Many benthic animals begin life with a planktonic larval stage during which coastal currents may move individuals far from shore. This trait is believed to allow individuals to develop away from nearshore predators and sibling competition, based on the assumption that mortality rates are weaker offshore. However, larvae developing offshore often fail to locate suitable coastal habitats. This results in a trade-off between nearshore mortality and offshore wastage with consequences for larval delivery to adult habitats that have not been fully appreciated. We use a reaction-diffusion model to show that when the nearshore larval mortality rate is high, larval supply can vary more than 10-fold with the offshore mortality rate. If this offshore rate is weak, then larval supply is maximized by an intermediate diffusion rate or larval duration. While a low-diffusivity coastal boundary layer typically improves the larval supply by decreasing wastage, it can also reduce the larval supply by preventing individuals from exploiting low offshore mortality rates. Finally, the cross-shore structure of the mortality rate may influence the alongshore transport of larvae by determining how far offshore they reside prior to settling, and, consequently, the alongshore currents they experience. Our observations contrast with the prior argument that larval supply decreases with diffusivity and larval duration due to wastage, and challenge the widespread decision to omit cross-shore heterogeneity from studies of alongshore movement. Scenarios in which spatial variability in the mortality rate has a large effect on recruitment are important both for understanding the biological consequences of the larval stage and from a modeling perspective.

许多底栖动物以浮游幼虫期开始生活，在此期间，沿海水流可能使个体远离海岸。据认为，基于死亡率在海上较弱的假设，该特征可使个人远离近海掠食者和同胞竞争。但是，在近海发展的幼体通常无法找到合适的沿海栖息地。这导致了近岸死亡率和近海浪费之间的权衡，这导致幼体向成年生境的传递尚未得到充分认识。我们使用反应扩散模型表明，当近岸幼虫死亡率很高时，幼虫供应量可以随近岸死亡率变化超过10倍。如果该离岸率很弱，则通过中间扩散率或幼体持续时间使幼体供应最大化。虽然低扩散率沿海边界层通常通过减少浪费来改善幼体供应，但它也可以通过防止个人利用低海上死亡率来减少幼体供应。最后，死亡率的跨岸结构可以通过确定幼虫在定居之前居住在近海的距离以及因此而经历的近海流来影响幼体的近岸运输。我们的观察结果与先前的观点相反，即先前的观点认为，幼虫的供给由于浪费而随着扩散率和幼虫持续时间的减少而降低，并挑战了从沿岸运动研究中省略跨岸异质性的广泛决策。