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

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 newly funded NSF grant, a collaboration between the Bracken and Adam Martiny Labs at UCI and Luke Miller’s lab at SJSU, supports 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. Traditional experimental methods for herbivore removal result in the loss of both the consumptive and facilitative effects of herbivores. In contrast, our experimental design allows us to partition the different effects of herbivores on marine primary producers. These methods, including observations, experiments, and modeling approaches, allow us 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.