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.

近岸海域的幼体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，而碎波带可作为半渗透性屏障，改变幼体向岸的输送过程。我们对取自美国加利福尼亚州圣迭戈至华盛顿州奥林匹克半岛的40个岩相潮间带站点的数据进行分析，将潮间带藤壶 (intertidal barnacle) 种群结构的变异与碎波带宽度 (surfzone hydrodynamics proxy，碎波带水动力学替代指标)、波高、沿岸风应力 (upwelling proxy，上升流替代指标)、太阳辐射以及纬度关联起来。我们在选定站点测定了藤壶的日沉降量与周补充量，并将这些指标与碎波带宽度进行关联分析。小藤壶属 (Chthamalus) 的种群密度与藤壶属 (Balanus) 呈负相关，而藤壶属及新补充个体的密度与太阳辐射呈负相关。在整个研究区域内，长期平均波高以及上升流强度与频率的指示因子，并不能解释藤壶属或新补充个体密度的变异。相较于宽度小于50米的反射型碎波带 (reflective surf zone) 站点，在宽度大于50米、带有海床裂流 (bathymetric rip currents) 的消散型碎波带 (dissipative surf zone) 站点中，藤壶属及新补充个体密度、日沉降量与周补充量最高可相差三个数量级。藤壶属与新补充个体密度的变异中有30%至50%可由碎波带宽度解释。我们选取了间距小于5公里的站点子集进行采样，这类站点的近岸水动力学 (如上升流 (upwelling)) 应极为相似。在碎波带宽度相近的配对站点中，藤壶属的种群密度并无显著差异。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，藤壶属种群密度、日沉降量与周补充量均显著更高。碎波带水动力学的主要驱动因子为波浪气候与岸坡坡度，且这些因子长期稳定存在；因此，站点特异性的碎波带水动力学稳定性应会带来藤壶种群特征的稳定性。碎波带水动力学的变异似乎在开阔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。