National Coral Reef Monitoring Program: Calcification Rates of Crustose Coralline Algae Derived from Calcification Accretion Units (CAUs) Deployed across the Northwestern Hawaiian Islands in 2010 and Retrieved in 2013 (NCEI Accession 0157722)

Calcification accretion units, or CAUs, are used to assess the current effects of changes in seawater carbonate chemistry on calcification and accretion rates of calcareous and fleshy algae in the Hawaiian and Mariana Archipelagos, American Samoa, and the Pacific Remote Island Areas as part of the NOAA National Coral Reef Monitoring Program (NCRMP).
Laboratory experiments reveal calcification rates of crustose coralline algae (CCA) are strongly correlated to seawater aragonite saturation state. Predictions of reduced coral calcification rates, due to ocean acidification, suggest that coral reef communities will undergo ecological phase shifts as calcifying organisms are negatively impacted by changing seawater chemistry.
Deployed on the seafloor for a period of time, CAUs allow for recruitment and colonization of CCA and hard corals. By measuring the change in weight of the CAUs, the reef carbonate accretion rate can be calculated for that time period. Monitoring net accretion over successive deployments allows for the detection of changes in calcification rates over time.
The calcification rate data described here are from CAUs that have been retrieved and replaced at existing, long-term monitoring sites during NOAA Pacific Islands Fisheries Science Center (PIFSC), Coral Reef Ecosystem Program (CREP) led NCRMP missions around the Northwestern Hawaiian Islands in 2013, in accordance with protocols developed by Price et al. 2012. There are typically (but not always) five CAU sites established at each location CREP visits with five units deployed at each site.
CAUs are composed of two 10 x 10 cm flat, square, gray PVC plates, stacked 1 cm apart, and are attached to the benthos using stainless steel threaded rods. Calcareous organisms, primarily crustose coralline algae and encrusting corals, recruit to these plates and accrete/calcify carbonate skeletons over 2-3 year deployments. Due to the simple, low-cost design and analysis, statistically robust numbers of calcification plates can easily be deployed, recovered, and processed to provide estimates of net calcification.
This study provides information about spatial patterns of algal calcification and accretion rates and serves as a basis for detecting changes associated with changing seawater chemistry due to ocean acidification. In conjunction with benthic community composition data (separate NCRMP dataset), the calcification rates will aid in determining the magnitude of how ocean acidification affects coral reefs in the natural environment.
Analysis of these data will expand scientists’ capacity for assessing coral reef resilience regarding the effects of ocean acidification outside of controlled laboratory experiments. These data can also be used in comparative analyses across natural gradients, thereby assisting efforts to determine whether key reef-building taxa can acclimatize to changing oceanographic environments. These data will have immediate, direct impacts on predictions of reef resilience in a higher carbon dioxide (CO2) world and on the design of reef management strategies.

钙化沉积单元（Calcification Accretion Units, CAUs）作为美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）国家珊瑚礁监测计划（National Coral Reef Monitoring Program, NCRMP）的一部分，被用于评估夏威夷群岛、马里亚纳群岛、美属萨摩亚以及太平洋偏远岛区的海水碳酸盐化学变化对钙化藻类和肉质藻类的钙化速率与沉积速率的当前影响。
实验室实验表明，结壳珊瑚藻（crustose coralline algae, CCA）的钙化速率与海水文石饱和度状态显著相关。由海洋酸化引发的珊瑚钙化速率下降预测显示，随着钙化生物受到海水化学变化的负面影响，珊瑚礁群落将发生生态相位转变。
将CAU部署于海底一段时间后，可为结壳珊瑚藻和硬珊瑚提供附着与定殖的条件。通过测量CAU的重量变化，可计算该时间段内的珊瑚礁碳酸盐沉积速率。对多次部署后的净沉积量进行监测，即可检测钙化速率随时间的变化情况。
本文所述的钙化速率数据，来源于2013年由美国国家海洋和大气管理局太平洋岛屿渔业科学中心（Pacific Islands Fisheries Science Center, PIFSC）珊瑚礁生态系统计划（Coral Reef Ecosystem Program, CREP）主导的西北夏威夷群岛周边国家珊瑚礁监测计划任务中，于现有长期监测站点回收并更换的CAU，所有操作均遵循Price等人2012年制定的实验规程。通常（但并非总是），CREP到访的每个监测点位会设置5个CAU监测点，每个监测点部署5个CAU单元。
CAU由两块10 cm×10 cm的扁平方形灰色聚氯乙烯（Polyvinyl Chloride, PVC）板组成，两块板间距1厘米堆叠，并通过不锈钢螺纹杆固定于海底底质表面。钙化生物（主要为结壳珊瑚藻和覆层珊瑚）会附着于这些板材之上，并在2~3年的部署周期内沉积碳酸盐骨架并完成钙化过程。由于其设计与分析流程简单且成本低廉，可轻松部署、回收并处理大量统计学意义显著的钙化板材，从而得到净钙化速率的估算值。
本数据集提供了藻类钙化与沉积速率的空间分布模式信息，可为检测海洋酸化引发的海水化学变化相关的生态改变提供基础依据。结合底栖群落组成数据（属于另一套国家珊瑚礁监测计划数据集），钙化速率数据将有助于量化海洋酸化对自然环境中珊瑚礁的影响程度。
对本数据集的分析将拓展科学家在受控实验室实验之外，评估海洋酸化对珊瑚礁恢复力影响的能力。本数据集还可用于跨自然梯度的比较分析，从而助力判断关键造礁类群是否能够适应海洋环境的变化。本数据集将直接为高二氧化碳（CO₂）未来海洋环境下的珊瑚礁恢复力预测以及珊瑚礁管理策略的制定提供即时且有效的支撑。