A comparative study of materials flows between seagrss-and seaweed-based ecosystemes in tropical lagoon.

本研究的目的是评估碳和氮的循环及其与生物群落的代谢耦合在海草床和海藻在热带泻湖。1994-1996年，我们在斐济苏瓦南部的热带泻湖进行了广泛的野外观测。在泻湖中，有一个密集的丁香海草床，也有Halimeda人口周围的海草床。以下是实地调查的一些结果。(1)结合已有的航摄资料和野外观察，德拉武尼岛附近的海草床在过去20年中扩大了约6倍。最近3年的野外观察也证实了这种尺寸的增加，表明海草床向海岸一侧扩展了22米。该岛人口约100人，在过去20年中相当稳定。但是，村里大约5-6年前就从井里配备了供水系统。可能的原因 ...更多信息 海草的增加是由于用水量的增加而引起的来自岛屿的营养负荷的变化。(2)随着海草床的变化，海鞘和壶藻等底栖生物群落分布也发生了变化。这些动物中的一些拥有共生藻类，这是热带泻湖中重要的初级生产者。这些动物的共生特性可能是控制其在海草床和仙掌藻群落中小规模分布的重要因素。(3)稳定同位素分析的15-N和13-C在各种生物群落和悬浮有机物在海草床及其附近的食物网结构在这个生态系统中提供了一些有趣的见解。利用海草及其附生藻类中13-C和15-N比值的显著差异（这部分是由于蓝绿色藻类的固氮作用），丝状藻类被认为是底栖动物和其他底栖动物的主要食物来源。利用C_2H_2法也证实了丝状蓝绿色的活性固氮作用。少

The Purpose of this study is to evaluate the cycling of carbon and nitrogen and their coupling with the metabolisms of biological communities in seagrass beds and in seaweeds in tropical lagoon. We made an extensive field observation in the tropical lagoon located at south of Suva, Fiji from 1994-1996. In the lagoon, there is a dense Syringodium seagress bed and also Halimeda population around the seagrass bed. Following are the some outcomes from the field survey.(1) Combing with the available data of aero-photographs and our field observation, the seagrass bed near the Dravuni Island expanded their size to about 6 times during the last 20 years. This increase in size was also confirmed for the latest 3 years field observation, indicating 22m expansion of seagrass bed to the shore side. The island has a population of some 100 peoples, which is rather stable during the last 20 years. But, the village equipped water supply system from the well about 5-6 years ago. Possible reason for th … More e seagrass increase is the change of nutrients load from the island due to the increase of water usage.(2) Together with the change of seagrass bed, we found the change of epibenthic community distribution such as Ascidians and Lagenophyra. Some of those animals harbor symbiotic alage, which are significant primary producers in the tropical lagoon. The symbiotic character of those animals seems to be important factor controlling the small scale distribution with in seagrass bed and Halimeda communities.(3) Stable isotope analyzes of 15-N and 13-C in various biological communities and suspended organic materials in the seagrass bed and its vicinity gave some interesting insight of food web structure in this ecosystem. Using the significant difference in both 13-C and 15-N rations in seagrass and their epiphytic algae, which are partially due to the nitrogen fixation by blue green algae, filamentous algae was suggested as a primary food source of epibenthic and other benthic animals. Active nitrogen fixation by filamentous blue green was also confirmed experimentally using C2H2 method. Less