Integrative Oceanography Division and Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States.
USGS Pacific Coastal and Marine Science Center Santa Cruz, Santa Cruz, CA, USA, Santa Cruz, California, United States.
PeerJ. 2024 Oct 31;12:e18290. doi: 10.7717/peerj.18290. eCollection 2024.
Mineral-rich hardgrounds, such as ferromanganese (FeMn) crusts and phosphorites, occur on seamounts and continental margins, gaining attention for their resource potential due to their enrichment in valuable metals in some regions. This study focuses on the Southern California Borderland (SCB), an area characterized by uneven and heterogeneous topography featuring FeMn crusts, phosphorites, basalt, and sedimentary rocks that occur at varying depths and are exposed to a range of oxygen concentrations. Due to its heterogeneity, this region serves as an optimal setting for investigating the relationship between mineral-rich hardgrounds and benthic fauna. This study characterizes the density, diversity, and community composition of macrofauna (>300 μm) on hardgrounds as a function of substrate type and environment (depth and oxygen ranges). Rocks and their macrofauna were sampled quantitatively using remotely operated vehicles (ROVs) during expeditions in 2020 and 2021 at depths above, within, and below the oxygen minimum zone (OMZ). A total of 3,555 macrofauna individuals were counted and 416 different morphospecies (excluding encrusting bryozoans and hydrozoans) were identified from 82 rocks at depths between 231 and 2,688 m. Average density for SCB macrofauna was 11.08 ± 0.87 ind. 200 cm and mean Shannon-Wiener diversity per rock (H') was 2.22 ± 0.07. A relationship was found between substrate type and macrofaunal communities. Phosphorite rocks had the highest H' of the four substrates compared on a per-rock basis. However, when samples were pooled by substrate, FeMn crusts had the highest H' and rarefaction diversity. Of all the environmental variables examined, water depth explained the largest variance in macrofaunal community composition. Macrofaunal density and diversity values were similar at sites within and outside the OMZ. This study is the first to analyze the macrofaunal communities of mineral-rich hardgrounds in the SCB, which support deep-ocean biodiversity by acting as specialized substrates for macrofaunal communities. Understanding the intricate relationships between macrofaunal assemblages and mineral-rich substrates may inform effects from environmental disruptions associated with deep-seabed mining or climate change. The findings contribute baseline information useful for effective conservation and management of the SCB and will support scientists in monitoring changes in these communities due to environmental disturbance or human impact in the future.
富含矿物质的硬底，如铁锰（FeMn）结壳和磷块岩，出现在海山和大陆边缘，由于其在某些地区富含有价值的金属，因此引起了人们对其资源潜力的关注。本研究聚焦于南加州边界区（SCB），该地区地形起伏不平，分布着 FeMn 结壳、磷块岩、玄武岩和沉积岩，它们的深度和暴露在不同的氧气浓度下。由于其不均匀性，该地区是研究富含矿物质的硬底与底栖动物之间关系的最佳场所。本研究以基质类型和环境（深度和氧气范围）为函数，描述了硬底上大型动物（>300 μm）的密度、多样性和群落组成。在 2020 年和 2021 年的考察中，使用遥控潜水器（ROV）对岩石及其大型动物进行了定量采样，采样地点位于含氧最小区（OMZ）之上、之中和之下。从 82 块岩石中，共记录了 3555 个大型动物个体和 416 个不同形态种（不包括固着的苔藓动物和水螅动物），深度范围在 231 至 2688 米之间。SCB 大型动物的平均密度为 11.08±0.87 ind. 200 cm，每块岩石的平均 Shannon-Wiener 多样性（H'）为 2.22±0.07。研究发现，基质类型与大型动物群落之间存在关系。与其他四种基质相比，磷块岩的 H'最高。然而，当按基质对样本进行分组时，FeMn 结壳的 H'和稀有度多样性最高。在所研究的所有环境变量中，水深对大型动物群落组成的解释方差最大。OMZ 内部和外部站点的大型动物密度和多样性值相似。本研究首次分析了南加州边界区富含矿物质的硬底上的大型动物群落，这些硬底为大型动物群落提供了专门的基质，支持了深海生物多样性。了解大型动物组合与富含矿物质的基质之间的复杂关系，可以为深海海底采矿或气候变化相关的环境干扰的影响提供信息。研究结果提供了有用的基线信息，有助于有效保护和管理南加州边界区，并将支持科学家在未来监测这些群落因环境干扰或人为影响而发生的变化。
