Data from: Alongshore variation in barnacle populations is determined by surfzone hydrodynamics

Larvae in the coastal ocean are transported toward shore by a variety of mechanisms. Crossing the surf zone is the last step in a shoreward migration and surf zones may act as semipermeable barriers altering delivery of larvae to the shore. We related variation in the structure of intertidal barnacle populations to surfzone width (surfzone hydrodynamics proxy), wave height, alongshore wind stress (upwelling proxy), solar radiation, and latitude at 40 rocky intertidal sites from San Diego, California to the Olympic Peninsula, Washington. We measured daily settlement and weekly recruitment of barnacles at selected sites and related these measures to surfzone width. Chthamalus density varied inversely with that of Balanus, and the density of Balanus and new recruits was negatively related to solar radiation. Across the region, long-term mean wave height and an indicator of upwelling intensity and frequency did not explain variation in Balanus or new-recruit densities. Balanus and new-recruit densities, daily settlement and weekly recruitment were up to three orders of magnitude higher at sites with wide (> 50 m), more dissipative surf zones with bathymetric rip currents than at sites with narrow (< 50 m) more reflective surf zones. Thirty to 50% of the variability in Balanus and new-recruit densities was explained by surfzone width. We sampled a subset of sites < 5 km apart where coastal hydrodynamics such as upwelling should be very similar. At paired sites with similar surfzone widths, Balanus densities were not different. If surfzone widths at paired sites were dissimilar, Balanus densities, daily settlement and weekly recruitment were significantly higher at sites with the wider more dissipative surf zone. The primary drivers of surfzone hydrodynamics are the wave climate and the slope of the shore and these persist over time, and therefore site-specific stability in surfzone hydrodynamics should result in stable barnacle population characteristics. Variations in surfzone hydrodynamics appear to play a fundamental role in regulating barnacle populations along the open coast, which in turn may have consequences for the entire intertidal community.

近岸海洋中的藤壶幼体可通过多种机制向岸输送。穿越碎波带（surf zone）是向岸迁移的最后一步，而碎波带可作为半透膜式屏障，改变幼体向岸的输送效率。本研究针对从加利福尼亚州圣迭戈至华盛顿州奥林匹克半岛的40个岩质潮间带站点，将潮间带藤壶种群结构的变异与碎波带宽度（碎波带水动力替代指标）、波高、沿岸风应力（上升流替代指标）、太阳辐射以及纬度进行关联分析。我们在选定站点测定了藤壶的每日附着量与每周补充量，并将这些指标与碎波带宽度相关联。小藤壶属（Chthamalus）密度与藤壶属（Balanus）密度呈负相关，且藤壶属密度与新补充个体密度均与太阳辐射呈负相关。整个研究区域内，长期平均波高以及上升流强度与频率的指示因子，均无法解释藤壶属及新补充个体的密度变异。藤壶属及新补充个体的密度、每日附着量与每周补充量，在宽度大于50米、发育有海底裂流的强消散型碎波带站点中，较宽度小于50米的强反射型碎波带站点最高可高出三个数量级。藤壶属及新补充个体的密度变异中有30%至50%可由碎波带宽度解释。我们选取了间距小于5千米的部分站点进行采样，这类站点的近岸水动力（如上升流）条件应极为相似。在碎波带宽度相近的配对站点中，藤壶属密度并无显著差异。若配对站点的碎波带宽度存在差异，则碎波带更宽、消散性更强的站点中，藤壶属密度、每日附着量与每周补充量均显著更高。碎波带水动力的主要驱动因子为波浪气候与岸坡坡度，且这些因子具有长期稳定性，因此特定站点的碎波带水动力稳定性应会带来藤壶种群特征的稳定。碎波带水动力的变化似乎在开放海岸藤壶种群的调控中发挥着基础性作用，而这进而可能对整个潮间带群落产生影响。