Collaborative Research: Fate of Recently Fixed N2 in the Eastern Gulf of Mexico: Does the Regeneration of N by Trichodesmium Support the Development of Gymnodinium Breve Blooms?

有毒赤潮鞭毛藻（Gymnodinium breve）的大量繁殖是佛罗里达陆架生态系统的一个重要特征。水华似乎是在西佛罗里达离岸18-75公里的一个少营养的中陆架地区开始和发展的。然而，这些水域的特点是溶解的无机氮和有机氮（DIN和DON）浓度都很低，而且尚不清楚G. breve华是如何满足其生长所需的氮的。环境氮浓度、模型预测和基于观察到的生物量的生长所需养分的化学计量学计算表明，来自河流、上升流和原位氮再生的氮输入不足以支持该地区观察到的短毛杆菌华。此外，未发表的研究、轶事信息和历史红潮监测数据表明，短毛杆菌华的时间和规模与墨西哥湾和大西洋沿岸水域丝状、固定N2的蓝藻Trichodesmium spp.的出现存在相关性。对于新近固定的N2产生的新N输入的命运和意义，以及这些新N被吸收到少营养海洋生态系统的营养转移途径，人们知之甚少。确定新氮在贫营养系统中的去向和固定氮输入对群落结构和功能的影响，对于准确评估新氮对再生和出口生产的影响至关重要。贫瘠西佛罗里达架子上的生态系统是一个理想的模型系统,检查新N输入从氮气固定的命运束毛藻属种虫害的途径促进营养转移N这个项目会检查花朵的g .谕令在西佛罗里达架子上的水是由氮气的释放和再生的喧嚣,也最近固定前共病或花朵的束毛藻属spp。目前的项目将检验这些假设一个为期三年的项目，包括实验室和实地研究，以：1)确定G. Breve对N的吸收和再生的能力和动力学；2)确定木霉从最近固定的N2中直接或间接再生NH4+和DON是否提供了足够的N底物来支持G. Breve的生长；3 .鉴定相关的群落，并检查营养途径，即从Trichodesmium sp .获得的新固定N2刺激低营养水域的生产。在西佛罗里达大陆架地区，将有积极的建模项目合作，重点研究毛霉菌和短孢菌的繁殖。

Blooms of the toxic red tide dinoflagellate, Gymnodinium breve, are an important feature of the Florida Shelf ecosystem. Blooms appear to initiate and develop in an oligotrophic, mid-shelf region 18-75 km offshore of west Florida. However, these waters are characterized by low concentrations of both dissolved inorganic and organic nitrogen (DIN and DON), and it is unclear how G. breve blooms meet their N demand for growth. Ambient N concentrations, model predictions, and stoichiometric calculations of nutrient requirements for growth based on observed biomass suggest that N inputs fromriverine, upwelling and in situ N regeneration are insufficient to support the observed G. breve blooms in this region. Furthermore, unpublished research, anecdotal information and historical red tide monitoring data suggest a correlation between the timing and magnitude of G. breve blooms and the occurrence of the filamentous, N2 fixing cyanobacteria, Trichodesmium spp. in both the Gulf of Mexico and Atlantic coastal waters. Little is known about the fate and significance of new N inputs derived from recently fixed N2 or of the pathways of trophic transfer whereby this new N is assimilated into oligotrophic marine ecosystems. It is critical to determine the fate of new N in oligotrophic systems and the effects of N inputs from N2 fixation on the community structure and function so that one can accurately assess the impact of new N on regenerated and export production.The oligotrophic west Florida Shelf ecosystem is an ideal model system in which to examine the fate of new N inputs from N2 fixation by Trichodesmium spp. and the pathways facilitating the trophic transfer of this N. This project will examine the idea that blooms of G. breve in west Florida shelf waters are supported by the release and regeneration of DIN and DON from N2 recently fixed by co-occurring or preceding blooms of Trichodesmium spp. The present project will examine these hypotheses with a three-year program consisting of laboratory and field studies to: 1) determine the capacity for and kinetics of N uptake and regeneration by G. Breve; 2) determine whether direct or indirect regeneration of NH4+and DON from recently fixed N2 by Trichodesmium provides sufficient N substrates to support the observed growth of G. Breve; and 3 identify associated communities and examine trophic pathways whereby newly fixed N2 derived from Trichodesmium spp. stimulates production in otherwise oligotrophic waters. There will be active collaboration with modeling projects focused on both Trichodesmium and G. breve blooms in the west Florida shelf region.