Collaborative Research: Identification of nitrogen sources for toxic Alexandrium blooms using a novel species-specific tracer, d15N-saxitoxin

美国和世界其他国家都受到有害藻华（HABs）的影响，对人类健康、海洋生态系统、渔业资源和当地经济产生负面影响。人为的营养负荷与赤潮发生率的增加有关，但这种关系是地点和生物体特异性的，并且仍然知之甚少。在这方面的主要挑战是确定自然与人为营养源在个别藻华物种发展中的相对重要性。鉴于发生有害藻华的浮游生物组合的多样性，以及缺乏适当的测量技术，这是极其困难的。在这个项目中，伍兹霍尔海洋研究所和德克萨斯大学奥斯汀分校的研究团队将采用一种新颖的方法来应对这一挑战：他们使用一种特定物种的HAB毒素的氮同位素特征（del15N）来识别促进细胞生长和毒素产生的氮源和化学形式。形成水华的鞭毛藻亚历山大藻（Alexandrium fundyense）及其一类生物活性化合物——石蜡毒素（saxitoxins, STXs）是一个理想的模式系统，因为STXs富含氮，通常只由混合浮游生物组合中的单一物种产生。指向性的总体假设是，一种有害藻华特异性毒素的同位素特征可以用来区分人为和自然的N来源，并提供比大量材料del15N更多的细节，包括导致特定有毒物种大量繁殖的N的来源、化学形式和处理。这一假设是基于地下水和污水中的人类和动物粪便相对于集水区的自然N源而言变得富含15n而无机肥料则耗尽15n的原理。虽然使用大量生物量的同位素比率del15N来识别沿海水域的氮源是一种被广泛接受的做法，但这种使用毒素作为物种特异性示踪剂或标记物的做法是新的，它将提供导致特定赤潮藻华的氮的明确来源、化学形式和处理的详细信息。更广泛的影响：该项目解决了所有有害藻华中毒综合征中最普遍的麻痹性贝类中毒（PSP）的根本问题，麻痹性贝类中毒是影响世界各国的一种主要贝类中毒。项目成果还可协助有关污染控制和其他水华缓解战略的政策决定，并可应用于一系列有害藻华物种——那些产生蛤蚌毒素的物种，以及那些产生其他富氮毒素的物种。项目成果将通过科学论文、在讲习班、国内和国际会议、部门研讨会和与媒体的讨论广泛传播。

The US and other countries throughout the world are affected by harmful algal blooms (HABs) that negatively impact human health, marine ecosystems, fisheries resources, and local economies. Anthropogenic nutrient loadings have been linked to expanding HAB incidence, but the relationship is site- and organism-specific, and is still poorly understood. The main challenge in this regard is to determine the relative importance of natural versus anthropogenic nutrient sources in the development of an individual HAB species. Given the diverse nature of the planktonic assemblage in which HABs occur, and the lack of appropriate measurement techniques, this is exceedingly difficult to accomplish.In this project, research teams at the Woods Hole Oceanographic Institution and University of Texas at Austin will take a novel approach to this challenge: They use use the nitrogen isotopic signature (del15N) of a species-specific HAB toxin to identify the nitrogen source and chemical form that promotes cell growth and toxin production. The bloom-forming dinoflagellate Alexandrium fundyense and its class of bioactive compounds, saxitoxins (STXs), are an ideal model system as STXs are nitrogen-rich and are typically only produced by a single species in mixed plankton assemblages. The guiding overall hypothesis is that the isotopic signature of a HAB-specific toxin can be used to discriminate between anthropogenic and natural sources of N and provide more details than bulk material del15N on the source, chemical form, and processing of N that lead to blooms of a particular toxic species. This hypothesis is based on the principle that human and animal waste in groundwater and sewage become 15N-enriched and inorganic fertilizers 15N-depleted, relative to natural sources of N in catchment waters. While the use of the isotopic ratio del15N of bulk biomass to identify nitrogen sources to coastal waters is a widely accepted practice, this use of a toxin as a species-specific tracer or marker is new and will provide details on the explicit source, chemical form, and processing of nitrogen that results in blooms of a particular HAB species. Broader Impacts: This project addresses fundamental issues underlying the most widespread of all HAB poisoning syndromes, paralytic shellfish poisoning (PSP), a major form of shellfish poisoning that affects countries throughout the world. Project results can also assist in policy decisions about pollution control and other bloom mitigation strategies, and can be applied to a range of HAB species - those that produce saxitoxins, as well as those that produce other toxins that are nitrogen rich. Project results will be broadly disseminated through scientific papers, presentations at workshops, domestic and international conferences, and departmental seminars, and discussions with the media.