陆源有机碎屑对三亚珊瑚礁区桡足类次级生产的影响效应研究

With the intensification of human activities, the sedimentation of the terrestrial source in coral reef ecosystem is increasing, which will not only affects the physiological activities of coral, but also affects the process of material utilization of other organisms in coral waters. As an important allochthonous carbon source, terrestrial organic detritus is essential for supporting secondary productivity of lake ecosystems, while its contribution to the secondary production of zooplankton in coral reef ecosystems remains unclear yet. The coral reef ecosystem of Sanya Bay was reported to have low primary production but high biomass of zooplankton, with a high contribution of terrestrial particulate organic matter to the surface sediments. Previous studies found that copepods consumed large amount of terrestrial plant preys as supplementary food. In order to evaluate the contribution of these terrestrial organic detritus to the secondary production of copepods, this project aimed to explore the composition and fraction of terrestrial organic detritus in the particulate organic carbon in different seasons, as well as the distribution of terrestrial organic detritus in food composition of coral reef copepods by using both molecular detecting method and stable isotope technology, and determine the contribution and nutritional support of terrestrial organic detritus to copepods by combining the field investigation and laboratory experiments. Furthermore, the role of copepods in buffering the exogenous organic particulate matter will be discussed. The results here are helpful to understand the dichotomy between the limited primary production and relatively high zooplankton stock in coral waters of Sanya Bay, as well as the pathway and destination of terrestrial organic detritus in the coral reef ecosystem.

随着人类活动的加剧，进入珊瑚礁生态系统的陆源沉降物日益增加，不仅影响珊瑚的生理活动，也会对水体生物的物质利用过程产生影响。陆源有机碎屑作为外源性碳源，被认为是淡水湖泊生态系统次级生产力的重要物质基础，但其对珊瑚礁生态系统中浮游动物次级生产的贡献还不明确。三亚湾珊瑚礁区是初级生产力的低值区，却拥有极高的浮游动物生物量。前期研究发现，礁区沉积物的陆源组分很高，不同桡足类优势类群均摄食大量陆生植物，为查明陆源有机碎屑对桡足类次级生产的影响效应，本项目计划结合现场调查和室内实验，综合运用分子生物学和稳定同位素技术，分析陆源有机碎屑的组成、分布及季节变化，阐释其对礁区桡足类的食物补偿效应和营养支持作用，进而探讨桡足类摄食对外源有机颗粒物输入的生态响应。研究结果有助于揭示珊瑚礁区“低浮游植物-高浮游动物”形成的物质基础，也可为理解陆源有机碎屑在珊瑚礁生态系统物质循环和生物生产过程中的作用提供科学指导。

随着人类活动的加剧，进入到珊瑚礁生态系统的陆源沉降物日益增多，以往多关注它们对珊瑚的影响，而对其进入到珊瑚礁生态系统后的生物利用过程关注较少。本项目以珊瑚礁区浮游动物优势类群桡足类为研究对象，通过现场调查和室内培养实验，分析了水体悬浮颗粒物的分布特征和季节差异，明确了陆源有机碎屑对水体颗粒有机碳的贡献及其对桡足类的食物补偿效应，探讨了陆源有机碎屑对桡足类次级生产的影响。结果显示：鹿回头珊瑚礁区浮游植物生物量偏低，Chla平均约为0.05µg/L，悬浮物颗粒物中有机碳含量较高，且呈现明显的季节差异，8月份最高。同位素分析显示陆源组分对颗粒有机碳的贡献比例约为60.80±9.60% ，且干季(85.80±6.70%)显著高于湿季30.10±6.00%)。对不同滤食性浮游动物类群的现场食物组成分析发现，无论是在干季还是湿季，桡足类均是陆源有机碎屑主要的摄食者，对其食物组成的贡献比例约为20%，而且珊瑚礁底栖桡足类并未摄食陆源有机碎屑，推测陆源有机碎屑可能主要在水体中被利用。室内不同浓度梯度悬浮物添加实验显示，悬浮颗粒物浓度增加会影响桡足类的摄食选择，使其摄食更多的陆源有机碎屑，但是陆源有机碎屑并不能独立支持桡足类的生长和繁殖，因此陆源有机碎屑可能只是在食物资源限制条件下的一种重要的补充物质来源，可维持桡足类基本生存，但并不能促进其种群的增长。