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We examined the nursery role of salt marshes for transient nekton by searching the literature for data on density, growth, and survival of juvenile fishes and decapod crustaceans in marshes and using meta-analyses to test hypotheses. We analyzed density data from 32 studies conducted throughout the world. Based on fish density, habitat types could be ranked from highest to lowest as: seagrass > vegetated marsh edge, nonvegetated marsh, open water, macroalgae, oyster reefs > vegetated inner marsh. However, patterns of habitat use varied among the 29 fish species represented. For decapod crustaceans (seven species), habitat types were ranked: seagrass > vegetated marsh edge > nonvegetated marsh, vegetated inner marsh, open water, macroalgae > oyster reef. We identified only 5 comparative studies on transient nekton growth in salt marshes. Fish growth in nonvegetated salt marsh was not significantly different from growth in open water or in macroalgae beds but was significantly lower than in seagrass. Growth of decapod crustaceans was higher in vegetated marsh than in nonvegetated marsh. Nekton survival in salt marsh (11 studies analyzed) was higher than in open water, lower than in oyster reef/cobble and not significantly different from survival in seagrass. When density, growth and survival are all considered, the relative nursery value of salt marshes for nekton appears higher than open water but lower than seagrass. Vegetated marsh appears to have a higher nursery value than nonvegetated marsh; however, tidal dynamics and nekton movement among marsh components complicates these comparisons. The available data have a strong geographical bias; most studies originated in the northern Gulf of Mexico or on the Atlantic coast of the United States. This bias may be significant because there is some evidence that salt marsh nursery value is dependent on geography, salinity regimes and tidal amplitude.

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Population genetic theory and empirical comparisons of sister and sympatric marine species show that life history traits related to dispersal, such as pelagic duration (PD), should affect the frequency and spatial scale of migration, and thus influence population genetic structure. However, recent global analyses have concluded that PD is poorly correlated with marine population genetic structure. Here, we identify and compare genetic structure between four pairs of synchronously diverging co‐distributed (SDC) species, drawn from standardized analyses of eight eastern North Pacific rocky intertidal invertebrates and one macrophyte. We test two hypotheses: H0, that species with similar dispersal potential have similar population genetic structure, and H1, that species with higher dispersal potential have lower population genetic differentiation. We find that differences in census population size (Nc), fecundity (F), and PD are sufficient to explain measured differences in population genetic structure (ϕST, DEST) between SDC species. However, theoretical differences in migration potential, calculated as a function of Nc, F, and PD, exceed empirical differences in migration, suggesting important roles for genetic drift and natural selection in structuring marine populations in the eastern North Pacific. A quantitatively similar relationship between PD and FST has been calculated for co‐distributed species from the Great Barrier Reef, suggesting that meta‐analyses of SDC species may reveal general patterns in how species' traits and geographical variation interact to structure populations.

Abstract. Understanding the mechanisms that create spatial heterogeneity in species distributions is fundamental to ecology. For nearshore marine systems, most species have a pelagic larval stage where dispersal is strongly influenced by patterns of ocean circulation. Concomitantly, nearshore habitats and the local environment are also influenced by ocean circulation. Because of the shared dependence on the seascape, distinguishing the relative importance of the local environment from regional patterns of dispersal for community structure remains a challenge. Here, we quantify the ''oceanographic distance'' and ''oceanographic asymmetry'' between nearshore sites using ocean circulation modeling results. These novel metrics quantify spatial separation based on realistic patterns of ocean circulation, and we explore their explanatory power for intertidal and subtidal community similarity in the Southern California Bight. We find that these metrics show significant correspondence with patterns of community similarity and that their combined explanatory power exceeds that of the thermal structure of the domain. Our approach identifies the unique influence of ocean circulation on community structure and provides evidence for oceanographically mediated dispersal limitation in nearshore marine communities.