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ABSTRACT For marine species with planktonic dispersal, invasion of open ocean coastlines is impaired by the physical adversity of ocean currents moving larvae downstream and offshore. The extent species are affected by physical adversity depends on interactions of the currents with larval life history traits such as planktonic duration, depth and seasonality. Ecologists have struggled to understand how these traits expose species to adverse ocean currents and affect their ability to persist when introduced to novel habitat. We use a high‐resolution global ocean model to isolate the role of ocean currents on the persistence of a larval‐producing species introduced to every open coastline of the world. We find physical adversity to invasion varies globally by several orders of magnitude. Larval duration is the most influential life history trait because increased duration prolongs species' exposure to ocean currents. Furthermore, variation of physical adversity with life history elucidates how trade‐offs between dispersal traits vary globally. 

Abstract A perturbative solution of simplified primitive equations for nonlinear weakly stratified upwelling over a frictional slope is found that resolves the vertical structure of velocity fields and can satisfy Ertel’s potential vorticity conservation in the stratified inviscid interior. The solution uses assumptions consistent with the model proposed by Lentz and Chapman, including a steady-state, constant cross-shore density gradient, no alongshore gradients, laterally inviscid, and consideration of cross-shore advection of alongshore momentum. The solution resolves the vertical structure of velocity fields (including subsurface maxima of compensational flow, not resolved by Lentz and Chapman) and can satisfy Ertel’s potential vorticity conservation in the stratified inviscid interior. The dynamics are similar to Lentz and Chapman; bottom stress balances alongshore wind stress in a homogeneous density ocean and is replaced by nonlinear cross-shore transport of alongshore momentum as the Burger number (S=αN/f, whereα,N, andfare the bottom slope, buoyancy frequency, Coriolis frequency, respectively) increases. When the solution uses the empirical relation between cross-shore and vertical density gradients proposed by Lentz and Chapman, vorticity conservation is not satisfied and the nonlinear momentum transport estimated by the solution linearly increases withS, asymptotically matching Lentz and Chapman forS< 1. When the solution conserves interior potential vorticity, the momentum transport is proportional toS²forS< 1 and is in better agreement with numerical simulations. 

The increase in genetic distance between marine individuals or populations with increasing distance has often been assumed to be influenced by dispersal distance. In turn, dispersal distance has often been assumed to correlate strongly with pelagic larval duration (PLD). We examined the consistency of these assumptions in species with long planktonic durations. Reviewing multiple marine species, Selkoe & Toonen (2011; Mar Ecol Prog Ser 436:291-305) demonstrated significant fit of a species’ PLD with metrics of genetic distance between sampling sites. However, for long dispersers (PLD >10 d) whose dispersal is more influenced by ocean currents, the fit of PLD and genetic connectivity metrics was not significant. We tested if using realistic ocean currents to determine simulated dispersal distances would produce an improved proxy for larval dispersal that correlates more strongly with genetic connectivity metrics. We estimated the dispersal distance of propagules for locations in the genetic studies compiled by Selkoe and Toonen with a global ocean model (Mercator, 1/12° resolution). The model-derived estimates of dispersal distance did not correlate better than PLD against the genetic diversity metrics globalF_STkm^-1and isolation-by-distance (IBD) slope. We explored 2 explanations: (1) our ocean circulation-based dispersal distance estimates are too simple to produce biologically meaningful improvement over PLD, and (2) IBD slope is not a powerful predictor of variation in dispersal distance between species with long PLD. Exploring these explanations suggests directions for future research which will enable better quantitative understanding of genetic diversity and its spatial distribution in coastal marine organisms. 

Exchange of material across the nearshore region, extending from the shoreline to a few kilometers offshore, determines the concentrations of pathogens and nutrients near the coast and the transport of larvae, whose cross-shore positions influence dispersal and recruitment. Here, we describe a framework for estimating the relative importance of cross-shore exchange mechanisms, including winds, Stokes drift, rip currents, internal waves, and diurnal heating and cooling. For each mechanism, we define an exchange velocity as a function of environmental conditions. The exchange velocity applies for organisms that keep a particular depth due to swimming or buoyancy. A related exchange diffusivity quantifies horizontal spreading of particles without enough vertical swimming speed or buoyancy to counteract turbulent velocities. This framework provides a way to determinewhich processes are important for cross-shore exchange for a particular study site, time period, and particle behavior.