Collaborative Research: Context-dependency of top-down vs. bottom-up effects of herbivores on marine primary producers

人类正在自上而下地修改海洋食物网，减少消费者的丰富度，并自下而上地向沿海栖息地添加营养物质。预测这些影响很复杂，因为食草动物既自上而下地影响初级生产者，通过吃掉它们，又自下而上地通过循环营养物质和促进藻类补充到当地海洋生态系统来影响初级生产者。该项目使用加州海岸营养物可获得性的自然梯度的实验操作来评估海洋群落中自上而下和自下而上过程之间的复杂相互作用。该项目包括在一个对公众有大量接触的地点进行实验和推广，调查人员将与社区和大学推广人员合作，向更广泛的受众传播这项研究。具体地说，该项目包括课程开发和推广机制，并将在海洋科学方面培训本科生和研究生。调查人员正在实施一套创新方法，以了解草食动物在海洋系统中扮演的多种角色。传统的食草动物去除实验方法导致了食草动物的消耗和促进作用的丧失。相比之下，研究人员的实验设计允许他们划分食草动物对海洋初级生产者的不同影响。这些方法，包括观察、实验和建模方法，使研究人员能够(I)计算草食动物对藻类多样性和丰度的消耗和促进作用的相对重要性；(Ii)确定温度、营养物质和草食动物对微生物群落的影响；以及(Iii)评估内部过程和空间补贴的相对重要性。

Humans are modifying marine food webs both from the top-down, by reducing consumer abundances, and from the bottom-up, by adding nutrients to coastal habitats. Predicting these impacts is complicated because herbivores affect primary producers both from the top-down, by eating them, and from the bottom-up, by recycling nutrients and facilitating the recruitment of algae into local marine ecosystems. This project uses experimental manipulations along a natural gradient in nutrient availability on the California coast to evaluate the complex interactions between top-down and bottom-up processes in marine communities. This project includes experiments and outreach in a location with substantial exposure to the public, and the investigators will work with community and university outreach personnel to communicate this research to broader audiences. Specifically, the project includes mechanisms for curriculum development and outreach and will train undergraduate and graduate students in marine science.The investigators are implementing a suite of innovative approaches to understand the multiple roles that herbivores play in marine systems. Traditional experimental methods for herbivore removal result in the loss of both the consumptive and facilitative effects of herbivores. In contrast, the investigators' experimental design allows them to partition the different effects of herbivores on marine primary producers. These methods, including observations, experiments, and modeling approaches, allow researchers to (i) calculate the relative importance of herbivores' consumptive and facilitative effects on algal diversity and abundance; (ii) determine the effects of temperature, nutrients, and herbivores on the microbial community; and (iii) evaluate the relative importance of internal processes and spatial subsidies.