基于大型海藻营养源的岛礁生态辐射机制与效能研究

Island reef has higher marine stock biomass and biodiversity than adjacent sea areas, often reveal the phenomenon that biomass and biodiversity decrease progressively along offshore distance-gradient (e.g., ecological radiation effect). Aims to understanding the material basis and mechanisms of above phenomenon, we propose following hypothesis: the high marine stock biomass, biodiversity and ecological radiation effect of island reef are based on high primary productivity, trophic diversity of macroalgae and transportation patterns of macroalgae detritus. Using SCUBA diving sampling and measuring, stable isotope analysis, carbohydrate composition analysis and FVCOM. Also, incorporating temporal & spatial distribution based on parallel transportation and sedimentation-resuspension effect of macroalgae detritus, change of physical & chemical traits during macroalgae degradation period, trophic relationship between macroalgae detritus and macrobenthos (contribution and functional diversity correlation coefficient), we assess the efficiency of detritus physical & chemical trait combining with macroalgae’s functional trait, food preference, diet consumption of secondary production. Furthermore, we investigate the correlation coefficient between macrobenthos and physical & chemical traits of macroalgae detritus. Finally, under the functional ecology concept, a geography assessment and boundary definition of island-reef ecological radiation effect was studied base on the trophic source, material and energy flow of detritus, assimilation efficiency of secondary production levels. This research aims to use functional trait of secondary production as an indicator of island reef ecological radiation effect, also, evaluating the capacity of ecological radiation effect based on trophic source - macroalgae and exploring the mechanism driving high marine stock biomass and biodiversity in island-reef habitat. In summary, this research will provide basic theories of scientific management and MPA (marine protected area) design.

岛礁海域的生物资源量和物种多样性普遍高于外围海域，并呈现自岛礁近岸向外辐射状递减的分布特征。为探索其物质基础及维持机制，本项目假设该现象源于岛礁周边大型底栖海藻初级生产力的支撑与辐射作用。拟运用水下原位测量、稳定同位素和碳水化合物组分分析及水动力数值模拟等方法，通过研究大型海藻碎屑的离岛输运与沉降—再悬浮过程、其物理生化属性的变化、离岛方向上底栖生物的大型海藻食源占比和功能多样性等，查明大型海藻碎屑在岛礁海域的时空分布规律、对大型海藻功能特征的指示度，以及大型海藻初级生产力对岛礁海域次级生产者的食物贡献。在此基础上，在功能生态学的理论框架下，以大型海藻为营养供源、以其碎屑为能流载体、以次级生产者的同化效率为水平，评估岛礁的生态辐射强度与边界，揭示岛礁的生态辐射机制与效能，为认知基于上行效应的岛礁海域生物资源养护与多样性维持等生态服务功能、岛礁型海洋保护区功能区划的界定和管理提供科学依据。

本项目通过研究大型海藻碎屑的离岛输运过程、对大型海藻的功能指示程度、次级生产者对藻体碎屑的利用模式等，揭示以岩礁生境大型海藻为营养源的岛礁生态辐射机制、评估其生态辐射效能，为岛礁海域的科学管理如岛礁型海洋保护区划界等提供理论依据。.主要研究结果有：1.马鞍列岛优势藻种主要有铜藻、瓦氏马尾藻、裙带菜、鼠尾藻及羊栖菜等，海藻场分布面积约6.51-13.43km2，大型褐藻生物量约为4311.19g/m2，大型海藻藻体有机碳含量为33.16±3.26%；2. 海藻场沉积物TOC、TN、C/N、δ13C和δ15N范围分别为0.70-2.41%、0.11-0.41%、5.53-6.48、−21.79-−19.60‰和1.56-4.26‰，大型海藻对沉积物有机质的贡献率时空分布特征为：7月＞8月＞6月，海藻场-岩礁区＞非海藻场-岩礁区＞非岩礁泥质区。大型海藻对沉积物有机质贡献率在2.30%-45.60%，大型海藻产生的碎屑有机质中有11.98%进入海藻场及沿岸海域的表层沉积物中；3.大型海藻碎屑的“临界粒径”为0.180mm，枸杞岛海藻场中65%的海藻碎屑分布在岛礁近岸200m范围内。藻体碎屑在分解过程中，其有机体密度、木质素、纤维素等化学组成成分含量逐渐下降；4. 水动力是控制海藻碎屑输运过程的重要因素，海藻场对海洋次级生产力的贡献主要集中在海藻场邻近海域，90%的海藻碎屑输运距离在5km以内，且在6h以内便沉至海底，枸杞岛近岸海藻场区域日沉积量为17.10g·m-2·d-1，海藻固碳量的11.98%进入了海藻场及其附近海域的沉积物中，有超过85%的海藻场固碳量进入水体成为POM的组分，随潮汐、洋流等物理过程向海藻场外输送，并为滤食生物和底栖生物提供能量来源；5. 基于海藻场底栖生物胃含物分析、DNA条形码数据及摄食选择结果，确定了岛礁海藻场以大型底栖动物驱动的3条食物链。6.海藻场中大型藻类对角蝾螺的摄食贡献率为94.5%，其主要摄食铜藻、海带及粗枝软骨藻等，角蝾螺的啃食作用可为海藻场提供(0.016-0.094)g/d的碎屑增量，且该过程产生的碎屑粒级主要为Φ＞250μm。稳定同位素分析—摄食选择偏好实验—螺类消化代谢物粒径分析的系列研究表明，角蝾螺在枸杞岛海藻场的群落食物网中，可以起到连接牧食食物链和碎屑食物链的重要作用。