicated statistically significant positive relationships between temperature and Mg and Sr incorporation into protoconchs, and inverse relationships between temperature and Sr (statoliths) and Ba (both protoconchs and statoliths) incorporation. These data, together with results from other studies, suggest that larval statoliths and protoconchs can meaningfully record variation in the physical and chemical properties of seawater and, hence, have potential as natural tags of natal origin. KEY WORDS: Protoconch · Kelletia kelletii · Larvae · Statolith · Trace elements · LA ICP-MS · DispersalResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 290: 145-163, 2005 artificially tagging and tracking larvae using radioactive isotopes, trace elements and chemical stains (e.g. Anastasia et al. 1998) have rarely been successful (e.g. Jones et al. 1999). Advection and diffusion in the water column, coupled with extremely high larval mortality rates during dispersal, make it exceedingly unlikely that tagged larvae will ever be recaptured (Levin 1990, Anastasia et al. 1998. Because of the inherent challenges associated with tag-recapture programs, recent interest has focused on the development of new tools that take advantage of natural environmentally-induced tags in the calcified otoliths (ear stones) of teleost fishes. Fish scientists have examined trace elements present in the otolith to reconstruct migration and dispersal patterns and to identify spawning grounds and juvenile nursery habitats (Gillanders & Kingsford 1996, Campana 1999, Swearer et al. 1999, Thorrold et al. 2001. The tremendous benefit associated with natural tags such as otoliths is that every larva is effectively tagged, thereby eliminating the probl...

Larval statoliths of the temperate neogastropod Concholepas concholepas (Bruguière, 1789) appear to have great utility for reconstructing larval dispersal history. Hatching marks on the statoliths seem to demarcate the natal core of recent recruits. Analysis of individual larval statoliths by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) indicates detectable levels of multiple trace elements. Differences in Ba/Ca, Zn/Ca, and Pb/Ca in the larval core of C. concholepas statoliths from 3 geographically separated sites in Chile suggest these mineralized hard parts could function as natural tags of natal origin and hence be useful in ecological studies of larval dispersal pathways. KEY WORDS: Concholepas concholepas · Larvae · Dispersal · Statolith · Trace elements · LA-ICP-MS Resale or republication not permitted without written consent of the publisherAs with fishes, there is a pressing need to understand processes affecting the settlement and survival of invertebrate larvae. For example, the management of commercially important marine invertebrates also requires knowledge about larval dispersal pathways. While DiBacco & Levin (2000) developed methods to track short-term movements of crab larvae between estuarine and coastal habitats, no effective means to track invertebrate larvae in the plankton from source to settlement exists (Levin 1990). Importantly, larval invertebrates possess mineralized structures, including statoliths, protoconchs, cuttlebones, carapaces, and larval skeletons, that could all potentially record recent dispersal histories. The statolith of molluscs, analogous in structure and function to the otolith, holds particular promise as a dispersal history recorder.Malacologists have frequently identified the presence of statoliths in molluscan larvae (see Ponder & Lindberg 1997 for a recent review) and have used statolith microstructure to obtain age and growth information (e.g. Jackson 1994, Bettencourt & Guerra 2001, Jackson & Moltschaniwskyj 2001; but see Villanueva 2000 for problems associated with differential increment deposition rates). Furthermore, Radtke (1983) suggested that the isotopic composition of aragonitic squid statoliths can be useful for ecological applications. Statolith structure varies substantially among gastropod families, ranging from multiple statoconia composed of various mineralized elements to single statoliths composed of calcium carbonate. The presence of regularly deposited growth rings in gastropod statoliths (and statoconia) remains largely unexplored (but see Grana-Raffucci & Appeldorn 1997). In addition, the potential use of the elemental composition of the gastropod statolith for reconstructing dispersal history has not been investigated.Here, we explore the utility of the mineralized statolith in gastropod molluscs for recording natal sources. First, we describe new methods to isolate larval statoliths in the temperate neogastropod Concholepas concholepas (Bruguière 1789). Next, we examine whether hatch marks delineate the ...

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Elemental signatures have been used as a tool to track individual organisms to their natal site in an attempt to understand stock structure and larval dispersal. However, factors that affect elemental signatures are not well understood. We conducted a factorial experiment using whelk Kelletia kelletii larvae from Salta Verde Point on Catalina Island, Los Angeles Harbor, and White Point, Palos Verdes peninsula, California, USA, to test the effects of egg source, temperature (10, 14 and 18°C) and culture seawater on the elemental composition of larval statoliths. Intra-capsular contents of newly laid capsules were also analyzed to explore whether maternal contributions might affect larval statolith chemistry. Using inductively coupled plasma mass spectrometry we quantified ratios of 7 elements to calcium in both intra-capsular contents and cultured statoliths and provided the first evidence of significant egg-source effects, independent of subsequently experienced environmental conditions, on statolith elemental signatures for Mg:Ca, Ba:Ca and Pb:Ca. Intra-capsular and statolith element ratios showed no clear relationship that might have indicated possible maternal transfer of elements to larvae. Culture seawater elemental concentration was positively related to statolith Ba:Ca and Pb:Ca, and temperature was negatively related to statolith Sr:Ca, Ba:Ca and Pb:Ca, while no significant effects were found for Mn:Ca or Zn:Ca. Effect-size estimates show that elements responded differently to factors within the variation measured in this study; the major effects for Ba and Pb were temperature and egg source, respectively. The significant effect of egg source on elemental signatures has potentially important implications for tracking free-spawned larvae. KEY WORDS: Statolith · LA ICP-MS · Dispersal · Egg source · Relative effects · Elemental signature · Kelletia kelletiiResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 353: 115-130, 2008 natural signatures of stock structure (e.g. , as records of dispersal and migration pathways (e.g. Ikeda et al. 2003) and for identifying spawning and nursery grounds (e.g. Gillanders & Kingsford 2003).In particular, the elemental composition of the larval calcified structures of fish (Swearer et al. 1999), crabs (DiBacco & Levin 2000), bivalves (Becker et al. 2007) and gastropods (Zacherl 2005) has potential to elucidate much useful information about larval origin and dispersal trajectories. Many larvae begin forming their calcified structures at or near the site of production and, thus, potentially carry a permanent elemental signature of the site of origin. When larvae enter the water column and move through ocean masses with variable physical and chemical characteristics, these changes can be recorded in the elemental composition of calcified structures. In principle, not only can the site of origin be identified, but subsequent larval movement also can be tracked using statolith elemental signatures.To identify any particul...