Effects of organic nitrogen and phosphorous on the selective growth of red tide flagellates in polluted seawaters.

赤潮对日本沿海海域的鱼类造成了严重损害。防止赤潮爆发是日本渔业面临的一个重要而紧迫的问题。本文介绍了赤潮浮游植物对有机氮和磷的利用，以及有机氮和磷对沿岸污染海域浮游植物生长和优势的影响。赤潮浮游植物、mikimotoi裸子藻、赤石异花藻和costatum骨骼肌利用有机氮和磷化合物生长。但这些物种对不同有机化合物的利用潜力存在差异。因此，所有这些物种都可以使用色氨酸和谷氨酸，而只有g.m ikmotoi可以使用尿素作为氮源。同样，发现G.mikimotoi和s.c ostum使用单磷酸酯作为磷源并产生碱性磷酸酶，但没有发现h.c akashiwo。在缺磷条件下，酶活性显著提高并增强。污染水体中有机氮和有机磷浓度较高。在这些水域，有机氮和磷对赤潮浮游植物生长的贡献与无机氮和磷相当。碱性磷酸酶可水解的磷占污染海水中溶解有机磷含量的30%以上。在非冬季，藻类细胞产生的碱性磷酸酶活性增加，利用有机磷化合物的浮游植物在污染的沿海海水中占主导地位。本研究揭示了赤潮浮游植物对有机氮和磷的潜在利用存在差异，这些差异可能反映在污染海域浮游植物的优势和演替上。

Serious fish damages by red tides have persisted in coastal seawater in Japan. Preservating red tide outbreak is an important and urgent issue for fisheries in Japan. Present paper describes the utilization of organic nitrogen and phosphorous by red tide phytoplankters, and their effects of organic nitrogen and phosphorous on the growth and the domination of the phytoplankton species in polluted coastal seawaters.Red tide phytoplankters, Gymnodinium mikimotoi, Heterosigma akashiwo and Skeletonema costatum were found to use organic nitrogen and phosphorous compounds for their growth. But these species differed in potential utilization of the different organic compounds. For that matter, all of these species could use tryptophan and glutamic acid, while only G.mikimotoi could use urea as a nitrogen source. Similarly, G.mikimotoi and S.costatum, but not H.akashiwo, were found to use mono-phosphoric esters as a phosphorous source and to produce alkaline phosphatase. The enzyme activity was markedly high and enhanced under the phosphate-depleted conditions.The concentration of organic nitrogen and phosphorous in the polluted coastal waters was fairly high. In these waters, contrib utions of organic nitrogen and phosphorous to the growth of red tide phytoplankters were comparable to those of inorganic nitrogen and phosphorous. The alkaline phosphatase hydrolyzable phosphorous constituted more than 30% of dissolved organic phosphorous contents in a polluted seawater. In nonwinter seasons when the alkaline phosphatase activities derived from algal cells increased, phytoplankters which could use organic phosphorous compounds dominated in the polluted coastal seawater.From the present study, it is revealed that potential utilization of organic nitrogen and phosphorous differs among red tide phytoplankton species, and that these differences could be reflected on the domination and/or succession of phytoplankton species in polluted seawaters.