Developmental Process and Material Flow in Tropical Seagrass Beds

以往的研究表明，巴布亚新几内亚海草床的热带海草生态系统具有由高度多样性的海草和底栖动物组成的多条食物链，处于海草分布的中心。而在斐济边缘海草床中，则有净林分。环境海水和海草植被内部的营养物浓度很低，而海草床沉积物间隙水的营养物浓度是环境海水的10-100倍。它是由沉积在沉积物中的碎屑分解而成的。裸底沉积物中有机碳和氮从底面到20 cm深度没有变化，C/N比值约为0.10 （g/g）。海草床沉积物中有机碳在20 cm深度下降到1/3，但碳中有机氮的变化不大。这表明氮在细菌代谢中从未丢失，并被海草有效地再次吸收。2 .更多。采用(1)标记法、(2)析氧法、(3)空隙气量法测定了丁香纯林的生物量和初级生产量。产量为2.5 ~ 11.2 g/m2/d。与巴布亚新几内亚的高多样性海草床相比，这一初级产量范围并不低，因为丁香林的林分非常密集。斐济海草床的特点是滤食性底栖动物丰富，尽管浮游植物贫乏。在动物中，双壳类动物可以通过海草和附生植物的碎屑在密集的海草林内高浓度积累的机制来维持自己。另外，附着在海草叶片上的复合海鞘生物量丰富（平均14.8 g/m2），由于与藻类共生，也有助于初级生产。我们的实验估计，海鞘的一半和一半营养来自共生藻类的CO2固定，次要营养来自滤食。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