Table_1_Water quality negatively impacts coral occurrence in eutrophic nearshore environments of the Florida Keys.docx

IntroductionCoral species are negatively impacted by anthropogenic stressors worldwide. Nearshore coastal ecosystems provide an excellent study system for the investigation of the impacts of local land-based stressors such as nutrients on coral assemblages due to their proximity to land based sources of pollution. The nearshore environs of the Florida Keys are an intensively developed and intensively managed system; Florida Keys waters have been characterized by chronic eutrophication since 1999. Benthic communities are known to change or “shift” under chronic eutrophication.
ObjectivesThis research examines the patterns of occurrence in stony corals correlating to detailed nearshore water quality measurements. The questions addressed are a) What are the coral assemblages within 500 meters of the shoreline, and which species are resilient to these environs? b) How does water quality impact coral occurrence?
MethodsThis study examined the immediate nearshore (0-500m) areas of 13 sites using a randomized blocked experimental design for both water quality and benthic sampling. Water quality parameters measured included chlorophyll-a, nitrates + nitrites (NOx), total nitrogen, total Kjeldahl nitrogen, total phosphorus, Salinity, pH, temperature, and dissolved oxygen. Benthic surveys documented stony coral occurrence using belt transects with point intercept measurements.
ResultsStony coral species occurrence was limited at most of the study sites. Siderastrea radians and Porites divaricata were the two common species that appear to have a higher tolerance to eutrophic conditions under these shallow water conditions. Of the 13 study sites, 2 sites had no coral species occurring; this analysis was based on the comparison between sites with and without stony coral species. Water column Chlorophyll-a, pH, dissolved oxygen saturation, temperature, NOx, N:P ratio, total nitrogen and total phosphorus were found to be significantly different between the sites with and without corals. Further multivariate analysis showed a clear clustering of the two groups.
ConclusionThe low overall diversity and the higher occurrences of stress tolerant species provide evidence of the effects of coastal eutrophication on the coastal Florida Keys ecosystem. Our data suggest that more conservative water quality thresholds should be posed to improve nearshore biodiversity and ecological functioning of coastal systems.

引言
全球范围内的珊瑚物种均受到人为胁迫因子的负面影响。近岸沿海生态系统因临近陆源污染源，为探究营养盐等局地陆源胁迫因子对珊瑚群落的影响提供了优质研究载体。佛罗里达礁岛群（Florida Keys）近岸区域是开发与管理强度均较高的系统；自1999年起，佛罗里达礁岛群海域长期处于富营养化状态。已知底栖群落在长期富营养化条件下会发生改变或“群落偏移”。

研究目标
本研究旨在探究与精细化近岸水质监测数据相关的石珊瑚出现模式。拟解决的科学问题包括：a) 海岸线500米范围内存在哪些珊瑚群落，哪些物种对该环境具备耐受能力？b) 水质如何影响珊瑚的出现情况？

研究方法
本研究采用随机区组实验设计，对13个样点的近岸（0-500米）区域开展水质与底栖生物采样。测定的水质参数包括叶绿素a、硝酸盐+亚硝酸盐（NOₓ）、总氮、凯氏总氮、总磷、盐度、pH值、水温以及溶解氧。底栖生物调查采用带状样带结合样点拦截法记录石珊瑚的出现情况。

研究结果
多数研究样点的石珊瑚物种出现率较低。微小星珊瑚（Siderastrea radians）和分歧多孔螅（Porites divaricata）是两种常见且对该浅水环境下的富营养化条件耐受度更高的物种。13个研究样点中，有2个未出现任何珊瑚物种；本分析基于有无石珊瑚物种的样点间对比展开。研究发现，有无珊瑚的样点在水柱叶绿素a、pH值、溶解氧饱和度、水温、NOₓ、氮磷比、总氮以及总磷等参数上均存在显著差异。进一步的多变量分析显示，两类样点呈现出清晰的聚类特征。

研究结论
整体多样性偏低且耐胁迫物种占比更高的现象，佐证了沿海富营养化对佛罗里达礁岛群沿海生态系统的影响。本研究数据表明，应设立更为严格的水质阈值，以提升近岸生物多样性并改善沿海生态系统的生态功能。