SBC LTER: Reef: Long-term experiment: Kelp removal: Urchin size frequency distribution

These data describe the size frequency distribution of red ( Mesocentrotus franciscanus ) and purple ( Strongylocentrotus purpuratus ) sea urchins within permanent plots of a long-term experiment designed to examine trajectories of change in the structure and productivity of kelp forest communities in response to changes in the frequency and severity of disturbance to giant kelp. The diameter of the test (shell without spines) was recorded to the nearest 0.5 cm for 50 red and 50 purple sea urchins located within a 40 m x 2 m area of each plot. Size frequency data of red and purple sea urchins are not collected in the continual kelp removal plots. When combined with size-mass relationships established in the laboratory these data were used to provide a non-destructive, in situ estimate of the dry mass per unit area of bottom for each species. The experiment was initiated in 2008 at five reef sites along the mainland coast of the Santa Barbara Channel and included an annual kelp removal treatment designed to simulate increases in the frequency and severity of winter wave disturbance and a continual kelp removal treatment that allowed the effects of giant kelp on the community to be evaluated. The last experimental removals of giant kelp occurred in winter 2016 or winter 2017, depending on the site. Data collection continued in all plots until spring 2023 to document the recovery trajectory of the reef fish community following the cessation of experimental kelp removal.本数据集记录了长期实验永久样地内红海胆（Mesocentrotus franciscanus）与紫海胆（Strongylocentrotus purpuratus）的体型频率分布。该长期实验旨在探究巨藻（giant kelp）扰动的频率与强度变化对海带森林群落结构及生产力的动态变化轨迹。 每个样地的40 m × 2 m调查区域内，选取50只红海胆与50只紫海胆，记录其壳径（无棘壳体），测量精度精确至0.5 cm。 持续移除巨藻的样地不采集两类海胆的体型频率数据。 结合实验室建立的体型-体重关系模型，本数据集可用于无损、原位（in situ）估算各物种的单位底面积干重。 本实验于2008年在圣巴巴拉海峡沿岸大陆架的5个礁区启动，设置两类实验处理：其一为年度巨藻移除处理，用于模拟冬季波浪扰动频率与强度的提升；其二为持续巨藻移除处理，用于评估巨藻对群落的影响效应。 各礁区的末次巨藻实验移除工作分别于2016年冬季或2017年冬季完成。所有样地的采样工作持续至2023年春季，以记录实验性巨藻移除停止后，礁区鱼类群落的恢复轨迹。