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

人类正在改变海洋食物网，从上到下，通过减少消费者的丰度，从下到下，通过向沿海栖息地添加营养物质。预测这些影响是复杂的，因为食草动物对初级生产者的影响既有自上而下的，通过吃掉它们，也有自下而上的，通过循环养分和促进藻类进入当地海洋生态系统。该项目采用实验操作沿着加利福尼亚海岸的自然梯度的营养可用性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。该项目包括在一个与公众有大量接触的地方进行实验和外展，研究人员将与社区和大学外展人员合作，将这项研究传播给更广泛的受众。具体而言，该项目包括课程开发和推广机制，并将培训海洋科学方面的本科生和研究生。研究人员正在实施一套创新的方法来了解食草动物在海洋系统中扮演的多重角色。传统的去除草食动物的实验方法导致草食动物的消耗和促进作用的损失。相比之下，研究人员的实验设计允许他们划分草食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、营养物质和食草动物对微生物群落的影响；(3)评估内部流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.