Developmental Process and Material Flow in Tropical Seagrass Beds

已有研究表明，位于海草分布中心的巴布亚新几内亚海草床具有由海草和底栖动物高度多样性组成的多条食物链。而在边缘的斐济海草床中，则有异叶丁香纯林。环境海水和海草植被内营养盐浓度很低，海草床沉积物间隙水中营养盐浓度是环境海水的10-100倍。它是由沉积物中堆积的碎屑分解而成的。裸底沉积物中有机碳和氮从底表面到20 cm深度没有变化，C/N比值约为10（g/g）。而海草床沉积物中有机碳在20 cm深度时减少到1/3，有机氮在碳中变化不大。这表明氮在细菌代谢过程中从未损失，并被海草有效地再次吸收。 ...更多信息 .采用（1）标记法、（2）放氧测定法、（3）空隙气体容量法测定了丁香纯林的生物量和初级生产力。生产率为2.5 - 11.2 g/m2/天。与巴布亚新几内亚的高多样性海草床相比，这种初级生产力的范围并不低，因为丁香林的林分非常密集。斐济海草床的特点是有大量的滤食底栖动物，尽管浮游植物贫乏。在这些动物中，双壳类可以通过海草和附生植物的碎屑在密集的海草林中高浓度积累的机制来维持自身。此外，复合海鞘附着在海草叶上，生物量丰富（平均）。14.8 g/m2），也有助于初级生产，因为与藻类共生。实验结果表明，海鞘的营养来源主要是共生藻固定CO2，其次是滤食性。在氮代谢方面，独立营养是有效的。少

It has been clarified by previous studies that tropical seagrass ecosystem has several food-chains consisting by high diversity of seagrasses and benthic animals in Papua New Guinean seagrass bed, which locates in center of seagrass distribution. Otherwhile, in marginal Fijian seagrass beds, there was pure stands of Syringodium isoetifolium.1. Concentration of nutrients in ambient seawater and within seagrass vegetation was very low, while it in interstitial water of seagrass bed sediment was 10-100 times of ambient seawater. It is originated from decomposition of detritus accumulated in sediments. Organic carbon and nitrogen in sediment of bare bottom did not change from bottom surface to 20 cm deep, and the C/N ratio was ca.10 (g/g). While, organic carbon in seagrass bed sediment reduced to 1/3 at 20 cm deep, but organic nitrogen did not change unlikely in carbon. This suggests that nitrogen has never been lost in bacterial metabolism and is effectively taken up again by seagrasses.2 … More . Biomass and primary production of Syringodium pure stand were measured by (1) marking method, (2) oxygen evolution measurement, (3) lacuna gas volumetry. The production rates were 2.5-11.2 g/m2/day. This range of primary production was not low compared with high diversity seagrass beds in Papua New Guinea, because of very dense stand in Syringodium stand.3. Characteristics of Fijian seagrass bed are in abundant filter feeding benthic animals, in spite of poverty in phytoplankton. Among the animals, bivalves can be sustained themselves by a mechanism in which detritus from seagrass and epiphytes is accumulated in high concentration within dense seagrass stands. Otherwhile, compound ascidians attached to seagrass leaf, having abundant biomass (ave. 14.8 g/m2), contribute also to primary production, because of symbiosis with algae. It was estimated by our experiments that the ascidians obtained half and half of nutrients from CO2 fixation by symbiotic algae and subordinate nutrition by filter feeding. In nitrogen metabolism, independent nutrition was effective. Less