NUTRITION OF THE GIANT CLAM TRIDACNA-GIGAS (L) .2. RELATIVE CONTRIBUTIONS OF FILTER-FEEDING AND THE AMMONIUM-NITROGEN ACQUIRED AND RECYCLED BY SYMBIOTIC ALGA TOWARDS TOTAL NITROGEN REQUIREMENTS FOR TISSUE-GROWTH AND METABOLISM
NUTRITION OF THE GIANT CLAM TRIDACNA-GIGAS (L) .2. RELATIVE CONTRIBUTIONS OF FILTER-FEEDING AND THE AMMONIUM-NITROGEN ACQUIRED AND RECYCLED BY SYMBIOTIC ALGA TOWARDS TOTAL NITROGEN REQUIREMENTS FOR TISSUE-GROWTH AND METABOLISM
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DOI：
10.1016/0022-0981(95)00044-r
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发表时间：
1995-08-10
影响因子：
2
通讯作者：
KLUMPP, DW
中科院分区：
文献类型：
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作者：
HAWKINS, AJS;KLUMPP, DW
我们比较了滤食性摄食和藻类共生体转移的氨氮对贻贝组织生长和新陈代谢所需总氮的相对贡献。同位素富集法表明，虫黄藻对高浓度(小于或等于15微米)N-15-铵的初级同化影响最大，如果不是全部的话。每天从天然海水中净吸收铵，这是根据营养史、光照史、氨浓度和可能的生物节律来调节的。虫黄藻也吸收宿主组织排泄的氮，包括从摄取的藻类吸收的N-15。随后从虫黄藻释放的N-15几乎100%被并入宿主组织，在至少10天内没有明显的损失。因此，虫黄藻基本上保存和循环利用了巨藻体内的所有含氮最终产物，这为巨贝提供了比非共生双壳贝类更好的营养优势。与富含颗粒物环境中的异养双壳贝类相比，巨藻具有更长的肠道通过时间，以及从摄入颗粒中吸收有机氮的高净效率和总效率(分别为78.1+/-9.4%和99.2+/-0.4%)。滤食和/或其他非自养过程是维持观察到的幼鱼生长速度所必需的氮源，但随着文蛤大小的增加而显著下降。即使在光照有限的多云条件下，黄藻对氨氮的总贡献也超过了约0.1g的摄食颗粒对氮的贡献，增加到10g的文蛤总需氮量的45%以上。从动黄藻转运的氨氮也满足了大于0.1g的颗粒饥饿的所有基本氮素需求。无论大小，摄取的颗粒和动黄藻获取的氨氮加在一起提供了大约总观测氮素需求的70%。我们强调有必要确定光照对溶解无机氮吸收的影响，并量化溶解有机质作为潜在的额外重要氮源，这可能进一步解释这种文蛤物种的高增长率。
We compare the relative contributions of filter-feeding and ammonium-nitrogen translocated from algal symbionts (zooxanthellae) towards the total nitrogen requirements for tissue growth and metabolism in the giant clam Tridacna gigas. Isotope enrichments suggest that zooxanthellae effected most if not all primary assimilation from high concentrations (less than or equal to 15 mu M) of N-15-ammonium. There was a net daily uptake of ammonium from natural seawater, which was modulated according to nutritional history, light history, ammonium concentration, and possible biological rhythmicity. Zooxanthellae also assimilated nitrogen excreted by host tissues, including N-15 absorbed from ingested alga. Nearly 100% of the N-15 subsequently released from zooxanthellae was incorporated in host tissues, with no significant loss from the clam over at least 10 days. Zooxanthellae therefore conserve and recycle essentially all nitrogenous end-products within T. gigas, affording giant clams a nutritional advantage over non-symbiotic bivalves. In further contrast with heterotrophic bivalves from particle-rich environments, T. gigas show longer gut passage times and high net and gross efficiencies (78.1 +/- 9.4% and 99.2 +/- 0.4%, respectively) with which organic nitrogen is absorbed from ingested particles. Filter-feeding and/or other non-autotrophic processes were essential as a source of nitrogen to maintain observed rates of juvenile growth, but declined in significance with increasing clam size. Even under cloudy conditions of limited irradiance, the total contribution of nitrogen acquired as ammonium by zooxanthellae exceeded the contribution from ingested particles in T. gigas larger than about 0.1 g, increasing to at least 45% of total nitrogen requirements in clams of 10 g. Ammonium-nitrogen translocated from zooxanthellae also satisfied all basal requirements for nitrogen in particle-starved clams larger than 0.1 g. Irrespective of size, ingested particles and ammonium-nitrogen acquired by zooxanthellae together supplied about 70% of the total observed nitrogen requirements. We stress the need to determine effects of irradiance on uptake of dissolved inorganic nitrogen, and to quantify dissolved organic matter as a potential additional significant source of nitrogen, that might further explain the high rates of growth in this clam species.