海水中的营养元素如氮、磷等的含量对当地的浮游动、植物结构(总种数、丰度、均匀度、多样性指数和多样性阀值)影响巨大。为了了解涠洲岛珊瑚礁生态区氮磷营养盐含量变化对生物生态的影响, 文章根据2007年12月至2008年10月对涠洲岛珊瑚礁生态区4个季节水环境参数与生物生态调查的数据资料, 重点分析不同形态的海水氮磷比值(N∶P)的分布及其与浮游动、植物结构的关系。结果表明, 涠洲岛珊瑚礁生态区N∶P较高, 年平均值为38.08±14.7, 属P限制较明显的海区。在N∶P季节变化上, 总体上受风生流影响较大的冬夏季明显高于春秋季; 在N∶P空间变化上, 由于一些特征影响因素, 出现了局部的特点, 例如, 在珊瑚礁覆盖度和基础生物量较高的东北和西北部海域, 溶解有机氮(dissolved organic nitrogen, DON)∶溶解有机磷(dissolved organic phosphorus, DOP)比值、溶解态氮(dissolved nitrogen, DN)∶溶解态磷(dissolved phosphorus, DP)比值和总氮(total nitrogen, TN)∶总磷(total phosphorus, TP)比值多出现高值, 风生流影响较大的北部和西南部海域, 溶解无机氮(dissolved inorganic nitrogen, DIN)∶溶解无机磷(dissolved inorganic phosphorus, DIP)比值和颗粒态氮(particulate nitrogen, PN)∶颗粒态磷(particulate phosphorus, PP)比值多出现明显低值, 受生活和养殖排污影响较大的南部海域, PN∶PP比值最高。生态系统内部生态过程的释放补充、风生流的携带补充和岛区的综合补充影响均得到了重要体现。相关分析显示, 不同形态N∶P比值之间的相关性以西南季风影响的春夏季最为显著, 东北季风影响较大的冬季次之, 秋季并不明显。不同形态N∶P比值在东北季风影响较大的秋冬季和受冷水团影响较大的春季受环境因子的影响较大, 其对浮游动、植物结构的影响比环境因子显著得多; 在浮游动、植物繁盛的秋季, 集中体现了DON∶DOP、DN∶DP与浮游动物总种数、丰度、多样性指数和多样性阀值的显著(P≤0.05)正相关影响; 而在浮游动、植物相对贫乏的春季, 则以DIN∶DIP、PN∶PP与浮游植物丰度、多样性指数的显著负相关以及DON∶DOP、DN∶DP、TN∶TP与浮游植物多样性阀值和均匀度的显著正、负相关影响为主, 突出体现了珊瑚礁生态区以生态过程为主导影响的特点。在5种形态N∶P比值中, 对珊瑚礁生态系基础生物量和基础生物结构影响最大的是DON∶DOP比值。

The level of nutrients in sea waters, such as N, P, etc., are believed to have impacts on plankton structures (total species number, species richness, species evenness, the diversity index, and diversity threshold value). In order to explore the biological and ecological impacts of N and P in the coral reef near Weizhou Island, N∶P ratio in different N and P forms and their relationship with plankton structures were analyzed based on the data collected from December 2007 to October 2008 in the coral reef near Weizhou Island. The result showed that ratio of N∶P in the coral reef near Weizhou Island was high and its annual-mean value was 38.08±14.7, suggesting that the sea area was obviously constrained by P. In general, seasonal variation of N∶P is influenced by wind-driven currents and consequently N∶P is much higher in winter and summer than in spring and autumn. Spatial variation of N∶P was influenced by some factors related to locations. In the sea areas of northeast and northwest where coral cover and primary biomass were higher, ratios of dissolved organic nitrogen (DON) over dissolved organic phosphorus (DOP), dissolved nitrogen (DN) over dissolved phosphorus (DP), and total nitrogen (TN) over total phosphorus (TP) were all higher. In the sea areas of north and southwest where wind-driven currents’ influence was stronger, ratios of dissolved inorganic nitrogen (DIN) over dissolved inorganic phosphorus (DIP) and particulate nitrogen (PN) over particulate phosphorus (PP) were much lower. In the sea area of south where pollutions of domestic sewage and sea farming were obvious, PN∶PP was the highest. The temporal and spatial variation of N∶P reflected the influence of ecosystem, wind-driven currents and human activities on the release, transfer, and supply of nutrients. Correlation analysis revealed the ratios of N∶P in different N and P forms were correlated one another significantly in spring and summer when southwest monsoon prevailed, somewhat significantly in winter when northeast monsoon prevailed, and not significantly in autumn. The ratios of N∶P in different N and P forms were influenced more obviously by environmental factors in autumn and winter when northeast monsoon prevailed and in spring when cold water mass appeared. The influence of N∶P on the structure of plankton was much greater than the environmental factors. In autumn when zooplankton and phytoplankton flourished, DON∶DOP and DN∶DP were positively correlated with the total species number, species richness, species evenness, the diversity index, and diversity threshold value of zooplanktons; in spring when zooplankton and phytoplankton were comparatively less, DIN∶DIP and PN∶PP were negatively correlated with the species richness and diversity index of phytoplankton (P≤0.05), and DON∶DOP, DN∶DP, and TN∶TP were positively correlated with species evenness of phytoplankton and negatively correlated with the diversity threshold of phytoplankton, indicating that in the coral reef it was the ecological process that plays a leading role in influencing the N∶P ratio. Among the N∶P ratios in five N and P forms, DON∶DOP ratio’s influence on primary biomass and biological structure of coral reef ecosystem was the greatest.