Use of multivariate control charts to assess the status of reef fish assemblages in the Northwestern Hawaiian Islands PeerJ

A distance-based multivariate control chart is a useful tool for ecological monitoring to detect changes in biological community resulting from natural or anthropogenic disturbances at permanent monitoring sites. It is based on a matrix of any distances or dissimilarities among observations obtained from species composition and abundance data, and bootstrapping techniques are used to set upper confidence bounds that trigger an alarm for further investigations. We extended the use of multivariate control charts to stratified random sampling and analyzed reef fish monitoring data collected annually on shallow (≤30 m) reefs across the Northwestern Hawaiian Islands (NWHI), part of the Papahānaumokuākea Marine National Monument. Fish assemblages in the NWHI were mostly stable, with exceptions in the south region (Nihoa, Mokumanamana and French Frigate Shoals) in 2012 and 2015 where changes in the assemblage structure exceeded the upper confidence bounds of multivariate control charts. However, these were due to changes in relative abundances of native species, and potentially related to the small numbers of survey sites and relatively low coral covers at the sites, particularly in 2015. The present study showed that multivariate control charts can be used to evaluate the status of biological communities in a very large protected area. Future monitoring of fish assemblages in the Papahānaumokuākea Marine National Monument should be accompanied by specific habitat or environmental variables that are related to potential threats to its shallow-water ecosystems. This should allow for more detailed investigations into potential causes and mechanisms of changes in fish assemblages when a multivariate control chart triggers an alarm. 2017 NOS (National Ocean Service) ONMS (Office of National Marine Sanctuaries) JIMAR (Joint Institute for Marine and Atmospheric Research) Submitted https://doi.org/10.7717/peerj.3651 CC BY 1948

基于距离的多元控制图（distance-based multivariate control chart）是生态监测的实用工具，可用于在长期监测站点中识别由自然或人为扰动引发的生物群落变化。该方法基于由物种组成与丰度数据得到的观测样本间任意距离或相异度矩阵，并通过自助法（bootstrapping）设置置信上限，当监测值超出该上限时即触发警报以启动后续调查。

本研究将多元控制图的应用范围拓展至分层随机抽样（stratified random sampling）场景，并分析了西北夏威夷群岛（Northwestern Hawaiian Islands, NWHI）——帕帕哈瑙莫夸基亚国家海洋保护区的组成部分——周边水深≤30米的浅海珊瑚礁的年度鱼类监测数据。

西北夏威夷群岛的鱼类群落整体较为稳定，仅南部区域（尼霍阿岛、莫库马纳马纳岛与法国护卫舰沙洲）在2012年和2015年出现例外：该区域的群落结构变化超出了多元控制图的置信上限。但此类变化仅源于本土物种相对丰度的改变，且可能与调查样点数量较少、样点珊瑚覆盖率偏低有关，2015年的情况尤为突出。

本研究证实，多元控制图可用于评估超大型保护区域内的生物群落健康状况。未来对帕帕哈瑙莫夸基亚国家海洋保护区鱼类群落的监测，应配套收集与浅海生态系统潜在威胁相关的特定生境或环境变量数据。如此一来，当多元控制图触发警报时，即可针对鱼类群落变化的潜在成因与机制开展更细致的调查研究。

2017年 美国国家海洋服务局（National Ocean Service, NOS）、国家海洋保护区办公室（Office of National Marine Sanctuaries, ONMS）、海洋与大气联合研究所（Joint Institute for Marine and Atmospheric Research, JIMAR） 投稿 https://doi.org/10.7717/peerj.3651 CC BY 1948