Bight 23 Benthic Infauna Abundance Harmonized

This report presents the results and interpretation of the macrobenthic infaunal component of the 2023 Southern California Bight (SCB) Regional Monitoring Program's Sediment Quality Assessment element. The Southern California Bight is a 100,000-square-mile body of water and submerged continental shelf and slope extending from Point Conception, California in the north to Cabo Colonet, Baja California, Mexico in the south. The primary objectives of this study were to measure the extent and magnitude of macrobenthic community composition across the Southern California Bight and to characterize the trends in that condition over the last 25 years (1998-2023). Samples of benthic macrofauna were successfully collected at 340 sites across the SCB using a random tessellation stratified design, ranging across 10 strata including 4 in enclosed embayments, 4 on the continental shelf, and 2 on the continental slope. Approximately one-third of those sites (115) were revisits of sites previously sampled in 2018, 2013, 2008, and either 2003 or 1998. An additional 8 samples were targeted from freshwater estuary strata. Samples were collected with a 0.1-m2 Van Veen grab, sieved on a 1-mm screen, preserved, and identified to the lowest possible taxonomic level. The entire dataset passed Quality Assurance/Quality Control Data Quality Objectives for sorting accuracy (98.5%), taxonomic identification accuracy (97.2%), taxonomic discrimination (95.6%), and counting accuracy (94.6%). Condition assessment was performed using the Benthic Response Index (BRI) for continental shelf samples, the California Sediment Quality Objectives Benthic Line of Evidence (SQO BLOE) framework for embayment samples with salinity greater than 27 PSU, and the US version of the Multivariate AZTI Marine Biotic Index (M-AMBI) for low salinity waters. Results indicated that more than 99% of the assessable portions of the region were in good condition (88.1% reference condition + 11.1% low disturbance condition) with less than 1% in poor condition. Embayment strata showed relatively poorer conditions, with over 35.5% of the embayment area in moderate (31.1%) or high disturbance (4.4%) condition categories, while continental shelf strata were in relatively better condition with no portions in moderate or high disturbance categories. The trend in habitat condition from 1998 to 2023 was relatively stable at the regional scale for offshore strata, while embayment strata showed a trend towards increasing amounts of poorer conditions in more recent survey years. Planning Documents: Bight23SedQualityQAPlan Bight23FieldManual Bight23MacrobenthicLabManual Bight23SedQualityIMPlan Assessment Reports: Bight'23 Benthic Infauna本报告呈现了2023年南加州湾（Southern California Bight, SCB）区域监测计划沉积物质量评估模块中大型底栖内栖生物组分的调查结果与解读。 南加州湾是一片面积达10万平方英里的水域与淹没大陆架、陆坡区域，北起美国加利福尼亚州康塞普西翁角，南至墨西哥下加利福尼亚州科洛内特角。 本研究的核心目标为：探明南加州湾范围内大型底栖生物群落组成的分布范围与规模，以及该群落状态在过去25年（1998年至2023年）间的变化趋势。 研究采用随机镶嵌分层设计，在SCB全域340个采样点位成功采集底栖大型动物群样本，覆盖10个分层区域，其中4个位于封闭海湾、4个位于大陆架、2个位于陆坡。其中约三分之一的点位（115个）为历史回访点位，曾于2018年、2013年、2008年以及2003年或1998年开展过采样。另有8个样本取自淡水河口分层区域。 样本采集采用0.1平方米范·维恩采泥器，经1毫米孔径筛网筛分后固定保存，并鉴定至尽可能低的分类学层级。 整套数据集通过了质量保证与质量控制的数据质量目标核查，其中分拣准确率达98.5%、分类鉴定准确率达97.2%、分类区分度达95.6%、计数准确率达94.6%。 针对大陆架样本采用底栖生物响应指数（Benthic Response Index, BRI）开展状态评估；针对盐度高于27实用盐度单位（PSU）的海湾样本，采用加州沉积物质量目标底栖证据链（California Sediment Quality Objectives Benthic Line of Evidence, SQO BLOE）框架；针对低盐水域，则采用美国版多变量AZTI海洋生物指数（Multivariate AZTI Marine Biotic Index, M-AMBI）。 调查结果显示，该区域可评估范围内超过99%的区域处于良好状态（其中88.1%为参照状态，11.1%为低扰动状态），仅不足1%的区域处于较差状态。海湾分层区域的状态相对较差，超过35.5%的海湾区域处于中扰动（31.1%）或高扰动（4.4%）状态类别；而大陆架分层区域状态相对更佳，无区域处于中扰动或高扰动状态。 1998年至2023年间，离岸分层区域的生境状态在区域尺度上保持相对稳定，而海湾分层区域在近年的调查中呈现出生境状态向更差方向发展的趋势。 规划文件：Bight23SedQualityQAPlan、Bight23FieldManual、Bight23MacrobenthicLabManual、Bight23SedQualityIMPlan 评估报告：Bight'23 Benthic Infauna